KR20190026211A - Passivation method of quantum dots and fabricating method of quantum dots-oxide composite using the same - Google Patents

Abstract

The present invention relates to quantum dots having improved fluorescence stability under a degradation condition without reducing quantum efficiency, and a production method thereof and, more specifically, to a quantum dot-oxide complex using the quantum dots and a production method thereof. The quantum dots according to the present invention complex an organic ligand on surfaces of the quantum dots and metal alkoxide and are surface-passivated so as to function as an additional protecting group while preventing the separation of the organic ligand. The quantum dot-oxide complex according to the present invention is that the quantum dots are distributed in a metal oxide matrix. The production method of the quantum dots comprises: preparing the quantum dots; and applying the metal alkoxide to the quantum dots to complex the organic ligand on the surfaces of the quantum dots with the metal alkoxide.

Description

TECHNICAL FIELD The present invention relates to a quantum dot passivation method and a quantum dots-oxide composite method using the same,

The present invention relates to a quantum dot and a method of manufacturing the same, and more particularly, to a quantum dot formed as a passivation for protecting the surface of a quantum dot and a method of manufacturing the same. The present invention also relates to the utilization of passivated quantum dots. More specifically, the present invention relates to a quantum dot-oxide complex in which quantum dots are distributed in a metal oxide, and a method for producing the same.

The quantum dots (QDs) having a semiconductor characteristic of a size of several tens of nanometers or less, that is, quantum dots (QDs), are different from the bulk particles due to the quantum confinement effect. As the size of the nanoparticles decreases, the bandgap of the nanoparticles increases, and as the size of the particles decreases, the emission wavelength becomes blue-shifted. In addition, when the particle size is extremely reduced, the proportion of the atoms or ions existing on the surface of the material increases. As a result, due to the extremely small size of the particles such as the lowering of the melting point or the decrease of the crystal lattice constant, It exhibits new optical, electrical and physical properties that could not be seen.

Among the semiconductor nanoparticles showing such changes in physical and optical properties, colloidal II-VI compound semiconductor quantum dots are attracting much attention due to high quantum efficiency (QY) of 60% or more and optical and chemical stability. As typical II-VI compound semiconductor quantum dots, CdSe and the like have been attracting attention with high quantum efficiency and stability, and many studies have been conducted. However, such quantum dots contain toxic components such as Cd ^{2 +} , which can cause many environmental problems.

In recent years, it has been proposed to replace Ⅱ-Ⅵ compound semiconductor quantum dots, which are highly toxic, with Ⅲ-Ⅴ compound semiconductor quantum dots (for example InP) or I-Ⅲ-VI chalcogenide quantum dots Cu-In-S) have been actively studied. Existing research has focused on improving the quantum efficiency of Cd-substituted quantum dots and some successful cases have been reported. However, it is a challenge to manufacture quantum dots having fluorescence stability for degradation environments such as long-term exposure to photons and heat.

It is helpful to form thick shells, such as multiple shells or compositionally gradient shells, to improve the light stability and thermal stability of quantum dots, but it is not sufficient to enhance fluorescence stability under degradation conditions. Conventionally, methods for physically surrounding quantum dots by separately coating quantum dots with chemically stable oxides for optical stability have been proposed.

Typically, the silica formed in the sol-gel reaction is coated individually on the quantum dots. However, there is a problem that during the reaction to form silica, the surface of the quantum dots chemically deteriorates and ultimately significantly reduces the quantum efficiency. Another example is to coat the surfaces of the quantum dots separately with In ₂ O ₃ , ZnGa ₂ O ₄ , Al ₂ O ₃ and the like. However, in the method of coating with the oxide proposed so far, inevitable damage occurs on the surface of the quantum dots and the quantum efficiency is lowered because the size of the final quantum dots increases.

A problem to be solved by the present invention is to provide a quantum dot having improved fluorescence stability under degradation conditions without reducing quantum efficiency and a method for producing the quantum dot.

Another problem to be solved by the present invention is to provide a complex using the quantum dot and a method of manufacturing the same.

The present invention proposes a method of passivating a surface of a quantum dot by in-situ complexing with a metal alkoxide. This method is advantageous in that the quantum efficiency of the quantum dot is not reduced as it is implemented in a very simple process.

