JP4538646B2 - Method for producing highly efficient phosphor - Google Patents

Description

  The present invention relates to a method for producing a phosphor with improved luminous efficiency.

  Nanocrystals of II-IV semiconductors (CdX: X is S, Se or Te) are known as quantum dots (QDot: Quantum Dot), and their size-dependent optoelectronic and photoluminescence (PL) characteristics Therefore, technical application is expected (for example, Non-Patent Document 1). In luminescent quantum dots, surface atoms with unsaturated bonds act as non-radiative recombination traps for electrons and holes. Electrons and holes trapped on the surface are either thermally activated to the initial excited state to produce delayed excitons, or are further thermally activated to eventually emit light from a weak deep trapped state (e.g. Non-patent document 2). This complex decay dynamics causes low luminous efficiency and prevents the application of quantum dots to light emitting devices.

  An optimal surface structure is required to produce a complete exciton PL from a quantum dot. In order to obtain an optimal surface structure, attention is focused on the properties and concentrations of precursors, as well as the choice of coordinating organic solvents, as well as the temperature in core and core / shell quantum dot synthesis. In addition, as a method for increasing luminous efficiency, it is known to form a protective layer (shell) on the surface of quantum dots (for example, Non-Patent Document 3).

  In the conventional method for forming a shell, a precursor for synthesizing a shell is added to a core quantum dot dissolved in a mixed solvent of TOP and TOPO. Since the melting point of TOPO is around 50 ° C., it was customary to heat to a high temperature of about 100 to 260 ° C. during the reaction.

Against this background, it has not been possible to create a good surface structure by synthesizing a protective layer on the surface of the quantum dot, which is the substrate (core), using an organic solvent other than TOPO at a low temperature of about room temperature. Not.
SV Gopenenko, Optical Properties of Semiconducting Nanocrystals 1998, Cambridge University Press, Cambridge. MG Bawendi et al., J. Chem. Phys. 1992, 96, 946. BODabbousi et al., J. Phys. Chem. B. 1997, 101, 9463-9475 Masaru Oda et al., Polymer Papers, Vol.61, No.1, Jan, 2004, 63-74

  The present invention is characterized in that (i) a substrate, (ii) a metal compound and / or (iii) a group 5B or group 6B element compound is added to an organic solvent and reacted at a low temperature of about 0 to 50 ° C. The main object of the present invention is to provide a method for producing a phosphor (high efficiency phosphor) with improved luminous efficiency.

  The present inventors have obtained unpurified CdX quantum dots in an organic solvent such as chloroform, hexane, and 1-butanol containing a metal compound and / or a group 5B or group 6B element compound and saturated with an inert gas at room temperature. Was allowed to stand for 12 hours, and it was found that 1) an increase in luminous efficiency, 2) particle growth and 3) focusing of the size distribution occurred, and the present invention was completed.

The present invention provides the following high-efficiency phosphor manufacturing method.
Item 1. A base material is reacted with at least one selected from the group consisting of a metal compound, a group 5B element compound, and a group 6B element compound in the presence of an organic solvent at a reaction temperature of 0 to 50 ° C. A method for producing a phosphor having a protective layer on the surface of a substrate, comprising forming a protective layer of a compound containing at least one element selected from the group consisting of metal, group 5B and group 6B.
Item 2. Item 2. The method for producing a phosphor according to Item 1, wherein the reaction temperature is 10 to 30 ° C.
Item 3. Item 3. The method for producing a phosphor according to Item 1 or 2, wherein the substrate is nanoparticles.
Item 4. Item 4. The method for producing a phosphor according to Items 1 to 3, wherein the substrate is CdSe or CdTe.
Item 5. Item 5. The method for producing a phosphor according to Item 1, wherein the average particle diameter of the nanoparticles is 1 to 30 nm.
Item 6. Item 6. The method for producing a phosphor according to Items 1 to 5, wherein the metal compound is a metal salt or a metal oxide.
Item 7. Item 7. The phosphor according to Items 1 to 6, wherein the metal compound of (ii) is Ga or In, and the Group 5B element is at least one selected from the group consisting of P, As, and Sb. Production method.
Item 8. Item 7. The phosphor according to Items 1 to 6, wherein the metal compound of (ii) is Cd or Zn, and the Group 6B element is at least one selected from the group consisting of S, Se, and Te. Production method.
Item 9. Item 9. The method for producing a phosphor according to Item 1-8, wherein the organic solvent is at least one selected from the group consisting of chloroform, hexane and 1-butanol.
Item 10. Item 10. The method for producing a phosphor according to Items 1 to 9, wherein an emission spectrum of the obtained nanoparticles has a half-value width of 40 nm or less.

