Application Of Quantum Dots And Their Composites In Pc-LEDs Packaging

As the mainstream of the lighting field,LED has the characteristics of environmental protection,energy saving,low cost,long life and so on.Among them,phosphor-converted LEDs（pc-LEDs,phosphor-converted LEDs）are the mainstream way to realize white light illumination.In the packaging process of pc-LEDs,phosphors are usually coated on the LED chips as down-conversion materials.Traditional phosphor materials have some shortcomings,such as wide emission spectrum,low fluorescence quantum efficiency,etc.In contrast,quantum dot fluorescent materials have extremely narrow fluorescence emission spectrum,high internal quantum efficiency,and extremely wide absorption.The advantages of spectrum and spectral color purity are high.The use of quantum dot materials as down-conversion materials in the packaging of pc-LEDs can make up for the lack of red light band in the white light pc-LEDs combined with traditional blue LED chips and yellow phosphors,and can adjust the emission light in the entire visible light band.It can achieve high color purity and color rendering index due to its narrow emission spectrum half-width.In this paper,Cs Pb X₃（X=Cl,Br,I）quantum dots were prepared by the optimized hot injection method,and they were coated with Si O₂ to improve the stability of the quantum dots.The obtained quantum dots were characterized and analyzed;using remote The packaging process encapsulates the synthesized Cs Pb Br_1.2I_1.8@Si O₂ on a blue LED chip to make a red light pc-LEDs device that can be used for plant growth.The Cs Pb Br_1.2I_1.8@Si O₂ is used with the yellow phosphor YAG:Ce³⁺The remote process is packaged on blue LED chips to produce white light pc-LEDs devices that can be used for lighting,and their color rendering properties are improved.（1）Synthesis of Cs Pb X₃（X=Cl,Br,I）quantum dots:using the optimized hot injection method,Cs₂CO₃,oleic acid and octadecene were stirred at 150°C to completely dissolve to obtain cesium oleate precursor;Pb X₂（X=Cl,Br,I）and octadecene were placed in a three-necked flask,oleic acid and oleylamine were added at 120°C,and then stirred to dissolve completely.The temperature was raised to 140-180°C,and 0.4 ml of cesium oleate precursor solution was taken.Quickly inject,take out the ice-water bath after 5-10 s and let it rapidly cool to room temperature to obtain Cs Pb X₃（X=Cl,Br,I）quantum dots.TEM characterization results show that the particle size distribution of Cs Pb Br₃ quantum dots prepared at 180℃for 5 s is 7.99 nm±0.82 nm uniform;the characterization results of fluorescence spectrophotometer show that the emission peak wavelength is 530 nm,and the full width at half maximum is about 22 nm,the absorption spectra of the prepared Cs Pb Br₃ quantum dots are very broad,and the full width at half maximum is very narrow.When the temperature increases from 140-180℃,the emission peak of the prepared Cs Pb Br₃ also red-shifts from 518 nm to 530 nm,while its full width at half maximum is almost unchanged,only about 22 nm.By adjusting the concentration and composition of halide ions,the emission spectrum can be adjusted from 480 to 660nm,and its half-height width is also found to increase from 19 nm to 26 nm.（2）Silica-wrapped Cs Pb X₃（X=Cl,Br,I）quantum dots:Based on the prepared Cs Pb X₃（X=Cl,Br,I）quantum dots,Si O₂ was synthesized by hydrolysis using APTES at room temperature for 30 min.The performance of the synthesized Cs Pb Br₃@Si O₂ was characterized.Compared with Cs Pb Br₃,the former can still maintain 45%of the initial fluorescence intensity after being exposed to air for 72 h,while the latter’s fluorescence intensity is only 10%of the initial fluorescence intensity after 6 h exposure.In addition,it is also verified that the water,polar solvents,and thermal stability of Cs Pb Br₃@Si O₂are significantly improved compared to Cs Pb Br₃.（3）Quantum dot LED packaging:Cs Pb Br_1.2I_1.8@Si O₂ is packaged on the LED chip through the remote packaging process,and the red quantum dots are used to realize red and white light emission,which improves the red light in traditional pc-LEDs devices.The problem of missing bands improves the color rendering of the device.