JP2001354954A - Ultrafine cadmium sulfide particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ultrafine cadmium sulfide particles having a narrow particle size distribution and an excellent luminescence efficiency. SOLUTION: The ultrafine cadmium sulfide particles comprise cadmium sulfide crystals having organic ligands bonded thereto and give a luminescence band with a half width less than 40 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ultrafine particles comprising a cadmium sulfide crystal having an organic ligand bonded thereto. More specifically, the present invention relates to a novel material having excellent light-emitting properties and applicable as various optical materials.

[0002]

2. Description of the Related Art It is known that semiconductor ultrafine particles exhibit properties different from bulk due to the quantum confinement effect, and are expected to be used as light emitting materials and storage materials. Among them, since cadmium sulfide ultrafine particles are relatively easy to produce, various production methods have been reported for a long time (Ber. Bunsenges. Phys. Che.
m. 88, 969 (1984)). But,
For example, Mat. Res. Soc. Symp. Pro
c. As reported in Vol. 435, p. 643 (1996), the emission spectrum of cadmium sulfide ultrafine particles produced by the conventional technique has an emission band on the short wavelength side appearing from 350 nm to 500 nm, and an emission band of 350 nm to 700 n.
Generally, there are two types of emission bands on the long wavelength side appearing over m. For this reason, it is argued that the emission band on the short wavelength side is emission from excitons and the emission band on the long wavelength side is emission from surface levels of ultrafine particles. Although the details of such emission behavior are not clear, the former emission wavelength is determined by the energy difference between the quantum level determined by the band gap energy (Eg) in the bulk state of the semiconductor and the quantum confinement effect (a function of the particle size). Conceivable.
The latter light emission from the surface level is considered to be due to factors that are difficult to control with the conventional technology, such as crystal lattice defects on the particle surface and the presence of organic substances. Therefore, the narrowing of the particle size distribution of the semiconductor ultrafine particles to narrow the emission energy to a desired wavelength width and the reduction of the emission from the surface level are two at the specific wavelength from the exciton controlled by the quantum confinement effect. It is considered to be effective for improving the luminous efficiency of the device.

[0003] Attempts to reduce the wavelength width of the emission band on the shorter wavelength side (usually evaluated by a half-value width) determined by the energy difference between quantum levels are described in, for example, D.S. Diaz et al .;
Phys. Chem. B, 103, 9854 (19
99). Here, a synthesis using cadmium (II) carboxylate and sodium sulfide as raw materials and dimethyl sulfoxide (DMSO) as a solvent is reported. Immediately after the reaction, a peak is at 510 nm and the half width is 10%.
Although a broad emission band of 0 nm is shown, it has been reported that when the reaction solution is stored in a dark place, the emission band has a peak at 402 nm and changes to a sharp emission band with a half width of 40 nm over about 3 weeks. However, not only is it not suitable for industrial production because long-term dark storage is required to achieve such a favorable emission band change, but even if a product exhibiting such favorable emission behavior is obtained, As described in the document, it is necessary to keep the property in a dark place in order to maintain the properties, and there is a problem in that the light emission characteristics are unstable.

[0004] L. Spanhel et al .; Am. Che
m. Soc. , 109, 5649-5655 (198
In 7), cadmium sulfide crystal ultrafine particles having a half-value width of about 25 nm are reported. However, since they do not have an organic ligand bonded thereto, their dispersibility in a medium other than water is extremely poor, and secondary particles are easily formed. There was a problem of aggregation.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide ultrafine particles made of cadmium sulfide crystal having a narrow particle size distribution and excellent luminous efficiency, and application means thereof. And an industrially advantageous production method for providing such ultrafine particles.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, have found that the reaction temperature during the production of ultrafine particles in a coordinating organic medium such as phosphine oxides is reduced. By precisely controlling or adding phosphonic acid, cadmium sulfide ultrafine particles with a narrow emission band wavelength width and excellent emission stability,
The present inventors have found that they can be produced by an unnecessary and simple method such as a long-term aging step in a dark place, and have reached the present invention.

That is, a first gist of the present invention is an ultrafine particle comprising a cadmium sulfide crystal to which an organic ligand is bound, which provides an emission band having a half width of less than 40 nm. Exists. A second gist of the present invention resides in the method for producing ultrafine particles, which comprises adding a raw material that gives a cadmium sulfide composition to a liquid phase that has been previously adjusted to 200 to 350 ° C.

