CN110016334B - Method for improving light emitting efficiency of pc-LEDs by using forward scattering enhanced quantum dot fluorescent powder - Google Patents
Method for improving light emitting efficiency of pc-LEDs by using forward scattering enhanced quantum dot fluorescent powder Download PDFInfo
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Abstract
The invention discloses a method for improving light-emitting efficiency of pc-LEDs by using forward scattering enhanced quantum dot fluorescent powder, wherein the particle diameter d of quantum dot fluorescent powder particles meets the condition that d is more than or equal to 0.1 lambda/pi (lambda is incident light wavelength, and pi is circumferential ratio), a multilayer core-shell structure is adopted, and quantum dot light-emitting layers are contained in the particles. The forward scattering enhancement characteristic enables the forward part light intensity to be larger than the backward part light intensity during light scattering, light intensity loss caused by multiple scattering/absorption due to backward scattering is effectively avoided, light extraction efficiency is improved, and the improvement of spectral efficiency is realized by combining narrow-band light emission of quantum dots.
Description
Technical Field
The invention relates to the technical field of photoelectricity, in particular to a method for enhancing light extraction efficiency of a forward scattering quantum dot fluorescent powder coating in pc-LEDs (light emitting diodes based on fluorescent powder conversion).
Background
Quantum Dots (QDs), which are essentially a nanoscale semiconductor material, typically have a particle size in the range of 1nm to 10 nm. Because of the function of quantum confinement, the energy band structure is not continuous, but the energy level structure is discrete, the optical behavior of the quantum confinement quantum. Just because of the quantum size effect, the fluorescent powder can be used as a fluorescent powder material, and the same material can realize the luminescence spectra of different wave bands only by changing the particle size of the same material. It has a high quantum yield, despite its simple preparation and low cost.
In pc-LEDs, compared with traditional micron-sized fluorescent powder, quantum dots have very narrow half-wave peak width and high color purity, and can greatly exceed the color gamut range of NTSC. Therefore, the LED based on the conversion of the multicolor quantum dots can obtain very high color rendering performance, and the Ra and R9 values of the LED can exceed 95 and are almost close to 100. The quantum dot coating is similar to the traditional fluorescent powder coating, photons emitted by the absorption chip are converted to emit photons with required wave bands, and the shape concentration of the quantum dot coating also influences the light color quality and the light effect. Usually, quantum dots and silica gel are uniformly mixed by means of a certain carrier material to obtain stable colloid, and the stable colloid is coated to prepare a colloid quantum dot layer. In contrast, in conventional white pc-LEDs packages, the phosphor (e.g., YAG: Ce3+, etc.) with a broadband emission spectrum suffers additional loss of Luminous Efficacy (LER) due to low visual sensitivity of its long-red and far-red components of the spectrum, i.e., loss of white spectral efficiency; in order to improve luminous efficiency LER, quantum dot fluorescent powder (QDs) with a peak value positioned in a wavelength region with high visual sensitivity and a narrower emission bandwidth (FWHM is 30nm) is a good choice, and the wavelength is adjusted to a green and red wave band with the most sensitive human vision by utilizing the narrow-band emission spectrum and the wavelength adjustable characteristic of the quantum dot fluorescent powder, so that high visual response can be obtained; meanwhile, the spectral bandwidth is reduced, the radiation energy is concentrated in the range with high visual sensitivity, and the low visual sensitivity luminous efficiency loss caused by long red light and far red light components of the traditional fluorescent powder is reduced. For plant lighting, pc-LEDs are used for packaging, and corresponding spectrums can be adjusted to fall in red and blue effective areas.
Therefore, quantum dot conversion luminescence is an important development trend of illumination and display, and has a wide application prospect.
Disclosure of Invention
The invention aims to solve the problem of how to further improve the light extraction efficiency coating of the quantum dot fluorescent powder. Because the size of the nano quantum dot is too small, the nano quantum dot is generally smaller than 12nm, Rayleigh scattering is easily caused to visible light, backward scattering is strong, and light intensity loss is easily caused. Experiments show that for a common blue LED chip, quantum dots smaller than 12nm cause light intensity loss, and the forward scattering enhancement particle size is more than 15 nm. Therefore, the invention provides the enhanced core-shell Quantum dot (FMS-QDs) fluorescent powder based on the Forward Scattering property, namely, a coating layer is added on the surface of a Quantum dot luminescent layer, or a Quantum luminescent layer grows on seed crystals, the Quantum dot fluorescent powder obtained after the size is increased is uniformly dispersed into a medium and coated on the surface of an LED chip in the light-emitting direction, the Forward Scattering enhancement and narrow-band luminescence are realized, the light-emitting efficiency can be improved, and the spectrum is fine and adjustable.
