Study On The Afterglow Performance And Mechanism Of Self-excited Phosphor SrCaGa₄O₈ Based On Defect State Regulation

The long persistent luminescence phenomenon means that after absorbing the energy of the external light source,it can still illuminate continuously when the light source is cut off.It is an energysaving,environmentally-friendly,green and healthy material that can be used in the fields of security display,biological imaging,information storage and so on.The long persistent phosphors have developed from the early sulphide-based matrix to the later aluminate matrix.Nowdays,the various matrixes are emerging one after another,and the development of long persistent phosphors have made great progress.However,there are still some problems those are difficult to solve.The long persistent luminescence mechanism is unclear,the luminescence color is single,and the phosphors are difficult to practically apply on large scale.It is well known that the long persistent luminescence process can be simplified to the capture,release,and recombination of carriers,which depend on the presence of defect states.The traditional long persistent luminescence mechanism model is based on the introduction of complex dopants.However,the presence of dopants will make the defect states and local energy levels complicated,causing the research of the long persistent luminescence mechanism model enter the bottleneck period,which seriously restricts the further development and wider application of long persistent phosphors.Therefore,in this paper,a method for simplifying the defect state was adopted,and the selfactivated phosphor was choosed as the research object,which was studied systematically,including the following three parts:Firstly,the selfactivated phosphor SrCaGa₄O₈ was prepared by high-temperature solid phase method,which exhibited the emission locating at 400 nm and 550 nm under excitation at 220 nm.By changing the matrix content and sintering atmosphere,it is found that there are three kinds of emitter in the matrix,which are gallium holes,oxygen holes,gallium ions,respectively.Besides,there are a series of traps of different depths.At high temperature,the SrCaGa₄O₈ host shows that the luminescence color changed from blue to yellow-green as the temperature increases.Based on the analysis of various high-temperature spectra and thermoluminescence curves,the carrier transmission path in the host including:transition to the conduction band after absorbing energy?captured by the defect state level?released to the gallium ion emitter from the trap.Secondly,based on the detailed research work of SrCaGa₄O₈ phosphor,the rare earth ion Pr³⁺ion was introduced as the luminescence center,and the characteristic luminescence of Pr³⁺ion was successfully realized by the energy transfer between the host and Pr³⁺ion.A series of thermoluminescence curves show that the defect state of SrCaGa₄O₈ host was changed by doping with Pr³⁺ion,which exhibited the continuous distribution,so that the SrCaGa4O8:Pr³⁺phosphor exhibited good thermal stability in the photoluminescence and long persistent luminescence at high temperature,which can be applied in the emergency of fire disaster or high power devices.The reasons of thermal stability and the model of carrier transition are explained by a large number of fluorescence spectra,thermoluminescence curves and long persistent luminesence decay curves.Meanwhile,the corresponding mechanism model is proposed.Thirdly,based on the research of SrCaGa₄O₈ phosphor,the dopant Tb³⁺ion was introduced as the luminescence center to realize the change of the defect level,two traps with different depths were presented.Under the excitation of 230nm,the abnormal luminescence of Tb³⁺ion dominated by ⁵D₃?⁷F_j was successfully obtained,the luminescence peaks are located at 380 nm,420 nm,440 nm,485 nm,which fully meets the light absorption requirements of cryptochromes and the SrCaGa₄O₈:xTb³⁺can be used to change the blooming period.Through the analysis of series thermoluminescence curves,fluorescence spectra and afterglow decay curves,it is found that the carriers in this phosphors are released into the emitter by two continuous tunneling processes,and the corresponding long persistent luminescence mechanism model is proposed.