[0008] A third aspect of the present invention resides in an optical material and a thin film-shaped product comprising the ultrafine particles.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. [Cadmium Sulfide Ultrafine Particles] The cadmium sulfide ultrafine particles of the present invention are made of cadmium sulfide crystals to which an organic ligand is bonded, and give an emission band having a half width of less than 40 nm. It is preferable that the half width of the emission band be smaller, because the emission efficiency at a specific wavelength increases. A more preferred half width is 36 nm or less, further preferably 33 nm or less, and most preferably 30 nm or less.

The ultrafine cadmium sulfide particles of the present invention utilize absorption / emission characteristics controlled by, for example, the quantum effect of cadmium sulfide crystals. It may contain a crystal structure. In particular, ultrafine particles having a substance having a larger band gap energy than cadmium sulfide (for example, a chalcogen element-containing compound semiconductor such as zinc oxide, zinc sulfide, zinc selenide, and magnesium selenide) as an outer shell of the cadmium sulfide crystal are excellent. In some cases, the stability of the emission characteristics may be exhibited.

The ultrafine cadmium sulfide particles of the present invention have an organic ligand, which will be described later, bonded to the surface of the ultrafine cadmium sulfide particles in order to avoid formation of coarse particles due to aggregation between the particle surfaces.
The emission band having a half width of less than 40 nm is a quantized energy such as an exciton level determined by a band gap energy (hereinafter, represented by Eg) and a quantum effect (a function of a particle diameter) in a bulk state of a semiconductor species. It is considered to be derived from the level. Therefore, the peak wavelength is expected to be on the higher energy side, that is, shorter wavelength than the wavelength determined by Eg. For example, although the Eg of cadmium sulfide changes depending on the measurement temperature, it can be changed according to the fourth edition of the Physical and Chemical Dictionary (Iwanami Shoten, 1987).
Year) is 2.42 eV, the wavelength is 512
It is calculated to be about nm or less. Therefore, the peak wavelength of the emission band having a half width of less than 40 nm is usually 350 nm.
To 510 nm, in particular, from the viewpoint of practical use as a luminous body in the near ultraviolet to visible region and controllability of emission wavelength (that is, particle diameter).
60-490 nm, more preferably 370-470 n
m, most preferably in the range of 380-450 nm. When the peak wavelength is smaller than the above wavelength range, the cadmium sulfide crystal grain size becomes extremely small, so that the control of the grain size becomes difficult and the emission intensity may be insufficient.

In order to narrow the half width of the emission band, it is effective that the particle size distribution of the ultrafine particles is narrow. Therefore, the particle size distribution of the cadmium sulfide ultrafine particles of the present invention is TE
The standard deviation of the particle size of the ultrafine particles observed in M is preferably 20% or less, more preferably 15% or less.
Or less, most preferably 10% or less. The size of the ultrafine cadmium sulfide particles of the present invention is generally 1 to 5 as a number average particle size observed by a transmission electron microscope (TEM).
It is 30 nm, preferably 1.5 to 20 nm, more preferably 2 to 15 nm. However, the particle diameter observed by the TEM is that in which the semiconductor crystal portion in the ultrafine particles is observed, and an organic ligand described later is actually bonded to the surface of the crystal. If the number average particle size is too small, it becomes difficult to control absorption and emission. Conversely, if this number average particle size is too large, the quantum effect is not remarkably exhibited, and the wavelength control of absorption and emission becomes difficult. (Ie, light scattering occurs).