The invention provides a method for improving the light emitting efficiency of pc-LEDs by using forward scattering enhanced quantum dot fluorescent powder.
The technical scheme of the invention is as follows:
a method for improving the light-emitting efficiency of pc-LEDs by using forward scattering enhanced quantum dot fluorescent powder is characterized in that quantum dot fluorescent powder particles are of a multilayer core-shell structure, comprise quantum dot light-emitting layers and have narrow-band light-emitting spectrums after being excited; the particle size d is more than or equal to 0.1 lambda/pi (lambda is the wavelength of incident light, pi is the circumferential ratio), mie scattering can occur, and the forward scattering of transmitted light can be enhanced on the particle size; the quantum dot fluorescent powder is used for a pc-LED packaging coating and is coated on the surface of an LED chip in the light emitting direction to form a quantum dot fluorescent powder coating.
The multilayer core-shell structure is used for improving the particle size of particles, Mie scattering occurs when visible light meets quantum dot fluorescent powder particles (the particle size d is more than or equal to 0.1 lambda/pi) which are wrapped and thickened, Rayleigh scattering occurs when the visible light meets the quantum dot fluorescent powder particles with common sizes (below 12 nm), the light intensity of a forward part is larger than that of a backward part when the light ray is subjected to Mie scattering, and the forward and backward light intensities are equal when the Rayleigh scattering occurs.
The multilayer core-shell structure comprises a structure of a quantum dot light-emitting layer/a cladding layer, or a structure of a seed crystal/a quantum dot light-emitting layer/a cladding layer; the quantum dot light-emitting layer and the cladding layer are one or more layers.
The multilayer core-shell quantum dot light-emitting layer is one or more of II-VI compounds of CdSe, ZnS, CdTe, ZnO, ZnTe, CdS, MgO, CaO, MgS, CaS, MgSe, CaSe, MgTe and CaTe, or part of other compounds MoSe2、In2O3One or a combination of (a).
The multilayer core-shell quantum dot can be two layers, three layers, four layers or even more layers. One method is that the inner core is used as a luminous layer, the size is 2-10 nm, and the thickness range of the coating layer on the outer surface is more than 10 nm; the other is that the inner core is not used as a luminous layer, the size is more than 2nm, the thickness of the luminous layer coated subsequently is 2-10 nm, and the thickness of the coating layer on the outer surface is more than 8 nm; wherein the wavelength satisfies the particle size d is more than or equal to 0.1 lambda/pi.
The coating material comprises a coating layer formed by CdSe, ZnS, CdTe, ZnO, ZnTe, CdS, MgO, CaO, MgS, CaS, MgSe, CaSe, MgTe and CaTe of II-VI groups, and also comprises other oxides of SiO2、TiO2、ZrO2、ITO、In2O3、SnO2. The oxide is coated on the quantum dots in a hydrolysis mode, and the obtained quantum dot fluorescent powder particles need to meet the requirement that the particle size is in a nanometer size, light Mie scattering can be caused, and forward scattering of transmitted light is enhanced. If the common blue light gallium nitride chip is coated, the integral grain diameter d is more than or equal to 15nm, and the grain diameter d is more than or equal to 24.9nm for red light.
The quantum dot fluorescent powder with forward scattering of light is matched with a dispersing agent and uniformly dispersed into a powder preparation adhesive, the shape of a light extraction layer is simply controlled, so that the light distribution can be improved to a certain extent, and in order to further improve the uniformity, the dispersing agent and the light dispersing agent are added into the light extraction layer. Common inorganic light diffusant silicon dioxide materials and organic dispersant tetrahydrofuran; uniformly mixing the QDs fluorescent powder and the powder mixing glue in a proportion of 1-35% of the adjustable mass fraction; the QDs phosphor can also be mixed with other phosphors in different ratios.
The powder mixing glue is one or a combination of more of silica gel, epoxy resin, polymethyl methacrylate (PMMA), Polycarbonate (PC) or photosensitive glue; the photosensitive glue comprises the following three types of negative photosensitive glue: SBQ photosensitive glue (polyvinyl alcohol cyclic acetal styryl pyridinium resin photosensitive glue), SBQ-PVA + high molecular emulsion + acrylic ester or organic styryl pyridinium resin photosensitive glue system or a combination of a plurality of systems; sensitizer + film-forming agent, i.e. photosensitizer + polymer compound, wherein the sensitizer is one or more of dichromate, chromate, diazo compound or azido compound; the film forming agent is one or more of polyvinyl alcohol (PVA), gum arabic, polyimide or polyvinyl acetate emulsion; and the macromolecular compound type with photosensitive group mainly comprises one or a combination of more of polyvinyl alcohol cinnamate, polyvinyl alcohol cinnamylidene acetate, polyvinyl oxyethyl cinnamate, polyvinylpyrrolidone or polyvinyl alcohol-p-azidobenzoate (PVAB).
