JP7797004B2 - Phosphor, its manufacturing method, and light-emitting device using same - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act (1) Published on November 27, 2021, published by Japan Society of Surface and Vacuum Science, The 9th International Symposium on Surface Science (ISSS-9) Lecture Proceedings, 01PS-43 P. 360 (2) The 9th International Symposium on Surface Science (ISSS-9) was held from November 28th to December 1st, 2021, sponsored by the Japan Society of Surface and Vacuum Science.

The present invention relates to a phosphor, a method for manufacturing the same, and a light-emitting device using the same. In particular, the present invention relates to a phosphor using carbon nanoparticles, a method for manufacturing the same, and a light-emitting device using the same.

Recently, a composition containing a carbon nanoparticle phosphor that emits blue to red light when irradiated with excitation light has been developed (see, for example, Patent Document 1). According to Patent Document 1, a composition containing a carbon nanoparticle phosphor that emits blue to red light when irradiated with excitation light is provided by a method including the steps of: hydrothermally synthesizing a solution in which an organic substance selected from the group consisting of citric acid, benzoic acid, glucose, fructose, and sucrose, amines, and one or more selected from inorganic acids and acetic acid are dissolved in an aqueous solvent; adding alcohol to the solution obtained by the hydrothermal synthesis step and stirring; and extracting the supernatant liquid of the solution obtained by the addition and stirring step. The emission wavelength of such carbon nanoparticle phosphors does not depend on the wavelength of the excitation light, making it possible to selectively obtain a desired emission wavelength. However, adjusting (tuning) the chromaticity has been difficult.

Graphene quantum dot phosphors have also been reported (see, for example, Non-Patent Document 1). Non-Patent Document 1 reports that nitrogen-doped graphene quantum dot phosphors are produced by hydrothermal synthesis using citric acid and ethylenediamine, and that the emission wavelength changes as the wavelength of the incident light changes. However, chromaticity cannot be adjusted.

International Publication No. 2018/163955

Dan Qu et al., SCIENTIFIC REPORTS 4, 5294, 2014

The present invention aims to provide a method for producing a carbon nanoparticle phosphor with tuned chromaticity, the carbon nanoparticle phosphor with tuned chromaticity obtained thereby, a light-emitting device using the same, and a test paper using the same.

The method for producing a carbon nanoparticle phosphor with adjusted chromaticity according to the present invention includes preparing a raw material solution in which at least a carbon source is dissolved in an organic solvent, and heating the raw material solution, thereby solving the above-mentioned problems.
The carbon source may be at least one selected from the group consisting of citric acid, citric acid monohydrate, ammonium citrate, benzoic acid, ascorbic acid, glucose, fructose, and sucrose.
when the carbon nanoparticle phosphor is irradiated with light having a wavelength in the range of 300 nm to 380 nm, the color of light emitted from the carbon nanoparticle phosphor satisfies 0.2≦x<0.3 and 0.25≦y≦0.4 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates, the organic solvent is a nitrogen-containing organic solvent;
When irradiated with light having a wavelength in the range of 300 nm to 380 nm, the color emitted by the carbon nanoparticle phosphor satisfies 0.3≦x<0.44 and 0.3≦y≦0.4 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates, the organic solvent is formamide and/or N-methylformamide, and the preparing step further comprises dissolving in the organic solvent at least one nitrogen source selected from the group consisting of ethylenediamine (EDA), diethanolamine (DEA), urea, thiourea, ethanolamine (EA), dopamine, L-cystine, L-arginine, ethylenediaminetetraacetic acid (EDTA), and cysteamine;
When irradiated with light having a wavelength in the range of 300 nm or more and 380 nm or less, the color emitted by the carbon nanoparticle phosphor satisfies 0.44≦x≦0.6 and 0.3≦y≦0.45 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates, the organic solvent may be formamide, and the preparing step may further include dissolving at least one nitrogen source selected from the group consisting of ammonium hydroxide, o-phenylenediamine, and p-phenylenediamine in the organic solvent.
when irradiated with light having a wavelength in the range of 300 nm to 380 nm, the color emitted by the carbon nanoparticle phosphor satisfies 0.2≦x<0.3 and 0.25≦y≦0.4 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates, the concentration of the carbon source in the organic solvent satisfies the range of 0.05 mol/L to 0.2 mol/L,
when the carbon nanoparticle phosphor is irradiated with light having a wavelength in the range of 300 nm to 380 nm, and the color of light emitted by the carbon nanoparticle phosphor satisfies 0.3≦x<0.44 and 0.3≦y≦0.4 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates, the concentration of the carbon source in the organic solvent satisfies the range of 0.05 mol/L to 0.2 mol/L, and the concentration of the nitrogen source in the organic solvent satisfies the range of 0.05 mol/L to 1.5 mol/L,
When irradiated with light having a wavelength in the range of 300 nm to 380 nm, the color of light emitted by the carbon nanoparticle phosphor satisfies 0.44≦x≦0.6 and 0.3≦y≦0.45 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates, the concentration of the carbon source in the organic solvent may satisfy the range of 0.05 mol/L to 0.2 mol/L, and the concentration of the nitrogen source in the organic solvent may satisfy the range of 0.05 mol/L to 3.0 mol/L.
when the carbon nanoparticle phosphor is irradiated with light having a wavelength in the range of 300 nm to 380 nm, the color of light emitted satisfies 0.2≦x<0.3 and 0.25≦y≦0.4 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates, the organic solvent is formamide;
when the carbon nanoparticle phosphor is irradiated with light having a wavelength in the range of 300 nm to 380 nm, the color of light emitted from the carbon nanoparticle phosphor satisfies 0.3≦x<0.44 and 0.3≦y≦0.4 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates, the organic solvent is formamide, the nitrogen source is at least one selected from the group consisting of ethylenediamine, diethanolamine, and urea,
When irradiated with light having a wavelength in the range of 300 nm to 380 nm, the color emitted by the carbon nanoparticle phosphor satisfies 0.44≦x≦0.6 and 0.3≦y≦0.45 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates, the organic solvent may be formamide and the nitrogen source may be ammonium hydroxide.
The carbon source may be citric acid.
Heating the raw material solution may involve heating the raw material solution at a temperature of 150° C. or higher and 230° C. or lower for a period of 5 hours or higher and 15 hours or lower.
The method may further include recovering a product produced by heating the raw material solution and heating the product in a vacuum.
The heating in a vacuum may involve heating the product at a degree of vacuum of 1 Pa or more and 10,000 Pa or less, at a temperature of 50° C. or more and 70° C. or less, for a period of 30 minutes or more and 12 hours or less.
The carbon nanoparticle phosphor containing carbon, oxygen, nitrogen, and hydrogen elements according to the present invention contains amorphous carbon and graphite-like carbon, and the nitrogen element includes pyridine-type nitrogen, amide-type nitrogen, pyrrole-type nitrogen, and graphite-type nitrogen, thereby solving the above-mentioned problems.
The content of the pyridine-type nitrogen may be greater than that of the graphite-type nitrogen, the amorphous carbon may be in the range of greater than 90% by volume and less than 99% by volume, the graphite-like carbon may be in the range of 1% by volume or more and less than 10% by volume, and when irradiated with light having a wavelength in the range of 300 nm or more and 380 nm or less, the color emitted by the carbon nanoparticle phosphor may satisfy the (x, y) values on the CIE 1931 chromaticity coordinates of 0.2≦x<0.3 and 0.25≦y≦0.4.
The amorphous carbon may be present in an amount of 95% by volume or more and 99% by volume or less, and the graphite carbon may be present in an amount of 1% by volume or more and 5% by volume or less.
The carbon element content p (atomic %), the nitrogen element content q (atomic %), and the oxygen element content r (atomic %) (where p+q+r=1) are respectively expressed as follows:
0.58≦p≦0.65
0.22≦q≦0.30
0.12≦r<0.16
may be satisfied.
The carbon element and nitrogen element contents p and q are
0.38<q/p≦0.41
may be satisfied.
The content of the pyridine-type nitrogen may be less than that of the graphite-type nitrogen, the amorphous carbon may be in the range of 45% by volume or more and 70% by volume or less, the graphite-like carbon may be in the range of 30% by volume or more and 55% by volume or less, and when irradiated with light having a wavelength in the range of 300 nm or more and 380 nm or less, the color emitted by the carbon nanoparticle phosphor may satisfy the (x, y) values on the CIE 1931 chromaticity coordinates of 0.3≦x<0.44 and 0.3≦y≦0.4.
The amorphous carbon may be present in an amount ranging from 53% to 68% by volume, and the graphite carbon may be present in an amount ranging from 32% to 47% by volume.
The carbon element content p (atomic %), the nitrogen element content q (atomic %), and the oxygen element content r (atomic %) (where p+q+r=1) are respectively expressed as follows:
0.57≦p≦0.65
0.20≦q<0.26
0.16≦r<0.19
may be satisfied.
The carbon element and nitrogen element contents p and q are
0.32<q/p<0.44
may be satisfied.
The content of the pyridine-type nitrogen may be less than that of the graphite-type nitrogen, the amorphous carbon may be in the range of 60% by volume or more and 90% by volume or less, the graphite-like carbon may be in the range of 10% by volume or more and 40% by volume or less, and when irradiated with light having a wavelength in the range of 300 nm or more and 380 nm or less, the color emitted by the carbon nanoparticle phosphor may satisfy the (x, y) values on the CIE 1931 chromaticity coordinates of 0.44≦x≦0.6 and 0.3≦y≦0.45.
The amorphous carbon may be present in an amount ranging from 60% to 83% by volume, and the graphite carbon may be present in an amount ranging from 17% to 40% by volume.
The carbon element content p (atomic %), the nitrogen element content q (atomic %), and the oxygen element content r (atomic %) (where p+q+r=1) are respectively expressed as follows:
0.58≦p≦0.65
0.15≦q≦0.21
0.19≦r≦0.21
may be satisfied.
The carbon element and nitrogen element contents p and q are
0.25<q/p<0.34
may be satisfied.
The carbon nanoparticle phosphor may have a diameter in the range of 1 nm to 20 nm. A light emitting device according to the present invention comprises at least an excitation source and a phosphor, and the phosphor comprises the carbon nanoparticle phosphor described above, thereby solving the above-mentioned problems.
The phosphor may be a resin molded body in which the carbon nanoparticle phosphor is dispersed.
The test paper according to the present invention for determining whether a test liquid contains water contains the above-mentioned carbon nanoparticle fluorescent material, thereby solving the above-mentioned problems.