[Cadmium Sulfide Raw Material] The cadmium sulfide ultrafine particles of the present invention are produced using a combination of a cadmium source such as an organic cadmium compound or cadmium oxide and a sulfur-containing compound as a cadmium sulfide raw material. As the organic cadmium compound, as described later, a compound which can be a cadmium source that gives cadmium sulfide crystals by thermal decomposition at a high temperature or the like is preferable, for example, dimethyl cadmium, diethyl cadmium, diisopropyl cadmium, dibutyl cadmium, dihexyl cadmium, dioctyl Cadmium, dialkyl cadmium having 2 to 20 total carbon atoms such as didecyl cadmium, methyl cadmium chloride, methyl cadmium bromide, methyl cadmium iodide, monoalkyl cadmium halides such as ethyl cadmium iodide, or cadmium dichloride,
Cadmium dihalides, such as cadmium dibromide, cadmium diiodide, and cadmium chloroiodide.
Among them, dimethyl cadmium, diethyl cadmium, dibutyl cadmium, dialkyl cadmium having 2 to 12 carbon atoms such as dihexyl cadmium, or monoalkyl cadmium halides such as methyl cadmium chloride, methyl cadmium bromide and methyl cadmium iodide. Are particularly preferably used, among which dimethyl cadmium,
Dialkyl cadmium having a total carbon number of 2 to 8, such as diethyl cadmium or di-n-butyl cadmium, is most suitable. These organic cadmium compounds may be used in combination of two or more as necessary. Further, in order to facilitate the handling of these organic cadmium compounds, aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as benzene, toluene and xylene, or tributylphosphine, trihexylphosphine and trioctyl A diluting solvent such as a trialkylphosphine such as phosphine may be present at the same time as the organic cadmium. These diluting solvents may be used in combination of two or more as necessary. The handling of these organic cadmium compounds is preferably performed in a dry inert atmosphere (for example, a rare gas such as nitrogen or argon) in order to avoid undesired decomposition and side reactions.

When cadmium oxide is used as a cadmium source, it is preferable to increase the surface area as fine particles having a particle size of about 10 μm or less. On the other hand, as the sulfur-containing compound, those which react with the cadmium source at a high temperature during the reaction to form cadmium sulfide crystals are preferable. For example, hexamethyldisilthiane [also known as bis (trimethylsilyl) sulfide], bis (tert-butyl) Examples thereof include compounds having an alkylsilyl group such as dimethylsilyl) sulfide and bis (tert-butyldiphenylsilyl) sulfide, alkali metal sulfides such as sodium sulfide and sodium hydrosulfide, and hydrogen sulfide. These sulfur-containing compounds may be used in combination of two or more as necessary. Further, in order to facilitate the handling of these sulfur-containing compounds, a diluting solvent may be present at the same time as in the case of the organic cadmium compound described above.
The handling of these sulfur-containing compounds is preferably performed in a dry inert atmosphere (for example, a rare gas such as nitrogen or argon) in order to avoid undesired decomposition and side reactions.

[Method for Producing Cadmium Sulfide Ultrafine Particles] The cadmium sulfide ultrafine particles of the present invention can be prepared, for example, in a liquid phase of a coordinating organic medium such as a molten phosphine oxide.
The organic cadmium compound and the sulfur-containing compound are particularly preferably produced by carrying out a reaction using the essential raw materials under specific temperature conditions, but the production method is limited as long as the ultrafine particles satisfy the above requirements. There is no. Such a preferred production method is hereinafter referred to as a hot soap method in the present invention.

It is considered that organic cadmium compounds and cadmium oxide, which are essential raw materials in the hot soap method, undergo controlled thermal decomposition to generate active reactive species and react with the coexisting sulfur-containing compound. Therefore, as the solvent constituting the liquid phase used here, a substance that can be heated beyond the thermal decomposition temperature of the organic cadmium compound, specifically, a substance having a boiling point of about 150 ° C. or more at atmospheric pressure is usually used. used. At this time, the liquid phase does not cause an undesirable effect on the raw material (eg, an undesirable decomposition reaction other than thermal decomposition such as solvolysis, or precipitation of a raw material component to be dissolved due to insufficient solubility). The choice of the substance is preferred.

Nonane, decane, dodecane, hexadecane, and solvents constituting the liquid phase satisfying the above conditions are
Aliphatic hydrocarbons such as octadecane or liquid paraffin; aromatic hydrocarbons such as xylene, naphthalene and anthracene; alkylamines having about 12 to 18 carbon atoms such as dodecylamine and hexadecylamine; The trialkylphosphine oxides represented by (1) are exemplified.

[0018]

Embedded image R ¹ R ² R ³ P ＝ O (1) In the general formula (1), R ¹ , R ² and R ³ each independently represent an alkyl group having 20 or less carbon atoms. The alkyl group has usually 1 to 20, preferably 3 to 16, more preferably 4 to 12, and most preferably 6 to 10, carbon atoms. Specifically, isopropyl, n-butyl, isobutyl, hexyl Groups, octyl group, decyl group, dodecyl group, etc., among which hexyl group, octyl group and decyl group are preferred. If the molecular weight of the alkyl group is too small, the application of the phosphine oxides to a suitable high-temperature reaction may be hindered because the boiling point of the phosphine oxides is too low. Conversely, if the molecular weight of the alkyl group is too high, it will be described later. Coordination force of the phosphine oxides may be significantly reduced.

