KR102047115B1 - I-Ⅲ-VI type blue light-emitting quantum dots and method for synthesizing the same - Google Patents

Abstract

Provided are I-III-VI quantum dots having high quantum efficiency while emitting blue light, and a method of manufacturing the same. The blue light emitting quantum dot according to the present invention is a quantum dot having an I-III-VI-based tetracomponent Zn-Ag-Ga-S core quantum dot and a ZnS shell, wherein Ag: (Zn + Ga in the Zn-Ag-Ga-S core quantum dot ) Is 1:30 to 1: 5, and the Zn / Ga molar ratio is greater than 0 and less than or equal to 2. In particular, the blue light emitting quantum dots with Zn-Ag-Ga-S core quantum dots and ZnS shells produced by the method according to the invention can have emission wavelengths between 440 and 460 nm and not only show a short very ideal blue wavelength of 450 nm It has high QY level of 58-69%, which is high enough for practical application in optical device fabrication. An example of implementing a blue light emitting quantum dot having such a wavelength and QY in a non-Cd system is not known yet.

Description

I-III-VI type blue light-emitting quantum dots and a manufacturing method therefor {I-III-VI type blue light-emitting quantum dots and method for synthesizing the same}

The present invention relates to a quantum dot of a non-Cd composition and a method of manufacturing the same, and more particularly, to an I-III-VI-based blue light emitting quantum dot and a method of manufacturing the same.

As the synthesis of high quality fluorescent colloidal semiconductor quantum dots (QDs) becomes possible, color conversion QD-light emitting diodes (LEDs) and QD-electroluminescent (EL) devices have also been developed. In the case of color conversion QD-LEDs, blue InGaN LED chips are most commonly used to excite various QDs with green-red light emission depending on the application. In order to implement a display device with high color reproducibility, only two types, QD with red light emission and QD with green light emission, are used. On the other hand, in lighting devices it is desirable to have a spectrum as wide as possible to achieve a high color rendering index (CRI), so it is preferable to use a QD with a wide emission spectrum or use QDs of various color combinations. have. The advantage is that blue QDs are not required for color conversion QD-LEDs, making them easy to commercialize, while EL devices require blue QDs for full-color display implementation, white illumination, or the like.

Blue QD has been synthesized with Cd-containing II-VI compositions, such as CdZnS, CdZnSe, and CdZnSeS, and has been utilized as an active light emitting element of monochromatic or multicolor EL-QD-LEDs. However, harmful Cd substances in blue QDs are undesirable for the manufacture of next generation products that are sustainable without destroying the environment.

Among the non-Cd composition candidates capable of emitting visible light, III-V-based InP has photoluminescence (PL), quantum efficiency (QY), and emission band width comparable to that of Cd QD. However, InP QD synthesis has been studied mainly with a focus on green-red luminescence and little on blue. Since InP has a relatively low energy bulk bandgap (1.35 eV at room temperature), for high energy blue emission, the InP QD must be either very small or located in a very strong quantum confinement region. Synthesis becomes very tricky. Several types of blue InP QDs with an emission peak wavelength of <480 nm have been proposed, but in this case, the QY of the QD is only 5-40%, depending on the core / shell structure, which is not satisfactory.

Another of the non-Cd composition candidates is II-VI ZnSe. The bandgap (2.69 eV) of ZnSe is larger than that of InP. Therefore, the size of the ZnSe QD must be relatively large in order to achieve an appropriate blue wavelength, which is also difficult for actual QD synthesis. For this reason, most of the ZnSe QDs developed to date show intermediate wavelengths between purple and blue.

I-III-VI chalcogenide is also one of the non-Cd composition candidates capable of emitting visible light. By varying the bandgap of QD through composition, size, and cationic off-stoichiometry adjustment, a wide emission band over green-red could be achieved. However, studies on solid fluorescence I-III-VI QDs emitting wavelengths shorter than about 500 nm (corresponding to cyan) are still lacking, and are mainly limited to Cu-In-S or Cu-Ga-S compositions. It is.

The problem to be solved by the present invention is to provide an I-III-VI-based quantum dot having a high quantum efficiency while emitting blue light and a manufacturing method thereof.

In order to solve the above problems, the quantum dot according to the present invention is a quantum dot having an I-III-VI-based tetracomponent Zn-Ag-Ga-S core quantum dot and a ZnS shell, and the Ag in the Zn-Ag-Ga-S core quantum dot (Zn + Ga) is 1:30 to 1: 5, and is a blue light emitting quantum dot characterized by a Zn / Ga molar ratio of greater than 0 and 2 or less.

The blue light emitting quantum dots may have an emission wavelength of 440 nm to 460 nm.

In the blue light emitting quantum dot according to the present invention, the ZnS shell is preferably a multi-shell.