The preparation method of the quantum dot fluorescent powder coating can be one of a dispensing method, an electrophoresis method, a spraying method, a dipping method, a spin coating method, a precipitation method and a printing method, or a combination of two or more methods.
The quantum dot fluorescent powder is used for packaging pc-LEDs, and the LEDs are single LED chips, or multiple LED chip groups on the same substrate, or a whole Wafer (Wafer).
The quantum dot fluorescent powder coating, namely the fluorescent powder coating coated on the light emitting surface of the LED, is in a mode of directly contacting the light emitting surface of the LED chip or is in a remote coating structure of the light emitting surface away from the light emitting surface of the LED chip.
The quantum dot fluorescent powder coating is naturally cured, heated and cured or photo-cured according to different curing modes of the powder mixing glue.
Drawings
FIG. 1 shows that in the quantum dot core-shell structure fluorescent powder based on forward scattering, the central 1 is a seed crystal, the second 2 is a quantum dot light emitting layer, the outermost 3 is a coating layer, the light wavelength is lambda, and the overall particle size d satisfies that d is more than or equal to 0.1 lambda/pi;
FIG. 2 shows that when light is scattered by particles, the light intensity is distributed with the angle, x is the direction of light transmission, the forward light intensity is greater than the backward light intensity (Mie scattering), and the particle diameter d is greater than or equal to 0.1 lambda/pi;
FIG. 3 shows that when light is scattered when it encounters a particle, the light intensity is distributed with the angle, x is the direction of light transmission, the forward light intensity is greater than the backward light intensity (Mie scattering), and the particle diameter d >0.1 lambda/pi;
FIG. 4 shows the distribution of light intensity with angle when the light encounters the scattering of the particles, z is the direction from which the light is transmitted, the forward light intensity is equal to the backward light intensity (Rayleigh scattering), and the particle size d is less than 0.1 lambda/pi;
fig. 5 shows that the quantum dot phosphor and other micron-sized phosphors are mixed and coated on the surface of a chip, wherein 1 is the chip, 2 is a multilayer quantum dot phosphor, and 3 is the other micron-sized phosphors.
Detailed Description
The invention is further described below with reference to the following figures and examples:
example 1
Taking 20ml of 0.05mol/L zinc acetate and 0.05mol/L sodium sulfide aqueous solution for hydrothermal reaction, generating ZnS crystal nucleus at 75 ℃, carrying out time control of an Ostwald curing process, obtaining ZnS seed crystal of about 7nm after 5 hours, then adopting an LSS three-phase system solvothermal method, taking 5mmol cadmium acetate, 5mmol selenium powder and adding 100mmol ethanol and 100mmol sodium oleate, stirring for 30 minutes, adding into the seed crystal solution, keeping for 1 hour at 85 ℃ under the stirring condition, growing a CdSe quantum luminescent layer of about 4nm, then taking zinc acetate and sodium sulfide, preparing a ZnS coating layer of about 5nm outside the zinc acetate and sodium sulfide, forming a ZnS/CdSe/ZnS multilayer core-shell structure shown in figure 1, carrying out centrifugal separation on products obtained by the reaction, washing precipitates with acetone and deionized water, then drying the precipitates in vacuum at 45 ℃, the QDs fluorescent powder with the particle size of about 16nm is obtained, and the particle size has a relation d of 0.107 lambda/pi (lambda of 470nm) with the blue light wavelength. And finally, uniformly dispersing 0.1g of product into 1g of silica gel according to the mass ratio of the powder to the gel of 1:10, coating the fluorescent powder slurry on the light emitting surface of the blue LED chip by adopting a dispensing method, heating the blue LED chip by using a drying oven (at 150 ℃) for 2 hours, and obtaining the light intensity distribution of the fluorescent powder particles when the fluorescent powder particles scatter light as shown in figure 2 through experiments.