The method for producing a carbon nanoparticle phosphor with chromaticity adjustment of the present invention includes preparing a raw material solution by dissolving at least a carbon source in an organic solvent and heating the raw material solution. The chromaticity can be adjusted (tuned) by appropriately selecting the type and concentration of the carbon source, the type of organic solvent, and the type and concentration of the nitrogen source. The carbon nanoparticle phosphor of the present invention contains carbon, oxygen, nitrogen, and hydrogen, and contains amorphous carbon and graphite-like carbon. The nitrogen includes pyridine-type nitrogen, amide-type nitrogen, pyrrole-type nitrogen, and graphite-type nitrogen. By adjusting the ratio of amorphous carbon to graphite-like carbon and controlling the composition ratio using the above method, the chromaticity can be adjusted. Using such a phosphor, a light-emitting device can be provided that has a chromaticity near the blackbody locus and emits light relatively close to natural light. The phosphor of the present invention exhibits reduced luminous intensity in response to water, allowing for the provision of a test paper that can determine whether a liquid contains water based on changes in luminous intensity.

FIG. 1 is a diagram showing a flow for producing a carbon nanoparticle phosphor with adjusted chromaticity according to the present invention. Schematic diagram showing a light-emitting device using the carbon nanoparticle phosphor of the present invention. Schematic diagram showing a test paper using the carbon nanoparticle phosphor of the present invention. FIG. 1 shows the reaction formula of Example 1 and the luminescence of the liquid sample of Example 1. FIG. 1 shows the reaction formulas of Examples 2 to 6 and the luminescence of the liquid samples of Examples 2 to 6. FIG. 1 shows the reaction formulas of Examples 7 and 8 and the luminescence of the liquid samples of Examples 7 and 8. FIG. 1 shows XRD patterns of powder samples of Examples 1, 2, and 7. TEM images of the liquid sample of Example 1 at various magnifications. TEM images of the liquid sample of Example 2 at various magnifications. TEM images of the liquid sample of Example 7 at various magnifications. FIG. 1 shows XPS spectra of liquid samples of Examples 1, 2, and 7. Figure 1 shows the deconvoluted HRXPS spectrum of the liquid sample of Example 1. Figure 1 shows the deconvoluted HRXPS spectrum of the liquid sample of Example 2. Figure 1 shows the deconvoluted HRXPS spectrum of the liquid sample of Example 7. FIG. 15 shows the change in the amount of nitrogen doping centers calculated from FIGS. 12 to 14. FIG. 1 shows ATR-FTIR spectra of liquid samples of Examples 1, 2, and 7. FIG. 1 shows the absorption spectra of the liquid samples of Examples 1, 2, and 7. FIG. 1 shows the emission spectra of the liquid samples of Examples 1, 2, and 7. FIG. 1 shows the absorption spectra of liquid samples of Examples 3 and 4. FIG. 1 shows the absorption spectra of liquid samples of Examples 5 and 6. CIE chromaticity diagram plotting the emissions of the liquid samples of Examples 1-8 FIG. 1 shows two-dimensional emission mapping of a liquid sample from Example 1. FIG. 2 shows two-dimensional emission mapping of a liquid sample from Example 2. FIG. 10 shows two-dimensional emission mapping of the liquid sample of Example 7. FIG. 10 is a diagram showing the appearance of a resin molded body according to Example 9. FIG. 10 is a diagram showing the fluorescence spectrum of a resin molded product according to Example 9. CIE chromaticity diagram plotting the luminescence of the resin molding of Example 9 Diagram showing the manufacturing procedure and testing of test strips A diagram showing the process of determination using test paper Emission spectra for various types of water 31 shows the dependence of the luminescence intensity of FIG. 30 on the concentration of heavy water.

Embodiments of the present invention will be described below with reference to the drawings. Note that like elements are numbered likewise and their description will be omitted.

(Embodiment 1)
In the first embodiment, a method for producing a carbon nanoparticle phosphor of the present invention in which the chromaticity is adjusted (tuned), and the carbon nanoparticle phosphor obtained thereby will be described.

Figure 1 shows the flow chart for producing the chromaticity-adjusted carbon nanoparticle phosphor of the present invention.

Step S110: Preparing a raw material solution by dissolving at least a carbon source in an organic solvent.
Step S120: Heating the raw material solution.
The inventors of the present invention have discovered that carbon nanoparticle phosphors can be obtained simply by heating a carbon source using an organic solvent, rather than by hydrothermal synthesis, and have found through experiments that the chromaticity can be adjusted along the blackbody locus by appropriately selecting the type and concentration of the carbon source, the type and concentration of the organic solvent, and the type and concentration of the nitrogen source. Each step will be described in detail.

The carbon source used in step S110 is not particularly limited as long as it is an organic substance that can be decomposed by heating in step S120 to produce carbon, but is preferably at least one selected from the group consisting of citric acid, citric acid monohydrate, ammonium citrate, benzoic acid, ascorbic acid, glucose, fructose, and sucrose. These organic substances are easily available and can be decomposed by heating in step S120 to produce a carbon nanoparticle phosphor. Of these, citric acid is preferred because it can produce a carbon nanoparticle phosphor that achieves a chromaticity and color temperature on or near the blackbody locus.

The organic solvent used in step S110 is not particularly limited, but preferably contains nitrogen. By including nitrogen, nitrogen-doped carbon nanoparticle phosphors can be obtained. Examples of such organic solvents include formamide and/or N-methylformamide. These are preferred because they can dissolve the carbon source described above.

