JP5019052B2 - CdSe quantum dot and method for producing the same - Google Patents

Description

  The present invention relates to CdSe quantum dots (nanocrystals) widely applied in industrial technology and life science technology, and a method for producing the same.

  CdSe quantum dots (nanocrystals) that are widely applied in industrial technology and life science technology need to be produced on a large scale. There are several requirements for quantum dots used in life science experiments: high quality (for example, very small dot size dispersion and high quantum yield), accuracy and reproducibility of the formation process, It should be possible to form quantum dot fractions with the same size and the same spectral characteristics in different batches.

  Conventionally, various methods have been reported in many literatures as methods for producing CdSe quantum dots. In early 1986, a method using a Cd and Se-containing substance having extremely strong toxicity was reported (see Non-Patent Documents 1 and 2). High quality, nearly uniform size CdSe quantum dot synthesis methods using a safer “green” chemistry approach have been published over the past few years (see Non-Patent Documents 3-9).

  In these methods, the “hot injection” method is basically used, and the Cd precursor and Se precursor are added to the reaction mixture at 280 to 320 ° C. at a high speed of millisecond scale. The formation of nanocrystals is very fast, occurs within a few minutes, and then grows and stops after about 10 minutes. In order to obtain nanocrystals of a desired size, it is necessary to stop the reaction at a desired time (for example, 5, 20, 30 seconds after the start of “hot injection”). The reaction is stopped by rapid cooling and charging into an organic solvent (chloroform, methanol, butanol, hexane, toluene). However, under such a constant high temperature, the reaction proceeds very rapidly, and it is difficult to accurately control the reaction stop.

In addition, in the synthesis at a high constant temperature, the growth rate of the nanocrystals in the reaction mixture is very high (Non-patent Document 6) (FIG. 7), so that quantum dots of different sizes are simultaneously formed in the reaction mixture. According to other literature reports, the dispersion of the quantum dot size fraction is 5 to 10%, and the best one is about 5% (Non-patent Document 6). The lowest size distribution of CdSe quantum dots has been reported by Tarapin et al. (See Non-Patent Document 11). Non-Patent Document 11 discloses that the size distribution of quantum dots having a diameter of 4 nm is about 4%, but does not disclose or suggest other sizes or size distributions. The quantum yield of the quantum dots was about 10-25%, which was very low.
FIG. 7 is a typical growth saturation curve of CdSe nanocrystals synthesized at a high constant temperature (eg, 290 ° C.), which is described in Qu, L. And Peng, X .; (See Non-Patent Document 6). Very rapid growth is observed 150 seconds after “hot injection”, followed by delayed growth and saturation.
It is very difficult to stop the reaction at several different times within this time (within 150 seconds) and to separate several sized quantum dot fractions from one reaction mixture. Furthermore, it is very difficult to separate only the desired size quantum dots from the separated reaction mixture.

As one variation of the “hot injection” method, a method in which the synthesis is started at a high temperature of about 320 to 340 ° C. and then the temperature is lowered and fixed at 360 to 290 ° C. has been reported (see Non-Patent Document 10). . In this case, it can be divided into quantum dots of several sizes. However, Non-Patent Document 10 does not report the size dispersion in these fractions, and the absorption spectrum of quantum dots after 15 minutes in Non-Patent Document 10 clearly shows a dispersion of 10% or more. ing. Furthermore, all CdSe quantum dots are of low quality, and the full width at half maximum of the fluorescence spectrum is about 60 to 70 nm (see FIG. 2 of Reference 10). In this method, since the reaction proceeds very quickly, it is difficult to accurately control the size and to obtain a plurality of monodispersed quantum dots of a desired size from one container. Moreover, the further temperature drop (to 240 to 260 ° C. or less) stops the crystal growth.
It is widely recognized that very fast crystal growth greatly reduces the reproducibility of uniformly sized CdSe quantum dots in a single reaction. In conventional methods with poor reproducibility, it is necessary to repeat several synthesis reactions in order to obtain nanocrystals of the desired size, desired spectral characteristics, and desired quality. Therefore, there is a problem that the amount of the toxic additive discharged to the environment is several times.