In one embodiment, InP / ZnSeS / ZnS quantum dots were prepared by applying multiple shells to InP quantum dots, and red light emitting quantum dots having an absolute quantum efficiency of 80% were prepared. Subsequently, an appropriate amount of titanium isopropoxide titanium isopropoxide and Ti (i-PrO) ₄ ) are reacted to complex the surface of the quantum dots.

According to the present invention, when the passaged quantum dots and the other quantum dots are subjected to thermal aging under a long-time UV irradiation environment, the stability of quantum dots in the quantum dots according to the present invention can be remarkably improved. This can be seen from the results of the metal alkoxide complexing Is due to the presence of the metal present on the surface of the quantum dots.

The present invention also provides a method of forming a quantum dot-oxide complex with primarily passivated quantum dots prepared by the method according to the present invention.

The quantum dot according to the present invention is characterized in that the organic ligand on the surface of the quantum dot and the metal alkoxide are surface-passivated so as to function as an additional protecting group while preventing the organic ligand from coming off.

Wherein the quantum dots are quantum dot core / shell structure, the core is InP or ABX (A = Cu ^+, Ag ^+, B = In ^{+ 3,} Ga ^{+ 3,} X = S ^2-, Se ^{2 -),} and the metal The alkoxide may be M ^{n +} (OR) _n (M ^{n +} = Ti ⁴⁺ , Zr ⁴⁺ , Al ³⁺ , Si ⁴⁺ , R being an alkyl group).

The quantum dot-oxide complex according to the present invention is such that these quantum dots are distributed in a metal oxide matrix.

At this time, the metal oxide may be any one of silicon oxide, titanium oxide, and aluminum oxide.

The method for fabricating the quantum dot includes: preparing a quantum dot; And applying a metal alkoxide to the quantum dot to cause the organic ligand on the surface of the quantum dot to be complexed with the metal alkoxide.

Preferably, the step of preparing and completing the quantum dot is performed in situ, wherein the step of preparing the quantum dot comprises: forming a core quantum dot from a solution containing precursors; And growing a quantum dot of a core / shell structure by applying a shell stock solution to a solution of the core quantum dots to form a shell on the core quantum dots, wherein completing the quantum dots comprises: And adding a metal alkoxide to the solution.

Particularly, the metal alkoxide is added while heating the solution in which the quantum dots are grown. At this time, the heating is performed in a temperature range where the metal alkoxide is decomposed and does not change into a metal oxide.

After passivation as in the above-described quantum dot manufacturing method, a sol-gel reaction for producing a quantum dot-oxide complex can be performed.

A preferred method of making a quantum dot-oxide complex comprises: forming a core quantum dot from a solution comprising precursors; Growing a quantum dot of a core / shell structure by applying a shell stock solution to a solution in which the core quantum dots are formed to form a shell on the core quantum dots; A first passivation step in which a metal alkoxide is added to a solution in which the quantum dots are grown to cause an organic ligand and a metal alkoxide on the surface of the quantum dots to be in situ complicated; And subjecting the first passivated quantum dot to a metal oxide forming sol-gel reaction for secondary passivation.

During the secondary passivation step, organic ligand dropout of the primary passivated quantum dot is prevented. At the same time, it acts as an additional protecting group.

According to the present invention, it is possible to provide quantum dots that effectively passivate the surface, and can use this to produce quantum dot-complexes in which excellent performance of quantum dots is maintained. Passivated quantum dots maintain high fluorescence stability even under degradation conditions.

In particular, the fabrication process of in-situ quantum dot synthesis and passivation makes the process simple and cost-effective. Also, since the passivation method according to the present invention does not increase the size of the quantum dots, the quantum efficiency is not reduced.

The quantum efficiency of the quantum dot according to the present invention is rather improved by the passivation using the metal alkoxide. The deterioration of the quantum dot according to the present invention does not occur even if the UV irradiation environment or the thermal aging state is continued. According to the experimental example, 72-75% of the initial quantum efficiency was maintained up to 12 hours and maintained until 120 hours.

According to the present invention, it is possible to form a quantum dot-metal oxide complex with a first-passivated quantum dot using a metal alkoxide. In this case, the organic ligand on the surface of the quantum dots is prevented from dropping out and acts as an additional protecting group. can do. Such quantum dot-oxide complexes can be used as high-efficiency light-converting materials for LEDs.