In order to solve the above problems, a method for manufacturing a blue light emitting quantum dot according to the present invention includes the steps of forming an I-III-VI based ternary Ag-Ga-S core quantum dot; Alloying Zn on the Ag-Ga-S core quantum dots to form an I-III-VI based four-component Zn-Ag-Ga-S core quantum dots; And forming a ZnS shell on the Zn-Ag-Ga-S core quantum dots.

At this time, the step of forming the Ag-Ga-S core quantum dot is preferably performed by heating a mixed solution of Ag, Ga and S precursor, sulfur (sulfur) and a solvent. The forming of the Zn-Ag-Ga-S core quantum dots may be performed by adding a Zn precursor into the mixed solution in which the Ag-Ga-S core quantum dots are formed.

Another blue light-emitting quantum dot manufacturing method according to the present invention comprises the steps of forming an I-III-VI-based four-component Zn-Ag-Ga-S core quantum dot; And forming a ZnS shell on the Zn-Ag-Ga-S core quantum dots. At this time, the step of forming the Zn-Ag-Ga-S core quantum dot may be performed by heating a mixed solution of a precursor, sulfur and a solvent of Zn, Ag, Ga and S.

In the method of manufacturing blue light emitting quantum dots according to the present invention, the forming of the ZnS shell may be performed by applying a ZnS stock solution.

The forming of the ZnS shell may be performed two or more times in succession, and may be performed by varying at least one of the type, concentration, and reaction temperature of each ZnS stock solution when the two or more consecutive times are performed.

In a preferred embodiment, the step of forming the Ag-Ga-S core quantum dots comprises silver iodide (AgI), silver nitrate (Ag nitrate), silver acetate (Ag acetate), silver bromide (AgBr) and silver chloride (AgCl). Either one of gallium acetylacetonate (Ga (acac) ₃ ), gallium iodide (GaI ₃ ), gallium acetate (Ga acetate), gallium chloride (GaCl ₃ ) and gallium bromide (GaBr ₃ ), 1-dodecane A mixed solution of thiol (dodecanethiol), 1-octanethiol (octanethiol), hexadecanethiol (hexadecanethiol) and decanthiol (decanethiol), sulfur, and oleylamine is carried out by heating, and The forming of the Zn-Ag-Ga-S core quantum dots is performed by adding ZnCl ₂ to the mixed solution in which the Ag-Ga-S core quantum dots are formed, and the forming of the ZnS shell is performed by zinc acetate and octa Applying a ZnS stock solution comprising decene and oleic acid; Applying another ZnS stock solution comprising lead, octadecene and oleic acid is performed.

In another preferred embodiment, the step of forming the Zn-Ag-Ga-S core quantum dots is ZnCl _2, AgI, silver nitrate (Ag nitrate), silver acetate (Ag acetate), silver bromide (AgBr) and silver chloride (AgCl) ), Any one of gallium acetylacetonate (Ga (acac) ₃ ), gallium iodide (GaI ₃ ), gallium acetate (Ga acetate), gallium chloride (GaCl ₃ ), and gallium bromide (GaBr ₃ ), 1- Dodecanethiol, 1-octanethiol, hexadecanethiol and decanethiol, a mixed solution of ZnCl _{2 ,} sulfur, and oleylamine was performed by heating, The forming of the ZnS shell may include applying a ZnS stock solution containing zinc acetate, octadecene and oleic acid, and applying another ZnS stock solution including zinc stearate, octadecene and oleic acid. .

In particular, in the blue light emitting quantum dot manufacturing method according to the present invention, in the Zn-Ag-Ga-S core quantum dot Ag: (Zn + Ga) is 1: 30 ~ 1: 5, Zn / Ga molar ratio is more than 0 It is preferable that it is large and 2 or less.

According to the present invention, a quantum dot having a Zn-Ag-Ga-S core quantum dot and a ZnS shell can be manufactured to implement a blue emission spectrum of very high PL and QY. An example of implementing a blue light emitting quantum dot having such a degree of QY in a non-Cd system is not known yet.

In particular, blue light emitting quantum dots with Zn-Ag-Ga-S core quantum dots and ZnS shells produced by the process according to the invention can have emission wavelengths between 440 and 460 nm and only show very ideal blue wavelengths as short as 450 nm. Rather, it has a high QY level of 58-69%, which is high enough for practical application in optical device fabrication.