In step S110, a raw material solution may be prepared by dissolving a nitrogen source in an organic solvent in addition to the carbon source described above. This allows for control of the amount of nitrogen doping. Such nitrogen sources include ethylenediamine (EDA), diethanolamine (DEA), urea, thiourea, ethanolamine (EA), dopamine, L-cystine, L-arginine, ethylenediaminetetraacetic acid (EDTA), cysteamine, ammonium hydroxide, o-phenylenediamine, p-phenylenediamine, etc. These can be dissolved in organic solvents, allowing for doping with pyridine-type nitrogen, amide-type nitrogen, pyrrole-type nitrogen, graphite-type nitrogen, etc.

Step S120 produces amorphous carbon and graphite-like carbon. There are no particular restrictions on the heating method used here, as long as it decomposes the carbon source and allows the carbon to react with the nitrogen in the organic solvent or the nitrogen in the nitrogen source. However, the raw material solution is preferably heated at a temperature of 150°C to 230°C for a period of 5 to 15 hours. Under these conditions, the reaction proceeds efficiently, resulting in the production of carbon nanoparticle phosphors. Heating is more preferably performed at a temperature of 170°C to 210°C for a period of 7 to 10 hours.

In this way, the carbon nanoparticle phosphor is obtained in a dispersed state in the solvent. However, if the carbon nanoparticle phosphor is to be obtained as a powder, the resulting product may be recovered by centrifugation or the like and heated in a vacuum, as shown in step S130 of Figure 1.

Preferably, the product is heated at a temperature of 50° C. to 70° C. for 30 minutes to 12 hours at a vacuum of 1 Pa to 10,000 Pa. This allows the product to be efficiently recovered.

The inventors of the present application have discovered that by selecting a carbon source, an organic solvent, and, if necessary, a nitrogen source, and adjusting their concentrations, it is possible to provide carbon nanoparticle phosphors with adjusted chromaticity, and even carbon nanoparticle phosphors that lie on or near the blackbody locus. For ease of understanding, carbon nanoparticle phosphors with adjusted chromaticity will be referred to as cyan, white, or orange carbon nanoparticle phosphors, and the manufacturing methods for these phosphors will be explained below.

<Cyan>
A cyan carbon nanoparticle phosphor is a carbon nanoparticle phosphor that, when irradiated with light having a wavelength in the range of 300 nm or more and 380 nm or less, emits light whose color satisfies the (x, y) values on the CIE 1931 chromaticity coordinates of 0.2≦x<0.3 and 0.25≦y≦0.4.

In this case, in step S110, it is sufficient to prepare a raw material solution by dissolving the above-mentioned carbon source in a nitrogen-containing organic solvent. This results in a higher content of pyridine-type nitrogen than that of graphite-type nitrogen, and the resulting solution contains amorphous carbon in the range of greater than 90% by volume and less than 99% by volume, and graphite-like carbon in the range of greater than 1% by volume and less than 10% by volume, thereby achieving the above-mentioned emission color. Here, the total amount of amorphous carbon and graphite-like carbon is 100% by volume.

More preferably, the concentration of the carbon source in the organic solvent is in the range of 0.05 mol/L to 0.2 mol/L. This range results in a cyanide-based carbon nanoparticle phosphor containing amorphous carbon in the range of 95% to 99% by volume and graphite-like carbon in the range of 1% to 5% by volume.

More preferably, the concentration of the carbon source in the organic solvent is in the range of 0.1 mol/L or more and 0.15 mol/L or less. Even more preferably, the organic solvent is formamide and the carbon source is citric acid. In this case, the specified composition formula described below is satisfied, and the deviation (Duv) from the blackbody locus within the above chromaticity coordinates can be kept within the range of ±0.03. The deviation from the blackbody locus was evaluated in accordance with the evaluation method disclosed in JIS Z8725.

<White type>
A white carbon nanoparticle phosphor is a carbon nanoparticle phosphor that, when irradiated with light having a wavelength in the range of 300 nm or more and 380 nm or less, emits light whose color satisfies the (x, y) values on the CIE 1931 chromaticity coordinates of 0.3≦x<0.44 and 0.3≦y≦0.4.

In this case, in step S110, the carbon source is dissolved in formamide and/or N-methylformamide as an organic solvent, and a raw material solution is prepared by further dissolving at least one nitrogen source selected from the group consisting of ethylenediamine (EDA), diethanolamine (DEA), urea, thiourea, ethanolamine (EA), dopamine, L-cystine, L-arginine, ethylenediaminetetraacetic acid (EDTA), and cysteamine. This results in a white carbon nanoparticle phosphor containing less pyridine-type nitrogen than graphite-type nitrogen, and containing amorphous carbon in a range of 45% to 70% by volume and graphite-like carbon in a range of 30% to 55% by volume. Here, the total amount of amorphous carbon and graphite-like carbon is 100% by volume.

More preferably, the concentration of the carbon source in the organic solvent is in the range of 0.05 mol/L to 0.2 mol/L, and the concentration of the nitrogen source in the organic solvent is in the range of 0.05 mol/L to 1.5 mol/L. This range results in a white carbon nanoparticle phosphor containing amorphous carbon in the range of 53 vol% to 68 vol% and graphite-like carbon in the range of 32 vol% to 47 vol%.

More preferably, the concentration of the carbon source in the organic solvent is in the range of 0.1 mol/L or more and 0.15 mol/L or less, and the concentration of the nitrogen source in the organic solvent is in the range of 0.05 mol/L or more and 1.0 mol/L or less. Within these ranges, white carbon nanoparticle phosphors can be obtained efficiently.

More preferably, the organic solvent is formamide, the carbon source is citric acid, and the nitrogen source is at least one selected from the group consisting of ethylenediamine, diethanolamine, and urea. In this case, the specified composition formula described below is satisfied, and the deviation from the blackbody locus within the above chromaticity coordinates can be kept within ±0.01.

<Orange>
An orange carbon nanoparticle phosphor is a carbon nanoparticle phosphor that, when irradiated with light having a wavelength in the range of 300 nm or more and 380 nm or less, emits light whose color satisfies the (x, y) values on the CIE 1931 chromaticity coordinates of 0.44≦x≦0.6 and 0.3≦y≦0.45.

In this case, in step S110, the carbon source described above is dissolved in formamide as an organic solvent, and at least one nitrogen source selected from the group consisting of ammonium hydroxide, o-phenylenediamine, and p-phenylenediamine is further dissolved to prepare a raw material solution. This results in a lower content of pyridine-type nitrogen than that of graphite-type nitrogen, and results in an orange carbon nanoparticle phosphor containing amorphous carbon in the range of 60% to 90% by volume and graphite-like carbon in the range of 10% to 40% by volume. Here, the total amount of amorphous carbon and graphite-like carbon is 100% by volume.

More preferably, the concentration of the carbon source in the organic solvent is in the range of 0.05 mol/L to 0.2 mol/L, and the concentration of the nitrogen source in the organic solvent is in the range of 0.05 mol/L to 3.0 mol/L. This range results in an orange carbon nanoparticle phosphor containing amorphous carbon in the range of 77 vol% to 83 vol% and graphitic carbon in the range of 17 vol% to 23 vol%.

More preferably, the concentration of the carbon source in the organic solvent is in the range of 0.1 mol/L or more and 0.15 mol/L or less, and the concentration of the nitrogen source in the organic solvent is in the range of 0.5 mol/L or more and 2.5 mol/L or less. Within these ranges, orange carbon nanoparticle phosphors can be obtained efficiently. Even more preferably, the concentration of the nitrogen source in the organic solvent is in the range of 0.5 mol/L or more and 1 mol/L or less.

More preferably, the organic solvent is formamide, the carbon source is citric acid, and the nitrogen source is ammonium hydroxide. In this case, the specified composition formula described below is satisfied, and the deviation from the blackbody locus within the above chromaticity coordinates can be kept within ±0.01.

