JP7773231B2 - Near-infrared light-emitting phosphor and light-emitting device - Google Patents

Description

The present invention relates to a near-infrared light-emitting phosphor and a light-emitting device comprising a light source and a phosphor. More specifically, the present invention relates to a near-infrared light-emitting phosphor that emits near-infrared light, and a light-emitting device that emits near-infrared light and comprises a light source and a phosphor.

Light-emitting diodes (LEDs) that use GaAs-based or InP-based compound semiconductors such as GaInAs are known as light-emitting devices that emit near-infrared light. These LEDs are widely used in a variety of remote control sensors, security systems, in-vehicle cameras, and for inspecting packages, contents, and foreign objects. Furthermore, because light in the near-infrared region has excellent biological permeability, it is ideal for quality inspection in the medical, agricultural, and food industries, as well as for measuring vital information such as hemoglobin and oxygen levels in the blood. Furthermore, because near-infrared light can also be used as a heat source, there is strong demand for it as a light-emitting device to prevent snow accumulation on LED traffic lights.

However, the near-infrared light emitted by LEDs has a narrow half-width and can only be used at specific wavelengths, making it insufficient as a light source for medical devices or spectroscopic analysis, where it is desirable to have light containing a variety of wavelength components.

As one of the phosphors that emit light in the near-infrared region, a phosphor doped with Cr ⁴⁺ is known (see, for example, Non-Patent Documents 1 and 2).

Non-Patent Document _{1 reports the luminescence characteristics of glass ceramics containing nanophosphors made of Zn2SiO4, Mg2SiO4, Li2MgSiO4, and Li2ZnSiO4 doped with Cr4 + when} ^excited _with light having a wavelength of 800 nm. However, glass ceramics are expensive because they must be processed into the desired shape after being cooled and solidified from a high-temperature melt, which has hindered their widespread use.

Non-Patent Document 2 reports the luminescence characteristics of phosphors obtained by adding Cr ⁴⁺ to Li ₂ MgSiO ₄ and Li ₂ ZnSiO ₄ when excited with light having a wavelength of 760 nm, but the luminescence intensity in the near-infrared region is insufficient.

Yixi Zhuang, Setsuhisa Tanabe, and Jianrong Qiu, J. Am. Ceram. Soc. , 97 [11] 3519-3523 (2014). Cecile Jousseume, Daniel Vivien, Andree Kahn-Harari, B. Z. Malkin, J. Mater. Chem. , 2002, 12, 1525-1529.

Conventional near-infrared emitting lighting devices are composed of only specific wavelength components with narrow half-widths, making them unsuitable for biological applications or analytical equipment, which require a wide range of wavelengths. Furthermore, by analogy with white LEDs, which combine blue LEDs with phosphors, there are high hopes for light-emitting devices that combine blue LEDs with near-infrared emitting phosphors.

The present invention was made in consideration of the above circumstances, and aims to provide a near-infrared light-emitting phosphor and a light-emitting device that emits near-infrared light.

Under these circumstances, the inventors have discovered a light-emitting device comprising a light source and a phosphor, which uses a phosphor that has high luminescence intensity when excited by red light, thereby emitting near-infrared light with a wide spectral range and high luminescence intensity. They have also discovered a phosphor suitable for this purpose. Its configuration is as follows:

The near-infrared light-emitting phosphor of the present invention is a powder of M(1) _2M (2)M(3) _O4 crystal (wherein M(1) is a metal element that is Li and/or Na, M(2) is at least one metal element selected from the group consisting of Zn, Mg, Ca, and Sr, and M(3) is an element that is Si) to which Cr has been added, and has a median average particle size in the range of 0.1 μm to 50 μm, thereby solving the above-mentioned problems.
The near-infrared light may have a peak in a wavelength range of 1050 nm or more and 1350 nm or less, and the half width of the peak may be 150 nm or more and 300 nm or less.
The M(1) may be Li.
It may be excited by light having a wavelength in the range of 600 nm to 800 nm.
It may be excited with light having a wavelength in the range of 380 nm to 480 nm.
The M(1) ₂ M(2) M(3) O ₄ crystal may be at least one selected from the group consisting of Li ₂ ZnSiO ₄ , Li ₂ MgSiO ₄ , and Li ₂ CaSiO ₄ .
The light emitting device according to the present invention includes a light emitting source and a phosphor, and the phosphor contains the near-infrared light emitting phosphor, thereby solving the above-mentioned problems.
The light emitting source may emit light having a peak in the wavelength range of 600 nm or more and 800 nm or less.
The light emitting source may be at least one selected from the group consisting of a light emitting diode (LED), a laser diode (LD), an inorganic electroluminescence (inorganic EL), and an organic electroluminescence (organic EL).

