KR101897254B1 - I-Ⅲ-VI type blue light-emitting quantum dots and method for synthesizing the same - Google Patents

Abstract

Provided are a I-III-VI-based quantum dot emitting blue light and having high quantum efficiency, and a manufacturing method thereof. According to the present invention, the quantum dot is a blue light-emitting quantum dot having I-III-VI-based quaternary Zn-Cu-Ga-S or Cu-Ga-Al-S core quantum dot and a ZnS shell, wherein Cu:(Zn+Ga) is 1:10 to 1:1 in the Zn-Cu-Ga-S and Cu:(Ga+Al) is 1:10 to 1:1 in the Cu-Ga-Al-S. The manufacturing method of a blue light emitting quantum dot comprises the steps of: forming a I-III-VI-based ternary Cu-Ga-S core quantum dot; alloying the Cu-Ga-S core quantum dot with Zn to form a I-III-VI-based quaternary Zn-Cu-Ga-S core quantum dot or alloying the same with Al to form a Cu-Ga-Al-S core quantum dot; and forming a ZnS shell on the Zn-Cu-Ga-S or the Cu-Ga-Al-S core quantum dot.

Description

I-III-VI blue light-emitting quantum dots and method for producing the same [

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

Color conversion QD-light emitting diodes (LEDs) and QD-electroluminescent (EL) devices have also been developed as the synthesis of high-quality fluorescent collimated semiconductor quantum dots (QDs) becomes possible. For color conversion QD-LEDs, blue InGaN LED chips are most commonly used to excite various QDs with emission in the green-red range depending on the application. In order to realize a display device having a high color reproducibility, only two types are used, that is, QD having red light emission and QD having green light emission. On the other hand, in an illumination device, it is preferable to use a QD having a wide emission spectrum or a QD of various colors because it has a broad spectrum as wide as possible in order to achieve a high color rendering index. In color conversion QD-LEDs, blue QD is unnecessary, which is easy to commercialize, while EL devices require blue QD for full-color display or white illumination.

Blue QD has been synthesized with Cd-containing II-VI composition such as CdZnS, CdZnSe, and CdZnSeS, and has been utilized as an active light emitting element of monochromatic or multicolor EL-QD-LED. However, harmful Cd materials in blue QDs are not desirable for the next generation of sustainable products without environmental degradation.

Of the non-Cd composition candidates capable of visible light emission, III-V InP has photoluminescence (PL), quantum efficiency (QY) and emission band width comparable to Cd QD. However, the synthesis of InP QD was mainly studied with a focus on green-red luminescence, and blue was rarely studied. Since InP has a relatively low energy bulk band gap (1.35 eV at room temperature), in order to achieve high energy blue luminescence, the InP QD must be of very small size or located in a very strong quantum confinement region, The synthesis becomes very tricky. Several blue InP QDs with an emission peak wavelength of <480 nm have been proposed, but in this case the quantum efficiency of QD is only 5-40%, depending on the core / shell structure.

The other candidate for the non-Cd composition is II-VI ZnSe. The bandgap of ZnSe (2.69 eV) is larger than that of InP. Therefore, in order to obtain a proper blue wavelength, the size of the ZnSe QD must be relatively large, which is also difficult for practical QD synthesis. For this reason, most of the ZnSe QDs developed so far 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 off-stoichiometry control, a broad emission band spanning green-red could be achieved. However, solid-state I-III-VI QDs that emit shorter wavelengths than about 500 nm (corresponding to cyan) have not yet been developed.

A problem to be solved by the present invention is to provide an I-III-VI series quantum dot having high quantum efficiency while emitting blue light, and a method for producing the same.

In order to solve the above problems, the quantum dot according to the present invention is a blue light emitting quantum dot having a Zn-Cu-Ga-S or Cu-Ga-Al-S core quantum dot of I-III-VI system component ZnS shell, Cu: (Zn + Ga) is 1:10 to 1: 1 in Cu-Ga-S and Cu: (Ga + Al) is 1:10 to 1: 1 in Cu-Ga-Al-S Is a blue light emitting quantum dot.

