KR101581231B1 - Method for producing quantum dot embedded silica and luminescent film comprising the silica - Google Patents

Abstract

The present invention relates to a technique for realizing a white light emitting device using quantum dots, and more particularly, to a method for manufacturing a white light emitting device using quantum dot containing silica particles improving the thermal stability, which is a disadvantage of conventional quantum dot light emitting devices, .

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing a quantum dot-containing silica particle and a light emitting polymer film comprising the silica particle,

The present invention relates to a technique for realizing a white light emitting device using quantum dots, and more particularly, to a method for manufacturing a white light emitting device using quantum dot containing silica particles improving the thermal stability pointed out as a disadvantage of a conventional quantum dot light emitting device and a light emitting polymer film And a manufacturing method thereof.

In recent years, not only Korea but also the whole world have suffered from environmental crisis such as energy crisis and global warming, and research has been actively carried out on light emitting diodes (LEDs) having advantages of high efficiency, environment friendly and small size in order to overcome them. It is most important to realize white light in order to be used as a solid light source to replace LED, fluorescent lamp, incandescent lamp, and LCD backlight unit, which have excellent advantages.

There are two ways to implement white light. There are two methods of obtaining a white color by applying a phosphor on a UV LED or a blue LED and a multi chip type using LED chips of different colors. Currently, the most commonly used white LED is a method of electronically combining a blue LED with a Y ₃ Al ₅ O ₁₂ : Ce ³⁺ (YAG: Ce) phosphor as a excitation source to a white light source by bonding it with a silicone resin. These white LEDs exhibit good efficiency, but it is difficult to mass-produce white LEDs having the same color coordinates due to color separation due to a wide wavelength interval of blue and yellow. Also, it is not easy to control important color temperature and color rendering index in illuminating light source.

One of the ways to overcome this difficulty is increasing interest in quantum dot LEDs that utilize QDs as excitation sources for blue LEDs. Quantum dots are compound semiconducting particles of several nm in size. If the size is small according to the quantum confinement effect, the long wavelength light is emitted when the light of short wavelength is large. Light sources using quantum dots are more advantageous than other light sources, and have lower power consumption, higher color reproducibility, and lower cost than OLEDs that use expensive organic dyes compared to conventional OLEDs. Do. In addition, in order to realize white light, white light can be realized by adjusting the emission wavelength through simple size adjustment of a single component quantum dot as compared with OLED, which must mix various organic materials.

However, there are problems with heat generation and compounding technology in utilizing quantum dots for display. Quantum dots have high self-thermal efficiency and therefore have a problem of life span of LED and self-heating. As the heat increases, the core portion in the quantum dots reacts with water or oxygen to oxidize, and the emission decreases as the oxidation proceeds. In addition, as a problem of quantum dots, various particles must be mixed to express natural colors.

In order to improve the stability of QDs, methods of coating QDs with SiO ₂ or polymers have been extensively tried. However, commercialized QD LEDs made using the QDs have not been reported.

The present inventors have completed the present invention by developing a technique capable of improving water and thermal stability of the quantum dots.

Accordingly, an object of the present invention is to provide a method of manufacturing a quantum dot-containing silica particle having a structure in which a plurality of quantum dots are embedded in spherical silica to improve the moisture and thermal stability of the quantum dots.

It is another object of the present invention to provide a method of manufacturing a light emitting polymer film in which a quantum dot is dispersed in an organic resin so that a quantum dot can be easily applied to an LED device.

The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above-described object of the present invention, first, the present invention provides a spherical silica particle; And a plurality of quantum dots embedded in the silica particles.

In a preferred embodiment, the quantum dot includes a core formed of II-IV or III-V or I-III-VI semiconductor particles of several nanometers in size and a shell formed by growing a semiconductor material having a large band gap outside the core .

In a preferred embodiment, the silica particles have a diameter of 50 to 300 nm.

The present invention also relates to a film formed of an organic resin; And a plurality of quantum dot-containing silica particles uniformly dispersed in the film as a whole.

In a preferred embodiment, the organic resin has a refractive index of 1.40 to 1.50.

In a preferred embodiment, the organic resin is ethoxylated trimethylol propane triacrylate (ETPTA).

In a preferred embodiment, the weight ratio of the quantum dot containing silica particles to the organic resin film is 1: 5 to 1:30.

In a preferred embodiment, the quantum dot is a CuInS ₂ / ZnS-OH composition.

The present invention also relates to a method of manufacturing a semiconductor device, comprising: a first step of growing a silica seed; Injecting quantum dots into the reactor of the first grown silica seed; And a step of secondarily growing the first grown silica seed so as to include quantum dots.