The light-emitting device of the present invention comprises a light source and a phosphor, and contains a near-infrared-emitting phosphor that emits near-infrared light when the phosphor is excited. This makes it possible to provide a light-emitting device that emits near-infrared light. In particular, the near-infrared light emitted by the phosphor has a peak in the wavelength range of 1050 nm to 1350 nm, with a half-width of 150 nm or more, resulting in a light-emitting device that emits near-infrared light with a wide spectral range. Such a light-emitting device is excellent as a near-infrared lamp.

1 is a schematic diagram showing a light-emitting device of the present invention. FIG. 2 is a schematic diagram showing another light-emitting device of the present invention. FIG. 2 is a diagram showing the emission spectrum of phosphor A. FIG. 10 is a diagram showing the excitation spectrum of phosphor A. FIG. 10 is a diagram showing the emission spectrum of phosphor C. FIG. 10 is a diagram showing the emission spectrum of phosphor D. FIG. 10 is a diagram showing the emission spectrum of phosphor E. FIG. 2 is a diagram showing the emission spectrum of phosphor F. 1 is an excitation and emission spectrum of a CaAlSiN ₃ :Eu phosphor.

The present invention will be described in detail below.
(Embodiment 1)
In the first embodiment, a light emitting device that emits near-infrared light using a phosphor that emits near-infrared light by red excitation and a light source will be described.
FIG. 1 is a schematic diagram showing a light-emitting device of the present invention.

Figure 1 shows a bullet-shaped light-emitting diode lamp as a specific example of a light-emitting device 1. As a light-emitting device, the light-emitting diode lamp includes a light source 4 and a near-infrared light-emitting phosphor 7 that emits near-infrared light when excited as a phosphor, thereby emitting near-infrared light.

In the light-emitting device 1 of Figure 1, a light source 4 is placed in a recess 2a in a lead wire 2 for mounting an element. The lead wire 2 is electrically connected to the lower electrode 4a of the light source 4, and the upper electrode 4b of the light source 4 is electrically connected to the lead wire 3 by a bonding wire 5. The light source 4 is covered with a first resin 6 in which a near-infrared light-emitting phosphor 7 is dispersed, and the entire element is sealed with a second resin 8. While Figure 1 shows a specific configuration example, this is merely an example, and those skilled in the art can easily modify it within the scope of ordinary skill in the art.

The light-emitting device of the present invention is composed of a light source and a phosphor, and emits near-infrared light by exciting the phosphor.

The near-infrared light-emitting phosphor 7 of the present invention preferably has a peak in the wavelength range of 1050 nm or more and 1350 nm or less, with a half-width of 150 nm or more. As a result, the light-emitting device 1 of the present invention has a peak in the wavelength range of 1050 nm or more and 1350 nm or less, with a half-width of 150 nm or more, and is therefore capable of emitting near-infrared light with a wide spectral range. While there is no particular upper limit for the half-width, a value of 300 nm or less makes it possible to provide a light-emitting device 1 that emits near-infrared light with a wide spectral range.

The near-infrared light-emitting phosphor 7 of the present invention is not particularly limited as long as it is a material that is excited mainly by red light, preferably light having a wavelength in the range of 600 nm to 800 nm, and emits a light component that has a peak in the wavelength range of 1050 nm to 1350 nm and a half-width of 150 nm or more. However, the material is preferably an inorganic crystal containing tetravalent Cr, and a phosphor that emits near-infrared light by luminescence derived from tetravalent Cr is preferred because of its high emission intensity.

The inorganic crystal of the near-infrared light-emitting phosphor 7 of the present invention is preferably an M(1) _2M (2)M(3) _O4 crystal (wherein M(1) is a metal element selected from the group consisting of Li and/or Na, M(2) is at least one metal element selected from the group consisting of Zn, Mg, Ca, and Sr, and M(3 ₎ is an element selected from the group consisting of Si and/ _or Ge) to which Cr has been added. This is preferable because it results in particularly high emission intensity. Examples of such phosphors include _Zn2SiO4 :Cr4 ⁺ , _Mg2SiO4 : _Cr4 ⁺ , _Li2MgSiO4 :Cr4 ⁺ , _{and Li2ZnSiO4} :Cr4 ⁺ . Here, ":Cr4 ⁺ " indicates that tetravalent Cr has been added to the respective host materials.

These phosphors are excited not only by the red light having a peak in the wavelength range of 600 nm to 800 nm mentioned above, but also by light having a peak in the wavelength range of 380 nm to 480 nm (blue-violet and blue), and can emit near-infrared light having a peak in the wavelength range of 1050 nm to 1350 nm and a half-width of 150 nm or more.