1 is a schematic diagram of a blue light emitting quantum dot according to the present invention.
2 is a flowchart illustrating an embodiment of a method for manufacturing a blue light emitting quantum dot according to the present invention.
3 is a flowchart illustrating another embodiment of a method for manufacturing a blue light emitting quantum dot according to the present invention.
4 shows the actual Zn / Ga of (a) absorption, (b) optical bandgap and (c) ICP analysis of Ag deficient AGS cores, ZAGS cores and AIGS cores synthesized with 1/8 molar ratio of Ag / Ga precursor; In / Ga molar ratio is shown.
(A) of Figure 5 AGS core QD, ZAGS core QD and AIGS core QD (Ahν) ² - and hν graph, (b) it is ² (Ahν) of AGS / ZnS, ZAGS / ZnS and AIGS / ZnS - hν It is a graph.
6 is _{Z 1. 0 AGS, Z 0. 25} AGS, AGS, AI 0.05 G 0.45 S, AI 0.1 G 0.4 S shows the PL spectra for the absorption of the core / shell QD.
7 is a _{Z 1. 0 AGS, Z 0. 25} AGS, AGS, AI 0.05 G 0.45 S, AI 0.1 G 0.4 S (a) absorption of a core / shell QD, (b) normalizing the PL spectrum, (c) UV -Irradiated fluorescence image and (d) PL peak wavelength and PL QY change.
(A), (b) of Figure 8 is a low magnification TEM image (c), (d) is a high-magnification TEM image, (a), (c) is _{Z 1. 0 AGS / ZnS, (} b), (d ) Is an AGS / ZnS QD sample.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention and to those skilled in the art to fully understand the scope of the invention. It is provided to inform you.

1 is a schematic diagram of a blue light emitting quantum dot according to the present invention.

Referring to FIG. 1, the present invention proposes a non-Cd quantum dot 10 capable of emitting blue light. The quantum dot 10 has an I-III-VI four-component Zn-Ag-Ga-S (hereinafter referred to as ZAGS) core QD 20 and a ZnS shell 30.

The core QD 20 according to the invention is a ZAGS composition. When the ZnS coating is formed on the core QD 20 to form a ZnS shell 30, both PL and QY are improved.

The present inventors must include Ag, Ga, and S in order to emit blue light of the I-III-VI-based quantum dot, that is, Ag-Ga-S (hereinafter, AGS) should be the basis, and in particular, the ratio of Ag and Ga is 1: As 30 to 1: 5, it was found that the chemical composition should be adjusted to the same amount or slightly lack of Ag (Non-stoichiometry off-stoichiometry). In addition, alloying Zn with the AGS composition results in blue light emission when the ZAGS composition is formed. When the ratio of Ag and Ga is 1/30 or more, blue light can be emitted through Zn addition, and when the ratio is larger than 1/5, blue light is not emitted.

In the ZAGS composition of the core QD 20, Ag: (Zn + Ga) is preferably 1:30 to 1: 5. In particular, the Zn / Ga molar ratio in each composition may be greater than zero and less than or equal to two. Where the Zn / Ga molar ratio is the actual molar ratio. If the Zn / Ga molar ratio is greater than zero, Zn is included at least. By including at least Zn in the AGS composition, the emission wavelength shifts blue. As the amount of Zn increases, the wavelength shifts bluer. When the Zn / Ga molar ratio is 1.24, the most ideal 450nm emission wavelength can be reached. Even if the Zn / Ga molar ratio is larger than 1.24, the emission wavelength hardly changes. However, when the Zn / Ga molar ratio is greater than 2, QY worsens. Therefore, it is not necessary to make Zn / Ga molar ratio larger than two.

As described above, adjusting the composition ratio between Ga and Zn, which may partially replace it, is performed to control the characteristics of the wavelength, but it is unique that the composition ratio of Ga and Zn is adjusted while the ratio of Ag and Ga is adjusted. It is. Under these compositional conditions, the four-component ZAGS core quantum dot can realize blue light emission very ideally.

The ZnS shell 30 may be formed in multiples, for example double or triple. That is, as shown, the ZnS shell may be formed first up to the portion indicated by the dotted line, and then the remaining ZnS shell may be formed up to the portion indicated by the solid line. In particular, since the ZnS shell forming process is performed continuously as described below, there may be virtually no layer discrimination in the ZnS shell 30. Each layer can have a different composition. The composition at this time may be changed discontinuously based on the dotted line or may be continuously changed throughout the ZnS shell 30. This multiple ZnS shell 30 has an excellent passivation effect. Accordingly, the QY of the quantum dot 10 may be improved.

As described above, according to the present invention, blue light emission may be realized by using the quantum dot 10 having the ZAGS core QD 20 and the ZnS shell 30. It can also show high QY.

The core QD 20 may be manufactured by hot colloid method, solvent thermal method, or heating-up or hot-injection, and the ZnS shell 30 may be It may also be carried out by a cation exchange process, a solvent heat method and the like, which will be described below.

2 is a flowchart illustrating an embodiment of a method for manufacturing a blue light emitting quantum dot according to the present invention.

First, a mixed solution prepared by mixing Ag, Ga and S precursors, sulfur and a solvent is heated to grow AGS core QD first (step S5).