1 is a schematic view for explaining a quantum dot passivation method according to the present invention and a method for manufacturing a quantum dot-oxide complex using the same.
2 (a) compares XRD patterns of InP, InP / ZnSeS, InP / ZnSeS / ZnS QD, and Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD, (TEM) image of pure InP / ZnSeS / ZnS QD (Comparative Example 1) and (c) TEM image of Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD (Experimental Example 1).
FIG. 3 is a high magnification X-ray photoelectron spectroscopic (XPS) scan result. Figure 3 (a) is Ti 2p, (b) is Ti 3s and _{Se 3d 5/2, (c} ) is Zn 2p, (d) is S 2p _3/2, and (e) is O 1s photoelectron peaks ( ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD), and (f) Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS Lt; RTI ID = 0.0 > O1s < / RTI >
FIG. 4 is a graph comparing Fourier transform infrared (FT-IR) spectra of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD.
Figure 5 shows the absorption of UV-visible light and the photo-luminescence of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complexed InP / Luminescence, PL) spectra. (a) shows the absorption spectrum of Ti (i-PrO) ₄ solution in chloroform.
6 (a) is a graph showing changes in relative QD emission areas of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complicated InP / ZnSeS / ZnS QD according to UV irradiation time. The error bar represents three repeated measurements for each sample. (b) and (c) show PL spectra of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD.
7A is a graph showing changes in the relative QD emission area of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complicated InP / ZnSeS / ZnS QD according to the thermal aging time at 150 ° C. It is a graph. The error bar represents the measurement repeated three times for each sample. (b) and (c) show PL spectra of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD.
8 shows changes in relative QD emission areas of pure InP / ZnSeS / ZnS QD (Comparative Example 2) and Zr (PrO) ₄ -complicated InP / ZnSeS / ZnS QD (Experimental Example 2) It is a graph.

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 for explaining a quantum dot passivation method according to the present invention and a method for manufacturing a quantum dot-oxide complex using the same.

In the present invention, a method of passivating a surface of a quantum dot by a simple method is proposed. In the present invention, an organic ligand on the surface of a quantum dot is compounded with a metal alkoxide such as titanium isopropoxide (Ti (i-PrO) ₄ ) to effectively passivate the surface of the quantum dot. Especially, quantum dot synthesis and in situ metal alkoxide complexing have a methodological feature.

Referring to FIG. 1, a quantum dot 10 is prepared. The quantum dot 10 may be a core / shell structure. In this case, the core may be InP and ABX (A = Cu ⁺ , Ag ⁺ , B = In ^{3 +} , Ga ^{3 +} , X = S ^2- , Se ^{2 -} ).

Next, a metal alkoxide is applied to the quantum dot 10 for primary passivation to perform quantum dot surface complexing. Then, the passively quantized point, i.e., the surface-complicated quantum dot 10 'for secondary passivation is subjected to a second passivation by a metal oxide forming sol-gel reaction. Through the second passivation, a quantum dot-oxide complex 30 is finally formed in which the surface-complicated quantum dot 10 'is dispersed in a metal oxide matrix 20.

Primary metal alkoxides that can be used in a passivation step is M ^{_n +} (OR) ⁿ is a metal compound represented by ^{(n +} M = Ti ^4+, Zr ^{+ 4,} Al ^{+ 3,} Si ^{+ 4,} R is an alkyl group).

The oxide base 20 may be at least one of metal oxides such as silicon oxide (silica), titanium oxide, aluminum oxide, and the like.

In one embodiment, InP / ZnSeS / ZnS quantum dots were prepared by applying multiple shells to InP quantum dots, and red light emitting quantum dots having an absolute quantum efficiency of 80% were prepared. Subsequently, an appropriate amount of Ti (i-PrO) ₄ are reacted to complex the surface of the quantum dots. The sol-gel reaction for silica synthesis is then advanced to form a quantum dot-silica complex.