The liquid phase in the hot soap method desirably contains an organic compound having a coordinating ability to a cadmium sulfide crystal to be formed (hereinafter, referred to as "organic ligand"). Although the mechanism of action of such organic ligands and the chemical structure actually present in the ultrafine particles are not yet completely understood, some kind of chemical bonds such as coordination bonds or covalent bonds with the constituent elements of the semiconductor composition, It is presumed that it is introduced as an organic component constituting the surface layer in one ultrafine particle, and as a result, there is an effect of preventing aggregation of the ultrafine particles and increasing dispersibility in an organic medium. As such organic ligands, phosphine oxides represented by the above general formula (1) are very preferably used. In order to increase the coordination force, a phosphine oxide having a molecular structure which does not reduce the electron-donating property of an oxygen atom is used. Are preferred.

Specific examples of the phosphine oxides represented by the general formula (1) include tributyl phosphine oxide, trihexyl phosphine oxide, trioctyl phosphine oxide (hereinafter abbreviated as TOPO), tridecyl phosphine oxide and the like. Alkyl phosphine oxides are exemplified, among which TOPO is most commonly used.

In some cases, trialkylphosphines such as tributylphosphine, trihexylphosphine, trioctylphosphine, and tridecylphosphine are preferably used as the organic ligand. Alternatively, alkylamines having about 12 to 18 carbon atoms, such as dodecylamine and hexadecylamine, can also be used as the organic ligand.

The content of the organic ligand in the cadmium sulfide ultrafine particles of the present invention is usually 10 to 90% by weight,
Preferably 20 to 85% by weight, more preferably 30 to 8% by weight.
0% by weight. There is no particular limitation on how to add the cadmium raw material and the sulfur-containing compound to the liquid phase reaction system of the hot soap method, a method in which the cadmium raw material and the sulfur-containing compound are mixed in advance in the aforementioned diluting solvent, Alternatively, a method of adding them in the reverse order can be exemplified. Among them, the method of mixing in the above-mentioned diluting solvent in advance may give preferable results in terms of control of the particle diameter and the like. Such mixing is carried out at a relatively low temperature, which is usually between 0 and 100 ° C, preferably between 5 and 80 ° C, more preferably between 10 and 70 ° C, most preferably between 15 and 60 ° C.
It is about ° C.

The ratio between the cadmium raw material and the sulfur-containing compound used is usually 0.5 ≦ Cd / S ≦
10, preferably 1 ≦ Cd / S ≦ 7, more preferably 1.5 ≦ Cd / S ≦ 5, most preferably 2 ≦ Cd / S ≦ 3 in terms of particle size control. In carrying out the hot soap method, the amounts of the cadmium raw material and the sulfur-containing compound, which are cadmium sulfide raw materials, are not particularly limited, but the weight of cadmium (Cd: formula weight = 112.41) in the entire liquid phase reaction solution As a percentage (wt%), it is usually 0.001 to 10 wt%, preferably 0.01 to 8 wt%, more preferably 0.05 to 10 wt% in terms of particle size control and productivity.
6 wt%, most preferably about 0.1 to 5 wt%.

The second aspect of the present invention, in particular, a preferred method for producing cadmium sulfide ultrafine particles for precisely controlling the reaction temperature will be described below. In the hot soap method, the liquid phase to which the cadmium sulfide composition raw material is added is 2
Pre-controlling the temperature to 00 to 350 ° C. gives very good results for controlling the particle size. The reason for this is not clear, but for example, C.I. B. Murray et al .; Am. Chem. So
c. 115, p. 8706 (1993), the two elementary processes, the formation of fine crystal nuclei and the growth of cadmium sulfide nanocrystals based on these nuclei, bring the initial temperature of the reaction into the above range. It is presumed that a proper balance can be obtained by controlling. In addition, the range of the above-mentioned initial liquidus temperature is more preferably 250 to 350 ° C, further preferably 270 to 330 ° C, and most preferably 280 to 320 ° C.
Control to ° C.