Trinade, T .; et al. Chem. Mater. 1997, 9 (2): 523-530. Foos, E .; E. et al. Chem. Mater. 2006, 18 (12): 2886-2894. Epifani, M .; et al. Chem. Mater. 2007, 19 (20): 4919-4924. Peng, X .; et al. J. et al. Am. Chem. Soc. 1997, 119 (30): 7019-7029. Peng, Z .; A. & Peng, X. J. et al. Am. Chem. Soc. 2001, 123: 183-184. Qu, L .; & Peng, X. J. et al. Am. Chem. Soc. 2002, 124 (9): 2049-2055. Peng, Z .; A. & Peng, X. J. et al. Am. Chem. Soc. 2001, 123: 1389-1395. Peng, Z .; A. & Peng, X. J. et al. Am. Chem. Soc. 2002, 124 (13): 3343-3353. Li, J. et al. J. et al. et al. J. et al. Am. Chem. Soc. 2003, 125 (41): 12567-12575. Xie, R.A. et al. J. et al. Am. Chem. Soc. 2005, 127 (20): 7480-7488. Talapin. et al. Nano Lett. 2001, 1: 207-211.

The object of the present invention is to solve the above-mentioned problems in the prior art. That is, an object of the present invention is to provide a method for producing CdSe quantum dots capable of synthesizing many kinds of CdSe quantum dots having a uniform size in a single reaction with high reproducibility and easy control.
Another object of the present invention is to provide a method for producing CdSe quantum dots, which can synthesize quantum dot fractions having a desired size and spectral characteristics and a high uniform size with high reproducibility.
A further object of the present invention is to provide an environmentally friendly method for producing CdSe quantum dots by increasing the utilization rate of Cd precursor or Se precursor (improving yield).

The inventors have found that CdSe quantum dots of a plurality of sizes can be obtained from one reaction by the method described below, and that high uniformity is achieved in the size of CdSe quantum dots in each fraction. The present invention has been completed.
That is, the present invention is a method for synthesizing CdSe quantum dots, in which a Cd precursor solution and a Se precursor solution are mixed, and the mixture is increased in temperature gradient from 0.10 ° C./min to 0.80 ° C./min. Preferably, heating is performed with a rising temperature gradient of 0.20 ° C./min to 0.55 ° C./min, and more preferably with a rising temperature gradient of 0.20 ° C./min to 0.50 ° C./min. To provide a method.
In the above method, the mixture is preferably heated in a temperature range of 110 ° C to 250 ° C.
In the above method, the atomic ratio of Cd in the Cd precursor solution to Se in the Se precursor solution is preferably 0.85: 1 to 1.10: 1, and 0.9: 1 to 1: 1. More preferably.
In the above method, the Cd precursor solution preferably contains a fatty acid having 10 to 18 carbon atoms, and more preferably contains a fatty acid having 18 carbon atoms.

Further, the quantum dot fraction of the present invention produced by the above method comprises quantum dots having a size of 5 nm or less, preferably 4 nm or less and a size distribution of 5% or less, and a quantum yield of 40 to 80%, It is a novel quantum dot fraction that exhibits an unprecedented narrow size distribution and high quantum yield, preferably 50 to 70%.
The full width at half maximum (FWHM) of the emission spectrum (photoluminescence) of the quantum dot fraction is 40 nm or less, and more preferably 27 to 30 nm.

  In the reaction, in the reaction, (1) CdSe quantum dots of a desired size are grown, and (2) almost complete suppression of the growth of new quantum dots is performed at each time point. This makes it possible to obtain a fraction of CdSe quantum dots having uniformity and a desired size.