Next, the carbon nanoparticle phosphor of the present invention obtained in this manner will be described.
The nanoparticle phosphor of the present invention is primarily composed of carbon, but by using the above-mentioned raw material solution, it contains carbon, oxygen, nitrogen, and hydrogen. The primary carbon component contains amorphous carbon and graphite-like carbon, and controlling the amounts of these components allows for control of the emission color, chromaticity, and color temperature. Amorphous carbon is non-crystalline carbon, while graphite-like carbon is crystalline carbon. In powder X-ray diffraction, if a broad peak is observed near 2θ = 20.5°, it is determined that amorphous carbon is present, and if a sharp peak is observed near 2θ = 27°, it is determined that graphite-like carbon is present.

The nanoparticle phosphor of the present invention contains pyridine-type nitrogen, amide-type nitrogen, pyrrole-type nitrogen, and graphite-type nitrogen as nitrogen elements. The emission color, chromaticity, and color temperature can be controlled by adjusting the content of these elements. Here, pyridine-type nitrogen, amide-type nitrogen, pyrrole-type nitrogen, and graphite-type nitrogen are represented by the following structural formula. Note that R in amide-type nitrogen may be hydrogen or an alkyl group having 1 to 5 carbon atoms. The presence of these nitrogen elements can be determined from the peak position of the N1s spectrum obtained by X-ray photoelectron spectroscopy (XPS) measurement. These nitrogen elements are sometimes collectively referred to as nitrogen doping centers.

The inventors of the present application have discovered that carbon nanoparticle phosphors can be obtained using the above-mentioned manufacturing method, and that by controlling the amount of amorphous carbon and graphite-like carbon, the quantitative relationship between the nitrogen doping centers, and the composition, carbon nanoparticle phosphors with adjusted chromaticity and even on or near the blackbody locus can be obtained. For ease of understanding, these carbon nanoparticle phosphors with adjusted chromaticity will be described as cyan, white, or orange carbon nanoparticle phosphors.

<Cyan>
A cyan carbon nanoparticle phosphor is a carbon nanoparticle phosphor that, when irradiated with light having a wavelength in the range of 300 nm or more and 380 nm or less, emits light whose color satisfies the (x, y) values on the CIE 1931 chromaticity coordinates of 0.2≦x<0.3 and 0.25≦y≦0.4.

In this case, the content of pyridine-type nitrogen is greater than that of graphite-type nitrogen. Furthermore, if the total amount of amorphous carbon and graphite-like carbon is taken as 100 volume %, the cyan carbon nanoparticle phosphor contains amorphous carbon in the range of greater than 90 volume % and less than 99 volume % and graphite-like carbon in the range of 1 volume % to less than 10 volume %. The significant increase in amorphous carbon results in cyan emission. The content of amorphous carbon and graphite-like carbon is calculated from the intensity ratio of the peaks at 2θ = 20.5° and 27° in powder X-ray diffraction.

Cyan carbon nanoparticle phosphors more preferably contain amorphous carbon in the range of 95% to 99% by volume and graphite-like carbon in the range of 1% to 5% by volume. This allows for a phosphor with good color purity.

In the cyan carbon nanoparticle phosphor, preferably, the carbon element content p (atomic %), the nitrogen element content q (atomic %), and the oxygen element content r (atomic %) (where p+q+r=1) are each
0.58≦p≦0.65
0.22≦q≦0.30
0.12≦r<0.16
This makes it possible to suppress the deviation from the blackbody locus in the chromaticity coordinates to within the range of ±0.03. More preferably, the contents p and q satisfy the relationship 0.38<q/p≦0.41.

<White type>
A white carbon nanoparticle phosphor is a carbon nanoparticle phosphor that, when irradiated with light having a wavelength in the range of 300 nm or more and 380 nm or less, emits light whose color satisfies the (x, y) values on the CIE 1931 chromaticity coordinates of 0.3≦x<0.44 and 0.3≦y≦0.4.

In this case, the content of pyridine-type nitrogen is less than that of graphite-type nitrogen, and the white carbon nanoparticle phosphor contains amorphous carbon in a range of 45% to 70% by volume and graphite-like carbon in a range of 30% to 55% by volume. The amorphous carbon content is also greater than that of graphite-like carbon. Here, the total amount of amorphous carbon and graphite-like carbon is taken as 100% by volume.

The white carbon nanoparticle phosphor more preferably contains amorphous carbon in a range of 53% to 68% by volume and graphite-like carbon in a range of 32% to 47% by volume. This enables blue-white, white, and warm-white light emission.

In the white carbon nanoparticle phosphor, preferably, the carbon element content p (atomic %), the nitrogen element content q (atomic %), and the oxygen element content r (atomic %) (where p+q+r=1) are each
0.57≦p≦0.65
0.20≦q<0.26
0.16≦r<0.19
This makes it possible to suppress the deviation from the blackbody locus in the chromaticity coordinates to within the range of ±0.01. More preferably, the contents p and q satisfy the relationship 0.32<q/p<0.44.

<Orange>
An orange carbon nanoparticle phosphor is a carbon nanoparticle phosphor that, when irradiated with light having a wavelength in the range of 300 nm or more and 380 nm or less, emits light whose color satisfies the (x, y) values on the CIE 1931 chromaticity coordinates of 0.44≦x≦0.6 and 0.3≦y≦0.45.

In this case, the content of pyridine-type nitrogen is less than that of graphite-type nitrogen. The orange carbon nanoparticle phosphor contains amorphous carbon in a range of 60% to 90% by volume, and graphite-like carbon in a range of 10% to 40% by volume. Here, the total amount of amorphous carbon and graphite-like carbon is 100% by volume.

The orange carbon nanoparticle phosphor more preferably contains amorphous carbon in a range of 60% to 83% by volume and graphite-like carbon in a range of 17% to 40% by volume. This enables light emission with excellent color purity.

In the orange carbon nanoparticle phosphor, preferably, the carbon element content p (atomic %), the nitrogen element content q (atomic %), and the oxygen element content r (atomic %) (where p+q+r=1) are each
0.58≦p≦0.65
0.15≦q≦0.21
0.19≦r≦0.21
This makes it possible to suppress the deviation from the blackbody locus in the chromaticity coordinates to within the range of ±0.01. More preferably, the contents p and q satisfy the relationship 0.25<q/p<0.34.

As described above, the carbon nanoparticle phosphor of the present invention emits light with chromaticity adjusted by controlling the amount of amorphous carbon and graphitic carbon, the amount of nitrogen doping center, and the composition. However, what is particularly noteworthy is that a single material can emit light with a deviation of ±0.01 from the blackbody locus.

In addition, the carbon nanoparticle phosphor of the present invention emits light when irradiated with light (excitation light) having a wavelength in the range of 300 nm to 380 nm, but the emission wavelength also changes as the wavelength of the excitation light changes. That is, as the wavelength of the excitation light becomes longer, the emission wavelength also red-shifts to the longer wavelength side. For example, when irradiated with light having a wavelength in the range of 300 nm to 380 nm, a white carbon nanoparticle phosphor satisfies the (x, y) values on the CIE 1931 chromaticity coordinates of 0.3≦x<0.44 and 0.3≦y≦0.4, emitting white light. However, when the excitation light has a wavelength of 450 nm, it emits green light, when the excitation light has a wavelength of 525 nm, it emits yellow-green light, when the excitation light has a wavelength of 550 nm, it emits orange light, and when the excitation light has a wavelength of 600 nm, it emits red light.

The carbon nanoparticle phosphor of the present invention is composed of nanoparticles with nano-order particle sizes, preferably with diameters in the range of 1 nm to 20 nm. This range results in high luminous efficiency.

The carbon nanoparticle phosphor of the present invention may have functional groups or bonds such as -OH, -CONH ₂ , C═O, -COOH, C═C, O—C═O, C—H, and N—H. This allows for highly efficient visible light emission. These bonds are confirmed by infrared absorption spectroscopy.