Example 2
The dosage is as in example 1, using hydrothermal reaction of zinc acetate and sodium sulfide in water solution to generate ZnS seed crystal, after controlling time of Ostwald ripening process, obtaining ZnS seed crystal of 7nm after 5 hours, then using LSS three-phase system solvothermal method, as example 1 operation, original prolonging reaction time about 1 hour, cadmium acetate and selenium powder to prepare CdSe quantum luminescent layer with about 5nm particle size, then preparing a ZnS coating layer with about 5nm outside the CdSe quantum luminescent layer, forming ZnS/CdSe/ZnS multilayer core-shell structure particle, centrifuging, filtering and drying to obtain QDs fluorescent powder with particle size of about 17nm, the particle size and blue light wavelength having relation d 0.13 lambda/pi. And finally, uniformly mixing the powder and the glue in a mass ratio of 1:15, vacuumizing by a defoaming machine to remove bubbles to obtain fluorescent powder slurry, coating the fluorescent powder slurry on the surface of the chip by a dispensing method, and heating by a drying oven (150 ℃) for 2 hours to obtain a cured fluorescent powder layer.
Example 3
After ZnS seed crystals were prepared according to example 1, the particle size was changed by extending the reaction time by about one hour based on example 2 by LSS three-phase solvothermal method or the like. After a CdSe quantum light emitting layer with the particle size of about 6nm is prepared by cadmium acetate and selenium powder, a ZnS coating layer with the particle size of about 5nm is prepared outside the CdSe quantum light emitting layer, the CdSe quantum light emitting layer is centrifuged, filtered and dried to obtain QDs fluorescent powder with the particle size of ZnS/CdSe/ZnS being about 18nm, the particle size of the QDs fluorescent powder is related to the wavelength of blue light, and d is 0.12 lambda/pi, and the subsequent operation is consistent with that of the embodiment 1 and is coated on a chip.
Example 4
After ZnS seed crystal is prepared according to the method, an LSS three-phase system solvothermal method is adopted, the reaction time is controlled, the particle size is changed, a CdSe quantum light-emitting layer with the particle size of about 7nm is prepared from cadmium acetate and selenium powder, a ZnS coating layer is prepared outside the ZnS seed crystal, centrifugation, filtration and drying are carried out, and the QDs fluorescent powder with the particle size of about 19nm is obtained, wherein the particle size has a relation d to the blue light wavelength of 0.126 lambda/pi. Weighing quantum dot fluorescent powder and powder preparation glue according to various different proportions, uniformly mixing the quantum dot fluorescent powder and the powder preparation glue, vacuumizing the mixed powder slurry by using a vacuum defoaming machine, and removing bubbles to obtain fluorescent powder slurry; uniformly spraying silica gel with a certain thickness on the surface of the glass by using a spray gun to serve as a light-pumping isolation layer, respectively coating fluorescent powder slurries with different mass powder-gel ratios on the layer, and drying the layer for 2 hours in a drying oven by heating (150 ℃) to obtain a cured fluorescent powder layer.
Example 5
After the ZnS seed crystal is prepared according to the method, the LSS three-phase system solvothermal method is adopted, the reaction temperature or time is controlled, and the particle size is changed. Preparing CdSe quantum luminescent layer with particle size of about 8nm from cadmium acetate and selenium powder, preparing a ZnS coating layer outside the CdSe quantum luminescent layer, centrifuging, filtering and drying to obtain the QDs fluorescent powder of ZnS/CdSe/ZnS with particle size of about 20nm, wherein d is 0.133 lambda/pi (lambda is 470nm) with the relationship between the particle size and blue light wavelength. The subsequent operation was identical to example 1.
Example 6
After ZnS seed crystal is prepared according to the method, an LSS three-phase solvothermal method is adopted, except that the reaction temperature or time is controlled, and the particle size is changed. And (2) reacting cadmium acetate with sodium sulfide to prepare a CdS quantum luminescent layer of about 7nm, wrapping a ZnS shell layer of 7nm to obtain a ZnS/CdS/ZnS multilayer core-shell structure, and centrifugally drying to obtain QDs fluorescent powder with the particle size of 21nm, wherein the particle size has a relation d to blue light wavelength of 0.14 lambda/pi. The subsequent operation was identical to example 1.
Example 7
Respectively taking 5mmol of precursors of cadmium, selenium, zinc and sulfur, heating and dissolving at 40 ℃ to obtain a solution, and preparing the water-soluble CdSe/ZnS core-shell quantum dots meeting the requirement of the luminescence wavelength by using an LSS three-phase solvothermal method as in example 1, wherein the size of the water-soluble CdSe/ZnS core-shell quantum dots is below 12nm, and the backward direction of Rayleigh scattering isThe components are larger, and the conventional fluorescent powder (such as YAG: Ce3+) SiO is further adopted2The film-coated sol method adopts tetraethoxysilane (TE0S) as a silicon source to realize the SiO on the surface of the CdSe/ZnS quantum dot through hydrolysis reaction2After the membrane is coated, the mixture is centrifuged, filtered and dried to obtain CdSe/ZnS/SiO with the size of about 22nm2The particle size of the quantum dot core-shell fluorescent powder has a relation d to the wavelength of blue light of 0.146 lambda/pi (lambda is 470 nm). The rest of the operation was the same as in example 1.