(1-x): x in the Zn-Cu-Ga-S and Al: Ga = (1-x): x in the Cu-Ga- x, it is preferable that 0.5 < x < 1. The ZnS shell is preferably a multi-shell.

According to an aspect of the present invention, there is provided a method of fabricating a quantum dot comprising: forming an I-III-VI system ternary Cu-Ga-S core quantum dot; Forming a Cu-Ga-Al-S core quantum dot by alloying Zn with the Cu-Ga-S core quantum dots to form an I-III-VI quaternary Zn-Cu-Ga- ; And forming a ZnS shell on the Zn-Cu-Ga-S or Cu-Ga-Al-S core quantum dots.

In the blue light emitting quantum dot manufacturing method according to the present invention, the step of forming the Cu-Ga-S core quantum dots is preferably performed by heating a mixed solution obtained by mixing Cu, Ga and S precursors, sulfur and a solvent. At this time, the step of forming the Zn-Cu-Ga-S core quantum dots may be performed by adding a Zn precursor to the mixed solution in which the Cu-Ga-S core quantum dots are formed, -S core quantum dot can be performed by adding an Al precursor to the mixed solution in which the Cu-Ga-S core quantum dots are formed.

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

The step of forming the ZnS shell may be performed two or more times in succession, and the concentration and the reaction temperature of each ZnS stock solution may be different when the ZnS shell is continuously performed more than twice.

In a preferred embodiment, the step of forming the Cu-Ga-S core quantum dots comprises forming a Cu-Ga-S core quantum dot comprising at least one of CuI, GaI, Dodecanethiol, ) Is carried out by heating a mixed solution in which the Cu-Ga-S core quantum dots are formed, and the step of forming the Zn-Cu-Ga-S core quantum dots is performed by adding ZnCl ₂ to the mixed solution in which the Cu- , The step of forming the ZnS shell comprises the steps of applying a ZnS stock solution containing zinc acetate, octadecene and oleic acid, and applying another ZnS stock solution containing zinc stearate, octadecene and 1-dodecanethiol .

In particular, in the method of manufacturing blue light emitting quantum dots according to the present invention, Cu: Ga is 1:10 to 1: 1 in the Cu-Ga-S core quantum dots and Cu: Zn + Ga) is 1:10 to 1: 1, and Cu: (Ga + Al) is preferably 1:10 to 1: 1 in the Cu-Ga-Al-S.

According to the present invention, a very high PL and a blue emission spectrum of quantum efficiency can be realized by using quantum dots having an I-III-VI system Zn-Cu-Ga-S or Cu-Ga-Al-S core quantum dots and a ZnS shell . An example of implementing a blue light emitting quantum dot having such a quantum efficiency in a non-Cd system is not yet known.

In particular, the blue light emitting quantum dots having Zn-Cu-Ga-S core quantum dots and ZnS shells manufactured by the method according to the present invention not only show emission wavelengths capable of modulating from 486 nm (sky blue) to 471 nm (blue) And a high quantum efficiency of 78-83%, which is high enough to be practically applicable to the present invention.