In general, A-In-X (A = Cu, Ag, X = S, Se) is the most studied I-III-VI ternary composition for visible light QD synthesis and typically exhibits lower energy emission than green. In the present invention, the AGS composition having a bandgap of about 2.43 eV, which is a bulk bandgap higher than the above composition, is selected, and through the Ag / Ga stoichiometric control, a short emission wavelength of less than 500 nm is once obtained. Let's first synthesize the core QD.

Starting materials for growing the AGS core QD include silver precursor silver iodide (AgI), gallium precursor gallium acetylacetonate (Ga (acac) ₃ ), sulfur precursor 1-dodecanethiol, sulfur And oleylamine, which is a solvent, may be used as a basic combination.

The ratio of starting material is in the range of Ag: Ga = 1: 30-1: 5 as mentioned above. In the case of a silver precursor, silver nitrate (Ag nitrate), silver acetate (Ag acetate), silver bromide (AgBr), or silver chloride (AgCl) may be used in addition to AgI. In the case of a gallium precursor, gallium iodide (GaI ₃ ), gallium acetate (Ga acetate), gallium chloride (GaCl ₃ ), gallium bromide (GaBr ₃ ), or the like may be used in addition to gallium acetylacetonate. In the case of the sulfur precursor, various alkyl thiol systems such as 1-octanethiol, hexadecanethiol, decanthiol, etc. may be used in addition to 1-dodecanethiol. In the case of a solvent, various fatty amines such as dodecylamine, trioctylamine, etc. may be used in addition to oleylamine.

Heating of the mixed solution can be done in several stages. First, it may be heated to 120 ℃ to perform degas (degas). Since the growth temperature may be raised to 240 ℃. At this time, N ₂ purging may be performed. This causes AGS core QDs to grow in the mixed solution.

Then, Zn precursor is added to the AGS core QD growth solution to alloy Zn to the AGS core QD to form a four-component ZAGS core QD 20 (step S10).

The ZAGS core QD 20 can be synthesized by alloying Zn into the AGS core QD (host) created in the previous step to achieve high energy or short wavelength emission in the blue range.

The Zn precursor used herein may be ZnCl ₂ , zinc acetate, or the like.

After the core QD 20 is formed, a ZnS shell 30 is formed by applying a ZnS stock solution on the core QD 20 (steps S20 and S30).

The forming of the ZnS shell may be performed two or more times in succession by performing S20 and S30. At this time, at least one of the type, concentration and reaction temperature of the ZnS stock solution in each step may be different. In the second reaction, the temperature may be higher or longer.

For example, after applying the ZnS stock solution to the resultant solution in which the core QD 20 is formed to form a ZnS shell, step S20 is performed, and then another ZnS stock solution is applied to the resultant solution to further form the ZnS shell. By doing so, step S30 is performed continuously to step S20.

The steps S20 and S30 may also be divided into two or more shell processes.

For example, the first ZnS stock solution of step S20 may be prepared using Zn precursor zinc acetate, octadecene solvent and oleic acid as a basic combination. At this time, in the case of zinc precursor, zinc stearate, zinc oxide, zinc nitride, zinc acetylacetonate, etc. may be used in addition to zinc acetate, and in case of oleic acid, stearic acid, myristic acid (myristic acid) may be used. The first ZnS shell reaction temperature in step S20 is in the range of 200 to 280 ° C, and the reaction time may be in the range of 1 minute to 2 hours. Preferably, the reaction is maintained at a temperature of 240 ° C. for 1 hour and 15 minutes.

The second ZnS stock solution of step S20 may also be based on Zn precursor zinc acetate, solvent octadecene and oleic acid, but different concentrations from the first ZnS stock solution. The second ZnS shell reaction temperature of step S20 may be the same state as the first ZnS reaction temperature, the reaction time may be shorter than the first ZnS reaction time. Preferably the reaction is maintained for 30 minutes at a temperature of 240 ℃.

The other ZnS stock solution of step S30 is different from the first and second ZnS stock solutions of step S20. For example, zinc stearate as a Zn precursor, 1-dodecanethiol as a sulfur precursor, and octadecene as a solvent can be prepared as a basic combination. In this case, in addition to zinc stearate, zinc acetate, zinc oxide, zinc nitride, zinc acetylacetonate, and the like may be used in the case of zinc precursors, and other types of alkylthiols may be used in the case of sulfur precursors.

The ZnS shell reaction temperature of step S30 is 180-300 degreeC, and reaction time can be 1 minute-24 hours. In the reaction of step S30, the temperature may be higher or longer than step S20. Preferably, the final reaction for further ZnS shell formation can proceed at 250 ° C. for 1 hour.

3 is a flowchart illustrating another embodiment of a method for manufacturing a quantum dot according to the present invention. In comparison with FIG. 2, FIG. 3 has a single step S15 in which step S5 and step S10 of FIG. 2 are combined.

