Nanjing University has made important progress in the field of high-efficiency and stable white LED research
The invention of the blue light-emitting diode (LED) promoted the development of contemporary lighting and display industries and was awarded the 2014 Nobel Prize in Physics. Compared with traditional incandescent lamps, fluorescent lamps and high-pressure gas discharge lamps, solid white LEDs, which enjoy the reputation of "the fourth generation of lighting sources", have the advantages of high luminous efficiency, energy saving and environmental protection, long life and safety and reliability. They are considered to be the 21st century. A new generation of environmentally friendly and energy-saving light sources. However, currently, the main way to realize white LED lighting is to use blue LEDs to excite rare earth luminescent materials with fluorescence, and then mix red, green and blue to produce white light. Rare earth luminescent materials have the spectral characteristics of 5d-4f and 4f-4f. Because of their small light absorption cross-section and low molar extinction coefficient, they often bring about the problem of "blue light overflow" in white light illumination and display backlight applications, causing consumers, especially It is the severe myopia and macular degeneration of the adolescents, which has caused widespread concern in the whole society.
In recent years, as a new type of luminescent material, lead halide perovskite has the characteristics of adjustable fluorescence spectrum, narrow half-value width, high fluorescence quantum yield, high defect tolerance, and simple liquid phase synthesis and low cost. , Light-emitting diodes and display devices have great potential. However, its ionic properties (decomposition with light, heat, water, and oxygen) and lead toxicity limit its practical application. Therefore, it is of great significance to find an environmentally friendly, stable and efficient perovskite material that can be practically applied to LEDs.
The team of Professor Zhengtao Deng from the School of Modern Engineering and Applied Science of Nanjing University has been committed to the basic research and industrial application of new phosphors for many years. Especially in the direction of white light LEDs and wide color gamut display devices, a series of progress has been made in the performance improvement and stability of luminescent materials in response to the bottleneck problem of luminescent materials in practical applications, such as: Angew. Chem., Int. Ed .2020, 59, 7738; Mater. Adv. 2021, 2, 1320; Chem. Commun. 2021, DOI: 10.1039/D0CC08253H; J. Mater. Chem. C2021DIO: 10.1039/D0TC05685E. Recently, the research group used a room temperature rapid crystallization method to prepare lead-free manganese halide perovskite materials with high photoluminescence quantum efficiency and high stability, and applied them to white light LED devices. Relevant results were recently published online in the internationally renowned materials science journal Advanced Functional Materials (impact factor: 16.836) under the title "StableandBrightPyridineManganeseHalidesforEfficientWhiteLight-EmittingDiodes".
The team used a room temperature rapid liquid phase synthesis method to prepare two organic-inorganic hybrid lead-free pyridine manganese halide perovskites on a large scale. The tetrahedral coordinated (C5H6N) 2MnBr4 emission peak is located at 521nm, with up to 95% fluorescence quantum yield, narrow half-width and excellent stability, while the octahedral coordinated C5H6NMnCl3 exhibits a red light emission of 648nm , The quantum yield is 40%. Compared with the all-inorganic CsPbX3 (X=Cl, Br) perovskite, its instability and toxicity have been effectively resolved. Through environmental stability test, ultraviolet light aging test and thermal stability test, pyridine manganese halide perovskite still maintains good performance. The white LED device prepared by mixing the green-emitting (C5H6N) 2MnBr4 phosphor and the red-emitting K2SiF6:Mn4+ phosphor has a light efficiency of 93.9lm/W when the driving current is 20mA. The white light LED has no attenuation in the emission intensity after 410 minutes of continuous work test in an atmospheric environment, and exhibits excellent device stability. Adjusting the ratio of (C5H6N) 2MnBr4 and C5H6NMnCl3 phosphors can obtain a series of warm white LEDs with continuously adjustable color coordinates. At the same time, after applying them to backlight display, the color coordinates of the NTSC 1931 color gamut coverage rate close to 104% is achieved. This work will promote the industrial application of low-cost LED lighting and backlight displays based on new luminescent perovskite materials.