The method for producing such near-infrared-emitting phosphor 7 is not particularly limited. For example, starting materials prepared from a mixture of a compound containing M(1), a compound containing M(2), and a compound containing M(3) in such a way that the composition ratio of the metal elements matches the composition ratio of the inorganic crystal described above may be fired. The compounds may be silicides, oxides, carbonates, etc. containing the respective metal elements. The firing may be a two-stage firing, for example, a first firing at a temperature greater than 700°C and less than 1500°C in an oxygen-containing atmosphere, followed by a second firing at a temperature greater than 500°C and less than 1200°C in an inert gas atmosphere such as argon.

In particular, the inorganic crystal of the near-infrared light-emitting phosphor 7 of the present invention preferably contains Si, and contains 1 atomic % to 6 atomic % of Cr relative to the Si element in the inorganic crystal. This is preferable because it results in high emission intensity, particularly in the near-infrared region. If the Cr content exceeds 10 atomic %, concentration quenching may occur, resulting in a decrease in external quantum efficiency.

The phosphor used in the light-emitting device 1 is preferably a powder with a median average particle size of 0.1 μm or more and 50 μm or less. This allows for easy dispersion in the light-transmitting body (referred to as first resin 6 in Figure 1) that makes up the LED, thereby increasing the luminous intensity. Examples of light-transmitting bodies include acrylic resin, silicone resin, and glass. These materials have excellent translucency to light from the light source 4, allowing for highly efficient excitation of the phosphor.

The median mean particle diameter d50 is defined as follows: In sedimentation measurements, particle diameter is defined as the diameter of a sphere with an equivalent sedimentation velocity; in laser scattering measurements, it is defined as the diameter of a sphere with equivalent scattering characteristics. The distribution of particle diameters is also called particle size (particle size) distribution. In particle size distributions, the particle diameter at which the total mass of particles larger than a certain particle size accounts for 50% of the total mass of the powder is defined as the mean particle diameter d50. This definition and terminology are well known to those skilled in the art and are described in various documents, such as JIS Z8901 "Test Powders and Test Particles" and Chapter 1 of "Fundamental Properties of Powders" (ISBN 4-526-05544-1), compiled by the Society of Powder Technology. In this study, samples were dispersed in water containing sodium hexamethacrylate as a dispersant, and the cumulative frequency distribution of particle diameters converted into volume was measured using a laser scattering measuring device. Note that the volume-converted and weight-converted distributions are equivalent. The particle size corresponding to 50% of this cumulative frequency distribution was determined and designated the median average particle size d50. Hereinafter, please note that the average particle size in this specification is based on the median value (d50) of the particle size distribution measured by the particle size distribution measurement means using the laser scattering method described above. Various means for determining average particle size other than those described above have been developed and are still being developed, and slight differences in the measured values may occur. However, the meaning and significance of average particle size itself is clear, and it should be understood that it is not necessarily limited to the means described above.

The phosphor used in the light-emitting device 1 is preferably a powder with an average primary particle aspect ratio of 1 or more and 20 or less. This is preferable because it facilitates dispersion in the light-transmitting body (first resin 6 in Figure 1) that constitutes the LED, thereby increasing the luminescence intensity. The average primary particle aspect ratio is determined by randomly selecting 100 particles from five fields of view in a scanning electron microscope photograph, measuring the long and short diameters of these particles, calculating the long diameter/short diameter value as the aspect ratio, and then calculating the proportion of particles with an aspect ratio of 20 or less.

The light source 4 used in the light-emitting device 1 is not particularly limited in wavelength as long as it can excite the near-infrared light-emitting phosphor 7, but preferably emits light with a peak in the wavelength range of 600 nm to 800 nm. This allows the near-infrared light-emitting phosphor 7 of the present invention to efficiently absorb light in the 600 nm to 800 nm range, increasing the emission intensity.

The light emitting source 4 is preferably at least one selected from the group consisting of a light emitting diode (LED), a laser diode (LD), an inorganic electroluminescent device (inorganic EL), and an organic electroluminescent device (organic EL). These light emitting sources are capable of emitting light in the above-mentioned wavelength range.

More preferably, the light source 4 is an LED or laser diode that emits light with a peak in the wavelength range of 600 nm to 800 nm and uses at least one semiconductor selected from the group consisting of GaAs, AlGaAs, GaP, GaAlP, and AlGaInP. Among these, red LEDs are preferred because they are inexpensive and have high emission intensity. GaAs, AlGaAs, GaP, GaAlP, and AlGaInP-based LEDs are preferred as such LEDs or laser diodes because they emit strong red light and are easy to excite the phosphor of the present invention.