  In the method for producing the phosphor of the present invention, a quantum dot is used as a base material, a metal compound is used as a source of metal ions, and / or a group 5B / 6B element compound compound is used as a source of group 5B / 6B atoms.

[Base material]
In the present invention, the substrate can be obtained according to a conventionally known method for producing quantum dots made of nanoparticles. For example, a metal compound dissolved in a coordinating organic solvent and a group 5B element compound or a group 6B element compound It is obtained by reacting the liquid compound serving as the supply source of the reaction at about 100 to 200 ° C., preferably about 110 to 150 ° C. in an inert gas atmosphere.

  (1) Metal compound: Examples of the metal of the metal compound include 2B to 3B group atoms. Examples of such metals include Zn and Cd (Group 2B); Ga and In (Group 3B).

  Examples of the metal compound include a metal oxide or a metal salt compound. As the metal oxide, oxides of various oxidation states in each metal can be widely used.

  Examples of metal salt compounds include organic acid salts of each metal (for example, monocarboxylates such as acetate and propionate, hydroxycarboxylates such as glycolate and lactate, dicarboxylates such as succinate, Polycarboxylates such as acid salts, aliphatic or aromatic sulfonates such as methanesulfonate and toluenesulfonate, carbonates, bicarbonates, etc.), nitrates, sulfates, hydrochlorides, hydrogen bromides Examples thereof include inorganic acid salts such as acid salts, hydrofluoric acid salts, perchloric acid salts and phosphates.

  (2) Coordinating organic solvent: Examples of the coordinating organic solvent include tri-n-octylphosphine (TOP), oxidized tri-n-octylphosphine (TOPO) and the like, and a mixed solution thereof is used. You can also. In addition, in order to help dissolution of the metal compound, for example, fatty acids such as stearic acid and amines such as hexadecylamine (HDA) may be added to the coordinating organic solvent.

  When a metal compound is dissolved in a coordinating solvent, for example, in the case of cadmium, cadmium acetate dihydrate (about 0.5 to 2 g, preferably about 1 to 1.5 g) is about 100 to 260 ° C., preferably Dissolve in a mixed solution of TOP (about 1 to 4 ml, preferably about 1 to 3 ml) and TOPO (about 1 to 4 g, preferably about 1 to 3 g) heated to about 110 to 180 ° C. under an inert gas atmosphere. be able to.

  (3) Group 5B element compound or group 6B element compound: When the compound serving as the source of the group 5B element compound or group 6B element compound is in a solid state, the group 5B element compound or group 6B element compound is replaced with the above-mentioned arrangement. It is preferable to dissolve in a neutral organic solvent under an inert gas atmosphere, and then cool to room temperature.

Examples of the compound that is a source of a group 5B atom (P, As, Sb, etc.) include {(R) ₃ Si} ₂ X (X represents a group 5B atom, and R represents the same or different C _{1 to} C A compound containing a silyl group represented by ₂₀ ) represents an alkyl group or a phenyl group. As such a compound, tris (trimethylsilyl) phosphide (P (TMS) ₃ ), tris (trimethylsilyl) arsenide (As (TMS) ₃ ), tris (trimethylsilyl) antimonide (Sb (TMS) ₃ ) or the like may be used. preferable.

Examples of the compound that is a source of a 6B group atom (S, Se, Te, etc.) include (R ′) ₃ PX ′ (X ′ represents a 6B group atom, and R ′ is the same or different, and C ₁ to A phosphine compound represented by (C _{20 represents} an alkyl group or a phenyl group). As such a compound, it is preferable to use tributylphosphine selenide, trioctylphosphine selenide, tributylphosphine sulfurated, trioctylphosphine sulfurated, tributylphosphine telluride, trioctylphosphine telluride, or the like.