In the production method of the present invention, it is highly preferable that the temperature drop of the liquid phase immediately after the addition of the raw materials is controlled to be within 80 ° C. Such a temperature drop is caused by adding a low-temperature raw material (usually a liquid). It is preferable from the viewpoint of workability that the organic cadmium compound and the sulfur-containing compound, which are the raw materials giving the cadmium sulfide composition, are added to the reaction system independently or as a mixture with a suitable diluting solvent. Such a raw material solution may be appropriately heated in advance to about 150 ° C. or lower as necessary, but excessive heating is not preferred because the raw material may be deteriorated. Therefore,
The addition of a low-temperature raw material solution in the initial liquid phase adjusted to the temperature range of 200 to 350 ° C. causes a decrease in the reaction temperature. Therefore, it is necessary to control the reaction temperature to be within 80 ° C. according to the present invention. One feature of the method. Such a temperature decrease width is more preferably within 60 ° C. in terms of particle size control,
Most preferably, it is controlled within 50 ° C. In the production method of the present invention, “immediately after the addition of the raw materials” when the plurality of raw materials are separately added to the reaction liquid phase means immediately after the completion of the addition of the last raw materials. For the purpose of realizing such a temperature reduction range, the raw material may be continuously added within a certain time.

In the production method of the present invention, it is preferable to grow cadmium sulfide crystals in a temperature range of 220 to 350 ° C. after the above-mentioned initial temperature control of the reaction. If the temperature is lower than this temperature range, the reaction may be extremely slow, and if the temperature is higher than this temperature range, the particle size control may be difficult. The growth temperature range for such crystals is more preferably 230-330 ° C, most preferably 240-330 ° C.
~ 320 ° C. In practice, the growth temperature of the crystal usually goes through a process in which the temperature is lowered immediately after the addition of the raw material and then continuously raised to a preferable predetermined temperature.
Therefore, it is preferable to control the temperature rising process or the constant temperature process after reaching the predetermined temperature within the above-mentioned temperature range of 220 to 350 ° C. There is no particular limitation on the heating rate in the heating process.

The reaction time in the production method of the present invention is usually from 1 second to 500
Minutes, preferably from 5 seconds to 400 in terms of particle size control and productivity.
Minutes, more preferably 10 seconds to 300 minutes, and most preferably 20 seconds to 200 minutes. If phosphonic acids are present in the liquid phase of the hot soap method, the particle size distribution of the resulting cadmium sulfide ultrafine particles may be reduced.
The phosphonic acids referred to herein are organic compounds having a phosphonic acid group, and the structure thereof is not limited as long as the amount thereof is not significantly reduced by volatilization or thermal decomposition at the temperature of the liquid phase. ,
Alkylphosphonic acids having about 6 to 18 carbon atoms such as octylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid, octadecylphosphonic acid, and arylphosphonic acids such as benzenephosphonic acid and naphthalenephosphonic acid And the like, among which decylphosphonic acid, dodecylphosphonic acid, alkylphosphonic acids having about 10 to 14 carbon atoms such as tetradecylphosphonic acid are preferably used in terms of boiling point and stability, and dodecylphosphonic acid is more preferably used. . The amount of the phosphonic acid used is usually 0.1 to 1 as a weight percentage at the time when the addition of the raw material to the liquid phase is completed.
5% by weight, preferably about 0.5 to 10% by weight, more preferably about 1 to 7% by weight, the addition may be made before the addition of the raw material, simultaneously with the addition of the raw material, or after the addition of the raw material, It is also possible to mix the raw materials in advance.

[Method of Purifying Cadmium Sulfide Ultrafine Particles] The cadmium sulfide ultrafine particles obtained by the above-described method are:
After being extracted from the reaction system, it may be used as it is after cooling, but as a method of raising the composition ratio of cadmium sulfide crystals in the ultrafine particles, a solvent material of a reaction liquid phase of a hot soap method or a diluting solvent of a raw material may be used. Solvents with high solubility but low solubility of the generated ultrafine particles, such as methanol, ethanol,
There is also a method of mixing with alcohols such as n-propanol, isopropyl alcohol and n-butanol. In this case, a suspension in which the ultrafine particles are precipitated is generated, and the purified ultrafine cadmium sulfide particles are separated by a separation method such as centrifugation.