1 is a schematic view of a quantum dot according to the present invention.
2 is a flowchart showing an embodiment of a method of manufacturing a quantum dot according to the present invention.
FIG. 3 shows (a) absorption of Cu-insufficient CGS / ZnS core / shell QD synthesized with Cu / Ga precursors at 1/4, 1/5 and 1/8 molar ratio and (b) normalized cyan- Lt; / RTI &gt;
Fig. 4 shows measured PL and simulated PL of representative CGS / ZnS QD samples with Cu / Ga = 1/8.
FIG. 5 is (a) absorption and (b) PL spectra of ZCGS core QD synthesized with different Zn precursors at 0, 0.25, 0.5, 1.0, and 1.5 mmol.
6 shows the results of conversion of the absorption spectrum of ZCGS core QD synthesized with different Zn precursors to 0, 0.25, 0.5, 1.0, and 1.5 mmol into a Tauc plot.
Fig. 7 shows (a) the XRD pattern of the ZCGS core QD synthesized with different amounts of Zn precursor, (b) the actual results obtained from the ICP results, and Nominal Zn / Cu molar ratio. (a) XRD patterns of representative ZCGS / ZnS core / shell QD with 1.5 mmol Zn for comparison are also included. (c) is a TEM photograph of the core / shell QD shown in (a) (scale bar: 10 nm).
8A is a low magnification TEM image (scale bar: 50 nm) of a 1.5 mmol Zn-based ZCGS / ZnS core / shell QD and FIG. 8B is a high magnification TEM photograph (scale bar: 5 nm).
FIG. 9 (a) is a ( Ahν ) ² - hν graph of ZCGS / ZnS QD synthesized with different amounts of Zn precursor, and FIG . ZCGS / ZnS &lt; RTI ID = 0.0 &gt; QD. &Lt; / RTI &gt;
10 is (a) absorption of (c) blue-blue luminescent ZCGS / ZnS QD prepared by varying the amount of Zn precursor, (b) normalized PL spectrum, and (c) peak wavelength-PL QY. (d) is a photograph of a solid-state light QD dispersion under UV lamp excitation.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It is provided to let you know.

1 is a schematic view of a quantum dot according to the present invention.

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

In one embodiment, the core QD 20 according to the present invention is a ZCGS composition. When the ZnS shell 30 is formed by applying ZnS coating to the core QD 20, PL and QY are improved.

The inventors of the present invention have found that Cu-Ga-S (hereinafter referred to as CGS) must be a base for an I-III-VI-based quantum dot to emit blue light, 10 ~ 1: 1, indicating that the chemical composition should be adjusted to the same or slightly deficient amount of Cu (non-stoichiometry). We have found that ZnS is alloyed with CGS composition to make ZCGS composition, or Al is alloyed to make Cu-Ga-Al-S composition to emit blue light. When the ratio of Cu to Ga is 1/10 or more, blue light emission can be achieved by addition of Zn or Al. When the ratio is more than 1, blue light emission does not occur.

In the ZCGS composition, the ratio of Cu: (Zn + Ga) is preferably 1:10 to 1: 1, and the ratio of Cu: (Ga + Al) in the composition of Cu-Ga-Al-S is preferably 1:10 to 1: Do. Particularly, when the composition is Zn: Ga = (1-x): x and Al: Ga = (1-x): x, 0.5 <x <1. The adjustment of the composition ratio between Ga and Zn or Al which can partially substitute Ga is performed to control the wavelength characteristics, but the adjustment of the composition ratio of Ga and Zn or Al is performed while the ratio of Cu and Ga is adjusted Is a peculiar matter of the present invention. Under these composition conditions, the quaternary core quantum dot can realize blue light emission.

The ZnS shell 30 can be formed in multiple, for example double or triple. That is, as shown in the figure, the ZnS shell may be formed up to the portion indicated by the dotted line, and then the remaining ZnS shell may be formed to the portion indicated by the solid line. In particular, since the ZnS shell forming process is performed continuously as described below, the layer discrimination in the ZnS shell 30 may be virtually absent. Each layer may have a different composition. The composition at this time may be discontinuously changed on the basis of a dotted line or may continuously change over the entire ZnS shell 30. This multi-ZnS shell 30 has excellent passivation effect. The quantum efficiency of the quantum dot 10 can be improved.

As described above, according to the present invention, blue light emission can be realized using the quantum dot 10 having ZCGS or Cu-Ga-Al-S core QD 20 and ZnS shell 30. And can also have a high quantum efficiency.