When the light source 4 is an LED, the light-emitting device can be manufactured using an excitation LED and a phosphor by known methods such as those described in Japanese Patent Application Laid-Open Nos. 5-152609 and 7-99345.

When electricity flows through the light source 4 of this light-emitting device 1 via the lead wire 2, the light source 4 emits red light, for example, light with a peak in the wavelength range of 600 nm to 800 nm. The near-infrared light-emitting phosphor 7 is excited by the red light emitted by the light source 4 and emits near-infrared light, for example, light with a peak in the wavelength range of 1050 nm to 1350 nm, with a half-width of 150 nm or more. This is how the light-emitting device 1 of the present invention operates.

Figure 2 is a schematic diagram showing another light-emitting device of the present invention.

Figure 2 shows a substrate-mounted chip-type light-emitting diode lamp as a specific example of the light-emitting device 11. The light-emitting diode lamp as the light-emitting device 11 includes a light source 14 and a near-infrared light-emitting phosphor 17 that emits near-infrared light when excited as a phosphor, thereby emitting near-infrared light.

In the light-emitting device 11 of Figure 2, a light source 14 is placed on a lead wire 12 fixed on a substrate 19. The lead wire 12 is electrically connected to the lower electrode 14a of the light source 14, and the upper electrode 14b of the light source 14 is electrically connected to the lead wire 13 by a bonding wire 15. The light source 14 is covered with a first resin 16 in which a near-infrared light-emitting phosphor 17 is dispersed, and the entire device is sealed with a second resin 18. A wall member 20 with a hole in the center is fixed on the substrate 19. While Figure 2 shows a specific configuration example, this is just one example, and those skilled in the art can easily modify it within the scope of ordinary skill in the art.

Here, the light emitting source 14 and near-infrared light emitting phosphor 17 are similar to the light emitting source 4 and near-infrared light emitting phosphor 7 described in Figure 1, respectively, and therefore their description will be omitted. Furthermore, components similar to those in Figure 1 are given the same names, and their description will be omitted.

When electricity flows through the light source 14 of this light-emitting device 11 via the lead wire 12, the light source 14 emits red light, for example, light with a peak in the wavelength range of 600 nm to 800 nm. The near-infrared light-emitting phosphor 17 is excited by the red light emitted by the light source 14 and emits near-infrared light, for example, light with a peak in the wavelength range of 1050 nm to 1350 nm, with a half-width of 150 nm or more. This is how the light-emitting device 11 of the present invention operates.

In Figures 1 and 2, when _{inorganic crystals such as those typified by Zn2SiO4:Cr4+, Mg2SiO4:Cr4+, Li2MgSiO4 : Cr4} ⁺ _, ^Li2ZnSiO4 _{: Cr4} ^{+ , etc., as mentioned above, are used as the near-infrared light-emitting phosphor 4} _, it goes without saying that the light sources 4, 14 can be those that emit light having a peak in the wavelength range of 380 nm or more and 480 nm or less (blue-purple and blue), in addition to those that emit red light.

In this case, the light source can be an LED or laser diode. These light-emitting elements include those made of nitride semiconductors such as GaN or InGaN, and by adjusting the composition, they can become a light source that emits light of a specified wavelength.

(Embodiment 2)
In the second embodiment, another light emitting device that emits near-infrared light using a phosphor that emits near-infrared light by red excitation and a light source will be described.

Embodiment 2 differs from Figures 1 and 2 in that the light emitting sources 4 and 14 emit light having a peak in the wavelength range of 300 nm or more and 480 nm or less, and further contain, as phosphors, a red phosphor that emits red light when excited by the light emitting source, in addition to the near-infrared light-emitting phosphors 7 and 17.

The light source emits light with a peak in the wavelength range of 300 nm to 480 nm. Such a light source is selected from at least one of the above-mentioned light-emitting diodes, LDs, inorganic ELs, and organic ELs. Among these, the light source is preferably an LED or laser diode. These light-emitting elements include those made of nitride semiconductors such as GaN and InGaN, and by adjusting their composition, they can become a light source that emits light of a specified wavelength.

The red phosphor is excited by light emitted by the light source and having a peak in the wavelength range of 300 nm to 480 nm, and emits light (red light) having a peak in the wavelength range of 600 nm to 800 nm. As a result, the red light from the red phosphor excites the near-infrared light-emitting phosphor, which emits near-infrared light, for example, light having a peak in the wavelength range of 1050 nm to 1350 nm, with a half-width of 150 nm or more.