Further, as a source compound of another group 6B atom, for example, {(R ″) ₃ Si} ₃ X ″ (X ″ represents a group 6B atom, and R ″ is the same or different C _1. a compound containing a silyl group represented by an alkyl group or a phenyl group -C ₂₀₎ can be used. As such a compound, bis (trimethylsilyl) sulfide (S (TMS) ₂ ), bis (trimethylsilyl) selenide (Se (TMS) ₂ ), bis (trimethylsilyl) telluride (Te (TMS) ₂ ) or the like may be used. preferable.

  (4) Inert gas: As the inert gas, for example, Ar, Kr, Xe or the like can be used. In this reaction, in order to prevent the oxidation of trioctylphosphine, it is preferable to remove oxygen in the air, that is, to remove air. For example, as the simplest method, argon is first introduced into a three-way flask to expel air, and once the air has been expelled, a gas balloon rubber balloon attached to one end of the three-way flask is filled with argon. In this state, the supply of argon is stopped and the inside of the flask is shut off from the air. Since the specific gravity of argon is greater than that of air, it is considered that the possibility of air entering is very small if the flask is kept stationary.

  (5) A combination of a metal compound and a group 5B element compound or a group 6B element compound: When using at least one selected from a group 2B atom, preferably Cd or Zn, as the metal of the metal compound, Is preferably a source compound composed of at least one selected from S, Se and Te.

  When at least one selected from the group 3B atoms, preferably Ga and In, is used as the metal of the metal compound, the group 5B atoms are preferably selected from at least one selected from P, As and Sb. The constituted compound can be preferably used.

  For example, in the case of trioctylphosphine selenide (TOPSe), the selenium pellet is preferably 100 to 200 ° C., more preferably 150 ° C., preferably 30 minutes to 3 hours, more preferably 2 (implemented) in an argon atmosphere. See Example 1) Can be prepared by dissolving in trioctylphosphine with vigorous stirring over time. The dissolution temperature is not particularly limited as long as the selenium pellets are dissolved in trioctylphosphine.

  (6) Average particle size: The average particle size of the quantum dots is about 1 to 30 nm, preferably about 2 to 10 nm. For the measurement of the particle diameter of the quantum dots, for example, 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 can be used. A preferable measurement method is an image analysis method using an image of a transmission electron microscope.

  The surface of the quantum dot obtained in this way has defects that inhibit light emission. A defect that inhibits light emission refers to an atom having an unsaturated bond present on the surface of the light-emitting quantum dot. Such surface atoms act as non-radiative recombination traps for electrons and holes. Electrons and holes trapped in the traps present on the surface are either thermally activated to the initial excited state, resulting in delayed exciton PL, or further thermally activated to eventually lower energy traps. It produces a weak light emission from the light.

[Formation of protective layer]
The metal compound ions and group 5B or group 6B element ions dissolved in the organic solvent cover the surface of the quantum dots as the substrate, as in the growth of a single crystal from a saturated solution. Thereby, it is considered that defects that inhibit the light emission present on the surface of the substrate are removed, and the light emission efficiency is improved. In the present invention, the layer that covers the surface of the quantum dots that are the base material is called a protective layer.

  The nanoparticles obtained by the above method are used as a base material (core), and reacted with a metal compound and / or a group 5B or 6B element compound in an organic solvent at a low temperature, that is, a shell is formed on the surface of the base material. Thus, a phosphor with improved luminous efficiency can be obtained.

As a metal compound and a 5B group or 6B group element compound, what is described in said (1) and (3) can be used. When these compounds are solid, it is preferable to use them by dissolving them in a coordinating organic solvent that is liquid at the reaction temperature when forming a protective layer such as trioctylphosphine (TOP). In addition, a protective layer can be formed using any one of a metal compound or a group 5B or 6B element compound, but any combination of a metal compound and a group 5B or 6B element compound is used. Are preferably used because of their high luminous efficiency.

  The high-efficiency phosphor of the present invention can be obtained by forming a protective layer on a base material with a metal compound and / or a group 5B or 6B element compound, and the protective layer is the same compound as the base compound Or may be formed of different compounds. In the present invention, the protective layer formation when the shell is formed of the same compound as the core substrate, homoepitaxy, and the protective layer formation when the compound forming the substrate and the shell compound are different, Sometimes called heteroepitaxy.