The core QD 20 may be manufactured by a hot colloid method, a solvothermal method or by heating-up or hot-injection, and the ZnS shell 30 A cation exchange process, a solvent heating method, and the like. Hereinafter, preferred embodiments of the production method will be described.

2 is a flowchart showing an embodiment of a method of manufacturing a quantum dot according to the present invention. In the case of forming the Cu-Ga-Al-S core QD, since it is the same except that Al is alloyed in comparison with the case of forming the ZCGS core QD, the following embodiment will exemplify the case of forming the ZCGS core QD .

First, a mixed solution prepared by mixing precursors of Cu, Ga and S, sulfur and a solvent is heated to grow the CGS 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 in visible light QD synthesis. In the present invention, a CGS composition having a band gap of 2.43 eV, which is higher than the above-mentioned composition, is selected and Cu / Ga stoichiometric control is used to achieve a short emission wavelength shorter than 500 nm for a long time, The CGS core QD of the ternary CGS is synthesized first.

Starting materials for growing CGS core QD include copper iodide (CuI) which is a copper precursor, gallium iodide (GaI) which is a gallium precursor, 1-dodecanethiol which is a sulfur precursor, sulfur, Oleylamine may be used as a basic combination.

The ratio of the starting materials is set in the range of Cu: Ga = 1: 10 to 1: 1 as mentioned above. In the case of the copper precursor, in addition to CuI, copper acetate, copper bromide, copper chloride and the like may also be used. In the case of the gallium precursor, in addition to GaI, gallium acetate, gallium chloride, gallium acetylacetonate and the like may be used. In the case of the sulfur precursor, various alkylthiol-based compounds such as octanethiol, hexadecanethiol, decanethiol, etc. may be used in addition to 1-dodecanethiol. In the case of a solvent, various fatty amines such as dodecylamine, trioctylamine and the like may be used in addition to oleylamine.

Heating of the mixed solution can be done in several steps. Degassing can be performed by first heating to 120 ° C. Thereafter, the temperature can be raised to a growth temperature of 240 ° C. At this time, N ₂ purging can be performed.

Then, a Zn precursor is added to alloy Zn with the CGS core QD to form a ZCGS core QD 20 (Step S10).

When Zn is alloyed into the CGS core QD (host) made in the previous step to synthesize the ZCGS core QD (20), high energy or short wavelength luminescence within the sky blue-blue range can be realized.

Zn precursor used here may be a ZnCl _2, zinc acetate acid.

In the case of forming the Cu-Ga-Al-S core QD, it proceeds in almost the same synthesis conditions (reaction temperature, reaction solvent, reaction time, and the like) as in the case of forming the ZCGS core QD and uses an Al precursor instead of the Zn precursor different. The Al precursor may be aluminum iodide, aluminum chloride, aluminum acetate or the like.

After the core QD 20 is formed, a ZnS stock solution is applied on the core QD 20 to form a ZnS shell 30 (steps S 20 and S 30).

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

For example, a ZnS stock solution is first applied to the resultant product formed with the core QD 20 to form a ZnS shell, followed by step S20, and another ZnS stock solution is applied to the resultant to form a ZnS shell, S30 are successively performed in step S20.

S20, and S30 can be divided into two or more shell processes.

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

The second ZnS stock solution in step S20 may be a zinc precursor, zinc acetate, octadecene and oleic acid, which are different in concentration from the first ZnS stock solution. The second ZnS shell reaction temperature in step S20 may be the same as the first ZnS reaction temperature, and the reaction time may be shorter than the first ZnS reaction time. The reaction is preferably maintained at a temperature of 240 DEG C for 30 minutes.

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

The reaction temperature of the ZnS shell in step S30 is in the range of 180 to 300 ° C, and the reaction time may be in the range of 1 minute to 24 hours. The temperature may be higher or longer than the step S20 in the reaction of step S30. Preferably, the final reaction for further ZnS shell formation can proceed for 1 hour at 250 &lt; 0 &gt; C.