Referring to Fig. 3, a ZAGS core QD 20 is formed from the beginning (step S15). Thereafter, a ZnS stock solution is applied on the core QD 20 to form a ZnS shell 30 (steps S20 and S30).

The step of forming the ZAGS core QD 20 is performed by heating a mixed solution in which precursors of Zn, Ag, Ga and S, sulfur and a solvent are mixed.

For example, the starting material for growing ZAGS core QD is Zn in addition to AgI, Ga (acac) ₃ , 1-dodecanethiol, sulfur, and oleylamine, starting materials for growing AGS core QD mentioned above. ZnCl ₂ as a precursor can be used as a basic combination. Only the type of starting material is different from that of the AGS core QD and the heating conditions, degassing, purging, reaction time, etc. can be the same or similar to that of the AGS core QD.

As described above, the present invention forms an I-III-VI-based four-component ZAGS core QD in which Zn is alloyed on the I-III-VI ternary system AGS core QD, and forms a ZnS shell. The forming of the ZAGS core QD may be performed in one step as shown in FIG. 3 or two steps as shown in FIG. 2.

As a result of the experiment, it was confirmed that the emission wavelength shifted blue in proportion to the amount of Zn added, which indicates that Zn was successfully alloyed with Ag-Ga-S according to the method of the present invention. In addition, the QY of the QD reached 58-69% after the formation of the ZnS shell according to the experimental method described below, and the result was not achieved in the InP QD having a similar emission band.

Hereinafter, the present invention will be described in more detail with reference to specific experimental examples. In the experimental example was prepared ZAGS core QD according to the present invention. As a comparative example, AGS core QD and Ag-In-Ga-S (hereinafter referred to as AIGS) core QD were also produced.

Experiment method:

Intentional non-stoichiometry between two cations (Ag, Ga) in the Ag-Ga-S composition underlying ZAGS core QD has a significant effect on the bandgap. In the experimental example, the Ag / Ga non-stoichiometric ratio was adopted as 1/8, but the Ag / Ga non-stoichiometric ratio was changed to 1/4, 1/5 and 1/8, and it was 1/8. It was the best in QY.

Comparative example AGS  core QD  Produce

A composition with an Ag / Ga stoichiometric ratio of 1/8 was chosen. 0.0625 mmol of AgI (99.999%), 0.5 mmol of Ga (acac) ₃ (99.99%) and 1 mmol of sulfur (99.998%) with 1.5 mL of 1-dodecanethiol (DDT≥98%) and oleyl amine (OLA , 70%) was added to a flask (three-neck flask) with 5 mL to prepare a mixed solution. The mixed solution was heated to 120 ° C. and degassed, followed by N ₂ purging to raise the growth temperature to 240 ° C. The AGS core QDs were grown by holding at this temperature for 30 minutes.

The present invention ZAGS  core QD  And Comparative example AIGS QD  Produce

In the following experimental example, 0.0625 mmol of AgI was applied to the four-component QD synthesis. To prepare ZAGS QD and AIGS QD, ZnCl ₂ (≥98%) and indium acetate (In (Ac) ₃ , 99.99%) were added to the mixed solution for AGS core QD growth, respectively. Each mixed solution was heated to 120 ° C, degassed, and then purged with N ₂ to raise the growth temperature to 240 ° C. The ZAGS core QD and AIGS QD were grown by holding at this temperature for 30 minutes.

In preparing the ZAGS core QD, ZnCl ₂ (≧ 98%) was added in amounts of 0.25 and 1.0 mmol, respectively, to prepare two samples with different Zn / Ga precursor molar ratios. In each sample, the precursor molar ratio is referred to as 0.5 (ZnCl ₂ 0.25mmol / Ga precursor 0.5 mmol) and ₂ (ZnCl 2 1.0mmol / Ga precursor 0.5 mmol) and Z and Z, respectively _{0. 25} AGS _{1. 0} AGS.

Similarly, in preparing AIGS core QDs, two samples with different In / Ga precursor molar ratios were prepared by adding In (Ac) ₃ in amounts of 0.05 and 0.1 mmol, respectively. Each sample will be referred to as AI _0.05 G _0.45 S and AI _0.1 G _0.4 S.

While using the AGS core QD and Z _{0. 25} AGS core QD and Z _1. There 0.5mmol the same for synthesizing ₀ AGS core _{QD Ga (acac) 3, AI} 0.05 G 0.45 S QD core and AI G _{0 .1 0.4} The synthesis of S core QDs reduced the amount of Ga (acac) ₃ to 0.45 and 0.4 mmol, respectively.

All ternary system and four component system core QD (Z _{0 1.} AGS core QD, Z _{0. 25} AGS core QD, QD core AGS, AI _0.05 G _0.45 S QD core and AI _{0.1 0.4} G S core QD) is then of the multi- It injected into the shell formation process similarly.

