Example 1
Selenium is dispersed in trioctylphosphine (TOP) to obtain a Se/TOP stock solution.
Indium acetate, zinc acetate, and palmitic acid are dissolved in 1-octadecene in a 200 milliliter (mL) reaction flask, subjected to a vacuum state at 120° C. for one hour. A mole ratio of indium:zinc:palmitic acid is 1:1:3. The atmosphere in the flask is exchanged with N2. After the reaction flask is heated to 200° C., a trioctylphosphine (TOP) solution of tris(trimethylsilyl)phosphine (TMS3P) and the Se/TOP stock solution is quickly injected, and the reaction proceeds at 300° C. for 10 minutes.
The reaction mixture then is rapidly cooled to room temperature and acetone is added thereto to produce nanocrystals, which are then separated by centrifugation and dispersed in toluene to obtain a toluene dispersion of the InPZnS cores.
The amount of the selenium is about 0.2 moles per one mole of zinc. The results of the TEM analysis confirm that the size of the InPZnS cores thus obtained is about 2.5 nm on average.
For the InPZnS cores, an ICP-AES analysis and a UV-Vis absorption spectroscopic analysis are conducted and the results are shown in Table 1 and
In a 200 mL reaction flask, indium acetate, zinc acetate, and palmitic acid are dissolved in 1-octadecene and the resulting solution is subjected to vacuum at 120° C. for 10 minutes. A ratio of the indium with respect to the palmitic acid is 1:3. The atmosphere in the flask is replaced with N2. While the resulting solution is heated to about 200° C., a trioctylphosphine (TOP) solution of tris(trimethylsilyl)phosphine (TMS3P) is quickly injected.
Then, a temperature is raised to 270° C. and kept for 10 minutes to synthesize a core. Then, the Se/TOP stock solution is injected thereto and a temperature of the reaction flask is kept at 300° C. for 10 minutes to form a ZnSe shell on the synthesized core.
The reaction mixture then is rapidly cooled to room temperature and acetone is added thereto to produce nanocrystals, which are then separated by centrifugation and dispersed in toluene.
The amount of the selenium is about 0.2 moles per one mole of zinc. The results of the TEM analysis confirm that the size of the core thus obtained is about 2.3 nm on average.
For the InP/ZnSe particles, an ICP-AES analysis and a UV-Vis absorption spectroscopic analysis are conducted and the results are shown in Table 1 and
The results of Table 1 and
Alloy Core/Shell Quantum Dot
Example 2
Selenium and sulfur are dispersed in trioctylphosphine (TOP) to obtain a Se/TOP stock solution and a S/TOP stock solution, respectively.
In a 200 mL reaction flask, zinc acetate and oleic acid are dissolved in trioctyl amine and the solution is subjected to vacuum at 120° C. for 10 minutes. The atmosphere in the flask is replaced with N2. While the resulting solution is heated to about 320° C., a toluene dispersion of the alloy core prepared in Example 1 is injected thereto and the Se/TOP stock solution and the S/TOP stock solution are injected into the reaction flask. A reaction is carried out to obtain a reaction solution including a particle having a ZnSeS shell disposed on the alloy core.
Then, at the aforementioned reaction temperature, the S/TOP stock solution is injected to the reaction mixture. A reaction is carried out to obtain a resulting solution including a particle having a ZnS based shell disposed on the ZnSeS shell.
An excess amount of ethanol is added to the final reaction mixture including the InPZnSe/ZnSeS/ZnS quantum dots, which are then centrifuged. After centrifugation, the supernatant is discarded, and the precipitate is dried and dispersed in chloroform to obtain a quantum dot solution (hereinafter, QD solution).
For the obtained QD solution, an ICP-AES analysis is made and the results are shown in Table 2. A photoluminescence spectroscopic analysis is made for the QD solution, and the results are shown in Table 3.
A ZnSeS/ZnS shell is formed in the same manner as in Example 2 except for using a core prepared in the same manner of Comparative Example 1. For the obtained QD solution, an ICP-AES analysis is made and the results are shown in Table 2. A photoluminescence spectroscopic analysis is made for the QD solution, and the results are shown in Table 3.