There are no restrictions on the material of the red phosphor as long as it can convert light in the wavelength range of 300 nm to 480 nm into light having a peak in the wavelength range of 600 nm to 800 nm, but among them, the group consisting of α-sialon:Eu (e.g., JP 2002-363554 A), Ca ₂ Si ₅ N ₈ :Eu, (Ca, Sr) ₂ Si ₅ N ₈ :Eu, CaAlSiN ₃ :Eu (e.g., WO 2005/052087 pamphlet) and (Ca, Sr)AlSiN ₃ :Eu are preferred due to their high conversion efficiency. Here, ":Eu" indicates that Eu has been added to the respective host materials.

For example, in the case of the light-emitting device 1 shown in Figure 1, when electricity flows to the light source via the lead wire 2, the light source emits blue light, for example, light with a peak in the wavelength range of 300 nm to 480 nm. The red phosphor is excited by this blue light and converts the blue light into light with a peak in the wavelength range of 600 nm to 800 nm. The near-infrared light-emitting phosphor 7 is then excited by the converted light with a peak in the wavelength range of 600 nm to 800 nm, and emits near-infrared light, for example, light with a peak in the wavelength range of 1050 nm to 1350 nm and a half-width of 150 nm or more. This is how the light-emitting device 1 of the present invention operates.

Similarly, in the case of the light-emitting device 11 shown in FIG. 2, when electricity flows to the light source via the lead wire 12, the light source emits blue light, for example, light with a peak in the wavelength range of 300 nm to 480 nm. The red phosphor is excited by this blue light and converts the blue light into light with a peak in the wavelength range of 600 nm to 800 nm. The near-infrared-emitting phosphor 7 is then excited by the converted light with a peak in the wavelength range of 600 nm to 800 nm, and emits near-infrared light, for example, light with a peak in the wavelength range of 1050 nm to 1350 nm and a half-width of 150 nm or more. This is how the light-emitting device 11 of the present invention operates.

[Production of near-infrared emitting phosphor]
<Phosphor A>
As a near-infrared emitting phosphor, Li ₂ ZnSiO ₄ :Cr ⁴⁺ in which M(1) is Li, M(2) is Zn, and M(3) is Si was prepared.

The raw material powders used were lithium carbonate powder, zinc oxide powder, silicon dioxide powder, and chromium oxide powder, with a metal atom ratio of Li:Zn:Si:Cr=2:1:0.96:0.04.
The mixture was weighed out so that the weight of the powder was 1000g, ethanol was added, and the mixture was mixed for 2 hours using a planetary ball mill. The resulting mixed slurry was dried and crushed, and subjected to a first firing in air at 1050°C for 6 hours. The product obtained by the first firing was thoroughly crushed, and subjected to a second firing in a mixed gas stream containing 4% by volume of hydrogen gas and the remainder of Ar gas at 700°C for 6 hours.

The elements contained in the resulting product were analyzed using powder X-ray diffraction and a scanning electron microscope (SEM; Hitachi High-Technologies Corporation, SU1510) equipped with an energy dispersive elemental analyzer (EDS; Bruker AXS, QUANTAX). The emission spectrum of the resulting product was measured using a multichannel spectrophotometer (Otsuka Electronics, MCPD916). The emission spectrum is shown in Figure 3. The emission spectrum of phosphor A was measured using the multichannel spectrophotometer at various excitation wavelengths. The excitation spectrum is shown in Figure 4.

<Phosphors B1 to B5>
As a near-infrared emitting phosphor, Li ₂ ZnSiO ₄ :Cr ⁴⁺ in which M(1) is Li, M(2) is Zn, and M(3) is Si was prepared.

As the ratio of metal atoms,
Li:Zn:Si:Cr=2:1:1-x:x
The phosphors were synthesized under the same conditions as for phosphor A, except that the phosphors were weighed out so that x was 0.005, 0.01, 0.02, 0.03, and 0.05. Phosphors B1 to B5 were products where x = 0.005, 0.01, 0.02, 0.03, and 0.05, respectively. The obtained products were subjected to X-ray powder diffraction to measure their emission spectra (excitation wavelength was 620 nm). The results are shown in Table 2.

<Phosphor C>
As a near-infrared emitting phosphor, Li ₂ MgSiO ₄ :Cr ⁴⁺ in which M(1) is Li, M(2) is Mg, and M(3) is Si was produced.

The raw material powders used were lithium carbonate powder, magnesium oxide powder, silicon dioxide powder, and chromium oxide powder. The metal atom ratios were as follows:
Li:Mg:Si:Cr=2:1:0.99:0.01
The phosphor was synthesized under the same conditions as those for phosphor A, except that the weight was weighed out so that the weight was 1000 ppm.

X-ray powder diffraction was performed on the resulting product, and the excitation-emission spectrum was measured. The results are shown in Figure 5.

<Phosphor D>
As a near-infrared emitting phosphor, Li ₂ CaSiO ₄ :Cr ⁴⁺ in which M(1) is Li, M(2) is Ca, and M(3) is Si was produced.