  As a combination of the metal compound and the group 5B or 6B element compound in the protective layer, for example, at least one selected from Ga and In as the metal element of the metal compound and P and As as the group 5B element A case where at least one selected from Cd and Zn is used as the metal element of the metal compound and at least one selected from S, Se and Te is used as the group 6B element.

Organic solvents include methanol, ethanol, 1-propanol, isopropanol, 1-butanol, isobutanol, ethylene glycol, benzyl alcohol and other alcohols; hexane, cyclohexane, heptane, isooctane, normal decane and other alkanes; CCl ₄ , halogenated carbon such as CHCl ₃ , CH ₂ Cl ₂ , CH ₃ Cl; aromatic hydrocarbons such as benzene, toluene, xylene, chlorobenzene, ethylbenzene, methylnaphthalene, etc. can be used, preferably CHCl ₃ , hexane and 1-butanol. The organic solvent is preferably saturated with an inert gas such as Ar, Kr, or Xe.

  In the formation of the protective layer, the low temperature means a temperature of about 0 to 50 ° C., preferably about 5 to 49 ° C., more preferably about 10 to 30 ° C., more preferably about 20 to 25 ° C., and below the boiling point of the organic solvent. It is preferable to adjust so that it becomes.

  At this temperature, the substrate, the metal compound and / or the group 5B or group 6B element compound are reacted in the organic solvent for about 6 to 15 hours, preferably about 12 hours, to form a protective layer on the substrate surface. A synthesis at a low temperature (particularly room temperature: about 23 ° C.) is preferable because it is considered to eliminate a temperature gradient in the reaction mixture. Moreover, it is preferable to leave still during reaction, and it is preferable that it is dark in order to avoid the influence by ultraviolet rays etc.

As a method for forming the protective layer, for example, when a CdSe protective layer is formed on a CdSe substrate in 1 butanol, 10 mL of 1 butanol is used, and about 1 to 10 μmol of CdSe nanoparticles are used as the substrate. Preferably, the amount of (CH ₃ COO) ₂ Cd · 2H ₂ O (molecular weight 266.4) is about 0.01 to 0.5 g, preferably about 0.05 g, and 6B group element, with respect to about 5.0 μmol. As a compound supply source, TOPSe (molecular weight: 448.96, specific gravity: 1.25) is used at about 10 to 1000 L, preferably about 500 L. As the organic solvent, chloroform and the above organic solvents can be used.

  In the solution, nanoparticles of CdSe do not exist as “CdSe” as a diatomic molecule, but are dispersed as nanoparticles. Therefore, the number of moles of the above CdSe nanoparticles is not represented by the number of moles of “CdSe” (number of molecules or atoms) as a diatomic molecule or atom but the number of moles (number of particles) as “nanoparticle”. Is done. In general, one nanoparticle contains several hundred to several tens of thousands of Cd and Se atoms depending on its size.

  For mixing of each reactant, a reactant and an organic solvent were placed in a glass container and dispersed with an ultrasonic wave.

  The protective layer preferably covers the surface of a single substrate, but if it is nano-sized and emits light, several substrates are aggregated / approached, and the protective layer is formed on the surface. Also good.

For example, when 1-butanol is used as an organic solvent, (CH ₃ COO) ₂ Cd has a low solubility in 1-butanol, so it is preferable to use it by dissolving it in TOP or ethanol in advance. When the highly efficient phosphor of the present invention is formed using other compounds, it can be carried out with reference to the above-mentioned example of CdSe.

  The formation of the protective layer on the surface of the particles is indirectly confirmed by measuring the shift of the absorption spectrum, the red shift of the emission spectrum, or the increase of the luminous efficiency. When the protective layer is formed, the emission spectrum has a maximum value of about 2 nm or more red-shifted, and the absorption spectrum is about 2 nm or more red-shifted before the protective layer is formed. Further, the luminous efficiency is increased by about 1.2 times or more compared with that before the protective layer is formed.