The results of Table 3 confirm that the quantum dots of Example 2 show significantly improved QY in comparison with the quantum dots of Comparative Example 2.
Example 3
A toluene dispersion of the alloy core prepared in Example 1 is added to a monomer/oligomer mixture prepared as below to obtain a composition, 1 gram (g) of which is drop casted on a glass substrate:
30 parts by weight of a lauryl methacrylate monomer, 36 parts by weight of a tricyclodecane dimethanol diacrylate monomer, 4 parts by weight of a trimethylol propane triacrylate monomer, 20 parts by weight of an epoxy diacrylate oligomer (purchased from Sartomer) are mixed to obtain a monomer/oligomer mixture. 1 part by weight of 1-hydroxy-cyclohexyl-phenyl-ketone, and 1 part by weight of 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide are added thereto to obtain a final mixture, which is then defoamed under vacuum.
The casted composition is covered with a poly(ethylene terephthalate) (PET) film and is UV-cured with a light intensity of 100 milliwatts per square centimeter (mW/cm2) for four minutes to produce a semiconductor-polymer composite film. For the obtained film, brightness is measured and the results are summarized in Table 4.
A quantum dot polymer composite is prepared in the same manner as in Example 3 except for using the core-shell quantum dots prepared in Comparative Example 1.
The results of Table 4 confirm that the quantum dots of Example 1 may show increased brightness and improved chemical stability in a composite film.
Example 4
(1) A dispersion of the quantum dots prepared in Example 2 is mixed with a solution of a binder polymer, which is a four membered copolymer of methacrylic acid, benzyl methacrylate, hydroxyethyl methacrylate, and styrene, (acid value: 130 milligrams (mg) per gram of KOH (mg KOH/g), molecular weight: 8,000 grams per mole (g/mol), acrylic acid:benzyl methacrylate:hydroxyethyl methacrylate:styrene (molar ratio)=61.5%:12%:16.3%:10.2%) (solvent: propylene glycol monomethyl ether acetate (PGMEA), a concentration of 30 percent by weight (wt %)) to form a quantum dot-binder dispersion.
To the quantum dot-binder dispersion prepared above, a hexaacrylate having the following structure (as a photopolymerizable monomer), ethylene glycol di-3-mercaptopropionate (hereinafter, 2T, as a multi-thiol compound), an oxime ester compound (as an initiator), TiO2 as a metal oxide fine particle, and PGMEA (as a solvent) are added to obtain a photosensitive composition.
Based on a total solid content, the prepared composition includes 40 wt % of quantum dots, 12.5 wt % of the binder polymer, 25 wt % of 2T, 12 wt % of the photopolymerizable monomer, 0.5 wt % of the photoinitiator, and 10 wt % of the metal oxide fine particle. The total solid content is about 25%.
(2) Preparation of a Pattern of a Quantum Dot Polymer Composite and a Thermal Treatment Thereof
The photosensitive composition obtained as above is spin-coated on a glass substrate at 150 revolutions per minute (rpm) for 5 seconds (s) to provide a film. The obtained film is pre-baked at 100° C. (PRB). The pre-baked film is exposed to light (wavelength: 365 nanometers (nm), intensity: 100 millijoules, mJ) under a mask having a predetermined pattern (e.g., a square dot or stripe pattern) for 1 s (EXP) and developed with a potassium hydroxide aqueous solution (conc.: 0.043%) for 50 seconds to obtain a pattern of a quantum dot polymer composite (thickness: 6 micrometers (μm)).
The obtained pattern is heat-treated at a temperature of 180° C. for 30 minutes under a nitrogen atmosphere. (POB)
For the obtained pattern film, a luminous efficiency of a pattern and maintenance of light emission after FOB (i.e., in comparison with the PRB) are measured and the results are shown in Table 5.
A quantum dot polymer composite pattern is prepared in the same manner as in Example 4 except for using the core-shell quantum dots prepared in Comparative Example 2 instead of the quantum dots of Example 2.
The results of Table 5 confirm that the quantum dots of Example 2 have greatly improved stability in comparison with the quantum dots of Comparative Example 2.
While this disclosure has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