The raw material powders used were lithium carbonate powder, calcium oxide powder, silicon dioxide powder, and chromium oxide powder. The metal atom ratios were as follows:
Li:Ca:Si:Cr=2:1:0.99:0.01
The phosphor was synthesized under the same conditions as those for phosphor A, except that the weight was weighed out so that the weight was 1000 ppm.

X-ray powder diffraction was performed on the resulting product, and the excitation-emission spectrum was measured. The results are shown in Figure 6.

<Phosphor E>
As a near-infrared emitting phosphor, Li ₂ MgGeO ₄ :Cr ⁴⁺ was prepared, in which M(1) is Li, M(2) is Mg, and M(3) is Ge.

The raw material powders used were lithium carbonate powder, magnesium oxide powder, germanium oxide powder, and chromium oxide powder. The metal atom ratios were as follows:
Li:Mg:Ge:Cr=2:1:0.99:0.01
The phosphor was synthesized under the same conditions as those for phosphor A, except that the weight was weighed out so that the weight was 1000 ppm.

X-ray powder diffraction was performed on the resulting product, and the excitation-emission spectrum was measured. The results are shown in Figure 7.

<Phosphor F>
As a near-infrared emitting phosphor, Li ₂ ZnGeO ₄ :Cr ⁴⁺ was prepared, in which M(1) is Li, M(2) is Zn, and M(3) is Ge.

The raw material powders used were lithium carbonate powder, zinc oxide powder, germanium oxide powder, and chromium oxide powder. The metal atom ratios were as follows:
Li:Zn:Ge:Cr=2:1:0.99:0.01
The phosphor was synthesized under the same conditions as those for phosphor A, except that the weight was weighed out so that the weight was 1000 ppm.

X-ray powder diffraction was performed on the resulting product, and the excitation-emission spectrum was measured. The results are shown in Figure 8.

Table 1 summarizes phosphors A to F and explains the results.

According to EDS, the presence of elements Li, Zn, Si, Cr, and O was confirmed in phosphor A, and the ratio of the number of atoms contained in Li:Zn:Si:O:Cr was measured to be Li:Zn:Si:Cr:O = 2:1:0.96:0.04:4. Furthermore, the powder X-ray diffraction pattern of phosphor A matched well with the crystal pattern of Li ₂ ZnSiO _4. From this, it was found that phosphor A is a substance in which Cr is added to Li ₂ ZnSiO ₄ , and its composition matches the charge composition. It was also confirmed that phosphors B to F also produced products with the desired crystal structure reflecting the charge composition.

FIG. 3 is a diagram showing the emission spectrum of phosphor A.
FIG. 4 is a diagram showing the excitation spectrum of phosphor A.

Figure 3 shows the emission spectrum of phosphor A when excited at 650 nm. As shown in Figure 3, phosphor A emitted near-infrared light with a peak at 1240 nm when excited at 650 nm. The half-width of the peak for phosphor A was 230 nm.

From Figure 4, it was found that phosphor A is efficiently excited with light having wavelengths in the ranges of 380 nm to 480 nm and 600 nm to 800 nm, and emits near-infrared light with a peak at 1240 nm. Preferably, when excited with red light having a wavelength in the range of 600 nm to 660 nm, the emission intensity of the near-infrared light can be increased.

The emission intensities and emission wavelengths of phosphors B1 to B5 are summarized in Table 2. Note that the emission intensities are expressed relative to the emission intensity of phosphor A.

Table 2 shows that phosphors B1 to B5, regardless of the amount of Cr added, are all excited by light with a peak in the wavelength range of 600 nm to 800 nm, and emit near-infrared light with a peak in the wavelength range of 1050 nm to 1350 nm.

Furthermore, according to Table 2, the emission intensity increases as the amount of Cr added increases. It was found that the emission intensity can be increased preferably when the amount of Cr added, x, is 0.01 or more and 0.06 or less (1 atomic % or more and 6 atomic % or less relative to Si), and more preferably when the amount of Cr added, x, is 0.03 or more and 0.05 or less (3 atomic % or more and 5 atomic % or less relative to Si).

FIG. 5 is a diagram showing the emission spectrum of phosphor C.
FIG. 6 is a diagram showing the emission spectrum of phosphor D.
FIG. 7 is a diagram showing the emission spectrum of phosphor E.
FIG. 8 is a diagram showing the emission spectrum of phosphor F.

Figures 5 to 8 all show the emission spectra of the phosphors when excited at 650 nm. The emission intensities are shown relative to the emission intensity of phosphor A.