  The average particle size after the protective layer is formed is about 2 to 4 nm, preferably about 2.4 to 3.0 nm. According to the method of the present invention, since the particle size distribution is narrow, a monochromatic phosphor can be obtained. If the element which comprises a protective layer is Cd or Se, the film thickness of the protective layer formed in the base-material surface is preferable that it is about 1-3 layers by the atomic size. Also, the weight ratio of the substrate: protective layer is preferably in the range of about 24: 1 to 20: 1.

  As another embodiment of the present invention, as a source of ions necessary for forming a protective layer on the surface of a substrate such as Cd, Se, Te, etc., a metal compound dissolved in TOPO, TOP, etc. and / or a group 5B or 6B A mixed solution of elemental compounds may be used. The mixed solution may be prepared according to the method described in the above [Substrate].

  For example, fatty acids such as stearic acid and amines such as hexadecylamine (HDA) may be added to the coordinating organic solvent such as TOPO and TOP in order to help dissolve the metal compound.

  Moreover, the quantum dot used as a base material was refine | purified with alcohols, such as 1-butanol, methanol, methanol, ethanol, 1-propanol, isopropanol, 1-butanol, isobutanol, ethylene glycol, benzyl alcohol, or these mixed solutions. Although a thing may be used, a non-purified thing may be used. In addition to TOP and TOPO, non-purified quantum dots contain ions that did not react during substrate formation (Cd ions, Se ions, Te ions, etc.), so Cd, Se, Te, etc. It is possible to form a protective layer on the surface of the substrate without newly adding a metal ion.

  The luminous efficiency of the nanoparticles in which the protective layer is formed and the defects on the surface of the base material are repaired is 1 in comparison with that before forming the protective layer when the metal compound ion, group 5B or group 6B ion is added separately. It is desirable that it be about twice or more, preferably about twice or more. Further, when both the metal compound ion and the 5B group or 6B group ion are added, it is desirably about twice or more, preferably about four times or more, compared with that before forming the protective layer.

  In addition, the high efficiency phosphor obtained by the method of the present invention desirably has a half-value width of about 60 nm or less, preferably about 50 nm or less, more preferably about 40 nm or less in the emission spectrum. Quantum dots can change their emission color systematically depending on their size. When the width of the emission spectrum is narrow, different biomolecules can be labeled using quantum dots of different sizes, and the biomolecules can be distinguished, for example, in a cell by the difference in emission color. Furthermore, when a protective layer is formed on the nanoparticle surface according to the method of the present invention, the light emission characteristics are extremely stable, and the light emission efficiency does not change even after about 6 months, preferably about 2 months. And

  According to the present invention, a phosphor with high luminous efficiency can be obtained by using quantum dots as a base material and forming a protective layer on the surface thereof. Unlike the conventional method that required a reaction at a high temperature to form a protective layer, the phosphor production method of the present invention is an extremely simple and safe method of standing at a low temperature of about room temperature. It is possible to form a protective layer on the surface of the quantum dots.

  Moreover, the phosphor obtained by the method of the present invention exhibits a narrow particle size distribution, thereby emitting monochromatic fluorescence. Furthermore, the phosphor obtained by the method of the present invention is extremely stable and can maintain a high light emission rate over a long period of time.

  Hereinafter, although an example is given and explained in detail, the present invention is not limited to these examples. In the examples, X represents Se or Te.

[Synthesis of CdX quantum dots]
Tri-n by dissolving Se (0.7896 g) or Te (1.276 g) pellets in TOP (7.4 g) at 150 ° C. under an argon atmosphere for 2 hours and then cooling the TOP solution to room temperature. -Stock solutions of octylphosphine selenium (TOPSe) and tri-n-octylphosphine tellurium (TOPTe) were prepared.

(CH ₃ COO) ₂ Cd (1 g) was dissolved in a mixed solution of TOP (˜2 ml) and TOPO (˜2 g) in a three-way round bottom flask at 120 ° C. under an argon atmosphere. TOPSe (˜4 ml) or TOPTe (˜4 ml) was injected into a (CH ₃ COO) ₂ Cd / TOP / TOPO solution maintained at 120 ° C. to produce CdSe and CdTe quantum dots, respectively. The reaction was continued at 120 ° C. for 30 minutes to synthesize monodisperse CdX quantum dots having PL (Photoluminescence) spectrum maximum values of ˜550 nm for CdSe and ˜600 nm for CdTe.