Thus, the present invention also relates to a quantum dot-oxide composite in which quantum dots are distributed in a metal oxide. The present invention relates to a method of forming quantum dot-oxide complexes with primary passivated quantum dots using metal alkoxides. The quantum dot-oxide complex can be used as a photoconversion material for LEDs. As described above, the present invention relates to the passivation of quantum dots and the stability of luminescence of quantum dots through the passivation, and furthermore, to the application as a light conversion material for LEDs through the passivation. The first passivated quantum dots using the metal alkoxide prevent the organic ligands from falling off the surface of the quantum dots, so that the surface does not deteriorate during the sol-gel reaction.

In the quantum dot 10, the core may be prepared by a hot colloid method, a solvothermal method, or by heating-up or hot-injection, a cation exchange process, a solvent heating method, etc. An exemplary embodiment of a quantum dot synthesis method and a passivation method will be described below.

First, the step of growing the core QD from the solution containing the precursors is performed. The mixed solution prepared by mixing the precursor and the solvent is heated to grow the core QD first. Heating of the mixed solution can be done in several steps. First, the degassing can be performed by heating at a degassing temperature, for example, 120 deg. Thereafter, the temperature can be raised to a growth temperature, for example, 240 ° C. At this time, N ₂ purging can be performed.

Next, a shell is formed. A shell can be formed by applying a stock solution for forming a shell to a mixed solution in which core QD is formed. The step of forming the shell may be performed two or more times in succession. At this time, the concentration of the stock solution in each step, the reaction temperature and the time may be different. The temperature of the second reaction may be higher or longer.

As such, the shells may be formed in multiple, e.g., double or triple, and each layer may have a different composition. The composition at this time may vary discontinuously or continuously. These multi-shells have excellent core QD passivation effects. The quantum efficiency of the quantum dot 10 can be improved. When the shell is formed, PL and QY are both improved as compared with the core QD state. Therefore, it is preferable to use a core / shell structure for the quantum dot 10.

The state of applying the stock solution to the mixed solution in which the core QD is formed is in a solution state in which quantum dots are synthesized. In the present invention, the metal alkoxide is added in a state where heating is maintained in the quantum dot growth solution to passivate the surface of the quantum dot 10 primarily. An effective quantum dot passivation can be achieved by simple operation of adding a metal alkoxide to the quantum dot growth solution while heating. Quantum dot synthesis and passivation proceed in-situ, making the process simple and cost-effective.

The metal alkoxide effectively passivates the surface of the quantum dot 10 while complicating the organic ligand on the surface of the quantum dot 10. Even when the first passivated quantum dot, that is, the surface-complicated quantum dot 10 ', is injected into the metal oxide-forming sol-gel reaction, the surface of the quantum dot is not chemically deteriorated unlike the prior art. Therefore, compared with the case where the sol-gel reaction proceeds immediately without the first passivation as in the present invention, the quantum dot-oxide composite of the present invention maintains excellent characteristics of the quantum dot.

As described in detail later in the Experimental Example, the inventors confirmed Ti-O species present on the surface of InP-based quantum dots from Ti (i-PrO) ₄ through XPS and FT-IR spectroscopy. Ti (i-PrO) ₄ - Foundation & duplexing the QD and non while applying UV and heat in the same conditions for a QD a result of monitoring the PL _{changes, Ti (i-PrO) 4} - a compliance duplexing QD is Ti (i -PrO) ₄ had better passivation and showed a great improvement in stability.

Hereinafter, the passivation effect of InP-based quantum dots through Ti- and Zr-alkoxide complexing will be described in more detail through detailed experimental examples.

Experimental Method:

Experimental Example  One: InP / ZnSeS / ZnS QD  And Ti (i-PrO) ₄ Complication

For the red luminescent InP / ZnSeS / ZnS multi-shell QD synthesis, 0.45 mmol of indium chloride (InCl ₃ , 99.999%), 2.2 mmol of zinc chloride (ZnCl ₂ , 99.999% The mixed solution was prepared by adding oleylamine (OLA, 70%) into a three-neck flask, and the mixed solution was degassed by heating at 120 ° C for 1 hour, then purged with N ₂ and heated to 180 ° C . Then, 0.35 ml of tris (dimethylamino) phosphine (P (N (CH ₃ ) ₂ ) ₃ ), P (DMA) ₃ , 97%) was rapidly injected, Core QD was grown. Then, a ZnSeS intermediate shell with a composition gradient was stepwise grown by alternately injecting anions and cation shell precursors in the following manner: Se stock solution (0.12 mmol of selenium (Se, 99.99%), 1 ml of trioctylphosphine TOP, 90%), and the mixture was reacted at 200 DEG C for 30 minutes. Then, Zn stock solution (1.58 mmol of zinc stearate dissolved in 4 ml of octadecene (ODE, 90%)) was injected and reacted at 220 ° C. for 30 minutes. Subsequently, a Se-S stock solution (0.06 mmol Se and 2 mmol sulfur (S, 99.99%) dissolved in 1.6 ml of TOP) was injected and reacted at 240 ° C. for 30 minutes. And allowed to react at 260 DEG C for 30 minutes. As a final step of the ZnSeS intermediate shell, another Se-S stock solution (0.02 mmol Se and 4 mmol sulfur (S, 99.99%) dissolved in 2 ml of TOP) was injected and reacted at 280 ° C for 30 minutes. The solution was injected again and reacted at 300 ° C for 60 minutes.

To continuously grow the cells outside the ZnS, 5 ml of 1-dodecanethiol was dropwise added dropwise, followed by reaction at 200 ° C for 60 minutes. For the multi-shell InP / ZnSeS / ZnS QD, 3 mmol of zinc acetate (98%) was dissolved in 3 ml of oleic acid (90%) and the reaction was maintained at 190 ° C for 120 min. Respectively. In-situ complexing of InP / ZnSeS / ZnS QD was performed by immediately injecting 7 mmol of Ti (i-PrO) ₄ (97%) into this quantum dot growth solution and holding at 190 ° C for 30 minutes.

The surface-passivated quantum dots thus prepared were dispersed in hexane, precipitated by addition of excess ethanol, and washed several times with a hexane / ethanol combination solvent using a centrifuge (9000 rpm, 10 min) ). Finally, as a comparative example, uncomplicated pristine InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complexed QD according to the present invention were redispersed in hexane or ODE and put into the test.

Experimental Example  2: zirconium Propoxide, Zr (PrO) ₄ )  Used Qdot  Passivation (Surface Modification) Process

In this experiment, green luminescent InP / ZnSeS / ZnS quantum dots were used instead of red luminescence quantum dots.

The overall reaction is the same as in Experiment 1 [Red InP / ZnSeS / ZnS quantum dot + Ti (i-PrO) ₄ ] experiment. After the green InP / ZnSeS / ZnS quantum dots were synthesized, Zr (PrO) ₄ After 0.5 to 4 mL of the solution was slowly injected, the reaction was maintained at 190 DEG C for 30 minutes and the temperature was gradually cooled to room temperature. The subsequent process is the same as in Experimental Example 1.

Qdot  Stability testing of dispersions

Comparative Example 1 (pure red emitting InP / ZnSeS / ZnS QD without Ti (i-PrO) ₄ complexing) and Experimental Example 1 (Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD) UV irradiation was performed to expose to the deteriorating condition, and the thermal aging was performed for the predetermined period in the same manner.

Comparative Example 2 (pure green luminescence InP / ZnSeS / ZnS QD without Zr (PrO) ₄ complexing) and Experimental Example 2 (Zr (PrO) ₄ -complexed InP / ZnSeS / ZnS QD) Exposure to deteriorating conditions and thermal aging were carried out in the same manner for a predetermined period.

For the UV irradiation test, the QD dispersion in hexane was continuously irradiated with UV light for 65 hours using a 65 nm-multiband UV lamp, and the change in PL intensity over time was monitored.

For thermal aging tests, the quantum dots were dispersed in an ODE with a high boiling point and each dispersion was placed in a 150 占 폚 contact oven for 4 hours.

Evaluation tools:

Cu K _α The crystal structure of quantum dots was analyzed using powder X-ray diffraction (XRD) (Rigaku, Ultima IV) using radiation. To obtain the quantum dot image, a TEM operation was performed using JEM-2100F (JEOL Ltd.) operating at 200 kV. Al K _alpha The chemical composition / transition was analyzed for QD films on Si substrates using XPS (Thermo VG) with x-ray (E = 1486.6 eV). FT-IR spectroscopy (Bruker, Vertex 70) was used to identify species on the QD surface. 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 QD dispersion was evaluated with a PL QY measurement system (C9920-02, Hamamatsu).