The present invention also relates to a method for preparing a film precursor composition, comprising: dispersing quantum dot-containing silica particles in an organic resin to prepare a film precursor composition; And forming a film with the film precursor composition.

In a preferred embodiment, the film precursor composition comprises the quantum dot-containing silica particles and the organic resin in a weight ratio of 1: 5 to 1:30.

First, according to the present invention, a plurality of quantum dots are embedded in the spherical silica, thereby improving moisture and thermal stability of the quantum dots.

In addition, according to the present invention, quantum dots can be easily applied to an LED device through a light emitting polymer film realized in a thin film form by dispersing spherical silica including a quantum dot in an organic resin.

1 is a schematic diagram of a quantum dot containing silica particle according to an embodiment of the present invention and a cross-sectional structure of a quantum dot included therein.
2A is a graph showing a PL emission spectrum of quantum dots synthesized in another embodiment of the present invention.
2B is a photograph of the UV excited state of the quantum dot shown in FIG. 2A.
FIG. 2C is an SEM image of a quantum dot-containing silica particle including a plurality of quantum dots shown in FIG. 2A prepared in another embodiment of the present invention. FIG.
FIG. 2D is an EDS spectrum graph of the quantum dot-containing silica particles shown in FIG. 2C and a photograph showing a lattice pattern obtained in TEM.
3 is a graph showing thermal quenching characteristics of the quantum dots and the quantum dot-containing silica particles prepared in the present invention.
4 (a) is a photograph of a phosphor plate prepared in another embodiment of the present invention, (b) is a photograph of a laminated light emitting polymer film on the phosphor plate shown in (a) (D) is a photograph of a light emitting polymer film under UV illumination, and (e) is a photograph of a driven state of a white LED device prepared in another embodiment of the present night .
5 is an EL spectrum graph of a white LED device including a phosphor plate and a light emitting polymer film prepared in another embodiment of the present invention. (A) shows the CIE color coordinates of a white LED device including a mixture of phosphor-quartz-containing silica particles, (b) shows a CIE color coordinate of a white LED according to the present invention The CIE color coordinates of the LED device are shown.
FIG. 6 is a graph showing peak emission intensities of a white LED device and a comparative example according to another embodiment of the present invention.

Although the terms used in the present invention have been selected as general terms that are widely used at present, there are some terms selected arbitrarily by the applicant in a specific case. In this case, the meaning described or used in the detailed description part of the invention The meaning must be grasped.

Hereinafter, the technical structure of the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments.

However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Like reference numerals used to describe the present invention throughout the specification denote like elements.

The technical feature of the present invention is to develop a light emitting polymer film comprising a quantum dot containing silica having a structure in which a plurality of quantum dots are embedded in spherical silica particles and silica containing a quantum dot in order to ensure moisture and thermal stability of the quantum dots, Has been developed to develop a new package structure in which a white LED device is laminated on a phosphor plate, thereby improving the thermal stability of the quantum dots contained in the light emitting polymer film.

Thus, the quantum dot containing silica particles of the present invention may be spherical silica particles; And a plurality of quantum dots embedded in the silica particles.

Here, the silica particles are spherical in order to secure a large surface area in contact with the quantum dots and may have a diameter of 50 to 300 nm. The quantum dots included in the spherical silica particles can be all well known quantum dots and many quantum dots included in the spherical silica particles can be disposed on the inner and outer surfaces of the spherical silica particles. Moisture and thermal stability, as well as efficiency. Quantum dots used in embodiments of the present invention include cores formed of II-IV or III-V or I-III-VI semiconductor particles of several nanometers in size; And a shell formed by growing a semiconductor material having a large band gap outside the core.

Next, the light emitting polymer film of the present invention comprises a film formed of an organic resin; And a plurality of quantum dot containing silica particles uniformly dispersed throughout the film.

Any organic resin known in the art can be used as long as it has a property capable of eliminating the refraction dispersion of light emitted from the quantum dots in the light emitting polymer film. For example, it may be an organic resin having a refractive index of 1.40 to 1.50. Such a refractive index range is a refractive index range similar to that of a silica particle embedded with a quantum dot, considering the structure of silica particles containing a quantum dot. Further, if the organic resin has a viscoelastic property, the quantum dot-containing silica particles may be uniformly dispersed in the organic resin, so that the organic resin may be a viscoelastic organic resin. In the examples of the present invention, ethoxylated trimethylol propane triacrylate (ETPTA) was used as an organic resin. The weight ratio of the quantum dot-containing silica particles to the organic resin film included in the light-emitting polymer film of the present invention is in the range of 1: 5 to 1:30, in which silica particles containing quantum dots are dispersed in an organic resin to form a thin film. .