The quantum efficiency of QD reached 78-83% after formation of the ZnS shell according to the experiment described below, and the InP QD having a similar emission band could not achieve the result. Hereinafter, the present invention will be described in more detail with reference to specific experimental examples.

The intentional stoichiometry between the two cations (Cu, In) in the Cu-In-S composition is known to have a significant effect on the bandgap. Specifically, the larger the amount of Cu deficiency is, the larger the band gap becomes. This is because the valence band maximum can be lowered by weakened repulsion between Cu d orbitals and S p orbits, thereby widening the band gap. In the present invention, the following experiments were carried out with different Cu / Ga stoichiometric ratios of 1/4, 1/5, and 1/8. As a result, the effect of Cu deficiency on the band gap of CGS composition there was.

Experimental Method:

0.1, or 0.0625 mmol of CuI (99.999%), 0.5 mmol of GaI (99.999%), and 0.5 mmol of CuI were prepared in order to synthesize ternary copper-deficient CGS core QD having Cu / Ga precursor at 1/4, 1/5, (99.99%) and 1 mmol of sulfur (99.998%) were placed in a three-neck flask with 1.5 mL of 1-dodecanethiol (DDT ≥98%) and 5 mL of oleylamine (OLA, 70% The mixed solution was heated to 120 캜 and degassed. The mixture was purged with N ₂ and the temperature was raised to 240 캜 at the growth temperature. The core QD was grown at this temperature for 5 minutes.

Following this synthesis step, a four component ZCGS core QD was synthesized. Zn / Cu precursor molar ratios of 0, 4, 8, 16, and 15% were obtained by adding ZnCl ₂ (≥98%) in amounts of 0, 0.25, 0.5, 1.0, And 24, respectively. All ternary and quaternary core QDs were equally injected into the following multi-shell forming process.

First, a first ZnS shell stock solution containing 8 mmol of reagent grade, 8 mL of oleic acid (OA, 90%) and 4 mL of 1-octadecene (ODE, 90%) was added slowly to the core QD growth solution at 240 & And allowed to react for 1 hour and 15 minutes.

A second ZnS shell stock solution containing 4 mmol of zinc acetate, 4 mL of OA, 2 mL of DDT and 2 mL of ODE was slowly added and reacted at the same temperature for 30 minutes. Then, another ZnS solution containing 4 mmol of zinc stearate (10-12% Zn basis), 4 mL of ODE and 2 mL of DDT was injected and the final shell reaction was conducted at 250 ° C for 1 hour. The synthesized quantum dots were precipitated by adding excess ethanol and purified by hexane / ethanol combination solvent using a centrifuge (9000 rpm, 10 minutes). Finally, the quantum dots were re-dispersed in hexane to analyze the spectrum.

Evaluation tools:

UV-Vis absorption and PL spectra of the quantum dots were recorded with an absorption spectrometer (Shimadzu, UV-2450) and a 500 W xenon lamp-mounted spectrophotometer (PSI Inc., Darsa Pro-5200). The PL quantum efficiency absolute value of the diluted quantum dot dispersion was evaluated with a PL QY measuring system (C9920-02, Hamamatsu). Cu K _α Structure and alloy characteristics of quantum dots were analyzed using powder X-ray diffraction (XRD) (Rigaku, Ultima IV) using radiation. The actual chemical composition of QD was analyzed with an inductively coupled plasma optical emission spectrometer (ICP-OES, OPTIMA 8300, PerkinElmer). To obtain the quantum dot image, a TEM operation was performed using a Tecnai G2 F20 operating at 200 kV.

result:

3, (A) absorption of Cu-insufficient CGS / ZnS core / shell QD synthesized with Cu / Ga precursors at 1/4, 1/5, and 1/8 molar ratio and (b) normalized green-blue emission PL spectra.

