Research On Fabrication And Properties Of White-light Inorganic Electroluminescent Devices By Optical Conversion

With the approaching of the 5G era and the maturity of artificial intelligence and blockchain technology,the modern society is developing in the direction of high informationization and intelligence.People's requirements for high performance,integration and safety of optoelectronic devices are also increasing.The alternating current electroluminescent(EL)devices are ideally suited for the flat light emitting due to their unique properties: compactness,robustness,and flexibility.However,for decades of research,some problems still exist.For example,low luminance,lack of reliable red phosphors,and luminous chromaticity are greatly affected by driving power,etc.As emerging semiconductor materials,the quantum dots(QDs),especially coreshell structure QDs,have the advantages of wide absorption spectrum,narrow emission spectrum,stable chemical properties,and high quantum yield,which make them the best choice as light conversion materials.This research is based on the colorimetric principle and conducted from two aspects of device structures and light conversion materials.With hybrid emitting layer and QDs,the luminance and chromatic stability of conventional white light EL devices are improved obviously.In addition,in the CIE1976 LUV color space,the luminous color of EL devices is accurately characterized and evaluated for color difference.The main contents of this research are as follows:First of all,this paper fabricated a blue-green EL device with hybrid structure.Its dense hybrid light-emitting layer structure improves the dielectric constant of the device,which increases the intensity of the electric field distributed on the surface of phosphor.As a result,the luminance of the EL device with hybrid structure is 28.3% higher than that with multilayer structure.On this basis,five white EL devices with different structures were designed by changing the position of the fluorescent pigment in the EL device.By studying the photometric,colorimetric and electrical properties of the devices,it is found that when the position of the fluorescent pigment changes,the spectra shapes and emission peaks of the white EL device with different structures are the same,but their emission intensity are different.It also shows that the excitation of fluorescent pigment is always the process of remote radiation energy transmission formed by the blue-green light emitted from phosphor,so as to stimulate its photoluminescence process.When the red fluorescent pigment RTS-4 is overcoated on the outside of the electroluminescent part with hybrid structure,the pigment has the highest down conversion efficiency.At the same time,the white light EL device achieves the highest luminance and color stability.Then,the research substitutes RTS-4 organic fluorescent pigments by synthesized Cd Se/Zn S core-shell QDs as red light conversion materials.The absorption band of the QDs is wider,and the absorbance increases with the decrease of wavelength.As a result,the absorption spectrum of QDs is better matched with the emission spectrum from the phosphor,and the radiation energy transfer efficiency from phosphor to QDs is higher.Therefore,when the QDs are overcoated on the outside of the electroluminescent portion with hybrid structure,the white EL device achieves a higher luminance.And when the frequency and voltage of the driving power change,the device's color conversion index can be stabilized above 60%,and the chromatic aberration is smaller.Here,this research proposes the calculation method of "color conversion index",which takes into account both of light conversion efficiency and human visual effect.It is defined as the visual power ratio of the excited photoluminescence to the absorbed blue-green light from phosphor by the light conversion materials.The relevant calculation code is written in the MATLAB software.After testing with experiments,it is found that the color conversion index is more reliable than the existing down conversion efficiency,luminous efficiency and other parameters.It realizes quantitative measurement for red light conversion materials to evaluate their color conversion effect in the white light EL devices.Finally,based on the CIE 1976 LUV uniform color space,the research recharacterized and analyzed the luminescent color of the EL devices fabricated before.We found that when the CIE xy chromaticity diagram characterizes the change trend and chromatic aberration of the luminescent color of the EL device,especially when the luminescent color is located in the blue region,there are obvious defects.The characterization based on the CIE 1976 LUV color space is more accurate and intuitive.In addition,it is also possible to perform quantitative chromatic aberration calculations on the difference in the color perception of the light emitted by different EL devices to the human eyes.