Next, the white LED device of the present invention includes a blue LED chip, a phosphor plate disposed on the LED chip, and a light emitting polymer film including the quantum dot-containing silica particles laminated on the phosphor plate. If necessary, the phosphor plate and the light emitting polymer film may not be a separate structure, but may be integrally formed by bonding the light emitting polymer film on the phosphor plate.

As described above, the white LED device of the present invention is different from the packaging structure of the known white LED device by inserting the phosphor plate between the blue LED chip and the light emitting polymer film, thereby enhancing the thermal stability of the quantum dots included in the light emitting polymer film. .

In particular, the phosphor plate significantly reduces the heat of the phosphor, and the phosphor plate with low thermal conductivity prevents heat stress from the LED chip to the QDES containing QDES and maintains a higher temperature gradient across the plate Because. This phosphor plate also protects and protects the organic resin, for example ETPTA, from the general photodamage on packaging caused by untransformed high energy radiation passed through it. The blue LED chip and the phosphor plate may be disposed apart from each other in order to further enhance the structural characteristics, that is, the thermal stability enhancement structure of the quantum dot.

On the other hand, the phosphor plate may be formed by forming an inorganic material and a phosphor uniformly in a plate form or by firing only a phosphor without an inorganic material. The inorganic material may have at least one of translucency and fluorescence as at least one of glass and transparent ceramics It will be possible. The phosphor may be all known phosphors and may be determined to be suitable for the white LED device in consideration of the luminescence characteristics of the quantum dots contained in the light emitting polymer film. In the embodiment of the present invention, glass frit composed of SiO ₂ -B ₂ O ₃ -RO (R = Ba, Zn, Mg) component is used as an inorganic material contained in the phosphor plate, Y ₃ Al ₅ O ₁₂ : Ce ³⁺ (YAG) phosphors were used. The quantum dots included in the light emitting polymer film were CuInS ₂ / ZnS-OH compositions.

The white LED device of the present invention can maintain 97% of the initial luminescence intensity even after 180 minutes of driving time when white light is emitted by applying power through a structure including a light emitting polymer film laminated on a phosphor plate.

Next, a white LED device manufacturing method of the present invention includes: preparing silica particles containing quantum dots; Preparing the light emitting polymer film containing the prepared quantum dot-containing silica particles uniformly dispersed therein; Preparing a phosphor plate; Disposing the prepared phosphor plate on a blue LED chip; And laminating the light emitting polymer film on the phosphor plate.

In some cases, the step of laminating the light emitting polymer film on the phosphor plate may be performed, and then the phosphor plate having the light emitting polymer laminated on the blue LED chip may be disposed. In the method of fabricating a white LED device in this order, the step of laminating the light emitting polymer film on the phosphor plate includes: coating the organic resin used for the light emitting polymer film on the phosphor plate; Laminating the light emitting polymer film on the coated organic resin; And reacting the organic resin to combine the phosphor plate and the surface of the light emitting polymer film that are in contact with each other to form an integral body. For example, ETPTA and a photoinitiator may be coated on the surface of a phosphor plate, and then a light emitting polymer film, Q-ETPTA, may be laminated and UV irradiation may be performed while moderately pressing the phosphor plate to bond the surfaces of the phosphor plate and the light emitting polymer film. In this case, since the air is not present between the fluorescent plate and the light emitting polymer film, it is possible to avoid the interference of air and to eliminate the refractive dispersion that may be generated.

On the other hand, the phosphor plate is not limited to be prepared or prepared simultaneously with the light emitting polymer film.

Here, the step of preparing the quantum dot-containing silica particles may include: a first step of growing a silica seed; Injecting quantum dots into the reactor of the first grown silica seed; And a step of secondarily growing the first grown silica seed so as to include the quantum dots. For example, silica seed is first grown on the silica particle growth step using the stober method, and a hydrophilic quantum dot (CuInS ₂ / ZnS-OH composition) is added to the silica particles to make a secondary particle of the silica particles to prepare a quantum dot embedded silica powder.

Preparing a light emitting polymer film by dispersing silica particles containing quantum dots in an organic resin to prepare a film precursor composition; And forming a film with the film precursor composition. For example, the film precursor composition may comprise an organic resin and silica particles containing a quantum dot in a weight ratio of 1: 5 to 1:15.

Example 1

Preparing Silica Particles Containing Qdots

The quantum dot-containing silica particles were prepared as follows by introducing quantum dots in the step of growing silica particles with the stober method.