Referring to Fig. 3 (a), the UV-vis absorption spectrum of the Cu-insufficient CGS / ZnS core / shell QD under the same ZnS shell condition shows that the larger the Cu / Ga stoichiometry ratio, , And 1/8 molar ratio, the spectrum is blue-shifted. Unlike II-VI and III-V QDs with exciton transitions, the radioactive recombination of photoexcited charges in I-III-VI QDs is governed by the internal gap state associated with the defect and is typically broad And has an emission band width.

FIG. 3 (b) shows changes in the normalized PL spectra of the CGS / ZnS core / shell QD according to the Cu / Ga ratio. As the degree of Cu deficiency increases, ie, 1/4, 1/5, and 1/8 As the mole ratio increases, the emission changes from teal to sky blue. All PL spectra include a predominantly high energy emission portion and a negligible low energy tail portion.

Fig. 4 shows measured PL and simulated PL of representative CGS / ZnS QD samples with Cu / Ga = 1/8. The CGS / ZnS QD representative sample of Cu / Ga = 1/8 emits blue light and can be decomposed into two light emitting elements as shown in Fig. The high energy emission component (which shows a peak at 486 nm) results from the radioactive recombination of holes trapped within the Cu vacancy (V _Cu ) acceptor-induction level and electrons in the conduction band (CB). And the low-energy tail emission component (which peaks at 605 nm) is due to donor-acceptor pair (DAP) recombination. Where Ga and / or Zn substituted for Cu sites, i.e. Ga _Cu and / or Zn _Cu (located during or near the core surface, generated during ZnS shelling) defects can act as donor levels. Regardless of the Cu / Ga ratio, all CGS / ZnS QDs showed an absolute QY of more than 80%, especially 86, 82 and 81% at 1/4, 1/5, and 1/8, respectively.

Zn ions were alloyed into a Cu / Ga = 1/8 CGS host with the shortest emission wavelength by simply adding 0-1.5 mmol of another Zn precursor in the core reaction step to transfer the light to the high energy side .

CGS and ZnS are similar to each other in crystal structure of chalcopyrite tetragonal and zinc blende, and CGS-ZnS alloy occurs because the lattice constants are similar to 5.35 Å and 5.40 Å. In particular, the ionic radii are 9.1Å (Cu ^+), 7.6Å (Ga ^{+ 3),} and in consideration of the point of 8.8Å (Zn ^{+ 2),} which is an alloy Zn ^{2 +} ions are replaced with Cu ^{+ + 3} rather than Ga something to do.

FIG. 5 is (a) absorption and (b) PL spectra of ZCGS core QD synthesized with different Zn precursors at 0, 0.25, 0.5, 1.0, and 1.5 mmol.

As can be seen in FIG. 5 (a), the absorption spectrum of the ZCGS core QD is blue-shifted with increasing Zn, i.e., from no Zn to 1.5 Zn, indicating that the Zn alloy actually occurred. In order to measure the optical band gap of each ZCGS core QD, (Ahν) ² - hν relational expression (A = absorption, h = Planck's constant, ν = optical frequency) using the result of converting an absorption spectrum into tau graph (Tauc plot) , And the results shown in Fig. 6 were obtained.

Referring to FIG. 6, it can be seen that the bandgap increases from 2.95 to 3.14 eV as the amount of added Zn increases.

Referring to FIG. 5 (b), CGS QD according to the present invention showed a measurable PL before formation of a ZnS shell, unlike the almost non-fluorescent CGS QD reported in the literature. This low energy and fairly wide PL are due to the DAP recombination mentioned above. As shown in FIG. 5 (b), which is the PL spectrum of the measured state of a series of ZCGS QD dispersions having the same optical density of 0.05 at 370 nm, the PL intensity is in proportion to the amount of Zn added, To 1.5 mmol Zn-based ZCGS QD up to 7%.

Based on the absorption and PL results in FIG. 5 above, the amount of Zn participating in forming the alloyed ZCGS phase introduced into the core QD is small and the remainder is passivating the core surface while forming a very partial ZnS shell It can be predicted that it acts as a shell precursor.

