Preparation And Luminescence Property Regulation Of Borophosphate Phosphors Based On Anionic Group Substitution

In recent years,phosphor-converted white light-emitting diodes(pc-WLEDs)have been widely used in the field of solid-state lighting.However,there are certain problems in the practical application of commercial solid-state lighting phosphors.In LED lighting,the goal is to achieve sunlight-like full-spectrum lighting,and therefore,single-substrate emitting white phosphors are of great interest.In this thesis,a series of novel color-tunable BaCaK(PO4)3-x(BO3)x:Eu2+and K2BaSr(PO4)2-x(BO3)x:Eu2+ phosphors have been designed and synthesized based on the modification of two phosphates Ba3CaK(PO4)3 and K2BaSr(PO4)2 by anionic group substitution;and a series of characterization and analysis methods were used to investigate the physical phase structure,photoluminescence properties,color tuning mechanism,thermal quenching behavior and practicality of the phosphors,and the specific research contents and results are as follows:The XRD patterns of the BaCaK(PO4)3-x(BO3)x:Eu2+samples synthesized under COreducing conditions were determined,and all the synthesized samples were determined to be pure phases.Crystal structure refinement models for x=0 and 0.2 were established based on the data obtained from step XRD scans.Under near-UV excitation at 405 nm,the emission spectra showed a redshift of 26 nm as well as a broadening of the emission band located near 550 nm.The redshift of the emission can be attributed to the enhancement of the crystal field strength and the reduction of the crystal structure rigidity,while the difference in the aberration values of the three cationic polyhedra leads to the broadening of the emission band.The modified phosphor successfully achieves white light emission at x=0.2,the phosphor corresponds to a quantum efficiency of 62%,and its emission intensity can be maintained at 150℃ with a relative intensity of 45%.The XRD patterns of the BaCaK(PO4)3-x(BO3)x:Eu2+phosphors synthesized under H2reducing conditions were measured,and it was determined that the synthesized samples were all in a single pure phase.Under near-UV excitation at 405 nm,the relative intensity of the emission band located in the range of 500 nm to 600 nm increased and the color coordinates shifted from(0.2389,0.3054)to(0.2057,0.2190),which is diametrically opposite to the color tuning direction of the synthesized samples under CO reduction conditions.This property was analyzed as a result of the biased occupation of Eu2+ in the crystal.The results of high temperature fluorescence spectra of BaCaK(PO4)3-x(BO3)x:0.02Eu2+(x=0,0.2)samples showed that the phosphor retained 34%of the relative intensity increasing to 40%of the relative intensity at 150℃.XRD results of K2BaSr(PO4)2-x(BO3)x:Eu2+phosphor show that all samples are in a single pure phase.A previously unreported emission band centered at 530 nm was observed in the emission spectrum under 365 nm near-UV excitation.Based on the spectral data,it is concluded that the phosphor achieves multicolor emission from dark blue to yellow-green and across white light.In combination with the crystal structure occupancy analysis,the new emission band should be attributed to the occupation of the K+lattice by the doped Eu2+,which was analyzed to be due to the elevated cationic disorder effect.The modified phosphor successfully achieves white light emission at x=0.2,the quantum efficiency of the phosphor corresponds to 67%,and its emission intensity can be maintained at 150℃ with 50%relative intensity.Further,the LED packaging and practical application performance tests of borophosphate phosphors with anionic group substitution were explored.White LED devices were encapsulated using 365 nm and 405 nm near-UV chips combined with K2BaSr(PO4)1.8(BO3)0.2:0.04Eu2+and Ba3CaK(PO4)2.6(BO3)0.4:0.02Eu2+phosphors synthesized in CO reduction condition,respectively.The performance parameters of the K2BaSr(PO4)1.8(BO3)0.2:0.04Eu2+encapsulated LED devices under 365 nm chip excitation are as follows:color coordinate value of(0.31,0.36),associated color temperature of 7024 K,color rendering index of 81.3,and luminous efficiency of 16.82 lm/W.Under 405 nm chip excitation,Ba3CaK(PO4)2.6(BO3)0.4:0.02Eu2+package LED device performance parameters are as follows:the color coordinate value is(0.31,0.37),the associated color temperature is 6295 K,the color rendering index is 70.2,and the luminous efficiency is 6.1 lm/W.The LED device performance parameters are as follows:the color coordinate value is(0.31,0.37),the associated color temperature is 6295 K,the luminous efficiency is 6.1 lm/W.