The carbon nanoparticle phosphor of the present invention may be dispersed in a solvent, resin, or the like. This reduces the effect of concentration quenching and increases luminous efficiency. Such solvents may include, for example, dimethyl sulfoxide (DMSO), dimethylformamide, or water in addition to the organic solvents used in synthesis. The resin may be any water-soluble polymer that transmits light with wavelengths from the ultraviolet to the visible range, such as polyvinyl alcohol, sodium polyacrylate, polyacrylamide, polyethyleneimine, polyethylene oxide, polyvinylpyrrolidone, or carboxyl vinyl polymer. Such resins can be used to provide resin molded products such as thin films obtained by spin coating or dripping, bulk products obtained by drying, and fibers obtained by electrospinning. Such resin molded products are easy to handle.

When dispersed in a solvent, resin, etc., the carbon nanoparticle phosphor content is preferably in the range of 0.01% by mass or more and 5% by mass or less. Within this range, high luminescence intensity and high quantum efficiency can be expected. More preferably, the carbon nanoparticle phosphor content is in the range of 0.01% by mass or more and 1% by mass or less.

(Embodiment 2)
In the second embodiment, a light emitting device using the carbon nanoparticle phosphor of the present invention will be described.
FIG. 2 is a schematic diagram showing a light-emitting device using the carbon nanoparticle phosphor of the present invention.

The light-emitting device of the present invention comprises at least an excitation source and a phosphor, and the phosphor includes the carbon nanoparticle phosphor described above. This configuration makes it possible to provide a light-emitting device that emits light of a desired color.

Excitation sources include light-emitting diodes, laser diodes, organic electroluminescent devices, semiconductor lasers, and fluorescent lamps, but those that emit light with a peak in the range of 200 nm to 600 nm are used. Among these, purple light-emitting diodes with a peak in the range of 330 nm to 420 nm are preferred, as they can efficiently excite the carbon nanoparticle phosphor of the present invention.

The light-emitting device 200 in Figure 2 is a substrate-mounted white light-emitting diode lamp. The light-emitting device 200 has lead wires 210 and 220, which are fixed to a white alumina substrate 230 with high visible light reflectance. A purple light-emitting diode element 240 with an emission peak wavelength of 405 nm is placed on one end of one of the lead wires 210 and electrically connected by conductive paste or the like. The purple light-emitting diode element 240 is electrically connected to the other lead wire 220 by a thin gold wire 250. The other ends of the lead wires 210 and 220 extend outside and function as electrodes.

The purple light-emitting diode element 240 is covered with a resin molded body 260 in which the carbon nanoparticle phosphor of the present invention is dispersed in resin. Here, the carbon nanoparticle phosphor is a white carbon nanoparticle phosphor. A wall member 280 made of a white silicone resin or the like is provided on the alumina substrate 230, and the purple light-emitting diode element 240 covered with the resin molded body 260 is located in the center of the wall member 280. In the center of the wall member 280, the purple light-emitting diode element 240 covered with the resin molded body 260 is sealed with a transparent resin 270 such as epoxy resin.

When current is applied to the lead wires 210, 220 of the light-emitting device 200, the purple light-emitting diode element 240 emits light with a peak wavelength of 405 nm. This light enters the resin molded body 260 of the present invention, exciting the carbon nanoparticle phosphors within the resin molded body 260, which then emit white light. The white light passes through the resin 270 and exits to the outside. In this way, the light-emitting device 200 functions to emit white light.

Here, resin molding 260 is configured to cover purple light-emitting diode element 240, but this is not limited to this. For example, resin molding 260 may be placed on the light-emitting surface of purple light-emitting diode element 240, or may be placed on resin 270. Alternatively, instead of resin 270, the entire structure may be resin molding 260.

In addition, while the resin molded body 260 has been described here as containing only carbon nanoparticle phosphors that emit white light as the phosphor, it goes without saying that cyan carbon nanoparticle phosphors or orange carbon nanoparticle phosphors may also be used. Furthermore, a wavelength-tunable laser may be used instead of the purple light-emitting diode element to provide a light-emitting device that can be tuned from white to red. Such modifications are also within the scope of the present invention.

Although a substrate-mounted white light-emitting diode lamp has been described with reference to Figure 2, the carbon nanoparticle phosphor of the present invention may also be used in a bullet-type white light-emitting diode lamp. Such modifications can be easily made by those skilled in the art.

(Embodiment 3)
In the third embodiment, a test paper using the carbon nanoparticle phosphor of the present invention will be described.
The present inventors have discovered that the luminescence intensity of the carbon nanoparticle phosphor of the present invention decreases when it comes into contact with water (H ₂ O) or heavy water (D ₂ O). By utilizing this property, a test paper can be provided that can easily determine whether a test solution contains water (H ₂ O) or heavy water (D ₂ O).

Figure 3 is a schematic diagram showing a test paper using the carbon nanoparticle phosphor of the present invention.

Test paper 300 consists of a backing paper 320 with an inspection area 310. The inspection area 310 contains the carbon nanoparticle phosphor described in embodiment 1. While there are no particular limitations on the backing paper 320, as long as it is paper capable of supporting the dispersed carbon nanoparticle phosphor, cellulose fiber is preferred. Cellulose fiber has surface functional groups such as -OH and -COOH, which adsorb the carbon nanoparticle phosphor and prevent it from aggregating with other particles. Therefore, the use of cellulose fiber reduces concentration quenching, provides excellent luminescence intensity, and allows for easy visual evaluation of the test paper.

In Figure 3, six test areas 310 are shown, but the test area may cover the entire mount. This division is advantageous for simultaneously identifying multiple test liquids. Such a test paper 300 is manufactured by dropping a composition in which carbon nanoparticle fluorescent material is dispersed onto the mount 320 and then drying it.

Next, a method for determining whether a test liquid contains water using such a test paper 300 will be described. Here, the water may be light water (H ₂ O) or heavy water (D ₂ O). First, a water-free liquid is dropped as a control into one of the test areas 310 of the test paper 300. Next, the test liquid is dropped into the other areas, and an excitation source is irradiated to observe the resulting light emission. If there is a test area where the light emission intensity is visually lower than that of the control, it can be determined that the test liquid in that area contains water.

Since the emission intensity decreases linearly with the water content, if the relationship between water content and emission intensity is maintained in advance, the water content can be determined by measuring the emission spectrum.

Furthermore, the luminescence intensity of the carbon nanoparticle phosphor of the present invention differs depending on whether it is light water or heavy water. The higher the proportion of heavy water, the higher the luminescence intensity; and the higher the proportion of light water, the lower the luminescence intensity. Utilizing these characteristics, the content of light water and heavy water in the test liquid can be determined.

The present invention will now be described in detail using specific examples, but please note that the present invention is not limited to these examples.

[Examples 1 to 8]
In Examples 1 to 8, carbon nanoparticle phosphors were synthesized using a solvothermal method.

Specifically, under the conditions shown in Table 1, a raw material solution was prepared by dissolving citric acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a carbon source, and optionally ethylenediamine (EDA, manufactured by Sigma-Aldrich Corporation, purity >99.5%, specific gravity D = 0.899 g/mL), dimethylamine (DEA, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), urea (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and ammonium hydroxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as nitrogen sources in formamide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as an organic solvent (step S110 in Figure 1). The raw material solution was then heated under the heating conditions shown in Table 1 (step S120 in Figure 1).

The resulting product was centrifuged (rotation speed: 800 rpm) and washed several times with Milli-Q water and ethanol. After washing, the product was dried in a vacuum (vacuum degree: 1 to 1000 Pa) at 60°C for 4 hours. In this way, powder samples of Examples 1 to 8 were obtained. Next, the powder samples of Examples 1 to 8 were dispersed in dimethyl sulfoxide (DMSO, Fujifilm Wako Pure Chemical Industries, Ltd.) and passed through a 20 nm syringe. At this time, the concentration of the product in DMSO was 0.0025% by mass (0.025 mg/mL). In this way, liquid samples of Examples 1 to 8 were obtained.