FIG. 7 (a) is an XRD pattern of a ZCGS core QD synthesized by varying the amount of Zn precursor. For comparison, an XRD pattern of a representative ZCGS / ZnS core / shell QD with 1.5 mmol Zn was also included. It is somewhat difficult to evaluate the exact crystal structure due to the small size of core QD due to the large reflection peak, but all ZCGS QDs are equally typical tetragonal. As the amount of Zn increases, the ZCGS QD reflection peak moves finer to the smaller 2 &amp;thetas; side, as Zn is alloyed into the CGS host and the ZnS shell is partially formed on the core surface. The results are consistent. On the other hand, in the case of ZCGS / ZnS QD, the reflection peak is the same as the zinc blended ZnS phase, which shows a noticeable narrow half width (FWHM) indicating that a thin layer of ZnS is properly deposited.

Fig. 7 (b) shows the results obtained from the ICP results. Nominal Zn / Cu molar ratio. The actual Zn / Cu molar ratio of the ZCGS core QD was lower than the nominal value by ICP analysis. These Zn species were detected from internal (ie, Zn-alloyed CGS core QD) and external (ie, partially formed ZnS shell).

As a result of TEM operation for all core / shell QDs, the size and shape were measured to be practically the same. FIG. 7 (c) is a high magnification TEM image (scale bar: 10 nm) of 1.5 mmol Zn-based ZCGS / ZnS core / shell QD shown in FIG. 7 (a), showing nearly spherical particles having an average size of 4.8 nm.

8A is a low magnification TEM image (scale bar: 50 nm) of a 1.5 mmol Zn-based ZCGS / ZnS core / shell QD and FIG. 8B is a high magnification TEM photograph (scale bar: 5 nm). Referring to FIG. 8 (a), a low-magnification TEM photograph shows a compact QD array having a high degree of monodispersibility, and a high magnification TEM photograph of FIG. 8 (b) shows a clear lattice fringe of each QD have. Indicating a high degree of crystallinity.

As can be expected from the result of FIG. 5 (a), the absorption spectrum of the ZCGS / ZnS core / shell QD changes blue as the amount of Zn increases. The result of measuring the optical bandgap of the ZCGS / ZnS QD by converting the absorption spectrum through the ( Ahν ) ² - hν relationship is shown in FIG. 9 (a). By comparison with FIG. 6, it can be seen that the amount of each core portion is slightly increased by about 0.1 eV. This increase in bandgap is due to the addition of ZnS to the ZCGS core QD during shell formation.

Referring to FIG. 9 (b), as the amount of core-synthesized Zn increases, the bandgap increase margin after shell formation becomes small, and from this, the initial ZnS shell formed during the core synthesis, to some extent, It can be seen that it is prevented from diffusing into the host.

10 is (a) absorption of (c) blue-blue luminescent ZCGS / ZnS QD prepared by varying the amount of Zn precursor, (b) normalized PL spectrum, and (c) peak wavelength-PL QY. (d) is a photograph of a solid-state light QD dispersion under UV lamp excitation.

Referring to FIG. 10 (b), the normalized PL of all ZCGS / ZnS QDs has almost the same spectral shape as that of all the CGS / ZnS as shown in FIG. 3 (b) Includes luminescence and DAP recombination minor luminescence. Referring to FIG. 10 (c), as the amount of Zn added to the core synthesis increases, the peak wavelength of PL shifts from 486 to 471 nm, which corresponds to the sky blue-blue range. After formation of the ZnS shell, PL QY dramatically improved to 78-83%, and these values were achievable repeatedly within the standard deviation ± 3% range.

Referring to Figure 10 (d), it can be seen that the ZCGS / ZnS QD dispersion brightens under UV irradiation. In view of the fact that the non-Cd blue QD emitters such as InP and ZnSe have not yet achieved a high QY as in the present invention, it has been found that a blue ZCGS / ZnS QD having a high emission wavelength close to 470 nm and high efficiency, Is unique.