First, the first ZnS shell stock solution containing 8 mmol of zinc acetate (Zn acetate dehydrate, reagent grade), 8 mL oleic acid (OA, 90%) and 4 mL 1-octadecene (ODE, 90%) was subjected to 240 ° C. core QD. The resulting solution was slowly added and reacted for 1 hour and 15 minutes. Thereafter, another ZnS solution containing 4 mmol zinc stearate (10-12% Zn basis), 4 mL OA, and 2 mL ODE was added dropwise dropwise thereto, and the final shell reaction was performed at 250 ° C. for 1 hour. The synthesized quantum dots were precipitated by adding excess ethanol and clarified with a hexane / ethanol combination solvent using a centrifuge (9000 rpm, 10 minutes). Finally, quantum dots were redispersed in hexane or chloroform and analyzed for spectral measurement.

Evaluation tool:

UV-Vis absorption and PL spectra of quantum dots were recorded with an absorption spectrometer (Shimadzu, UV-2450) and a 500 W xenon lamp-mounted spectrophotometer (PSI Inc., Darsa Pro-5200), respectively. The absolute PL QY value of the diluted quantum dot dispersion was evaluated using the PL QY measurement system (QE-2000, Otsuka Electronics) and measured relative QY for coumarin 1 (absolute QY 73%) ethanol dispersion with the same 0.05 optical density at 370 nm. Verified by. The actual chemical composition of the QD was analyzed with an inductively coupled plasma optical emission spectrometer (ICP-OES, OPTIMA 8300, PerkinElmer). To obtain the quantum dot image, TEM operation was performed using JEM-2100F (JEOL Ltd.) operating at 200 kV.

result:

4 shows the actual Zn / Ga of (a) absorption, (b) optical bandgap and (c) ICP analysis of Ag deficient AGS cores, ZAGS cores and AIGS cores synthesized with 1/8 molar ratio of Ag / Ga precursor; In / Ga molar ratio is shown. The error bar of FIG. 4C is based on three measurements.

Referring to FIG. 4A, the ZAGS core to which Zn is added is blue shifted and the AIGS core to which In is added is redshifted compared to the AGS core. As compared to FIG. 4 (a), the absorption spectrum of the ZAGS core QD gradually shifts blue with increasing Zn amount, indicating that Zn alloying actually occurred. Given that the bandgap of AGS satisfying the stoichiometry is 2.51-2.73 eV, the bandgap of ZnS is higher than that of 3.54 eV, and the bandgap of Ag-In-S is lower than that of 1.87 eV. solution). Ag-deficient AGS bandgap of the present invention was 2.43 eV.

In order to measure the optical bandgap of each core QD, the absorption spectrum was converted into a Tauc plot using the ( Ahν ) ² - hν relationship ( A = absorption, h = Planck's constant, ν = optical frequency). 5 was obtained.

(A) of Figure 5 AGS core QD, ZAGS core QD and AIGS core QD (Ahν) ² - and hν graph, (b) it is ² (Ahν) of AGS / ZnS, ZAGS / ZnS and AIGS / ZnS - hν It is a graph. The optical bandgap (E _g ) -QD composition graph of FIG. 4B is derived from FIG. 5.

The actual QD composition evaluated by ICP is the same as in (c) of FIG. 4, and shows that the actual value (molar ratio in core QD) is smaller than the nominal value (precursor molar ratio). That it is, in the Z _{0. 25} AGS nominal value and the actual value of inde 0.5 0.49 degree, from ₀ Z _1. AGS nominal value is two inde is 1.24 degree of the actual values. Therefore, it should be noted that the Zn amount in ZAGS / ZnS does not originate only from the core. For example, the actual Zn / Ga molar ratio is 1.24, the Z _{0 1.} AGS QD if the core is uniform in the crude grades, and the resulting band gap should be much higher than the 3.07 eV value shown in (b) of FIG. Thus, it can be seen that a significant amount in the Zn precursor was also consumed to form the ZnS shell.

All core QDs were surface passivated with ZnS shells under the same conditions. Comparing Figs. 5 (a) and 5 (b), the absorption curve shapes of the core / shell QDs are similar to the absorption curve shapes of the corresponding core QDs, respectively, except that a blue shift of <90 meV is more dependent on the QD composition. The difference is that it involves.

This increase in bandgap is due to cation exchange and / or alloying between the core QD and the shell during the formation of the ZnS shell in the previously grown core QD. In the existing Cu-In-S QD, the band gap increase is known to be remarkable as the ZnS shell is formed, whereas in the AGS-based QD of the present invention, the band gap increase due to the shell formation does not seem to be very noticeable. This comparison of the ionic radii of 8.8Å Zn ^{2 +} and the ionic ^{radius, Cu + (9.1Å), Ag} + (12.9Å), In 3 + (9.4Å), Ga 3 + (7.6Å) for the host to understand the QD do.