The liquid samples of Examples 1 to 8 were irradiated with a lamp emitting light with a wavelength of 365 nm. The results are shown in Figures 4 to 6. The powder samples of Examples 1 to 8 were subjected to X-ray diffraction analysis using an X-ray diffractometer (Rigaku Corporation, Rint Ultima III). The results are shown in Figure 7. The liquid samples of Examples 1 to 8 were prepared using the dispersion method and observed using a high-resolution transmission electron microscope (HR-TEM) (JEOL Corporation, JEM 2100F). The results are shown in Figures 8 to 10. Chemical state analysis and composition analysis of the liquid samples of Examples 1 to 8 were performed using an X-ray photoelectron spectroscopy (XPS) analyzer (ULVAC-PHI, Inc., Quautera SXM). The results are shown in Figures 11 to 15 and Table 2.

FTIR spectra of the liquid samples of Examples 1 to 8 were obtained by attenuated total reflection infrared spectroscopy (ATR-FTIR) using a spectrophotometer (Nicolet iS50 FTIR, manufactured by Thermo Scientific). Each measurement was accumulated 50 times. The results are shown in Figure 16. The absorption spectra of the liquid samples of Examples 1 to 8 were measured using an ultraviolet-visible-near-infrared spectrophotometer (V-570, manufactured by JASCO Corporation). The results are shown in Figure 17. The emission spectra of the liquid samples of Examples 1 to 8 were measured using a spectrofluorometer (FP-8500, manufactured by JASCO Corporation). The CIE chromaticity (x, y) was calculated from the emission spectra. These results are shown in Figures 18 to 24. These results will be summarized below.

FIG. 4 is a diagram showing the reaction formula of Example 1 and the luminescence of the liquid sample of Example 1.
FIG. 5 shows the reaction formulas of Examples 2 to 6 and the luminescence of the liquid samples of Examples 2 to 6.
FIG. 6 shows the reaction formulas of Examples 7 and 8 and the luminescence of the liquid samples of Examples 7 and 8.

Figures 4 to 6 are shown in grayscale. Figure 4 shows that when the liquid sample of Example 1 was irradiated with a UV lamp, it emitted blue (cyan-based) light. Figure 5 shows that when the liquid samples of Examples 2 to 6 were irradiated with a UV lamp, they emitted light ranging from bluish-white to white to warm white (white-based). Figure 6 shows that when the liquid samples of Examples 7 and 8 were irradiated with a UV lamp, they emitted light ranging from orange (orange-based). This demonstrates that a fluorescent composition (phosphor) can be obtained by carrying out the method described in Figure 1. Furthermore, as shown in Table 1, it was demonstrated that the emitted color can be changed by selecting the nitrogen source and concentration.

Figure 7 shows the XRD patterns of the powder samples of Examples 1, 2, and 7.

As shown in Figure 7, all XRD patterns show a broad peak near 2θ = 20.5° and a sharp peak near 2θ = 27°, indicating that amorphous carbon and graphite-like carbon are the main components. Although not shown, the powder samples of Examples 3 to 6 and 8 also showed similar patterns. The volume percentages of amorphous carbon and graphite-like carbon were calculated from the ratio of these peak intensities. The results are shown in Table 2.

Table 2 shows that the amorphous carbon content is greater than that of graphite-like carbon, but the content varies depending on the emitted color. Phosphors that emit cyan light have very little graphite-like carbon and significantly more amorphous carbon; phosphors that emit white light have a relatively high amount of graphite-like carbon, but more amorphous carbon; and phosphors that emit orange light have a small amount of graphite-like carbon and more amorphous carbon.

FIG. 8 shows TEM images of the liquid sample of Example 1 at various magnifications.
FIG. 9 shows TEM images of the liquid sample of Example 2 at various magnifications.
FIG. 10 shows TEM images of the liquid sample of Example 7 at various magnifications.

Figure 8 confirms a layer structure derived from amorphous carbon, as indicated by the dotted line. Furthermore, when the circled area was enlarged, lattice fringes were observed, indicating crystalline graphite-like carbon. Figures 9 and 10 confirm numerous nanoparticles, indicated by black spots, with particle sizes ranging from 1 nm to 20 nm. The particle size was determined by obtaining a transmission electron microscope (TEM) image at a magnification of 1000x or greater and measuring the particle sizes of at least 100 nanoparticles in any 500 nm square area. Since nanoparticles are not perfectly spherical, the longest diameter is taken as the particle size of the nanoparticle. These findings demonstrate that carbon nanoparticle phosphors are dispersed in the liquid sample.

Figure 11 shows the XPS spectra of the liquid samples of Examples 1, 2, and 7.

Figure 11 shows that carbon, oxygen, and nitrogen elements are present in the carbon nanoparticle phosphors in the liquid samples of Examples 1, 2, and 7. Note that peaks due to elements in the solvent (DMSO) have been removed from the XPS spectra. The liquid samples of Examples 3 to 6 and 8 also exhibited similar XPS spectra.

According to the composition analysis in Table 3, in the carbon nanoparticle phosphor of the present invention, the carbon element content p (atomic %), the nitrogen element content q (atomic %), and the oxygen element content r (atomic %) (where p+q+r=1) are, respectively:
0.58≦p≦0.65
0.22≦q≦0.30
0.12≦r<0.16
If the above condition is satisfied, blue (cyan) light is emitted.
0.57≦p≦0.65
0.20≦q<0.26
0.16≦r<0.19
If the above conditions are met, the light will be bluish white to white to warm white (white-based),
0.58≦p≦0.65
0.15≦q≦0.21
0.19≦r≦0.21
It was shown that when the above condition is satisfied, orange light is emitted.

FIG. 12 shows the deconvoluted HRXPS spectrum of the liquid sample of Example 1.
FIG. 13 shows the deconvoluted HRXPS spectrum of the liquid sample of Example 2.
FIG. 14 shows the deconvoluted HRXPS spectrum of the liquid sample of Example 7.

Figures 12 to 14 all show the results of deconvolution of the N-1s peak in the XPS spectrum shown in Figure 11. Figures 12 to 14 show four main peaks, corresponding to binding energies of 398.7 eV, 399.6 eV, 400.3 eV, and 401.3 eV, respectively. These peaks are therefore types of nitrogen doping centers within the carbon framework, corresponding to pyridine-type nitrogen, amide-type nitrogen, pyrrole-type nitrogen, and graphite-type nitrogen, respectively. Although not shown, the deconvoluted HRXPS spectra of the liquid samples of Examples 3 to 6 and 8 were similar.

Figure 15 shows the change in the amount of nitrogen doping centers calculated from Figures 12 to 14.

Figure 15 shows that the quantitative relationship of nitrogen doping centers varies depending on the emission color. In particular, the relationship between pyridine-type nitrogen and graphite-type nitrogen contributes to the emission color, and the same investigation was conducted for Examples 3 to 6 and 8. The results are shown in Table 4.

According to Table 4, there is a tendency that phosphors that emit cyan light have a greater amount of pyridine-type nitrogen than graphite-type nitrogen, phosphors that emit white light have a lesser amount of pyridine-type nitrogen than graphite-type nitrogen, and phosphors that emit orange light have a lesser amount of pyridine-type nitrogen than graphite-type nitrogen.

Figure 16 shows the ATR-FTIR spectra of the liquid samples of Examples 1, 2, and 7.

It was found that the carbon nanoparticle phosphors in the liquid samples of Examples 1, 2, and 7 had C=O bonds due to amide bonds (near 1697 cm ^-1 ), C=C bonds due to aromatics (near 1530 cm ^-1 ), and OH bonds and C-H bonds due to phenols (near 1310 to 1380 cm ^-1 ). This indicates that the carbon nanoparticle phosphors of the present invention have functional groups and bonds such as -OH, C=O, C=C, and C-H.

Figure 17 shows the absorption spectra of the liquid samples of Examples 1, 2, and 7.