The effects of the present invention include the following.
1. An accurate and easy-to-control CdSe quantum dot manufacturing method is provided. For example, it is possible to obtain CdSe quantum dots having a desired emission wavelength with a wavelength accuracy of 2 to 3 nm.
2. A method for producing CdSe quantum dots with very high reproducibility is provided. Therefore, a quantum dot having a target size can be easily obtained.
3. A method for producing CdSe quantum dots capable of producing a plurality of uniformly sized CdSe quantum dot fractions without purification from a single reaction mixture is provided. That is, since two or more (for example, five or more, further 6 to 10) CdSe quantum dot fractions of uniform size are sequentially synthesized over time in one reaction mixture, by sequentially obtaining fractions Fraction of uniform size can be obtained without stopping heating and purifying each. A further size selection step promotes the aggregation of quantum dots and reduces the production yield of the final non-aggregated product. The quantum dot fraction of the present invention is initially non-aggregated, has high transparency, and does not require size selection and purification.
4). It is possible to use Cd precursors and Se precursors almost completely, and provide an environmentally friendly method for producing CdSe quantum dots.
5. CdSe quantum dot fractions with very high quantum yield are provided. Needless to say, the CdSe quantum dot fraction having a very high quantum yield can be advantageously used in all industrial technology and life science technology fields using CdSe quantum dots.
6). The size distribution provides a very narrow CdSe quantum dot fraction. The CdSe quantum dot fraction having a very narrow size distribution can be advantageously used particularly in the life science technical field.
7). It provides a CdSe quantum dot fraction with a very narrow full width at half maximum (FWHM) of the emission spectrum (ie, a sharp spectrum). CdSe quantum dot fractions with very narrow emission spectrum full width at half maximum (FWHM) can be advantageously used in multiple labeling and imaging, multiple sensing, 2D and 3D displays, and fluorescence standards.

  The method of the present invention grows quantum dots by heating a mixture of a Cd precursor solution and a Se precursor solution at a temperature gradient increase rate of 0.20 ° C./min to 0.55 ° C./min. It is a method to make it. The method of the present invention will be described in detail below.

In the present specification, the Cd precursor means a substance (compound or simple element) that serves as a Cd supply source for forming CdSe nanoparticles or nanocrystals. Examples of Cd precursors include cadmium oxide (CdO), dimethyl cadmium ((CH ₃ ) ₂ Cd), cadmium acetate ((CH ₃ COO) ₂ Cd), cadmium chloride (CdCl ₂ ), cadmium nitrite (Cd ( NO ₃ ) ₂ ). Among these, dimethyl cadmium and cadmium oxide are preferable. Considering the toxicity of dimethylcadmium, cadmium oxide is most preferable.

In this specification, the Se precursor means a substance (compound or simple element) that is a Se supply source for forming CdSe nanoparticles or nanocrystals. Examples of Se precursors include selenium shot (Se-shot), powdered Se (Se-powder), selenium oxide (SeO ₂ ), selenourea, diethyl selenium, and diethyl selenocarbamate (Diethylselencarbate). Can be mentioned. Of these, selenium shot and powdered Se are preferred, and powdered selenium is most preferred.

In this specification, the Cd precursor solution is a solution obtained by mixing the Cd precursor with a solvent. However, depending on the type of the Cd precursor and the solvent, the Cd precursor solution includes not only a complete solution but also a dispersion.
The Cd precursor concentration in the Cd precursor solution is preferably about 1.0 to 2.0 mass% with respect to the weight of the precursor solution. For example, it is preferable to use about 0.45 to 0.50 g of Cd precursor for 8 g of fatty acid, 8 g of TOPO and 12 g of HDA.

As a solvent for adjusting the Cd precursor solution, a fatty acid having 10 to 18 carbon atoms is preferably used, and a fatty acid having 18 carbon atoms is more preferably used. Due to the presence of these fatty acids, it is possible to keep the size distribution of the quantum dots in a narrow range. Examples of preferred fatty acids include oleic acid, stearic acid, and palmitic acid. Of these, oleic acid or stearic acid is preferred, and stearic acid is most preferred.
It is preferable that the usage-amount of a fatty acid is about 20-40 mass% with respect to the weight of a precursor solution.

In order to adjust the Cd precursor solution, it is preferable to add a coordinating solvent. In this specification, the coordinating solvent is a solvent capable of coordinating around a metal atom in a coordination bond.
Examples of coordinating solvents include trioctylphosphine oxide (TOPO), trioctylphosphine (TOP), hexadecylamine (HDA), tetradecylphosphonic acid (TDPA), dodecylamine (DDA), dioctylamine (DOA) , Trioctylamine (TOA), tributylphosphine (TBP), hexylphosphonic acid (HPA), octadecylphosphonic acid (ODPA), octadecylamine (ODA), octadecene (ODE), and triethylorthoformate (TEOF) . Two or more kinds of coordinating solvents may be used. Among the coordinating solvents, TOPO, HDA and ODA are most preferable as the solvent for Cd.
In addition, it is preferable to use a combination of TOPO and HDA. In this case, it is preferable to use HDA in excess (eg, TOPO: HDA = 2: 3 to 2: 5 (mass ratio)).
The amount of the coordinating solvent used is preferably about 50 to 98% by mass with respect to the weight of the precursor solution.