Experiment result:

2 (a) compares XRD patterns of InP, InP / ZnSeS, InP / ZnSeS / ZnS QD, and Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD, (TEM) image of pure InP / ZnSeS / ZnS QD (Comparative Example 1) and (c) TEM image of Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD (Experimental Example 1).

2 (a), XRD of InP / ZnSeS formed with XRD of InP and intermediate shell ZnSeS and XRD and Ti (i-PrO) ₄ -complexed InP / ZnSeS / The XRD pattern difference of ZnSeS / ZnS QD can be confirmed. It can be seen that the reflection peak of InP QD shifts toward the larger 2θ and that there is no separate peak of ZnSe or ZnS, so that ZnSeS shelling with graded composition gradually changes. In the case of InP / ZnSeS / ZnS, the reflection peak shifted toward the larger 2θ as the ZnS fraction increased.

In the case of Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD, the position of the reflection peak was not changed but only the intensity was decreased. From this, Ti (i-PrO) ₄ It can be confirmed that the molecules are adhered or successfully complicated to cause a decrease in the diffraction intensity.

Referring to FIG. 2 (b), the average size of InP / ZnSeS / ZnS QD is about 6.8 nm. Referring to FIG. 2C, Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS The average size of the QD is not substantially different from that of FIG. 2 (b). Thus, it can be seen that the coating of the QD surface with the TiO _x phase, which can be formed through thermal decomposition of Ti (i-PrO) _{4 in} the growth solution, has not occurred. That is, the heating in the present experimental example was carried out in a temperature range where the metal alkoxide was not decomposed and changed into a metal oxide. Therefore, quantum efficiency is not lowered by increasing the quantum dot size during passivation.

To confirm the presence of Ti species on the surface of the QD, XPS analysis was performed on the QD of Comparative Example 1 and Experimental Example 1. 3 shows a result of a high magnification XPS scan. Figure 3 (a) is Ti 2p, (b) is Ti 3s and _{Se 3d 5/2, (c} ) is Zn 2p, (d) is S 2p _3/2, and (e) is O 1s photoelectron peaks ( ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD), and (f) Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS Lt; RTI ID = 0.0 > O1s < / RTI >

First, Fig. 3 (a), (b) With reference _{to, Ti (i-PrO) 4} - Foundation & duplexing the QD is looks for peaks at 464.7, 458.9, and 62.4eV This Ti 2p _1/2, respectively, 2p _{3 / 2} , and 3s peaks, and is due to Ti-O bonds from Ti (i-PrO) ₄ -QD surface-complexed.

(B) in Fig. 3, (c), but _{Se 3d 5/2, Zn 2p} , S 2p 3/2, and not shown in the drawings, as shown in (d) In 3d peak also was observed, Ti present in the QD surface (i-PrO) ₄ Screening of photoelectrons emitted from QD by molecules reveals that the peak intensity at Ti (i-PrO) ₄ -complexed QD is lower than that of pure QD.

As shown in FIG. 3 (e), the O 1s peak difference is large in the two QDs. The O1s peak of pure QD is derived from the atmospheric component adsorbed on the carboxylate QD ligand and QD film. On the other hand, the O 1s peak of Ti (i-PrO) ₄ -complexed QD can be decomposed into two sub-spectra having binding energies of 531.7 and 530.4 eV, as shown in Fig. 3 (f). The 531.7 eV peak is equal to the O 1s peak of the pure QD above. The 530.4 eV peak is due to the oxygen of the Ti-O bond from Ti (i-PrO) ₄ .

FT-IR measurements were also performed to support the above XPS results. FIG. 4 is a graph comparing FT-IR spectra of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD.

As shown in FIG. 4, both QDs exhibit strong bands related to CH and COO ^- stretching. Particularly, the 2850 and 2920 cm ^-1 bands correspond to methyl (-CH ₃ ) and methylene (-CH ₂ ) groups, respectively, and they are aliphatic groups such as oleate group, stearate group and dodecyl group lt; / RTI > is an aliphatic surface ligand species.