[Influence on luminous efficiency]
After cooling the reaction solution to room temperature, in order to find out which factor of Cd ion, Se ion, Te ion, or oxygen is essential for the luminous efficiency, the non-purified CdX quantum dots were mixed with chloroform and hexane saturated with argon and oxygen. Alternatively, each was dissolved in 1-butanol and allowed to stand. Furthermore, in order to compare the influence on the luminous efficiency by purifying or not purifying, the CdX quantum dots prepared as described above were purified using 1-butanol and methanol.

  In order to find out which factor of Cd ion, Se ion, Te ion or oxygen is essential for enhancing luminous efficiency, the purified CdSe quantum dots are dissolved in an organic solvent saturated with argon or oxygen for 12 hours. Left to stand. The effect of standing on the luminescence properties of CdX quantum dots was investigated using UV-Vis absorption (Hitachi U-4100 spectrophotometer) and PL spectrometer (Hitachi F-4500 fluorescence spectrophotometer).

  The luminous efficiency of the quantum dots prepared and left as described above was measured by comparing the integrated intensity (area) of the spectrum of the sample with the integrated intensity (area) of a standard substance having a known luminous efficiency.

  Coumarin 540 (emission efficiency 0.62 in ethanol) was used for evaluation of CdSe emission efficiency, and rhodamine B (emission efficiency 0.65 in ethanol) was used as a reference sample for evaluation of CdTe emission efficiency.

[Protection layer formation in non-purified CdX quantum dots]
Protection layer formation by Cd ions and Se ions or Te ions on CdX core quantum dots was identified by the addition of Cd ions and Se ions or Te ions into 1-butanol solution of purified CdX quantum dots.

Three samples were prepared to compare the effect of adding each ion on PL and the absorption properties of purified CdX quantum dots. Each sample containing purified CdSe quantum dots (5.1 μmol) in a 1-butanol solution (10 mL) saturated with argon was prepared in a glass bottle under an argon atmosphere. Hereinafter, in the case of CdSe, only TOPSe (500 μL) is added to the first bottle, and (CH ₃ COO) ₂ Cd · 2H ₂ O (0.05 g) is added to the _second bottle for 5 minutes. And dispersed with ultrasonic waves. To the third bottle, TOPSe (500 μL) and (CH ₃ COO) ₂ Cd · 2H ₂ O (0.05 g) were added and dispersed with ultrasound. Since the solubility of (CH ₃ COO) ₂ Cd · 2H ₂ O in 1-butanol was low, (CH ₃ COO) ₂ Cd · 2H ₂ O was dissolved in TOP or methanol before being dissolved in 1-butanol. All samples were left in the dark for 12 hours at room temperature.

  1 and 2 show changes in PL and absorption spectra of unpurified CdSe and CdTe quantum dots after standing for 12 hours in an organic solvent saturated with argon at room temperature.

  Red shift of both PL spectrum and absorption spectrum, reduction of half width (fwhm) of PL spectrum and 0.11 to 0.27 in chloroform and 0.05 to 0 in 1-butanol .12 enhancement of CdSe efficiency; and enhancement of CdTe emission efficiency of 0.15 to 0.41 in hexane, 0.08 to 0.30 in chloroform and 0.05 to 0.14 in 1-butanol. It was observed.

  No changes were observed in the PL and absorption spectra for samples that were allowed to stand in an organic solvent saturated with argon or oxygen. In addition, no change was observed in the luminous efficiency. The red shift observed in the PL and absorption spectra can only be attributed to the growth of CdX quantum dots. The source of CdX quantum dot growth will be unreacted Cd ions and X ions left in the unpurified CdX quantum dots. Cd ions and X ions coordinated by TOPO and TOP are immediately dissolved in chloroform, hexane and 1-butanol. Cd ions and X ions dissolved in these organic solvents covered the atomic state on the surface of the CdX quantum dots in the same manner as the growth of single crystals from a saturated solution.

  Covering the atomic state of the surface removes surface traps. This is an action that may enhance the luminous efficiency.