As described above, a ternary CGS / ZnS QD having a modulatable PL in the cyan-blue range is first synthesized using a nonstoichiometric Cu / Ga ratio to be copper deficient. Zn was alloyed to a CGS QD host of Cu / Ga = 1/8 by simply adding an amount different from the Zn species used in the core synthesis to subsequently move the light emission to the blue side. Some of the added Zn species participated in the alloying of the CGS host to produce a four component ZCGS QD, which was verified by optical, crystal structure, and compositional analysis. When a suitable shell is formed, the core QD is alloyed to a high degree and not only shows a modulated emission wavelength from 486 nm (sky blue) to 471 nm (blue), but also a level of 78-83% ZCGS / ZnS QD having high QY can be manufactured.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation in the embodiment in which said invention is directed. It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the appended claims.

10: Quantum dot
20: Zn-Cu-Ga-S or Cu-Ga-Al-S core QD
30: ZnS shell

Claims (11)

delete delete delete Forming a III-VI-based ternary Cu-Ga-S core quantum dot;
Forming a Cu-Ga-Al-S core quantum dot by alloying Zn with the Cu-Ga-S core quantum dots to form an I-III-VI quaternary Zn-Cu-Ga- ; And
And forming a ZnS shell on the Zn-Cu-Ga-S or Cu-Ga-Al-S core quantum dots,
The step of forming the Cu-Ga-S core quantum dots is performed by heating a mixed solution of a precursor of Cu, Ga and S, sulfur and a solvent,
The step of forming the Zn-Cu-Ga-S core quantum dots is performed by adding a Zn precursor to the mixed solution in which the Cu-Ga-S core quantum dots are formed, Forming an Al precursor in the mixed solution in which the Cu-Ga-S core quantum dots are formed,
Wherein the Zn precursor or Al precursor is introduced into the Cu-Ga-S core quantum dots to alloys and the remaining passivates the surface of the Cu-Ga-S core quantum dots when Zn or Al is alloyed. Way. 5. The method of claim 4, wherein in the step of forming the Cu-Ga-S core quantum dots, Cu / Ga, which is the molar ratio of the Cu precursor to the Ga precursor, is 1/8,
Wherein the Zn / Cu mole ratio between the Zn precursor and the Cu precursor in the step of forming the Zn-Cu-Ga-S core quantum dots is 4 to 24. 6. The method of claim 5, wherein Zn is further alloyed to the Zn-Cu-Ga-S core quantum dots during the step of forming a ZnS shell on the Zn-Cu-Ga-S core quantum dots . 5. The method of claim 4, wherein the step of forming the ZnS shell is performed by applying a ZnS stock solution. 8. The method of claim 7, wherein the step of forming the ZnS shell is performed two or more times continuously. 9. The method of claim 8, wherein the concentration and the reaction temperature of each ZnS stock solution are different from each other when the ZnS stock solution is continuously conducted twice or more. 5. The method of claim 4, wherein the step of forming the Cu-Ga-S core quantum dots comprises forming a Cu-Ga-S core quantum dots on a substrate using CuI, GaI, Dodecanethiol, Sulfur, oleylamine) is heated,
The step of forming the Zn-Cu-Ga-S core quantum dots includes
ZnCl ₂ is added to the mixed solution in which the Cu-Ga-S core quantum dots are formed,
The step of forming the ZnS shell comprises the steps of applying a ZnS stock solution containing zinc acetate, octadecene and oleic acid, and applying another ZnS stock solution containing zinc stearate, octadecene and 1-dodecanethiol Emitting quantum dot. 5. The method of claim 4, wherein the ratio of Cu: Ga is 1:10 to 1: 1 at a molar ratio of the Cu-Ga-S core quantum dots, Is 1:10 to 1: 1, and Cu: (Ga + Al) is 1:10 to 1: 1 at a mole ratio of the Cu-Ga-Al-S core quantum dots.

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