Figure 17 shows that all samples effectively absorb light in the wavelength range of 200 nm to 600 nm. Although not shown, the absorption spectra of the liquid samples in Examples 3 to 6 and 8 were similar.

FIG. 18 shows the emission spectra of the liquid samples of Examples 1, 2 and 7.
FIG. 19 is a diagram showing the absorption spectra of the liquid samples of Examples 3 and 4.
FIG. 20 shows the absorption spectra of the liquid samples of Examples 5 and 6.

Figures 18 to 20 show the emission spectra when each liquid sample was irradiated with an excitation wavelength of 370 nm. Figures 19 and 20 also show the emission spectrum of Example 2 shown in Figure 1.

The emission spectrum of Example 1 showed a peak at 450 nm, indicating blue light emission. The emission spectrum of Example 7 showed a peak at 616 nm, indicating orange light emission. On the other hand, the emission spectrum of Example 2, unlike those of Examples 1 and 7, showed a broad emission spectrum with multiple wavelength components, with peaks at 478 nm, 514 nm, and 612 nm. This also demonstrated that the carbon nanoparticle phosphor in the liquid sample of Example 2 emitted white light.

The emission spectra of Examples 3 to 6 showed a broad emission spectrum with multiple wavelength components, similar to that of Example 2, but the differences in the intensity of each wavelength component resulted in white light emission with different color rendering properties.

From the above, by adopting the method of the present invention, it is possible to provide carbon nanoparticle phosphors that emit blue (cyan-based), white, or orange light by selecting the raw material components and adjusting their concentrations. Furthermore, the present invention provides a method for synthesizing carbon nanoparticle phosphors that allow for excellent adjustment of color rendering properties.

Figure 21 shows a CIE chromaticity diagram plotting the emissions of the liquid samples of Examples 1 to 8.

The chromaticity x and y values calculated from the emission spectra in Figures 18 to 20 were plotted on the CIE 1931 chromaticity diagram. Figure 21 also shows the blackbody locus. Carbon nanoparticle phosphors are available whose emitted color can be changed by selecting raw materials and adjusting their concentrations, but surprisingly, it was found that the emitted color can also change along the blackbody locus. For example, it was found that a white carbon nanoparticle phosphor that emits white light can emit light with a deviation of ±0.01 (a range of -0.01 to +0.01) from the blackbody locus, depending on the conditions.

FIG. 22 shows two-dimensional emission mapping of the liquid sample of Example 1.
FIG. 23 shows two-dimensional emission mapping of the liquid sample of Example 2.
FIG. 24 shows two-dimensional emission mapping of the liquid sample of Example 7.

Figures 22 to 24 are shown in grayscale, with brighter areas indicating light emission. Figures 22 to 24 show that for all liquid samples, the emission wavelength changes when the wavelength of the excitation light is changed. The dependency of the excitation wavelength on the emission wavelength for liquid sample Example 7 in Figure 24 is smaller than that for liquid samples Example 1 in Figure 22 and Example 2 in Figure 23. This is thought to be because the liquid sample in Example 7 contains a carbon nanoparticle phosphor that emits orange light, but as shown in the absorption spectrum in Figure 17, absorption decreases at wavelengths above 600 nm, making it difficult to emit light. For simplicity, the above results are summarized in Table 5.

[Example 9]
In Example 9, the powder samples of Examples 2 to 4 were used to produce a thin film resin molded body in which carbon nanoparticle fluorescent material was dispersed in polyvinylpyrrolidone (PVP, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

PVP powder (2 g) was added to deionized water (60 mL) and held at 90°C for 3 hours to prepare a PVP aqueous solution (PVP concentration: 3.3% by mass). The powder samples obtained in Examples 2 to 4 (100 μg each) were added to 4 mL of PVP aqueous solution and stirred. This was drop-cast onto a quartz substrate and dried at 90°C for 1 hour to obtain a thin-film resin molded product. The carbon nanoparticle phosphor content in the resin molded product thus obtained was 0.07% by mass. The powder samples of Examples 2 to 4 are referred to as W-CD1, W-CD2, and W-CD3, respectively, and the resulting resin molded products are referred to as W-CD1@PVP, W-CD2@PVP, and W-CD3@PVP.

The appearance of the resulting resin molded article was observed and irradiated with a lamp emitting light with a wavelength of 365 nm. The observation results are shown in Figure 25. The emission spectrum of the resin molded article was measured using a spectrofluorophotometer. The CIE chromaticity (x, y) was calculated from the emission spectrum. These results are shown in Figures 26 and 27. These results will be summarized below.

Figure 25 shows the appearance of the resin molded body according to Example 9.

Figure 25(A) shows that the resin molded body of Example 9 is transparent in the visible range. Figure 25(B) shows that when irradiated with an ultraviolet lamp, all of the resin molded bodies of Example 9 emitted light in a range of colors from bluish-white to white to warm white (white-based). These emitted colors were similar to those of the liquid samples of Examples 2 to 4.

Figure 26 shows the fluorescence spectrum of the resin molded body of Example 9.

As shown in Figure 26, all of the resin molded products from Example 9 exhibited broad emission spectra, containing multiple wavelength components with peaks at 478 nm, 514 nm, and 612 nm. These emission spectra were similar to those of the liquid samples from Examples 2 to 4.

Figure 27 shows a CIE chromaticity diagram plotting the light emission of the resin molded body of Example 9.

Figure 27 also shows the blackbody locus. As with Examples 2 to 4, it was found that the white carbon nanoparticle phosphor that emits white light emits light with a deviation of ±0.01 (a range of -0.01 to +0.01) from the blackbody locus, even when combined with a resin or other material to form a molded product.

[Example 10]
In Example 10, test strips were prepared in which the powder sample of Example 2 was dispersed.
FIG. 28 shows the manufacturing procedure and testing of the test strip.

The powder sample of Example 2 was dispersed in DMSO to prepare a phosphor dispersion liquid (0.3% by mass, 3 mg/mL). Cellulose filter paper (Whatman®, cellulose filter) was used as the mount, and the phosphor dispersion liquid was dropped into three locations, areas 1 to 3, and dried at 80°C to obtain a test paper. Next, light water and heavy water were dropped as the test liquid into areas 1 and 3, respectively. In this case, water was used as the test liquid, so area 2, to which nothing was dropped, served as the control. This was irradiated with an ultraviolet lamp and the light emission was observed. The results are shown in Figure 29.

Figure 29 shows how the test paper is used for the assessment.

Figure 29 (A) shows the appearance of a test paper in which a phosphor dispersion liquid has been dropped onto cellulose filter paper, dispersing carbon nanoparticle phosphors. The carbon nanoparticle phosphors are contained in three areas, regions 1 to 3.

Figure 29(B) shows the test paper irradiated with an ultraviolet lamp before the test liquid is dropped on it. From Figure 29(B), it can be seen visually that there is no change in the luminescence intensity. Figure 29(C) shows the test paper irradiated with an ultraviolet lamp after the test liquid is dropped on it. When irradiated with an ultraviolet lamp, the luminescence intensity decreased in areas 1 and 3, where light water and heavy water were dropped, respectively, compared to area 2, which is the control. This demonstrates that the use of the test paper of the present invention makes it possible to easily determine whether a test liquid contains water.

Next, water containing 0 vol%, 2.5 vol%, 5 vol%, 10 vol%, 20 vol%, and 100 vol% heavy water was dropped onto the test paper carrying the carbon nanoparticle phosphor, and the emission spectrum was measured using a spectrophotometer. The results are shown in Figures 30 and 31.

FIG. 30 shows emission spectra for various types of water.
FIG. 31 is a graph showing the dependence of the luminescence intensity of FIG. 30 on the concentration of heavy water.

Figure 30 shows the emission spectrum when each area of the test paper is irradiated with an excitation wavelength of 370 nm. Figure 30 also shows the emission spectrum of the control (area where no water has been dropped). Figure 30 shows that the emission intensity of the peak near 600 nm decreases as the heavy water content decreases, i.e., as the light water content increases.

