Study On Spectral Characteristics And Multifunctional Application Of Double Perovskite Phosphor

Temperature,as a physical quantity,has been deeply involved in people’s production and life,and human skin is the most common tool to sense temperature.The emergence of temperature sensors has made temperature detection more flexible and quantitative.For traditional contact temperature sensors,their application is limited because they cannot work in extremely harsh environments such as strong acids,strong alkalis,and high pressures.Non-contact temperature sensors can easily perform temperature measurement tasks without the need for human contact.In recent years,the research on optical temperature sensors based on fluorescence intensity ratio（FIR）has been increasingly vigorous.Based on the difference in fluorescence intensity of rare earth ions’thermal coupling energy levels and temperature,these sensors can minimize errors caused by power fluctuations and material inhomogeneity,thus exhibiting high sensitivity and low error rate.In addition,for the implementation of WLED,the red phosphor with high luminescence performance can be combined and matched with other two basic color phosphors to form white light with high luminescence efficiency.Therefore,based on the above two aspects,this paper used the double-perovskite structure of La₂Mg Sn O₆ as the host matrix,and Bi³⁺/Sm³⁺and Er³⁺/Eu³⁺as co-doped ion combinations to explore their energy transfer,fluorescence characteristics,thermal stability,and characteristics of optical temperature sensors based on FIR.The paper also studied the local asymmetric sites and luminescence characteristics of Eu³⁺in red fluorescent powder doped with Eu³⁺/Ge⁴⁺ions.（1）La₂Mg Sn O₆:x Bi³⁺and La₂Mg Sn O₆:0.02Bi³⁺,y Sm³⁺phosphors were synthesized by high-temperature solid-phase method.The trend of the XRD main diffraction peak shift and refined data showed that Bi³⁺occupies three sites and showed a preferential occupation with concentration changes.When the Bi³⁺concentration was less than or equal to 0.02 mol,it occupied a large number of Sn⁴⁺and Mg²⁺sites,and then La³⁺sites were occupied in large numbers.The gradual introduction of Bi³⁺caused the tolerance factor T_f of perovskite to deviate from the standard value of 1.Gaussian fitting of the emission peak of single-doped Bi³⁺proved that it has three luminescent centers,and the emission spectrum showed a red shift of6 nm at 0.02 mol.After fitting the fluorescence decay curve,the average lifetime and energy transfer efficiency were calculated and analyzed,proving that Bi³⁺and Sm³⁺have energy transfer,and the transfer efficiency is as high as 59.07%.Temperature-dependent fluorescence spectra showed that the thermal stability of the Bi³⁺characteristic peak and Sm³⁺characteristic peak of the co-doped fluorescent powder has certain differences.Based on the FIR fitting and calculation,it was proved that La₂Mg Sn O₆:0.02Bi³⁺,y Sm³⁺fluorescent powder has good optical temperature sensitivity,and the maximum absolute sensitivity S_a-max is 0.0055 K^-1,and the maximum relative sensitivity S_r-max is 0.88%K^-1.It indicates that it has certain potential in the application of optical temperature sensors.（2）La₂Mg Sn O₆:x Er³⁺and La₂Mg Sn O₆:0.075Er³⁺,y Eu³⁺phosphors were prepared by high-temperature solid-phase method.XRD and refined data showed that Eu³⁺and Er³⁺occupy the La³⁺site.The emission spectrum of Er³⁺and the excitation spectrum of Eu³⁺have certain overlap,indicating that there is energy transfer between Er³⁺and Eu³⁺.Temperature-dependent fluorescence spectra analysis showed that they have good thermal stability.Based on the FIR and temperature-exponential relationship of the characteristic peaks at 555 nm and 706 nm,the temperature-sensitive characteristics of La₂Mg Sn O₆:0.075Er³⁺,y Eu³⁺fluorescent powder were fitted and studied.The maximum absolute sensitivity S_a-max is 0.0026 K^-1,and the maximum relative sensitivity S_r-max is 1.09%K^-1.（3）La₂Mg Sn O₆:0.04Eu³⁺,y Ge⁴⁺（y=0-0.9）phosphors were prepared by high-temperature solid-phase method.XRD and refined data showed that Ge⁴⁺occupies the Sn⁴⁺site.The proportion changes of the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions in the emission spectrum proved that Eu³⁺is in a locally asymmetric site.The lifetime of Ge⁴⁺doping was calculated by fluorescence decay fitting.The lifetime increases significantly after Ge⁴⁺introduction,from 87.27 ns to 236.01 ns.The corresponding thermal activation energy was calculated by temperature-dependent spectra analysis,and it showed strong thermal stability.The emission intensity at 403K was maintained at 68%of the initial temperature（303 K）.The CIE chromaticity coordinates showed that the fluorescent powder has high color purity of 93.87%and low CCT of 2010 K.It indicates that it has potential as a red fluorescent powder in LED applications.