  The Cd precursor is added to the fatty acid and / or the coordinating solvent at room temperature and then heated to at least 150 ° C. to dissolve to dissolve the Cd precursor, thereby producing a Cd precursor solution. The Cd precursor solution may then be lowered in temperature as needed. Once the Cd precursor solution is in solution, it is stable, and solid precipitation does not occur even when the temperature is lowered.

In this specification, the Se precursor solution is a solution obtained by mixing the Se precursor with the coordinating solvent. However, depending on the type of the Se precursor and the coordinating solvent, the solution is not a complete solution. This includes cases where As the coordinating solvent, the same ones described for the Cd precursor solution can be used.
The Se concentration in the Se precursor solution is preferably about 5 to 15% by mass, and more preferably 8 to 12% by mass, based on the weight of the precursor solution. For example, it is preferable to use 0.71 g to 0.79 g of powdered Se with respect to 7 g of TOP.

  The Se precursor is added to the coordinating solvent at room temperature, and then heated to at least 150 ° C. to dissolve the Se precursor to produce an Se precursor solution. If necessary, the Se precursor solution may be lowered in temperature thereafter. The Se precursor solution once in solution is stable, and no solid precipitates or the like are produced even when the temperature is lowered.

In the method of the present invention, the atomic ratio of Cd in the Cd precursor solution to Se in the Se precursor solution is preferably 0.85: 1 to 1.10: 1, more preferably 0.9: 1 to 1: 1. Preferably there is.
When the Se precursor is used at a ratio higher than that shown above, the growth is not completely saturated in a constant temperature state, and the quantum dots continue to grow. That is, FIG. 1a shows the growth curves of CdSe quantum dots at 210 ° C. at two Cd: Se ratios (1: 1 and 1: 5), but in the case of a ratio of 1: 5, Quantum dot growth continues. In the presence of excess Se precursor, quantum dots are newly formed continuously, which results in several different sized quantum dots being simultaneously present at each time in the reaction mixture. FIG. 1b is an emission spectrum of CdSe quantum dots at Cd: Se = 1: 5, where the dotted line on the left represents the spectrum after 10 minutes at 200 ° C. and the black line on the right represents the spectrum after 2 hours at 210 ° C. This figure clearly shows that there are newly grown small quantum dots. In the state where the Cd: Se precursor ratio is 1: 1 or the Cd precursor is slightly higher, the growth start (nucleation) of new quantum dots is suppressed, and a single spectrum is shown even after 2 hours. (FIG. 1c). This suppression is more powerful than the growth suppression of already formed “old” quantum dots. Therefore, the formation of new quantum dots stops completely simultaneously with the “old” quantum dots already formed in the reaction mixture (FIGS. 1a and 1c). On the other hand, if an excess of Cd precursor is used (Cd: Se precursor ratio is greater than 1: 1), the quantum dots aggregate in the synthesized first mixture.

In the method of the present invention, the Cd precursor solution described above and the Se precursor solution are mixed.
Before mixing, it is preferable to heat at least 150 ° C. for at least 30 minutes in order to sufficiently dissolve the Cd precursor solution.
The Se precursor solution is also preferably heated at least at 150 ° C. for at least 30 minutes in order to achieve sufficient dissolution.
The temperature of the Cd precursor solution or Se precursor solution is appropriately adjusted, and both are mixed. The temperature of each solution is preferably adjusted so that the temperature after mixing becomes the initial temperature for starting nucleation. Specifically, for example, by adjusting the temperature of one precursor solution to 150 ° C., cooling the temperature of one precursor solution to about room temperature, and quickly mixing both precursor solutions, about 110 ° C. The initial temperature can be adjusted.
CdSe nucleation begins as soon as both precursor solutions are mixed. Since good nucleation is observed around 110 ° C., the initial temperature is preferably set to 110 ° C. to 120 ° C., preferably around 110 ° C.