It was found that phosphors C to F were all excited by light with a peak in the wavelength range of 600 nm to 800 nm, and emitted near-infrared light with a peak in the wavelength range of 1050 nm to 1350 nm. For simplicity, the relative intensity, emission wavelength, and half-width of each phosphor are summarized in Table 3.

[Light-emitting device]
A light-emitting device was fabricated using the synthesized near-infrared emitting phosphor.

Example 1
The bullet-shaped light-emitting diode lamp 1 shown in FIG. 1 was fabricated using phosphor A as the near-infrared light-emitting phosphor 7. First, a red light-emitting diode element serving as a light source 4 was bonded to the recess 2a of the lead wire 2 for element placement using a conductive paste, electrically connecting the lead wire 2 to the lower electrode 4a of the red light-emitting diode element and securing the red light-emitting diode element. Next, the upper electrode 4b of the red light-emitting diode element was wire-bonded to the lead wire 3 using a bonding wire 5 for electrical connection. An appropriate amount of pre-prepared near-infrared light-emitting phosphor 7 was then applied to the recess 2a using a dispenser so as to cover the red light-emitting diode element and cured to form a first resin 6. Finally, the tip 2b of the lead wire 2 including the recess 2a, the red light-emitting diode element, and the first resin 6 containing the dispersed near-infrared light-emitting phosphor 7 were entirely sealed with a second resin 8 using a casting method. An epoxy resin with a refractive index of 1.6 was used for the first resin 6, and an epoxy resin with a refractive index of 1.36 was used for the second resin 8.

In manufacturing this light-emitting device, near-infrared light-emitting phosphor 7, phosphor A (with a median average particle size of 0.1 μm to 50 μm and an average aspect ratio of primary particles of 20 or less), was mixed into epoxy resin at a concentration of 40% by mass, and an appropriate amount of this was dropped using a dispenser to form a first resin with dispersed phosphor. When current was passed through the conductive terminals, the red light-emitting diode element emitted red light of 660 nm, and was excited by this red light to emit near-infrared light with an emission wavelength of 1240 nm and a half-value width of 230 nm. This was equivalent to the emission spectrum shape of the phosphor alone. Excitation by the red light-emitting diode element resulted in high luminous efficiency in the near-infrared range.

Example 2
The bullet-shaped light-emitting diode lamp 1 shown in Fig. 1 was produced using phosphor A as the near-infrared light-emitting phosphor 7. Since the lamp was the same as in Example 1 except that a blue light-emitting diode element was used as the light source 4, a description thereof will be omitted.

When current was passed through the conductive terminals, the blue light-emitting diode element emitted blue light of 450 nm, and was excited by this blue light to emit near-infrared light with an emission wavelength of 1240 nm and a half-width of 230 nm. This was equivalent to the emission spectrum shape of the phosphor alone.

Example 3
The bullet-shaped light-emitting diode lamp 1 shown in Fig. 1 was produced using phosphor A as the near-infrared light-emitting phosphor 7. Since the lamp was the same as in Example 1 except that an ultraviolet light-emitting diode element was used as the light source 4, a description thereof will be omitted.

When a current was passed through the conductive terminals, the ultraviolet light-emitting diode element emitted ultraviolet light of 385 nm, and was excited by this ultraviolet light to emit near-infrared light with an emission wavelength of 1240 nm and a half-width of 230 nm. This was equivalent to the emission spectrum shape of the phosphor alone.

Example 4
The bullet-shaped light-emitting diode lamp 1 shown in FIG. 1 was fabricated using phosphor A as the near-infrared light-emitting phosphor 7 and a blue light-emitting diode element as the light source 4. In addition to phosphor A as the near-infrared light-emitting phosphor 7, CaAlSiN ₃ :Eu phosphor was used as a red phosphor. Specifically, phosphor A was mixed with an epoxy resin at a concentration of 25% by mass and CaAlSiN ₃ :Eu phosphor at a concentration of 26% by mass, and an appropriate amount of this was dropped using a dispenser to form a first resin in which the phosphors were dispersed. The rest of the process is the same as in Example 1, so a description thereof will be omitted. The CaAlSiN ₃ :Eu phosphor was produced by the method described in International Publication No. 2005/052087, and its excitation and emission spectra are shown in FIG. 9.

FIG. 9 shows the excitation and emission spectra of the CaAlSiN ₃ :Eu phosphor.

As shown in FIG. 9, the CaAlSiN ₃ :Eu phosphor was excited by light having a peak in the wavelength range of 300 nm to 480 nm, and was a red phosphor having a peak in the wavelength range of 600 nm to 800 nm.