1. Quantum dot synthesis

CuInS ₂ / ZnS quantum dots (QDs) The quantum dots having a size of about 3 nm with a structure similar to the schematic diagram shown in FIG. 1 were synthesized by heating. The quantum yields of quantum dots synthesized in solution were about 60 %. Shell formation was achieved by proper injection of ZnS shell stock solution and subsequent agitation. After shell formation was completed, ligand exchange was performed to disperse the quantum dots in ethanol. The ligand was ligand exchanged to act as a hydroxyl group to disperse the quantum dots in a polar solvent.

2. Synthesis of silica particles containing QDs

Quantum dot embedded silica (QDES) was synthesized by the stoow method and modified sol - gel chemistry by seed growth.

That is, for the first 30 minutes, the silica seed was grown, and a quantum dot having a ligand acting as a hydroxyl group was injected, followed by further growth for 1 hour and 30 minutes to obtain a quantum dot containing a quantum dot structure having the structure shown in FIG. The kava was synthesized. At this time, the ligand acting as a hydroxyl group on the quantum dot ensures that quantum dots are effectively trapped in the silica matrix instead of absorbing the quantum dots on the surface of the spherical silica.

Example 2

Emission polymer film preparation

A light emitting polymer film containing silica particles containing quantum dots in an organic resin was prepared as follows.

First, ethoxylated trimethylolpropane triacrylate (ETPTA) was used as an organic resin. ETPTA has an index of refraction matched with the refractive index of silica particles in colloidal state, so that the refraction dispersion of light can be removed It has been selected to disperse silica particles containing QDs and also has viscoelasticity, which is an organic resin capable of uniform dispersion of QDs including organic QDs in organic resins. Ethanol dispersed with silica particles containing quantum dots was centrifuged and dried at 60 ° C for 6 hours. And then mixed with ETPTA at a weight ratio of 1:10. At this time, 2-hydroxy-2-methyl-1-phenyl-2-propanone, a photoinitiator, was added. ETPTA film (Q-ETPTA)] having a uniform thickness of 0.4 mm was prepared by applying the mixture to a glass slide and then curing with another glass slide while keeping it in a UV irradiation state for 10 minutes . Thereafter, the light emitting polymer film in which the cured quantum dot-containing silica particles were dispersed was sliced in the form of a thin circular disk of appropriate size.

Example 3

Prepare prototype white LED device

1. Preparation of Silica Particles Containing Qdots

The procedure of Example 1 was repeated to prepare the quantum dot-containing silica particles.

2. Preparation of Emission Polymer Film Containing Silica Particles Containing Qdots

Emitting polymer film (Q-ETPTA) was prepared in the same manner as in Example 2. At this time, the light emitting polymer film emits orange light because the quantum dot included therein is CuInS ₂ / ZnS.

3. Phosphor plate preparation

Considering the orange light emitted by the glass frit composed of SiO ₂ -B ₂ O ₃ -RO (R = Ba, Zn, Mg) component and the light emitting polymer film, Y ₃ Al ₅ O ₁₂ : Ce ³⁺ After the phosphors were mixed, pellet molding was carried out, followed by heat treatment in an atmosphere of 600 ° C. to prepare a phosphor plate (PiG) of the type shown in FIG. 4 (a).

4. White LED device preparation

A white LED device having the structure as shown in the schematic diagram of FIG. 4 (c) was manufactured as follows. That is, a prototype white LED device (PiG + Q-ETPTA film) was fabricated by laminating a light emitting polymer film on a phosphor plate prepared as shown in FIG. 4 (b) and then separating it from a blue LED chip having a wavelength of 450 nm.

Comparative Example 1

A coloring LED element 1 (Y-ETPTA + Q-ETPTA film) was prepared in the same manner as in Example 3, except that the phosphor was dispersed in ETPTA instead of the phosphor plate to prepare YAG: Ce ³⁺ film ).

Comparative Example 2

Prototype Comparative Example by arranging a light emitting polymer film made of YAG: Ce ³⁺ and the quantum dot-containing silica particles prepared in Example 1 on a blue LED chip without using a phosphor plate. White LED element 2 (YAG + QDES conformal LED).

Comparative Example 3

Prototype by arranging a light emitting polymer film made of YAG: Ce ³⁺ and the quantum dot prepared in Example 1 on a blue LED chip without using a phosphor plate. Example 1 A white LED element 2 (YAG + QD conformal LED ).

Experimental Example 1

The photoluminescence (PL) spectrum of the CuInS ₂ / ZnS quantum dots synthesized in Example 1 was analyzed, UV excitation state observation, SEM, TEM observation and EDS spectrum were analyzed, and the results are shown in FIGS. The emission spectrum consisted of a broadband peak at 550 nm to 600 nm excitation at 450 nm.