In the method of the present invention, the first quantum dot fraction may be obtained by heating at a constant temperature (for example, 110 ° C.) for a fixed time (at least 30 minutes) before heating with the rising temperature gradient.
Thereafter, other fractions can be obtained by heating at an increasing temperature gradient of 0.10 ° C./min to 0.80 ° C./min.
Thereafter, from the initial temperature, it is 0.10 ° C / min to 0.80 ° C / min, preferably 0.20 ° C / min to 0.55 ° C / min, and more preferably 0.20 ° C / min to 0.50. The mixture is heated with an increasing temperature gradient of ° C / min.
In the present specification, “heating with a rising temperature gradient” refers to a mode in which the heating device is controlled so that the temperature of the reaction mixture gradually increases, but the scale of the reaction to be performed, the stirring method, the heating Of course, the case where the temperature of the reaction mixture slightly increases or decreases depending on the type of control method or the like is included.
As a method of heating the temperature of the reaction mixture with an increasing temperature gradient, a person skilled in the art, such as a combination of a heating bath such as an oil bath, a heating means such as a throwing heater, a mantle heater, a hot stirrer, and a controller for controlling the heating means. A well-known method is mentioned.
In the present specification, the temperature of the mixture means the temperature of the mixture itself, and does not mean the temperature of a heating device such as an oil bath.
It is preferable to perform the said heating within the temperature range of 110 to 250 degreeC. When heating at lower temperatures, nucleation stops and low quality quantum dots are produced (eg, <10% quantum yield, broad photoluminescence spectrum, large size distribution). At temperatures above 250 ° C., quantum dots with diameters> 5 nm are obtained and the production yield is also very low.
Further, from the viewpoint of improving the crystallinity of the quantum dots and obtaining CdSe quantum dots having a high quantum yield, the reaction is performed under an inert atmosphere, for example, a nitrogen stream or an argon stream, throughout the reaction of the present invention. It is preferable.

The method of the present invention makes it possible to synthesize two or more (6 to 10) uniformly sized CdSe quantum dots simultaneously and reproducibly in a single reaction. This synthesis is achieved by a slow rising temperature gradient and is only possible if the above technical specifications are observed. This is made possible by the following situation.
Discovery of conditions that keep the attributes (mainly narrow size distribution) of newly synthesized quantum dots constant (without change) for a relatively long time at a certain set temperature.
Discovery of conditions that completely stop the formation of new quantum dots in the presence of free Cd and Se precursors in the reaction mixture.

In the method of the present invention, the rising temperature gradient from 0.10 ° C./min to 0.80 ° C./min indicates that the crystal growth curve in the synthesis process of the obtained quantum dots is linear with respect to time, as shown in FIG. It is preferable to control the temperature gradient so as to increase. By achieving such a temperature gradient, a plurality of monodispersed CdSe quantum dots of a target size can be manufactured in one pot with accurate size control and high reproducibility.
In the method of the present invention, the rising temperature gradient is 0.10 ° C / min to 0.80 ° C / min, preferably 0.20 ° C / min to 0.55 ° C / min, more preferably 0.20 ° C / min to 0. 50 ° C / min.
When the rising temperature gradient is higher than 0.20 ° C./min, the size distribution is preferably narrowed. In addition, the size distribution is preferably narrowed when the rising temperature gradient is lower than 0.50 ° C./min.

The quantum dot fraction obtained by the above method has a size of 5 nm or less, a size distribution of 5% or less, and a quantum yield of 50 to 70%. More specifically, for example, a quantum dot fraction having a diameter of ˜3 nm and a size distribution of 2.58% is obtained.
FIG. 4 shows an HR-TEM image of four-color CdSe quantum dots obtained by the single reaction method of the example. This corresponds to a size of 2.38 ± 0.10 nm, 3.04 ± 0.12 nm, 3.66 ± 0.14 nm, 4.25 ± 0.11 nm, respectively.
The full width at half maximum (FWHM) of the emission spectrum of the quantum dot fraction is 40 nm or less, and more specifically, 35 nm or less. FIG. 5 represents the normalized fluorescence emission spectra of six different sized CdSe quantum dots obtained in the examples. The full width at half maximum is about 27 to 30 nm in all the spectra, which indicates that the obtained CdSe quantum dot fraction has a very narrow size distribution.