[Thin Film Molded Article] The above-mentioned cadmium sulfide ultrafine particles of the present invention can be molded by a conventional method and applied to various uses. One example is a thin film molded article. Such a thin film-shaped molded product is obtained by using the cadmium sulfide ultrafine particles of the present invention obtained by the above-mentioned production method in a suitable solvent (for example, an aromatic solvent such as toluene, an aliphatic hydrocarbon such as hexane, a ketone solvent such as acetone, Dissolved or dispersed in an ether-based solvent such as tetrahydrofuran or a halogenated solvent such as chloroform, methylene chloride or chlorobenzene), and then dissolved or dispersed in a desired substrate, for example, a glass substrate, indium-doped tin oxide (commonly known as ITO), metal or graphite. It can be molded by casting and coating on a conductive substrate such as silicon, a semiconductor substrate such as silicon, a resin substrate such as polymethyl methacrylate (PMMA), polystyrene, or aromatic polycarbonate.

At the time of molding by such casting coating, an appropriate organic binder component, for example, a resin such as polymethyl methacrylate (PMMA), polystyrene or aromatic polycarbonate, a wax, or a silicone oil or the like must be dissolved in a solvent. Is also possible. In this case, the amount of the organic binder component is usually 1 to 90% by weight based on the total amount of the ultrafine particles, and the mechanical strength, brightness, absorbance and
From the viewpoint of optical characteristics such as light transmittance, it is preferably 5 to 80% by weight, more preferably 10 to 70% by weight, and most preferably 15 to 60% by weight.

The thin-film molded article of the present invention may contain any additives, for example, heat stabilizers, light absorbers such as ultraviolet rays, antioxidants, oxygen scavengers, as long as the effects are not significantly impaired. It is also possible to add a moisture absorbent or the like. The thin film-shaped body may be formed into a flat shape or a curved surface having an arbitrary curvature. The thickness of the thick film is not particularly limited, but is preferably, for example, about 0.003 to 5000 μm, preferably 0.004 to 1 in terms of luminance, absorbance, or light transmittance.
About 000 μm, more preferably 0.005 to 500 μm
m, most preferably about 0.005 to 100 μm.

Further, a layer having an additional function on one or both sides of the thin film-shaped molded product (for example, a protective layer against mechanical damage, a gas barrier layer, a light blocking layer, a heat insulating layer, an electrode layer, etc.).
May be provided as needed. The thin film-shaped molded article of the present invention described above is industrially useful as a planar illuminant used for a display or a lighting device or the like utilizing the emission characteristics of the ultrafine particles, or as a high-density recording layer utilizing the absorption and emission characteristics. is there.

[0033]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto without departing from the scope of the present invention. [Measurement device] (1) Emission spectrum: F250 manufactured by Hitachi, Ltd.
In a spectrofluorometer 0, the solution sample was measured with an optical path length of 1c.
m in a quartz cell. (2) Number average particle size: H-9000U manufactured by Hitachi, Ltd.
Observation was performed using an HR transmission electron microscope (acceleration voltage: 300 kV, vacuum degree during observation: about 7.6 × 10 ⁻⁹ Torr).

Example 1 Production of Cadmium Sulfide Ultrafine Particles First, a raw material solution was placed in a glove box kept at room temperature in a dry nitrogen atmosphere, and tri-n-butylphosphine (purity> 90%, manufactured by Tokyo Chemical Industry Co., Ltd.) was used. ) Was purified by a vacuum distillation method, and 2.55 g of the purified product was placed in a 20 mL vial.
0.56 g of dimethyl cadmium (purity 99 +%) hexane diluent (10% by weight) manufactured by Strem Chemicals
And shaken for a few minutes. To this, hexamethyldisilthiane (0.028 g) manufactured by Fulka was added and shaken for several minutes to prepare. The Aldr was then placed in a 50 mL three-necked round bottom flask equipped with a thermocouple for monitoring the reaction liquid phase temperature, an air-cooled Liebig condenser, and a rubber septum stopper.
ich trioctylphosphine oxide (purity 90
%) And a magnetic stirrer, and a dry argon gas was passed for 15 minutes to replace the inside of the flask with an argon atmosphere. The thermocouple was connected to a digitally set temperature controller. After the stirring is started, the internal temperature is 30
The temperature was raised to 0 ° C. The raw material solution was taken out of the glove box, 2 mL was taken into a syringe whose inside was replaced with dry argon, and injected into the flask through a rubber septum stopper for about 0.1 second. The liquid inside the flask turned yellow, confirming that the reaction had started. Immediately after injection of the stock solution, the reaction liquid phase temperature dropped to about 260 ° C. When the temperature of the temperature controller was immediately set to 300 ° C., the reaction liquid phase temperature reached 300 ° C. in about 15 minutes. Twenty minutes after the injection of the raw material solution, the mixture was cooled to room temperature to stop the reaction. Purification was performed according to the following procedure. That is, 10 mL of methanol manufactured by Wako Pure Chemical Industries, Ltd. was added to the reaction flask and stirred for 5 minutes to obtain a suspension containing a yellow-white precipitate. This suspension was centrifuged at 3000 rpm for 15 minutes. The precipitate obtained by centrifugation was dried under a stream of nitrogen, then dried under vacuum, and dried under vacuum at room temperature for 15 hours. Thus, about 60 mg of concentrated ultrafine cadmium sulfide particles were obtained. The number average particle size of the ultrafine particles is about 4 nm, and the
Emission spectrum of a 3 wt% concentration solution (excitation light is 366
nm) are shown in FIG. The half value width of the peak of the emission band having the peak wavelength at 431 nm was 31 nm.