The 1450 and 1550 cm < ^-1 > bands correspond to the symmetric and asymmetric modes of the carboxy group of fatty acids on the QD surface, respectively. The 810 cm ^-1 band measured only in the Ti (i-PrO) ₄ -complexed QD sample demonstrates that the QD surface is adequately complexed with Ti (i-PrO) ₄ .

5 shows (a) UV-visible absorption and (b) PL spectra of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD. (a) shows that Ti (i-PrO) ₄ in chloroform The absorption spectrum of the solution is shown.

5 (a), the absorption curve of Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD is equal to that of pure InP / ZnSeS / ZnS QD up to about 350 nm and then converges to a short wavelength region . As shown in the figure, Ti (i-PrO) ₄ The absorption spectrum of the solution increases sharply at 350 nm or less. Thus, the absorption difference in this short wavelength region shows that Ti (i-PrO) ₄ is complexed on the QD surface. The isopropyl group of Ti (i-PrO) ₄ can be complexed or conjugated through a hydrophobic reaction with the hydrocarbon chains of various organic ligands (e.g., oleic acid group, stearic acid group, dodecyl group) on the QD surface .

Referring to FIG. 5 (b), PL characteristics are maintained even when Ti (i-PrO) ₄ is complexed. In addition, the QY of Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD is 83%, which is slightly higher than the QY of 80% of pure InP / ZnSeS / ZnS QD. Therefore, it can be seen that the passivation of the InP / ZnSeS / ZnS QD surface using Ti (i-PrO) ₄ has improved the QY.

Two kinds of QDs were evaluated for stability under exposure to 365 nm UV light. 6 (a) is a graph showing changes in relative QD emission areas of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complicated InP / ZnSeS / ZnS QD according to UV irradiation time. The error bar represents three repeated measurements for each sample. (b) and (c) show PL spectra of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD.

As shown in Fig. 6, the two differences are significant, and Ti (i-PrO) ₄ -complexing in the Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD passivates the QD surface It is very effective for After 24 hours of irradiation, the pure InP / ZnSeS / ZnS QD retained only 30% of the initial QY, and QD agglomeration occurs when the time is longer. This decrease in efficiency is a result of the QD surface being damaged by the elimination of surface ligands and the photochemical oxidation of the QD surface. In pure InP / ZnSeS / ZnS QD, after 72 hours, the QD lost its colloidal properties and precipitated.

On the other hand, in the Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD, 72-75% of the original QY was maintained up to 12 hours and maintained until 120 hours. At this time, it can be seen that Ti (i-PrO) ₄ effectively passivates the QD surface and suppresses the elimination of the surface ligand, since the QD does not aggregate or precipitate and maintains the colloidal property.

In addition, the same results as in InP / ZnSeS / ZnS QD were obtained when the Ti (i-PrO) ₄ and InP / ZnSeS / ZnS QD were simply mixed at 25 ℃ after UV irradiation. Therefore, passivation can not be obtained only by the presence of Ti (i-PrO) ₄ and InP / ZnSeS / ZnS QD, and it is found that the passivation can be obtained by carrying out the Inchture reaction in the state of heating as in the present invention .

Referring to FIGS. 6 (b) and 6 (c), pure InP / ZnSeS / ZnS QD is red shifted from 618 nm to 625 nm after 24 hours as the UV irradiation time increases. This is the result of the loss of surface ligands due to UV irradiation and the detrimental effect of quantum limitation.

On the other hand, QD was dispersed in an ODE having a high boiling point and heated to 150 DEG C to evaluate thermal stability. 7A is a graph showing changes in the relative QD emission area of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complicated InP / ZnSeS / ZnS QD according to the thermal aging time at 150 ° C. It is a graph. The error bar represents the measurement repeated three times for each sample. (b) and (c) show PL spectra of pure InP / ZnSeS / ZnS QD and Ti (i-PrO) ₄ -complexed InP / ZnSeS / ZnS QD.

Referring to FIG. 7 (a), the pure InP / ZnSeS / ZnS QD decreases the PL intensity by 45% after 4 hours. In contrast, Ti (i-PrO) ₄ -complexing InP / ZnSeS / ZnS QD is maintained at 93%. Referring to FIGS. 7 (b) and 7 (c), the red shift due to the increase in time was only generated in pure InP / ZnSeS / ZnS QD.