The particle size can be measured by an image analysis method using an image of a transmission electron microscope, a dynamic light scattering method, a laser diffraction / scattering measurement method, or the like. Unless otherwise stated in this specification, the particle size means the diameter of the particle measured by HR-TEM (High Resolution Transmission Electron Microscope) method and absorption spectrum.
The quantum yield can be measured by the method described in Reiss et al. That is, the spectral integrated emission of quantum dots in chloroform (or hexane) at an emission wavelength of 365 nm is a ratio of the emission of rhodamine 6G having the same optical density (<0.05) to that of an ethanol solution. Unless stated otherwise herein, quantum yield means that measured by the method of Reiss et al.

<Example 1>
A CdSe quantum dot fraction was produced by the following method.
(A) First fraction Se powder (0.7896 g) is added to trioctylphosphine (TOP, 7.4 g) and the mixture is heated to 150 ° C. (under a nitrogen stream) to give a TOP-Se stock solution. Created.
Separately, CdO (0.450 g) and stearic acid (8 g) were heated to 150 ° C. in a three-necked flask under an argon atmosphere. After CdO dissolved, the solution was cooled to room temperature. To the solution was added trioctylphosphine oxide (TOPO, 8 g) and 1-heptadecyl-octadecylamine (HDA, 12 g) and the mixture was heated again to 150 ° C. At this temperature, 4 mL of TOP-Se stock solution was quickly injected into the reaction chamber (containing the cadmium precursor) to initiate nucleation.
In order to prevent further growth of CdSe quantum dots, the temperature of the chamber was maintained at 110 ° C. for 40 minutes to obtain a fraction of the first color (blue fluorescent color). 2 mL was withdrawn from the reaction mixture by syringe and added into 20 mL of chloroform.

Further, five CdSe quantum dot fractions having a uniform diameter were obtained as follows. In addition, each fraction was extracted from the reaction mixture with a syringe and treated in chloroform in the same manner as the first fraction. In the following experiment, the reaction mixture in the flask was heated by immersing the flask in an oil bath and controlling the temperature of the oil bath with a heater equipped with a temperature gradient variable device (PC-4200, manufactured by ASONE). And gradually increased at the rate described below.
(B) Second fraction The temperature of the above mixture (110 ° C.) is increased at a constant rate to 120 ° C. over 50 minutes (0.20 ° C./min), and the second color (dark green fluorescent color) Fractions were obtained.
(C) Third fraction The temperature of the above mixture (120 ° C.) is increased at a constant rate to 150 ° C. over 60 minutes (0.50 ° C./min), and the third color (yellowish green fluorescent color) Fractions were obtained.
(D) Fourth fraction The temperature of the above mixture (150 ° C.) is increased at a constant rate to 190 ° C. over 80 minutes (0.50 ° C./min), and the fourth color (yellow fluorescent color) A fraction was obtained.
(E) Fifth Fraction The temperature of the above mixture (190 ° C.) was increased at a constant rate to 220 ° C. over 100 minutes (0.30 ° C./min), and the fifth color (orange fluorescent color) A fraction was obtained.
(F) Sixth Fraction The temperature of the above mixture (220 ° C.) was increased at a constant rate to 250 ° C. over 120 minutes (0.25 ° C./min), and the fifth color (red fluorescent color) A fraction was obtained.
By the above temperature rise process, the time-dependent linear or linear quantum dot growth curve shown in FIG. 2 can be obtained, and the CdSe quantum dot size distribution at each growth time can be kept uniform over a long period of time. It became. The growth curve of quantum dots is linear over 7 hours by the slow rise temperature gradient method (FIG. 2), and this linearity allows strict control of the growth process.

The obtained quantum dot fraction was characterized by high-resolution transmission electron microscope (HRTEM), DLS (Dynamic Light Scattering), spectrophotometry and spectrofluorimetry.
The UV / VIS absorption spectrum method was measured using a spectrophotometer manufactured by Shimadzu Corporation. The photoluminescence (PL) spectrum was measured using a spectrofluorometer manufactured by Shimadzu Corporation. HRTEM images were obtained by operating a JEOL transmission electron microscope at 300 kV.
By the above method, fractions having uniform diameters of six types shown in the following table were obtained.
The mean ± standard deviation was obtained from the absorption spectrum of each quantum dot fraction obtained by three different syntheses according to the following formula (Yu, WW, Qu, L., Guo, W. Peng, X. Chem. Mater. 2003, 15, 2854).

a formula:
D = (1.6122 × 10 ⁻⁹ ) λ ⁴ − (2.6575 × 10 ⁻⁶ ) λ ³ + (1.6242 × 10 ⁻³ ) λ ² − (0.4277) λ + 41.57

* 1: Obtained from the cumulative emission ratio in chloroform using rhodamine 6G as a standard substance (absorption of 100%).