Example 2 When the temperature inside the flask when the raw material solution was injected was 200
FIG. 1 shows the fluorescence spectrum of cadmium sulfide ultrafine particles produced by the same method as in Example 1 except that the temperature of the reaction liquid phase immediately after the injection decreased to about 165 ° C. The excitation light used a wavelength of 366 nm. The half bandwidth of the emission band having the peak wavelength at 448 nm was 37 nm.

Example 3: Method for adding phosphonic acids In a glove box under a dry nitrogen atmosphere, tributylphosphine (2.25 g), a 10% by weight solution of dimethylcadmium in n-hexane (0.56 g), and hexamethyldiamine were added. Silthiane (0.033 mL) was mixed in a glass bottle and sealed with a rubber stopper (a septum supplied by Aldrich) (this mixed solution is hereinafter referred to as “raw material solution A”). Separately from the raw material solution A, a tripyrrole brown Pyrex (registered trademark) glass flask equipped with an air-cooled Liebig reflux tube and a thermocouple for controlling the reaction temperature was used as a reaction vessel. Octylphosphine oxide (6.5 g) and tetradecylphosphonic acid (0.13 g) were added, and dried under reduced pressure at room temperature for 15 minutes. During this time, the inside atmosphere was restored to atmospheric pressure with dry argon gas, and then the pressure was reduced again. Thereafter, the temperature was raised to 300 ° C., and the above-mentioned raw material solution A (3 mL) was injected at once with a syringe, and this time was regarded as the reaction start time. Five minutes after the start of the reaction, the heat source was removed, and when cooled to about 50 ° C., anhydrous methanol (0.6 mL) was added to dilute the mixture, and the mixture was allowed to cool to room temperature. The reaction solution was poured into anhydrous methanol (22.5 mL) in a dry nitrogen atmosphere and stirred at room temperature for 5 minutes to generate an insoluble matter. This insoluble matter was centrifuged (3500 rpm), and the supernatant was removed by decantation to obtain a yellow solid. This solid was dissolved in purified toluene (1 mL), and anhydrous methanol (15 m
L), stirred at room temperature for 5 minutes, and centrifuged and decanted in the same manner as above to separate a yellow solid precipitate. The solid was dried at room temperature under a stream of dry nitrogen and then vacuum dried at room temperature overnight to obtain a yellow solid powder (45.5 mg).
The yellow solid powder thus obtained is soluble in toluene, and the emission spectrum of the toluene solution (excitation wavelength 366 n
m) gives an emission band having a peak wavelength of 435 nm, and the half width of this emission band is 27 nm. This emission spectrum is shown in FIG.