Example 8
In accordance with the sequence of operations before the above examples, except that the cladding layer was changed to tetrabutyl titanate Ti (OC)4H9)4The TiO on the surface of the CdSe/ZnS quantum dot is a titanium source and is realized by hydrolysis reaction2After the film is coated, the film is centrifugally dried, and CdSe/ZnS/TiO with the size of 23nm can be obtained2Quantum dot core-shell, d 0.15 λ/pi (λ 470 nm). Finally, 0.1g of quantum dot fluorescent powder (or the up-conversion ultraviolet fluorescent powder and red powder are mixed), 0.4ml of photosensitive resist (prepared by mixing PVA solution and ADC solution) and uniformly mixing the two; and coating the phosphor powder slurry mixed with the photosensitive resist on the surface of the LED chip by adopting a dispensing method, exposing for 0.75ms and finishing development.
Example 9
The precursor is consistent with the embodiment 1, after ZnS seed crystal is prepared, an LSS three-phase solvothermal method and the like are utilized to prepare a water-soluble CdSe quantum dot luminescent layer meeting the luminescent wavelength requirement, the size is below 12nm, the backward component of Rayleigh scattering is larger, and the traditional fluorescent powder (such as YAG: Ce3+) SiO is further adopted2The film-coated sol method adopts tetraethoxysilane (TE0S) as a silicon source to realize the SiO on the surface of the ZnS/CdSe quantum dot through hydrolysis reaction2The film is centrifuged after controlling the thickness, filtered and dried to obtain ZnS/CdSe/SiO with the size of about 24nm2The quantum dot core-shell has a relationship between the particle size and the blue light wavelength, and d is 0.16 lambda/pi (lambda is 470 nm). The rest of the operation was the same as in example 1.
Example 10
SiO in example 102Modified to TiO2With tetrabutyl titanate Ti (OC)4H9)4Is a titanium source to obtain CdTe/ZnS/TiO2And (4) quantum dot core shell. The rest of the operation was the same as in example 1.
Example 11
Respectively taking 5mmol of precursors of cadmium, tellurium, zinc and sulfur, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, controlling the synthesis reaction temperature at 85 ℃, controlling the reaction time, firstly preparing CdTe seed crystals with the particle size of 8nm, wrapping quantum dots ZnS with the thickness of about 7nm, and then wrapping a layer of SiO 10nm in a hydrolysis mode and the like2To obtain CdTe/ZnS/SiO with the thickness of 25nm2The quantum dot core shell has a relationship between the particle size and the wavelength of blue light, namely d is 0.167 lambda/pi (lambda is 470 nm). The rest of the operation was the same as in example 1.
Example 12
SiO in the above example2Modified to TiO2With tetrabutyl titanate Ti (OC)4H9)4Is a titanium source to obtain 25 nanometer CdTe/ZnS/TiO2And (4) quantum dot core shell. The rest of the operation was the same as in example 1.
Example 13
Respectively taking precursors of 5mmol of cadmium, tellurium, zinc and sulfur, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvent method, synthesizing and reacting at 85 ℃, controlling the reaction time, firstly preparing CdTe seed crystals of 8nm, wrapping quantum dot layers of ZnS about 7nm, and wrapping a SiO layer of 11nm in a hydrolysis mode2To obtain CdTe/ZnS/SiO with the thickness of 26nm2Quantum dot core-shell, d 0.173 λ/pi (λ 470 nm). The rest of the operation was the same as in example 1.
Example 14
SiO in the above example2Modified to TiO2To obtain CdTe/ZnS/TiO2And (4) quantum dot core shell. The rest of the operation was the same as in example 1.
Example 15
Respectively taking 5mmol of precursors of cadmium, tellurium, zinc and oxygen, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, synthesizing and reacting at 85 ℃, controlling the reaction time, firstly preparing 7nm CdTe seed crystal, wrapping a quantum dot layer ZnO of about 7nm, and wrapping a layer of 13nm SiO by a hydrolysis mode2To obtain CdTe/ZnO/Si with the thickness of 27nmO2Quantum dot core-shell, d 0.18 λ/pi (λ 470 nm). The rest of the operation was the same as in example 1.
Example 16
SiO in the above example2Modified to TiO2To obtain CdTe/ZnO/TiO2And (4) quantum dot core shell. The rest of the operation was the same as in example 1.