  In addition to the growth of CdX and the formation of a protective layer on the surface, the spectrum fwhm, which is the basis of the particle size distribution in the CdX aggregate, also decreased with the standing time. The reduction of the size distribution in the set is known as focusing. The critical size of the quantum dots, defined by the equilibrium between growth and decomposition, exists in the growing colloidal solution of any precursor concentration. The intrinsic polydispersity of the particles in the colloidal solution stems from the growth of particles larger than the critical size at the expense of smaller particles. This growth is called Ostwald ripening, during which larger particles have a positive growth rate and smaller particles have a negative growth rate. This contradictory effect results in an expansion of the size distribution called dispersion within the set. In particular, if the initial size of the nanocrystals present in the solution is slightly larger than the critical size, focusing of the size distribution occurs even in the growing colloidal solution. Size distribution focusing and dispersion are currently only observed in nanocrystal growth at high temperatures (> 180 ° C.), and Oswald tripping and size distribution focusing at room temperature have not been reported.

  Before investigating the effects of Cd ions and Se ions or Te ions on crystal growth, leave purified CdX quantum dots in chloroform, hexane or 1-butanol for 12 hours without adding Cd ions, Se ions or Te ions. A control test was conducted.

  In samples saturated with argon or oxygen, no red shift of the PL and absorption spectra and no change in fwhm of the PL spectrum was seen. Luminous efficiency showed a ~ 1.2 fold enhancement in the sample after standing for 12 hours. However, this enhancement was smaller than that of unpurified CdX quantum dots (see FIGS. 1 and 2). This small enhancement is probably due to dislocation or relaxation of the surface atomic structure in the organic solvent. More importantly, there was no change in the luminous efficiency of the purified CdX quantum dots between samples saturated with argon or oxygen before and after standing for 12 hours.

  In order to confirm the idea that a protective layer is formed on a CdX quantum dot in the presence of added Cd ions and Se ions or Te ions, Cd ions and Se ions or Te ions are purified with a purified quantum dot in an organic solvent. At different concentrations.

  FIG. 3 shows the results for CdSe. The PL spectrum and the absorption spectrum (inset) of a CdSe quantum dot which left standing in 1-butanol saturated with argon for 12 hours and added Cd ion or Se ion or both ions of Cd and Se are shown. Standing was always carried out in 1-butanol saturated with argon, but the luminous efficiency was measured in 1-butanol or chloroform.

  The addition of Se ions caused an increase in luminous efficiency of 0.05 to 0.07 in 1-butanol and 0.11 to 0.14 in chloroform. No changes in PL spectral maximum and fwhm were observed. The increase in luminous efficiency associated with the addition of Se ions was comparable to that processed without the addition of any ions. Also, the addition of Cd ions caused an increase in luminous efficiency of 0.05 to 0.13 in 1-butanol and 0.11 to 0.18 in chloroform. This enhancement is greater than the sample to which Se ions were added. The enhancement of luminous efficiency associated with the addition of Cd ions is due to exciton free electron interaction. Again, no changes in PL spectrum peak and fwhm were observed.

  The size distribution increases in all reported methods for forming a surface protective layer using a wider band gap material, but the increase in size distribution is observed when standing with only Cd ions or Se ions. Not. More importantly, the addition of both Cd and Se ions adds 0.05 to 0.20 in 1-butanol and 0.11 in chloroform in addition to the red shift of the PL and absorption spectra. Showed a further enhancement in luminous efficiency of 0.27 to 0.27. However, although the cause is unknown, the fwhm of the PL spectrum did not change contrary to the observation in FIG. 1 and FIG. The red shift of the PL and absorption spectra is due to the growth of CdSe particles in 1-butanol. The enhancement of luminous efficiency is due to the surface coating.

  The enhanced luminous efficiency was stable after standing for 12 hours. No changes in absorption spectrum and PL spectrum, or emission efficiency were observed even after 2 months.

  Addition of Cd ions and Se ions or Te ions into 1-butanol leads to the accumulation of the CdX layer (protective layer) on the CdX core quantum dots. This accumulation is similar to the growth of epitaxial thin films on the same type of substrate. For this reason, this is called homoepitaxy.