COMPARATIVE EXAMPLE 1 Production of Ultrafine Cadmium Sulfide Fine Particles by Conventional Technique L. Colvin et al .; Am. Chem. So
c. , 114, p. 5221 (1992) (reverse micelle method) to produce ultrafine cadmium sulfide particles. At room temperature under a nitrogen atmosphere, heptane (250 mL) manufactured by Junsei Chemical Co., Ltd. was placed in a 300 mL flask, and 22.2
g of aerosol OT (AOT) manufactured by Wako Junyaku Co., Ltd. were prepared. Cadmium perchlorate hexahydrate (1.17 g, manufactured by Kishida Chemical Co., Ltd.) was dissolved in ultrapure water (6 mL) with nitrogen bubbling, and then added to one AOT heptane solution. On the other hand, 0.18 g of sodium sulfide 9 hydrate manufactured by Wako Pure Chemical Industries, Ltd.
mL) and added to the other AOT heptane solution. When both flasks were stirred for 1 hour, a colorless and transparent liquid was obtained. At room temperature, the liquid containing cadmium was added to the liquid containing sulfur over 15 minutes with a syringe, whereby a clear yellow liquid was obtained. 0.4
When 5 mg of thiophenol manufactured by Kishida Chemical Co., Ltd. was slowly added, the solution turned yellow-white. The mixture was filtered through a membrane filter having a diameter of 0.5 μm, and washed three times with 300 mL of petroleum ether. The filtrate was dissolved in 10 mL of pyridine and filtered. The clear yellow filtrate was added to 200 mL of petroleum ether, reprecipitated and filtered again. In this way,
About 15 mg of cadmium sulfide ultrafine particles were obtained. The number average particle diameter of these ultrafine particles is about 4 nm, and about 0.
The emission spectrum of the solution having a concentration of 03 wt% was measured. FIG. 2 shows the obtained fluorescence spectrum. Excitation light is 420n
A wavelength of m was used. The half width of the light emitting band having the peak wavelength at 556 nm was 123 nm.

Comparative Example 2: When the temperature drop in the liquid phase of the hot soap method is large At room temperature, in a glove box kept in a dry nitrogen atmosphere, tri-n-butylphosphine (purity> 90%) manufactured by Tokyo Chemical Industry Co., Ltd. ) Is purified by vacuum distillation.
Take 55 g into a 20 mL vial and add Strem Chem
0.56 g of dimethyl cadmium (purity 99 +%) hexane diluent (10% by weight) manufactured by Iicals was added and shaken for several minutes. To this, 0.070 g of hexamethyl-disilthiane manufactured by Fulka was added and shaken for several minutes to obtain a raw material solution. Manufactured by the same method as the method of manufacturing cadmium sulfide ultrafine particles in Example 1, except that the temperature inside the flask before injecting the raw material solution was reduced to 360 ° C., and the reaction liquid phase temperature immediately after the injection was reduced to about 290 ° C. FIG. 1 shows the fluorescence spectrum of the obtained cadmium sulfide ultrafine particles. The excitation light is 366
A wavelength of nm was used. The half bandwidth of the light emitting band having the peak wavelength at 463 nm was 68 nm.

[0039]

The cadmium sulfide ultrafine particles of the present invention have a narrow particle size distribution and excellent luminous efficiency, so that they can be applied as various optical materials.

[Brief description of the drawings]

1 is an emission spectrum diagram of cadmium sulfide ultrafine particles obtained in Examples 1 and 2 and Comparative Example 2. FIG.

FIG. 2 is an emission spectrum diagram of ultrafine cadmium sulfide particles obtained in Comparative Example 1.

FIG. 3 is an emission spectrum diagram of cadmium sulfide ultrafine particles obtained in Example 3.

Claims (9)

[Claims] 1. Ultrafine cadmium sulfide fine particles comprising cadmium sulfide crystals bonded with an organic ligand and giving an emission band having a half width of less than 40 nm. 2. The cadmium sulfide ultrafine particles according to claim 1, wherein a peak wavelength of an emission band having a half width of less than 40 nm is in a range of 350 to 510 nm. 3. The method for producing ultrafine cadmium sulfide particles according to claim 1, wherein a cadmium sulfide raw material is added to a liquid phase which has been previously adjusted to 200 to 350 ° C. 4. The method for producing cadmium sulfide ultrafine particles according to claim 3, wherein the temperature drop of the liquid phase immediately after the addition of the raw material is within 80 ° C. 5. The method for producing cadmium sulfide ultrafine particles according to claim 3, wherein the cadmium sulfide crystal is grown in a temperature range of 220 to 350 ° C. 6. The method for producing ultrafine cadmium sulfide particles according to claim 3, wherein the liquid phase contains phosphine oxides. 7. The method for producing ultrafine cadmium sulfide particles according to claim 3, wherein phosphonic acids are present in the liquid phase. 8. An optical material comprising the cadmium sulfide ultrafine particles according to claim 1 or 2. 9. A thin film-shaped compact comprising the cadmium sulfide ultrafine particles according to claim 1 or 2.