6 is _{Z 1. 0 AGS, Z 0. 25} AGS, AGS, AI 0.05 G 0.45 S, AI 0.1 G 0.4 S shows the PL spectra for the absorption of the core / shell QD. Referring to FIG. 6, it can be seen that a large Stoke's shift in the range of 550-650 meV appears. As is well known, the PL (fluorescence) spectrum is seen to occur at longer wavelengths than the absorption spectrum, and this is the stoke shift.

7 is a _{Z 1. 0 AGS, Z 0. 25} AGS, AGS, AI 0.05 G 0.45 S, AI 0.1 G 0.4 S (a) absorption of a core / shell QD, (b) normalizing the PL spectrum, (c) UV -Irradiated fluorescence image and (d) PL peak wavelength and PL QY change.

With reference to FIG. (B), (c) when Z 7 _1. amber (amber) of AI _{0.1 0.4} G S from the blue light-emitting of ₀ AGS (PL peak at 450nm) is colored according to the composition to (PL peak at 570nm) This is consistent with the result of the bandgap change seen earlier. As shown in (d) of FIG. 7, the PL QY is higher than any PL QY reported in the range of 58-69%.

In I-III-VI-based QDs, non-radioactive recombination occurs in a gap state, resulting in a large stoke shift, and thus, a fundamental problem is that it is difficult to achieve blue light emission having an appropriate peak wavelength (for example, 450 nm). Thus, it is the Z _{1. 0} AGS / ZnS QD is at the peak wave length of 450nm is achieved a very surprising result Zn is contained at a high content as in the present invention. As seen in FIG. 6, the stoke shift can be obtained by plotting the absorption and PL spectra together, and in the present invention it was in the range of 550-650 meV.

Radioactive recombination occurs in II-VI systems such as CdSe and III-V systems such as InP. In contrast, in the I-III-VI system, PL is generated by recombination of charges at a defect level in a gap. Therefore, a stoke shift of> 200 meV is inevitable in the I-III-VI system. These levels in the gap are related to the vacancy, substitutional sites, and interstitial sites of cations and anions and these defects act as acceptors or donors.

As with bulk materials, there are various point defects as described above in I-III-VI based tetracomponent QDs because of the increased degrees of freedom due to the inclusion of two cations. Recombination channels of I-III-VI based QDs have been proposed in two respects. One is a donor-acceptor pair (DAP) recombination, which relates to deep acceptor levels from cationic vacancy or invasive anion sites and shallow donor levels from anionic vacancy or invasive cation sites. The other is commonly referred to as “free-to-bound” recombination, with Delocalized Conduction Band (CB) electrons and point defects (primarily acceptor V _Cu). Or V _Ag ). We consider that PL in ZAGS is the result of CB-to-V _Ag rather than DAP recombination.

The stoke shift in the AGS-based QD, which is the basis of the present invention, is larger than in the previously reported CIS and ZCIS, as shown in FIG. This may be due to the difference in energy levels between V _Cu and V _Ag . V _Ag Level is V _Cu CB-to-V _Cu because it is located far from the valence band relative to the level CB-to-V _Ag vs. Recombination Recombination results in lower energy release. Large stoke shifts, i.e., minimal spectral overlap between absorption and PL, are highly desirable features for applying QD to the utilization of DC-LEDs and the like. This is because the internal QD-light resorption is effectively reduced.

(A), (b) of Figure 8 is a low magnification TEM image (c), (d) is a high-magnification TEM image, (a), (c) is _{Z 1. 0 AGS / ZnS, (} b), (d ) Is an AGS / ZnS QD sample. The size of each QD was similar to each other, and the average diameter ranged from 5.0-5.3 nm and there were some differences in composition.

As described above, based on the composition that emits light of light blue-cyan by adjusting the band gap to about 2.43 eV using a non-stoichiometric Ag / Ga ratio that causes Ag deficiency, the wavelength is blue shifted by adding Zn to it. ZAGS core QDs were grown. Excessive addition of Zn in the ZAGS core QD synthesis and formation of a suitable ZnS shell can lead to a high degree of alloying of the core QDs to a luminescence wavelength between 440 and 460 nm, especially at 450 nm (ideal blue) emission wavelengths. In addition, it is possible to manufacture a ZAGS / ZnS QD having a high QY that can be practically applied to optical device fabrication. _1. In particular, Z ₀ AGS QD may be because the light emitting wavelength 450 nm to the blue emission, and the light emitting element used in the display field as a blue light emitting EL device, for the production. That is, it can be used as an active light emitting element of monochromatic or multicolor EL-QD-LED by replacing the existing Cd-containing II-VI composition.