It can be confirmed that the quantum dot synthesized through FIGS. 2A and 2B has a typical color change corresponding to the size. The quantum dots collected by the precipitation show red emission due to the enlarged size compared to the prepared quantum dots.

As shown in FIGS. 2c and 2d, it can be seen from the very rapid seeding technique that the quantum dot particles of about 3 nm in size are trapped in the spherical silica having a diameter of about 230 nm and embedded in silica particles.

In order to confirm the chemical reaction between the CuInS2 / ZnS quantum dots and the silica, the energy dispersion spectrum (EDS) of the silica particles containing the quantum dots was measured by energy dispersive X-ray spectroscopy, phases were present as distinctive compositions. As seen from the EDS measurement of the QDES sample with QdS, the chemical reaction between the CuInS2 / ZnS quantum dots and the silica was not detected.

Also, it was confirmed that the quantum dots in the TEM image shown in Fig. 2 (d) are almost monodisperse spherical shapes.

Experimental Example 2

A graph showing the thermal stability of the quantum dot (QD) and the quantum dot-containing silica particles (QDES) prepared in Example 1 and the resultant thermal quenching characteristics is shown in FIG.

From FIG. 3, it can be seen that as the temperature increases from RT to 150 DEG C, the emission intensity of the QDES decreases more smoothly than that of the QD. These results show that the quantum dot-containing silica particle structure of the present invention improves the thermal stability of the quantum dots. Generally, quantum dots have low thermal stability, but the oxide formed by the temperature increase diffuses into the core of QD and causes photo-oxidation. Compared to QD, QDES, on the other hand, has a buffered silica matrix that absorbs damage from thermal shock, which can improve QDES stability. However, further improvements may be needed to reduce heat damage to the quantum dots in the LED chip.

Experimental Example 3

In order to confirm whether quantum dot embedded silica can be actually used for a white light emitting device, various prototype LEDs prepared in Example 3, Comparative Example 1 and Comparative Example 2 were subjected to various forward bias current values EL characteristics were measured and analyzed, and the results are shown in Fig.

FIG. 5 shows EL measurement results of Example 3 white LED devices under various forward bias currents. From FIG. 5, it can be seen that the prototype white LED device (PiG + Q-ETPTA film) obtained in Example 3 exhibits excellent optical characteristics . ≪ / RTI > Example 3 White LEDs emit white light with a CIE color coordinate of (0.363, 0.324) and a CRI of 91 under a bias current of 20 mA.

The image inserted in FIG. 5 shows the CIE chromaticity of the white LED device. The coordinates corresponding to the point (a) are those produced by Comparative Example 1, while the coordinates of the point (b) are those made by Comparative Example 2. [

Experimental Example 4

The prototype LED prepared in Example 3, Comparative Example 1 and Comparative Example 2 was tested for the driving time of the LED at 150 mA in order to confirm whether the quantum dot embedded silica could actually be used for the white light emitting device And the thermal stability was measured. The results are shown in FIG.

6 shows that the white LED according to the embodiment of the present invention retains 97% of the initial light emission intensity at a time when 180 minutes have elapsed since the start of emission of white light by applying power, . ≪ / RTI > On the other hand, Comparative Example 2 showed 70% and Comparative Example 3 showed 36%. In the case of Comparative Example 1, thermal stress occurred as the driving time passed, and the luminescence was weakened by about 30% of the initial luminescence intensity.

From the above experimental results, it can be seen that the white LED device including the quantum dot containing silica particles of the present invention, the light emitting polymer film including the silica particles, the phosphor plate and the light emitting polymer film has excellent optical characteristics.

Therefore, it is apparent that the white LED device of the present invention improves the stability of the conventional quantum dot LED and shows a CRI optical characteristic higher than that of a general LED, in a white light emitting device packaging (a phosphor plate + a light emitting polymer film including a quantum dot) . As a result, various high-efficiency white light sources can be realized through the present invention.

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, Various changes and modifications will be possible.

Claims (11)

delete delete delete delete delete delete delete delete A first step of growing a silica seed;
Injecting quantum dots into the reactor of the first grown silica seed; And
And a second step of growing the first grown silica seed so as to include quantum dots.
Dispersing the quantum dot-containing silica particles in an organic resin to prepare a film precursor composition; And
And forming a film with the film precursor composition.
11. The method of claim 10,
Wherein the film precursor composition comprises the quantum dot-containing silica particles and the organic resin in a weight ratio of 1: 5 to 1:30.

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