The absorption wavelength of each fraction is shown in FIG.
FIG. 4 shows HR-TEM images of four different size quantum dots. The size calculated from the HR-TEM image closely matched the size calculated from the absorption spectrum. The fluorescence spectrum of the quantum dots was very sharp and the full width at half maximum was about 30 nm (FIG. 5).

<Example 2>
Se powder (0.7896 g) was added to trioctylphosphine (TOP, 7.4 g) and the mixture was heated to 150 ° C. (under a nitrogen stream) to make a TOP-Se stock solution.
Separately, CdO (0.450 g) and stearic acid (8 g) were heated to 150 ° C. in a three-necked flask under an argon atmosphere. After CdO dissolved, the solution was cooled to room temperature. To the solution was added trioctylphosphine oxide (TOPO, 8 g) and 1-heptadecyl-octadecylamine (HDA, 12 g) and the mixture was heated again to 150 ° C. At this temperature, 4 mL of TOP-Se stock solution was quickly injected into the reaction chamber (containing the cadmium precursor) to initiate nucleation.
The temperature of the above mixture (110 ° C.) was increased at a constant rate to 180 ° C. over 700 minutes (0.10 ° C./min) to obtain fraction A.
The average size of fraction A quantum dots was about 3 nm, the size distribution was about 12%, and the quantum yield was about 28%.

<Example 3>
Se powder (0.7896 g) was added to trioctylphosphine (TOP, 7.4 g) and the mixture was heated to 150 ° C. (under a nitrogen stream) to make a TOP-Se stock solution.
Separately, CdO (0.450 g) and stearic acid (8 g) were heated to 150 ° C. in a three-necked flask under an argon atmosphere. After CdO dissolved, the solution was cooled to room temperature. To the solution was added trioctylphosphine oxide (TOPO, 8 g) and 1-heptadecyl-octadecylamine (HDA, 12 g) and the mixture was heated again to 150 ° C. At this temperature, 4 mL of TOP-Se stock solution was quickly injected into the reaction chamber (containing the cadmium precursor) to initiate nucleation.
The temperature of the above mixture (110 ° C.) was increased to 270 ° C. over 200 minutes at a constant rate (0.80 ° C./min) to obtain fraction B. The average size of the fraction B quantum dots was about 3.5 nm, the size distribution was about 9%, and the quantum yield was about 40%.

<Example 4>
Using the quantum dot growth curve obtained in Example 1, synthesis of the desired CdSe quantum dot fraction (size 3.5 nm) was attempted.
The experiment was started with the same protocol as in Example 1, and a fraction was obtained after 4 hours and 20 minutes. The obtained fraction had a size of 3.55 ± 0.09 nm, indicating high reproducibility of the present invention.
Further, the experiment was performed twice with the same protocol, and fractions were obtained after 4 hours and 20 minutes. As a result, fractions with sizes of 3.48 ± 0.11 nm and 3.52 ± 0.10 nm were obtained. The results supported the high reproducibility of the invention.
FIG. 6a shows an HR-TEM image of the fraction obtained in the above experiment (1 out of 3 times), FIG. 6b shows an absorption spectrum (λ _max = 568 nm), and FIG. 6c shows a fluorescence spectrum (λ _max = 585 nm).

  As described above, the method of synthesizing CdSe quantum dots according to the slow rising temperature gradient method of the present invention makes it possible to accurately control the separation of monodisperse quantum dot fractions having exactly the desired size and desired spectrum, in the reaction mixture. The growth of the existing quantum dots present in does not affect the separation of the next fraction. The resulting quantum dots are very high quality (the best and very good size distribution with a uniform dispersion of 95% to 97%), show high fluorescence (quantum yield reaches 80%), High permeability (no particle aggregation). Moreover, like other methods already reported, “hot injection” required for fast nucleation around 300 ° C. (this operation is very fast (millisecond range) and requires precise operation at high temperatures. The reaction is at risk of making the reproducibility even lower). In the method of the present invention, the size distribution of the quantum dots is very narrow. Moreover, the size distribution is improved in the synthesis process.