Thus, it can be seen that Ti (i-PrO) ₄ -complexing is an effective means for not only suppressing the photooxidation of the QD surface but also preserving the surface ligand even in a deteriorated environment.

8 shows changes in relative QD emission areas of pure InP / ZnSeS / ZnS QD (Comparative Example 2) and Zr (PrO) ₄ -complicated InP / ZnSeS / ZnS QD (Experimental Example 2) It is a graph.

Referring to FIG. 8, Zr (PrO) ₄ The change in luminescence characteristics of the green quantum dots differs depending on the presence or absence of the surface treatment. Basically, the result is substantially similar to that of [red InP / ZnSeS / ZnS quantum dot + Ti (i-PrO) ₄ ].

On the other hand, the quantum dots used in the experimental examples are based on InP, but it is of course possible to apply the passivation method according to the present invention to quantum dots of other compositions.

To improve the stability of the quantum dots, the material used for the alkoxide complexing in Experimental Example 1 was Ti (i-PrO) ₄ , and the material used in Experimental Example 2 was Zr (PrO) ₄ . However, additional metal alkoxide candidates that can work in addition to these materials are listed below.

Titanium butoxide (Ti (BuO) ₄ ), methoxide (Ti (MeO) ₄ ), ethoxide (Ti (EtO) ₄ )

Zr series: Zirconium butoxide (Zr (BuO) 4), tert-butoxide (Zr (t-BuO) 4), ethoxide (Zr (EtO) 4)

Series Al: Aluminum tert-butoxide (Al ( t-BuO) 3), tri-sec-butoxide (Al (ts-BuO) 3), ethoxide (Al (EtO) 3)

Sn system: Tin (IV) tert-butoxide (Sn (t-BuO) ₄ )

Si series: Tetraethyl orthosilicate (TEOS), Tetramethyl orthosilicate (TMOS)

Zn system: Zinc methoxide (Zn (MeO) ₂ )

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
10 ': primary passivated quantum dot
20: oxide base
30: complex

Claims (10)

A quantum dot surface-passivated so that the organic ligand on the surface of the quantum dot is complexed with the metal alkoxide to prevent the organic ligand from coming off and to serve as an additional protecting group. The method of claim 1 wherein the quantum dots are quantum dot core / shell structure, the core is InP or ABX (A = Cu ^+, Ag ^+, B = In ^{+ 3,} Ga ^{+ 3,} X = S ^2-, Se ^{2 -} ) and the metal alkoxide is M ^{n +} (OR) _n (M ^{n +} = Ti ⁴⁺ , Zr ⁴⁺ , Al ³⁺ , Si ⁴⁺ ). A quantum dot-oxide composite according to claim 1, wherein the quantum dots are distributed in a metal oxide matrix. 4. The quantum dot-oxide composite according to claim 3, wherein the metal oxide is any one of silicon oxide, titanium oxide and aluminum oxide. Preparing a quantum dot; And
And applying a metal alkoxide to the quantum dot to cause the organic ligand on the surface of the quantum dot to be complexed with the metal alkoxide. 6. The method of claim 5, wherein the step of preparing and completing the quantum dot is performed in-situ,
The step of preparing the quantum dot includes:
Forming a core quantum dot from a solution comprising precursors; And
Growing a quantum dot of a core / shell structure by applying a shell stock solution to a solution in which the core quantum dots are formed to form a shell on the core quantum dots,
Wherein the completing step is a step of adding a metal alkoxide to the solution in which the quantum dots are grown. The method according to claim 6,
Wherein the metal alkoxide is added while heating the solution in which the quantum dots are grown. The method according to claim 7, wherein the heating is performed in a temperature range where the metal alkoxide is decomposed and does not change into a metal oxide. Forming a core quantum dot from a solution comprising precursors;
Growing a quantum dot of a core / shell structure by applying a shell stock solution to a solution in which the core quantum dots are formed to form a shell on the core quantum dots;
A first passivation step in which a metal alkoxide is added to a solution in which the quantum dots are grown to cause an organic ligand and a metal alkoxide on the surface of the quantum dots to be in situ complicated; And
And subjecting the first passivated quantum dot to a metal oxide forming sol-gel reaction to perform a second passivation. 10. The method of claim 9, wherein organic ligand dropout of the first passivated quantum dot is prevented during the secondary passivation step.

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