Example 17
Respectively taking 5mmol of precursors of cadmium, tellurium, zinc and oxygen, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, controlling the synthesis reaction temperature at 85 ℃, controlling the reaction time, firstly preparing ZnO seed crystals with the particle size of 8nm, coating CdTe of quantum dots with the ZnO seed crystals with the particle size of 8nm, and coating a SiO layer with the particle size of 12nm in a hydrolysis mode2To obtain ZnO/CdTe/SiO with the thickness of 28nm2Quantum dot core-shell, d 0.187 λ/π (λ 470 nm). The rest of the operation was the same as in example 1.
Example 18
SiO in the above example2Modified to TiO2To obtain ZnO/CdTe/TiO2And (4) quantum dot core shell. The rest of the operation was the same as in example 1.
Example 19
Respectively taking 5mmol of precursors of cadmium, sulfur, zinc and oxygen, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, controlling the reaction temperature at 85 ℃, firstly preparing 6nm CdS seed crystals, wrapping 8nm quantum dot layer ZnO, and then coating a layer of 10nm SiO by hydrolysis2Obtaining CdS/ZnO/SiO with the thickness of 24nm2And (4) quantum dot core shell. The rest of the operation was the same as in example 1.
Example 20
SiO in the above example2Modified to TiO2To obtain CdS/ZnO/TiO2And (4) quantum dot core shell. The rest of the operation was the same as in example 1.
Example 21
Respectively taking 5mmol of precursors of cadmium, zinc and oxygen, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, controlling the reaction temperature at 85 ℃, firstly preparing CdO seed crystals with the diameter of 8nm, and wrapping quantum dot layers with the diameter of about 7nmZnO, coating a layer of SiO by hydrolysis2To obtain CdO/ZnO/SiO with the thickness of 25nm2And (4) quantum dot core shell. The rest of the operation was the same as in example 1.
Example 22
SiO in the above example2Modified to TiO2To obtain CdO/ZnO/TiO2And (4) quantum dot core shell. The rest of the operation was the same as in example 1.
Example 23
Respectively taking 5mmol of precursors of cadmium, zinc and oxygen, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, controlling the synthesis reaction temperature at 85 ℃, controlling the reaction time, firstly preparing ZnO seed crystals with the particle size of more than 6nm, wrapping a quantum dot luminescent layer CdO with the particle size of more than 3nm, and wrapping a layer of SiO with the particle size of 17nm in a hydrolysis mode2Obtaining ZnO/CdO/SiO with the thickness of 26nm2And (4) quantum dot core shell. The rest of the operation was the same as in example 1.
Example 24
SiO in the above example2Modified to TiO2To obtain ZnO/CdO/TiO2And (4) quantum dot core shell. The rest of the operation was the same as in example 1.
Example 25
Respectively taking 5mmol of precursors of cadmium, zinc and sulfur, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, controlling the synthesis reaction temperature at 85 ℃, firstly preparing ZnS seed crystal of 7nm, wrapping a quantum dot luminescent layer CdS of 4nm, and wrapping a SiO layer of 16nm in a hydrolysis mode2Obtaining ZnS/CdS/SiO with the thickness of 27nm2The quantum dot core shell has a relation d of 0.121 lambda/pi between the particle size and the wavelength of blue light (lambda of 470 nm). The rest of the operation was the same as in example 1.
Example 26
SiO as in example 252By substitution with TiO2And increasing the thickness of the coating layer to obtain ZnS/CdS/TiO2The total particle size of the quantum dot fluorescent powder is 30nm, and a red light LED chip is adopted, wherein the particle size has a relation d of 0.121 lambda/pi with red light wavelength (lambda of 775 nm). And coated onto the red LED chip surface according to the procedure of example 1.
Example 27
The intermediate light-emitting layer in example 25 was replaced with one of CdSe, CdTe, ZnO, ZnTe, CdS, MgO, CaO, MgS, CaS, MgSe, CaSe, MgTe, and CaTe using different precursors, and the thickness of the cladding layer was controlled to obtain ZnS/light-emitting layer/SiO2The total particle size of the quantum dot fluorescent powder is 30nm, and the particle size of the red LED chip is related to the red wavelength (lambda is 775nm) by d is 0.121 lambda/pi. And coated onto the red LED chip surface according to the procedure of example 1.
Example 28
Respectively taking 5mmol of precursors of cadmium, zinc and sulfur, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, controlling the synthesis reaction temperature at 85 ℃, firstly preparing ZnS seed crystal of 8nm, wrapping a quantum dot luminescent layer CdS of 4nm, and wrapping a SiO layer with the thickness of 17nm in a hydrolysis mode2Obtaining ZnS/CdS/SiO with the thickness of 31nm2The quantum dot core shell has a relationship between the particle size and the blue light wavelength (lambda 775nm), and d is 0.125 lambda/pi. The red LED chip was taken and the rest of the operation was the same as in example 1.