Quantum dots are widely applied in two main fields.
(1) Industrial technology fields include LEDs, solar cell sensitization, fluorescent standards for wavelength calibration, fiber light sensors, UV coating and curing techniques.
(2) Life science technologies include in vitro and in situ optical imaging of molecules and cells, in vivo deep tissue optical imaging, development of various imaging probes, optics and MRI, optics and PET, optics and X Various applications using combinations of lines, recent detection of toxins, explosives and other, photosensitization of tumor cells, time-resolved spectral imaging, etc.
Quantum dots produced by the method of the present invention can be used in the above fields.

2 is a growth curve of CdSe quantum dots at 210 ° C. with two types of Cd: Se ratios. It is a fluorescence spectrum of the CdSe quantum dot in Cd: Se = 1: 5. It is a fluorescence spectrum of the CdSe quantum dot in Cd: Se = 1: 1. It is a growth curve of CdSe quantum dots under the condition of a controlled slow rise temperature gradient. Figure 6 is a normalized absorption spectrum for six different sized CdSe quantum dots. It is a HR-TEM image of four-color CdSe quantum dots obtained by a single reaction method. 6 is a normalized emission spectrum of six different sized CdSe quantum dots. The HR-TEM image of the CdSe quantum dot of the design size (size 3.5nm) by the slow temperature rising gradient method is shown. The absorption spectrum ((lambda) _max = 568 nm) of the CdSe quantum dot of the design size (size 3.5 nm) by a slow rise temperature gradient method is shown. The fluorescence spectrum ((lambda) _max = 585 nm) of the CdSe quantum dot of the design size (size 3.5 nm) by a slow rise temperature gradient method is shown. It is a saturation curve of CdSe quantum dot growth at a constant synthesis temperature (290 ° C.) (conventional method).

Claims (10)

The mixture of Cd precursor solution and Se precursor solution is heated with an increasing temperature gradient from 0.10 ° C./min to 0.80 ° C./min so that the crystal growth curve of CdSe quantum dots is linear with time. A method for synthesizing CdSe quantum dots, characterized in that, by adjusting, two or more CdSe quantum dots each having a uniform diameter are synthesized in one pot. The method according to claim 1, wherein the heating is performed in a temperature range of 110 ° C. to 250 ° C. The method according to claim 1 or 2, characterized in that the atomic ratio of Cd in the Cd precursor solution to Se in the Se precursor solution is 0.85: 1 to 1.10: 1. The method according to any one of claims 1 to 3, wherein the Cd precursor solution contains a fatty acid having 10 to 18 carbon atoms. The method according to any one of claims 1 to 4, comprising heating from 110 ° C to 120 ° C with an increasing temperature gradient of 0.20 ° C / min to 0.5 ° C / min. 6. A method according to any one of the preceding claims comprising heating from 120 ° C to 150 ° C with an increasing temperature gradient of 0.20 ° C / min to 0.50 ° C / min. The method according to any one of claims 1 to 6, comprising heating from 150 ° C to 190 ° C with an increasing temperature gradient of 0.20 ° C / min to 0.50 ° C / min. The method according to any one of claims 1 to 7, comprising heating from 190 ° C to 220 ° C with an increasing temperature gradient of 0.20 ° C / min to 0.5 ° C / min. The method according to any one of claims 1 to 8, comprising heating from 220 ° C to 250 ° C with an increasing temperature gradient of 0.20 ° C / min to 0.5 ° C / min. Cd precursor solution and Se precursor solution are mixed and adjusted to 110 ° C.,
Increasing the temperature of the mixture (110 ° C.) to 120 ° C. over 50 minutes,
Increase the temperature of the above mixture (120 ° C) to 150 ° C over 60 minutes,
Increase the temperature of the above mixture (150 ° C.) to 190 ° C. over 80 minutes,
Increase the temperature of the above mixture (190 ° C.) to 220 ° C. over 100 minutes,
Increasing the temperature of the mixture (220 ° C.) to 250 ° C. over 120 minutes;
It makes and adjusts so that the linear relative time crystal growth curve of CdSe quantum dots, the method according to any one of claims 1 to 9.