When a current was passed through the conductive terminals, the blue light-emitting diode element emitted blue light of 450 nm, which, together with the red light emitted by the CaAlSiN ₃ :Eu phosphor, excited the phosphor of the present invention, emitting near-infrared light with an emission wavelength of 1240 nm and a half-value width of 230 nm. This was equivalent to the emission spectrum shape of the phosphor alone. The emission intensity in the near-infrared range was higher than in Example 2. This was because the blue light from the LED was converted to red by the second phosphor and then converted to near-infrared light, thereby increasing the excitation efficiency of the first phosphor.

Example 5
1 was produced using phosphor A as the near-infrared light-emitting phosphor 7 and a red light-emitting diode as the light source 4. The lamp was the same as in Example 1 except that a silicone resin with a refractive index of 1.51 was used as the first resin 6 and a silicone resin with a refractive index of 1.41 was used as the second resin 8, and therefore a description thereof will be omitted.

When current was passed through the conductive terminals, the red light-emitting diode element emitted red light of 660 nm, and was excited by this red light to emit near-infrared light with an emission wavelength of 1240 nm and a half-width of 230 nm. This was the same emission spectrum shape as that of the phosphor alone.

Example 6
The bullet-shaped light-emitting diode lamp 1 shown in Figure 1 was produced using phosphor A and phosphor C as the near-infrared light-emitting phosphor 7 and a red light-emitting diode element as the light source 4. Phosphor A and phosphor C were each mixed into an epoxy resin at a concentration of 20 mass%, and an appropriate amount of this was dropped using a dispenser to form a first resin in which the phosphors were dispersed. The rest of the process was the same as in Example 1, so a description thereof will be omitted.

When current was passed through the conductive terminals, the red light-emitting diode element emitted red light of 660 nm, and was excited by this red light to emit near-infrared light with an emission wavelength of 1190 nm and a half-value width of 280 nm.

Example 7
The chip-type light-emitting diode 11 for substrate mounting shown in FIG. 2 was fabricated using phosphor A as the near-infrared light-emitting phosphor 7. A blue light-emitting diode was positioned as the light source 4 on the lower electrode 14a, and was connected to the upper electrode 14b by a bonding wire 5. The manufacturing procedure was substantially the same as that of Example 1, except for the part where the lead wires 12, 13 and the wall member 20 were fixed to the alumina ceramic substrate as the substrate 19. In this example, the wall member 20 was made of white silicone resin, and the same epoxy resin was used for the resins 16 and 18. Phosphor A was used as the near-infrared light-emitting phosphor 7, and it was confirmed that near-infrared light was emitted.

The light-emitting device of the present invention is a light-emitting device composed of a light source and a phosphor. By using the phosphor of the present invention, it is possible to create a near-infrared light-emitting device with a sufficiently wide half-width and sufficiently high brightness. Going forward, it is expected to be widely used not only as a light source for medical equipment and spectroscopic analysis, but also as an alternative to halogen lamps, and as a snow-melting and anti-freezing measure for white LED lamps and LED traffic lights, making a significant contribution to industrial development.

1. Light-emitting device (bullet-type light-emitting diode lamp)
2, 3 Lead wire 4 Light source 5 Bonding wire 6 First resin 7 Near-infrared light-emitting phosphor 8 Second resin 11 Light-emitting device (chip-type white light-emitting diode lamp for substrate mounting)
12, 13 Lead wire 14 Light emitting source 15 Bonding wire 16 First resin 17 Near-infrared light emitting phosphor 18 Second resin 19 Substrate 20 Wall member

Claims (7)

Cr is added to M(1) _2M (2)M(3) _O4 crystal (wherein M(1) is a metal element that is Na , M(2) is at least one metal element selected from the group consisting of Ca and Sr, and M(3) is an element that is Si),
A near-infrared light-emitting phosphor that emits near-infrared light and is a powder having a median average particle size in the range of 0.1 μm to 50 μm. the near-infrared light has a peak in a wavelength range of 1050 nm or more and 1350 nm or less,
2. The near-infrared light-emitting phosphor according to claim 1, wherein the half-value width of the peak is 150 nm or more and 300 nm or less. 3. The near-infrared light-emitting phosphor according to claim 1 , which is excited by light having a wavelength in the range of 600 nm to 800 nm. The near-infrared light-emitting phosphor according to claim 1 or 2 , which is excited by light having a wavelength in the range of 380 nm to 480 nm. A light emitting device comprising a light source and a phosphor,
A light emitting device, wherein the phosphor contains the near-infrared light emitting phosphor according to any one of claims 1 to 4 . The light emitting device according to claim 5 , wherein the light emitting source emits light having a peak in a wavelength range of 600 nm to 800 nm. 7. The light emitting device according to claim 5, wherein the light source is at least one selected from the group consisting of a light emitting diode (LED), a laser diode (LD), an inorganic electroluminescence (inorganic EL), and an organic electroluminescence (organic EL).