Example 29
SiO in the above example2Modified to TiO2The growth time is shortened, the ZnS layer is 8nm, the CdS layer is 4nm, and a layer of TiO with the thickness of 8nm is coated2Obtaining ZnS/CdS/TiO with the thickness of 20nm2The quantum dot core shell is prepared by taking a purple light LED chip, coating the particle size of the purple light LED chip and the purple light wavelength lambda of the purple light LED chip, wherein d is 0.157 lambda/pi, and coating the purple light LED chip on the surface according to the operation of example 1.
Example 30
Respectively taking 5mmol of precursors of cadmium, zinc and sulfur, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, controlling the synthesis reaction temperature at 85 ℃, firstly preparing ZnS seed crystal of 7nm, wrapping a quantum dot luminescent layer CdS of 6nm, and then wrapping a SiO layer of 8nm in a hydrolysis mode2Obtaining ZnS/CdS/SiO with the thickness of 21nm2The particle size is related to the violet wavelength λ of 400nm, and d is 0.164 λ/π. The rest of the operation was the same as in example 1.
Example 31
The above embodimentSiO of (2)2Modified to TiO2Obtaining 21nm ZnS/CdS/TiO2After the quantum dot phosphor, the violet LED chip was coated according to the procedure of example 1.
Example 32
Respectively taking precursors of 5mmol of selenium, molybdenum, sulfur and zinc, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, controlling the reaction temperature at 85 ℃, firstly preparing ZnS seed crystals with the particle size of 7nm, and coating a 6nm quantum dot light-emitting layer MoSe2Then coating a layer of 8nm SiO by means of hydrolysis2Obtaining ZnS/MoSe with the thickness of 21nm2/SiO2The particle size has a relationship of d 0.164 λ/π to violet light wavelength λ 400 nm. The rest of the operation was the same as in example 1.
Example 33
Respectively taking precursors of 5mmol of indium, zinc, sulfur and selenium, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, controlling the reaction time at 85 ℃, firstly preparing ZnS seed crystals of 7nm, and wrapping a quantum dot light-emitting layer In of 6nm2Se3Then coating a layer of 8nm SiO by means of hydrolysis2Obtaining ZnS/In with a thickness of 21nm2Se3/SiO2The particle size is related to the violet wavelength λ of 400nm, and d is 0.164 λ/π. The rest of the operation was the same as in example 1.
Example 34
Respectively taking 5mmol of precursors of cadmium, zinc and sulfur, heating and dissolving at 40 ℃ to obtain a solution, adopting an LSS three-phase solvothermal method, controlling the reaction temperature at 85 ℃, firstly preparing a CdS seed crystal of 8nm, wrapping a quantum dot layer ZnS of 6nm, and wrapping a SiO seed crystal of 8nm in a hydrolysis mode2Obtaining CdS/ZnS/SiO with the thickness of 22nm2The quantum dot core shell has a particle size and a violet wavelength lambda of 400nm, and d is 0.173 lambda/pi. The rest of the operation was the same as in example 1.
Example 35
SiO as in example 312Modified to TiO2Obtaining CdS/ZnS/TiO with the size of 22nm2After the quantum dot phosphor was applied, the violet LED chip was obtained, and the rest of the operation was the same as in example 1。
Example 36
Based on the above hydrolysis coating example, 4 layers of core-shell structure are adopted, and TiO in the third layer2(SiO2) Coating a layer of SiO outside by hydrolysis2(TiO2) Or other oxides to further increase the core-shell thickness. The resulting phosphor was applied to an LED chip as in example 1.
Example 37
The quantum dot phosphor and the micron phosphor of the above example are mixed together in a mass ratio of 1:1, and made into a slurry in the manner of example 1 to be coated on a chip, so as to form a coating layer as shown in fig. 5.
Claims (10)
1. A method for improving the light emitting efficiency of pc-LEDs by using forward scattering enhanced quantum dot fluorescent powder is characterized in that:
(1) the quantum dot fluorescent powder particles are of a multilayer core-shell structure, comprise quantum dot light emitting layers and have narrow-band light emitting spectrums; the particle diameter d is more than or equal to 0.1 lambda/pi, lambda is the incident light wavelength, and pi is the circumference ratio;
(2) the quantum dot fluorescent powder is used for a coating of pc-LED packaging, is coated on the surface of an LED chip in the light emitting direction, causes Mie scattering, and enhances the forward scattering of transmitted light because the light intensity of a forward part is higher than that of a backward part in scattering;
in the characteristic (2), the coating of the common blue-light gallium nitride chip needs to meet the requirement that the overall grain diameter d is more than or equal to 15nm, and the coating of the common blue-light gallium nitride chip needs to meet the requirement that the overall grain diameter d is more than or equal to 24.9 nm.