Although the preferred embodiments of the present invention have been shown and described above, the present invention is not limited to the specific preferred embodiments described above, and the present invention belongs to the present invention without departing from the gist of the present invention as claimed in the claims. Various modifications can be made by those skilled in the art, and such changes are within the scope of the claims.

10: quantum dot
20: Zn-Ag-Ga-S Core QD
30: ZnS Shell

Claims (11)

A quantum dot having a Zn-Ag-Ga-S core quantum dot and a ZnS multishell,
In the Zn-Ag-Ga-S core quantum dot, Ag: (Zn + Ga) is 1:30 to 1: 5, Zn / Ga molar ratio is greater than 0 and less than or equal to 2, and Ag / Ga ratio is 1/4 to 1 / And a light emitting wavelength in the range of 440-460 nm. delete Forming an Ag-Ga-S core quantum dot;
Alloying Zn with the Ag-Ga-S core quantum dot to form a Zn-Ag-Ga-S core quantum dot; And
Forming a ZnS multishell on the Zn-Ag-Ga-S core quantum dots,
In the Zn-Ag-Ga-S core quantum dot, Ag: (Zn + Ga) is 1:30 to 1: 5, Zn / Ga molar ratio is greater than 0 and less than or equal to 2, and Ag / Ga ratio is 1/4 to 1 / 8 and a light emission wavelength in the range of 440-460 nm. The method of claim 3, wherein the forming of the Ag—Ga—S core quantum dots is performed by heating a mixed solution of Ag, Ga, and S precursors, sulfur, and a solvent. The method of claim 4, wherein the forming of the Zn-Ag-Ga-S core quantum dots is performed by adding a Zn precursor to the mixed solution in which the Ag-Ga-S core quantum dots are formed. Quantum dot manufacturing method. Forming a Zn-Ag-Ga-S core quantum dot; And
Forming a ZnS multishell on the Zn-Ag-Ga-S core quantum dots,
The step of forming the Zn-Ag-Ga-S core quantum dot is performed by heating a mixed solution of a precursor, sulfur and a solvent of Zn, Ag, Ga and S,
In the Zn-Ag-Ga-S core quantum dot, Ag: (Zn + Ga) is 1:30 to 1: 5, Zn / Ga molar ratio is greater than 0 and less than or equal to 2, and Ag / Ga ratio is 1/4 to 1 / 8 and a light emission wavelength in the range of 440-460 nm. The method of claim 3 or 6, wherein the forming of the ZnS multishell is performed by applying a ZnS stock solution. The method of claim 7, wherein the forming of the ZnS multishell is performed two or more times in succession. The method of claim 8, wherein at least one of a kind, a concentration, and a reaction temperature of each ZnS stock solution is different when the two or more successive runs are performed. The method of claim 3, wherein the forming of the Ag-Ga-S core quantum dots comprises silver iodide (AgI), silver nitrate (Ag nitrate), silver acetate (Ag acetate), silver bromide (AgBr), and silver chloride (AgCl). Any one of gallium acetylacetonate (Ga (acac) ₃ ), gallium iodide (GaI ₃ ), gallium acetate (Ga acetate), gallium chloride (GaCl ₃ ) and gallium bromide (GaBr ₃ ), 1-dode Heated a mixed solution of any one of dodecanethiol, 1-octanethiol, hexadecanethiol, and decanthiol, sulfur, and oleylamine Doing,
Forming the Zn-Ag-Ga-S core quantum dots
ZnCl ₂ is added to the mixed solution in which the Ag-Ga-S core quantum dot is formed,
Forming the ZnS multishell comprises applying a ZnS stock solution comprising zinc acetate, octadecene and oleic acid, and applying another ZnS stock solution comprising zinc stearate, octadecene and oleic acid. A blue light emitting quantum dot manufacturing method, characterized in that. The method of claim 6, wherein the forming of the Zn-Ag-Ga-S core quantum dots comprises ZnCl ₂ , silver iodide (AgI), silver nitrate (Ag nitrate), silver acetate, silver bromide (AgBr), and Any one of silver chloride (AgCl), gallium acetylacetonate (Ga (acac) ₃ ), gallium iodide (GaI ₃ ), gallium acetate (Ga acetate), gallium chloride (GaCl ₃ ) and gallium bromide (GaBr ₃ ) One, 1-dodecanethiol, 1-octanethiol, hexadecanethiol and decanethiol, any one of the sulfur (sulfur), and oleylamine (oleylamine) Performed by heating the mixed solution,
Forming the ZnS multishell comprises applying a ZnS stock solution comprising zinc acetate, octadecene and oleic acid, and applying another ZnS stock solution comprising zinc stearate, octadecene and oleic acid. A blue light emitting quantum dot manufacturing method, characterized in that.

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