Spectral Performance Modulation Of (Sr_1-xM_x)LiAl₃N₄:Eu²⁺（M=Ca,Mg） Luminescent Materials And Their Application In White LED Packaging

Due to their high luminous efficiency,long service life and safety,white LEDs have been used in a wide range of industries,such as displays and light-ing,among others.High quantum efficiency and excellent thermal stability are two major issues that need to be addressed in any area of LED application.In the current widely used white LED packaging method,the lack of red light component results in a cold white light and a low color rendering index（CRI<80）,so there is an urgent need to develop red light emitting phosphors to compensate for the lack of red light.At present,some red phosphors found can solve the problem of insufficient red light emission,but their emission spectrum is wide,resulting in a large part of the spectrum beyond the visual recognition range of the human eye,greatly reducing the luminous efficiency of fluores-cence in the recognisable range of the human eye.To address these problems,the development of phosphors with high luminous quantum efficiency,excel-lent thermal stability and narrow band emission is essential in the implementa-tion of high quality white LEDs.In this paper,Sr Li Al₃N₄ narrow-band red pow-der is used as the research object,and the system is investigated for structural property modulation as well as luminescence thermal stability improvement through cation substitution.The main elements are as follows:1.A series of SrLiAl₃N₄:xEu²⁺（0≤x≤0.05）nitride red phosphors have been successfully synthesized under low pressure conditions using pure nitride raw materials,and their crystal structures and luminescence properties have been investigated.The results show that a series of Sr Li Al₃N₄:0.02Eu²⁺lumi-nescent materials with high phase purity can be obtained by the low-pressure sintering method.With the doping of Eu²⁺,two excitation peaks exist in the range of 300-600 nm,and the peak of the emission spectrum is located at 650nm with a half-peak width of 55 nm;the luminescence intensity of the samples shows a trend of increasing and then decreasing,and the optimum doping con-centration is x=0.02.The variable temperature spectra show that when the temperature reaches 150℃,the luminescence intensity of Sr Li Al₃N₄:0.02Eu²⁺The luminous intensity of Sr Li Al₃N₄:0.02Eu²⁺can maintain 93.86%of the in-itial intensity,which indicates that the phosphor has excellent thermal stability.The method of spin-coating the phosphor onto a glass substrate and combining it with a blue chip to make a WLED device shows good color stability at dif-ferent driving currents,which provides a new idea for the design and practical application of WLED devices.2.A series of Sr_1-xCa_xLiAl₃N₄:2%Eu²⁺（0≤x≤0.8）solid solutions were synthesized by cation substitution(Ca²⁺→Sr²⁺)and sintered by low pressure.Experimental results showed that the emission spectra of the solid solutions were red-shifted from 654 nm to 687 nm with increasing Ca²⁺concentration under blue light excitation at 468 nm.crystal structure changes,spectral shifts and Ca²⁺occupancy in the lattice of the solid solutions were carefully investi-gated by Rietveld refinement and crystal field theory.The best crystalline sam-ple of Sr_0.7Ca_0.3Li Al₃N₄:0.02Eu²⁺was also found among different concentra-tions of solid solution samples.Interestingly,the phosphor has an unusually prominent thermal stability,with the emission intensity of the sample increas-ing abnormally with increasing temperature,reaching 109.91%at 425 K.Fi-nally the phosphor was combined with a commercially available YAG:Ce³⁺yel-low phosphor and an LED blue chip to obtain a warm white WLED device with low color temperature（4044 K）and high lumen efficiency（99.2 lm/w）,with a color rendering index Ra=83.5.3.A series of Sr_1-xMg_xLiAl₃N₄:2%Eu²⁺（0≤x≤0.6）solid solutions were synthesized by cation substitution(Mg²⁺→Sr²⁺)and using low-pressure sinter-ing.The experimental results show that with the increase of Mg²⁺concentration,the crystal structure shrinks,the lattice mismatch is severe and the XRD dif-fraction peaks are gradually shifted towards the large angle direction.The emis-sion spectrum of the solid solution sample was red-shifted from 655 nm to 687nm under the excitation of blue light at 460 nm.The thermal stability of the Mg²⁺substituted sample was compared and it was found that the Mg²⁺substi-tuted sample was able to maintain an emission intensity of 91.0%of the initial intensity at 150°C better than the commercial Sr₂Si₅N₈:Eu²⁺phosphor at 86.5%.Finally,the phosphor was combined with a commercial YAG:Ce³⁺yellow phosphor and an LED blue chip to obtain a white WLED device with a color temperature of 4496 K,lumen efficiency（59.9 lm/w）and color rendering index Ra=80.1.