2. The method of claim 1 for improving the light extraction efficiency of pc-LEDs by using forward scattering enhanced quantum dot phosphors, wherein: the multilayer core-shell structure is a structure of a quantum dot light-emitting layer/a cladding layer, or a structure of a seed crystal/a quantum dot light-emitting layer, or a structure of the seed crystal/the quantum dot light-emitting layer/the cladding layer; the quantum dot light-emitting layer and the cladding layer are one or more layers; the thickness of the quantum dot light emitting layer is 2-10 nm.
3. According to claimThe method for improving the light emitting efficiency of pc-LEDs by using the forward scattering enhanced quantum dot fluorescent powder is characterized in that: the quantum dot light emitting layer is II-VI compound selected from one or more of CdSe, ZnS, CdTe, ZnO, ZnTe, CdS, MgO, CaO, MgS, CaS, MgSe, CaSe, MgTe and CaTe, or MoSe, other element compound2、In2Se3One or a combination of (a).
4. The method of claim 1 for improving the light extraction efficiency of pc-LEDs by using forward scattering enhanced quantum dot phosphors, wherein: the coating layer of the multilayer core-shell structure is a II-VI compound or other oxide SiO2、TiO2、ZrO2、ITO、In2O3、SnO2One or more combinations of (a); the particle diameter d of the coated particles is more than or equal to 0.1 lambda/pi.
5. The method of claim 1 for improving the light extraction efficiency of pc-LEDs by using forward scattering enhanced quantum dot phosphors, wherein: the coating component is a mixture obtained by dispersing the quantum dot fluorescent powder into the powder preparation glue, or a mixture obtained by mixing and dispersing the quantum dot fluorescent powder and other fluorescent powder into the powder preparation glue.
6. The method of claim 1 for improving the light extraction efficiency of pc-LEDs by using forward scattering enhanced quantum dot phosphors, wherein: the coating mode is traditional glue dispensing, electrophoresis, spraying, dipping, spin coating, deposition and printing.
7. The method of claim 1 for improving the light extraction efficiency of pc-LEDs by using forward scattering enhanced quantum dot phosphors, wherein: the surface of the LED chip in the light emergent direction is the surface of the chip or any surface which is away from the chip and is along the light emergent direction.
8. The method of claim 1 for improving the light extraction efficiency of pc-LEDs by using forward scattering enhanced quantum dot phosphors, wherein: the LED chip is an organic or inorganic light emitting diode; the light emitting diode chip is a single light emitting diode chip, or a plurality of light emitting diode chip groups on the same substrate, or a whole wafer.
9. The method of claim 5 for improving the light extraction efficiency of pc-LEDs by using the forward scattering enhanced quantum dot phosphor, wherein: the powder preparation glue is one of thermosetting glue and photosensitive glue; the thermosetting adhesive is one or a combination of silica gel, epoxy resin, polymethyl methacrylate (PMMA) and Polycarbonate (PC) thermosetting adhesive; the photosensitive colloid is three types of negative photosensitive glue: the preparation method comprises the following steps of (1) preparing a photosensitizer and a film-forming agent, namely a photosensitizer and a high molecular compound, wherein the photosensitizer is one or a combination of more of dichromate, chromate, diazo compounds or azido compounds, and the film-forming agent is one or a combination of more of polyvinyl alcohol (PVA), gum arabic, polyimide or polyvinyl acetate emulsion; ② a high molecular compound type with photosensitive group, which is selected from one or more of polyvinyl alcohol cinnamate, polyvinyl alcohol cinnamylidene acetate, polyvinyl oxyethyl cinnamate, polyvinylpyrrolidone or polyvinyl alcohol-p-azidobenzoate (PVAB); SBQ photosensitive glue, namely one or a combination of a plurality of polyvinyl alcohol cyclic acetal styryl pyridinium resin photosensitive glue, SBQ-PVA + high molecular emulsion + acrylic ester or organic styryl pyridinium resin photosensitive glue systems; the photosensitive glue is one or more of the combination of the above.
10. The method of claim 5 for improving the light extraction efficiency of pc-LEDs by using the forward scattering enhanced quantum dot phosphor, wherein: the curing mode of the powder mixing glue is heating curing, natural curing or photosensitive curing according to different types of the powder mixing glue.
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