In CdX quantum dots, reported core / shell structures include CdS / Cd (OH) ₂ , CdS / HgS, CdSe / PbS, CdSe / CdS, CdSe / ZnS, and CdSe / ZnSe. They all showed enhanced luminous efficiency, enhanced PL stability and decreased luminescence lifetime. However, distortion at the non-uniform core / shell junction resulting from mismatch in lattice constant is assumed to play a major role in the final luminous efficiency. On the other hand, homoepitaxy, in which the epitaxial layers are formed on the same material, is a known method in the semiconductor industry that avoids lattice distortion at the core / shell junction. The above results are the first reports on the homoepitaxial protective layer formation of CdX quantum dots.

  Luminous efficiency of CdX quantum dots is enhanced with growth by standing in an organic solvent at room temperature and focusing of the size distribution. From this example, it was found that there is a clear relationship between the luminous efficiency enhancement and the Cd ion and Se ion or Te ion concentration in the solution. In addition, formation of a protective layer by Cd ions and Se ions or Te ions leads to the growth of CdX quantum dots in an organic solvent such as chloroform, hexane, 1-butanol at room temperature. Furthermore, CdX quantum dots formed with a homoepitaxial protective layer exhibit stable PL.

  Surface protection layer formation of CdX quantum dots at room temperature in an organic solvent provides safe and environmentally friendly surface protection layer formation.

Figure 7 shows changes in the PL spectrum of unpurified CdSe quantum dots before and after 12 hours standing, representing enhanced luminous efficiency, particle growth and size distribution focusing. A shows the result of standing in chloroform saturated with argon and B in 1-butanol saturated with argon. All PL spectra were recorded using 400 nm excitation. After 12 hours of standing, the PL maximum shifted from ~ 542 nm to ~ 547 nm in chloroform and from ~ 542 nm to ~ 558 nm in 1-butanol. The fwhm decreased from ˜33 nm to ˜29 nm in both chloroform and 1-butanol after standing for 12 hours. The vertical axis represents relative luminous efficiency; the horizontal axis represents wavelength. The trace in the inset shows the absorption spectrum corresponding to the PL spectrum. Figure 7 shows changes in the PL spectrum of unpurified CdTe quantum dots before and after 12 hours of standing, representing enhanced luminous efficiency, particle growth and size distribution focusing. A shows the result of standing in chloroform saturated with argon, and B shows the result in 1-butanol saturated with argon. All PL spectra were recorded using 480 nm excitation. After standing for 12 hours, the PL maximum shifted from ~ 590 nm to ~ 597 nm in chloroform and from ~ 590 nm to ~ 608 nm in 1-butanol. The fwhm decreased from ˜33 nm to ˜30 nm in both chloroform and 1-butanol after standing for 12 hours. The vertical axis represents relative luminous efficiency; the horizontal axis represents wavelength. The trace in the inset shows the absorption spectrum corresponding to the PL spectrum. Saturated with argon for 12 hours, without Ce and Se ions added, and with different concentrations of Cd or Se ions, and with both Cd and Se ions added Shows the change in the PL spectrum of purified CdSe quantum dots in purified 1-butanol (10 mL). Neither PL maximum value (˜542 nm) nor fwhm (˜30 nm) was changed when Cd ion or Se ion was added alone. In contrast, the addition of both Cd ions and Se ions shifted the PL maximum maximum value from ˜546 nm to ˜553 nm. However, fwhm (˜30 nm) did not change. The vertical axis represents relative luminous efficiency; the horizontal axis represents wavelength. The trace in the inset shows the absorption spectrum corresponding to the PL spectrum.

Claims (3)

CdSe or CdTe nanoparticles having an average particle diameter of 1 to 30 nm as a substrate , and at least one selected from the group consisting of Cd, Zn, Se and Te , in the presence of an organic solvent, a reaction temperature of 10 to 30 ℃ reacted with, and forming a protective layer of CdSe or Cd on the surface of the CdTe nanoparticles, Zn, compounds containing at least one element selected from the group consisting of Se and Te, CdSe or A method for producing a phosphor having a protective layer on the surface of CdTe nanoparticles . The method for producing a phosphor according to claim 1 , wherein the organic solvent is at least one selected from the group consisting of chloroform, hexane, and 1-butanol. 3. The method for producing a phosphor according to claim 1, wherein the emission spectrum of the obtained nanoparticles has a half width of 40 nm or less.

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