Figure 31 shows a plot of the emission intensity at an emission wavelength of 600 nm against the heavy water content. Figure 31 shows that the emission intensity increases linearly with the heavy water content.

This can be used to detect light water (H ₂ O) contained in heavy water (D ₂ O) or to determine its amount. This can be used as a simple and inexpensive test paper to detect the amount of light water or heavy water. Furthermore, by using DMSO, DMF, acetonitrile, ethanol, etc. instead of heavy water (D ₂ O), it is possible to determine the presence and amount of light water (H ₂ O) in them.

The present invention is advantageous in that it allows carbon nanoparticle phosphors with chromaticity adjustments to be produced simply by adjusting the raw materials. Furthermore, light-emitting devices can be provided using such carbon nanoparticle phosphors. In particular, carbon nanoparticle phosphors with specific compositions are excellent as phosphors that emit white light with high color rendering properties, making them suitable for use in white light-emitting devices such as white LEDs. Furthermore, because the luminous intensity of this material is significantly reduced by water, it can be used to provide a simple test paper that can measure the amount of water in heavy water, ethanol, etc., based on changes in luminous intensity.

200 Light emitting device 210, 220 Lead wire 230 Alumina substrate 240 Purple light emitting diode element 250 Gold thin wire 260 Resin molded body 270 Resin 300 Test paper 310 Test area 320 Mounting paper

Claims (18)

A carbon nanoparticle phosphor containing carbon, oxygen, nitrogen, and hydrogen elements,
Contains amorphous carbon and graphitic carbon,
The nitrogen element includes pyridine-type nitrogen, amide-type nitrogen, pyrrole-type nitrogen, and graphite-type nitrogen;
the content of the pyridine-type nitrogen is greater than that of the graphite-type nitrogen;
The amorphous carbon is in the range of more than 90% by volume to 99% by volume,
The graphite carbon satisfies the range of 1% by volume or more and less than 10% by volume,
A carbon nanoparticle phosphor, wherein when irradiated with light having a wavelength in the range of 300 nm to 380 nm, the color of light emitted by the carbon nanoparticle phosphor satisfies 0.2≦x<0.3 and 0.25≦y≦0.4 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates. the amorphous carbon satisfies the range of 95% by volume or more and 99% by volume or less,
The carbon nanoparticle phosphor according to claim 1 , wherein the graphite-like carbon is contained in an amount of 1% by volume or more and 5% by volume or less. The carbon element content p (atomic %), the nitrogen element content q (atomic %), and the oxygen element content r (atomic %) (where p+q+r=1) are respectively expressed as follows:
0.58≦p≦0.65
0.22≦q≦0.30
0.12≦r<0.16
The carbon nanoparticle phosphor according to claim 1 or 2 , which satisfies the above. The carbon element and nitrogen element contents p and q are
0.38<q/p≦0.41
The carbon nanoparticle phosphor according to claim 3 , which satisfies the above. A carbon nanoparticle phosphor containing carbon, oxygen, nitrogen, and hydrogen elements,
Contains amorphous carbon and graphitic carbon,
The nitrogen element includes pyridine-type nitrogen, amide-type nitrogen, pyrrole-type nitrogen, and graphite-type nitrogen;
the content of the pyridine-type nitrogen is less than that of the graphite-type nitrogen;
the amorphous carbon satisfies the range of 60% by volume or more and 90% by volume or less,
the graphite-like carbon satisfies the range of 10% by volume or more and 40% by volume or less,
A carbon nanoparticle phosphor, wherein when irradiated with light having a wavelength in the range of 300 nm to 380 nm, the color emitted by the carbon nanoparticle phosphor satisfies 0.44≦x≦0.6 and 0.3≦y≦0.45 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates. the amorphous carbon satisfies the range of 60% by volume or more and 83% by volume or less,
The carbon nanoparticle phosphor according to claim 5 , wherein the graphite-like carbon satisfies a range of 17% by volume to 40% by volume. The carbon element content p (atomic %), the nitrogen element content q (atomic %), and the oxygen element content r (atomic %) (where p+q+r=1) are respectively expressed as follows:
0.58≦p≦0.65
0.15≦q≦0.21
0.19≦r≦0.21
The carbon nanoparticle phosphor according to claim 5 or 6 , which satisfies the above. The carbon element and nitrogen element contents p and q are
0.25<q/p<0.34
The carbon nanoparticle phosphor according to claim 7 , which satisfies the above. The carbon nanoparticle phosphor according to any one of claims 1 to 8 , wherein the carbon nanoparticle phosphor has a diameter in the range of 1 nm to 20 nm. A light emitting device comprising at least an excitation source and a phosphor,
A light emitting device, wherein the phosphor comprises the carbon nanoparticle phosphor according to any one of claims 1 to 9 . The light emitting device according to claim 10 , wherein the phosphor is a resin molded body in which the carbon nanoparticle phosphor is dispersed. A test paper for determining whether a test liquid contains water,
The test paper contains carbon, oxygen, nitrogen, and hydrogen elements, and also contains amorphous carbon and graphite-like carbon, and the nitrogen element contains a carbon nanoparticle fluorescent material containing pyridine-type nitrogen, amide-type nitrogen, pyrrole-type nitrogen, and graphite-type nitrogen. The method for producing the carbon nanoparticle phosphor according to claim 1 comprises:
preparing a raw material solution by dissolving at least a carbon source in an organic solvent;
heating the raw material solution;
It encompasses
The method wherein the organic solvent is a nitrogen-containing organic solvent. The method according to claim 13 , wherein the concentration of the carbon source in the organic solvent satisfies the range of 0.05 mol/L to 0.2 mol/L. The method for producing a carbon nanoparticle phosphor according to claim 5 comprises:
preparing a raw material solution by dissolving at least a carbon source in an organic solvent;
heating the raw material solution;
It encompasses
the organic solvent is formamide;
The method wherein the preparing step further comprises dissolving at least one nitrogen source selected from the group consisting of ammonium hydroxide, o-phenylenediamine, and p-phenylenediamine in the organic solvent. the concentration of the carbon source in the organic solvent satisfies the range of 0.05 mol/L or more and 0.2 mol/L or less;
The method according to claim 15, wherein the concentration of the nitrogen source in the organic solvent satisfies the range of 0.05 mol/L to 3.0 mol/L. The method according to any one of claims 13 to 16, wherein the carbon source is at least one selected from the group consisting of citric acid, citric acid monohydrate, ammonium citrate, benzoic acid, ascorbic acid, glucose, fructose, and sucrose. A method for producing a carbon nanoparticle phosphor with chromaticity adjustment, comprising:
The carbon nanoparticle phosphor contains carbon, oxygen, nitrogen, and hydrogen elements, and includes amorphous carbon and graphite carbon, and the nitrogen element includes pyridine-type nitrogen, amide-type nitrogen, pyrrole-type nitrogen, and graphite-type nitrogen;
the content of the pyridine-type nitrogen is less than that of the graphite-type nitrogen, the amorphous carbon is in the range of 45 vol% to 70 vol%, and the graphite-like carbon is in the range of 30 vol% to 55 vol%,
When irradiated with light having a wavelength in the range of 300 nm to 380 nm, the color emitted by the carbon nanoparticle phosphor satisfies 0.3≦x<0.44 and 0.3≦y≦0.4 in terms of the (x, y) values on the CIE 1931 chromaticity coordinates;
preparing a raw material solution by dissolving at least a carbon source in an organic solvent;
heating the raw material solution;
It encompasses
the organic solvent is formamide;
The preparing step includes dissolving a nitrogen source, which is ethylenediamine, in the organic solvent;
the carbon source is citric acid;
the concentration of the carbon source in the organic solvent satisfies the range of 0.05 mol/L or more and 0.2 mol/L or less;
The method, wherein the concentration of the nitrogen source in the organic solvent satisfies the range of 0.05 mol/L to 1.5 mol/L.