Modification And Properties Of Sr₃Al₂O₅Cl₂-Based Long Afterglow Materials

With the increasing development of materials science,the research of long afterglow luminescent materials has received extensive attention in the last 30 years and many new long afterglow materials have been developed.However,the long afterglow materials that can be used commercially at present are mainly blue and green at short wavelengths,but research reports on long wavelength emission,especially red long afterglow materials,are still rare.In this thesis,Sr₃Al₂O₅Cl₂ was chosen as the substrate material,Eu²⁺was used as the luminescence center and trivalent rare earth ions Dy³⁺/Tm³⁺were co-doped as the trap center.The ion substitution method was used to moderate the emission wavelength and luminescence and duration of afterglow,and finally a variety of red long afterglow materials with excellent performance were successfully synthesized.1.1.Mg²⁺-doped Sr₃Al₂O₅Cl₂:Eu²⁺,Dy³⁺phosphors were successfully synthesized by using a high-temperature solid-phase method,and the Mg²⁺doping significantly enhanced their orange-yellow afterglow.Rietveld refinement of the prepared phosphors showed that all Eu²⁺ions were almost completely occupied on the Sr²⁺sites,while the occupancy of Dy³⁺in the lattice was increased by the incorporation of Mg²⁺.All phosphor samples with different concentrations of Mg²⁺exhibit the characteristic broadband emission spectra of the 5d→4f jump of Eu²⁺,peaking at 609 nm with orange luminescence.The incorporation of Mg²⁺ions also improve the afterglow performance by creating suitable electron traps in the phosphor,and the phosphor samples with an Mg²⁺content of 0.3 exhibit the best long afterglow performance.Thermoluminescence tests revealed that the introduction of Mg²⁺resulted in deeper trap levels（～0.72 e V）and an increase in trap concentration.2.Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺,Dy³⁺（x=0,0.2,0.4）long persistence phosphors were prepared by using a high temperature solid phase method.At the same excitation wavelength,the B³⁺-doped Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺,Dy³⁺phosphor displayed a redshift from 609 nm to 625 nm with increasing B³⁺concentration.XRD measurements indicated that Al³⁺could be replaced by B³⁺in the Al O₄ tetrahedral site,leading to lattice shrinkage and enhanced field strength of the crystal,which was the main reason for achieving the main reason for the redshift in the emission spectra.The afterglow of Sr₃Al₂O₅Cl₂:Eu²⁺,Dy³⁺is rather weak,while the sample co-doped with B³⁺shows a longer and stronger afterglow.Analysis of the thermoluminescence reveals that when B³⁺is introduced into the lattice,deeper electron traps are generated and the concentration of electron traps increases significantly.Thus,B³⁺ion substitution achieves redshift and afterglow enhancement of Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺,Dy³⁺phosphors.3.Finally,S^2-doped Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺,Tm³⁺red phosphors were investigated.The prepared samples were subjected to Rietveld refinement and the results showed that the occupancy of Tm³⁺in the matrix lattice increased after S^2-replaced the original O^2-lattice sites.The emission spectra of the samples demonstrated that the emission peak was red-shifted from610 nm to 630 nm with increasing S^2-content.the main reason for the red-shift phenomenon is that the incorporation of S^2-into the lattice not only increases the energy level splitting of the crystal field,but also has a positive effect on the center-of-mass shift.In addition,the afterglow of the S^2-doped sample has a stronger initial brightness and longer duration,thus,by doping with S^2-,a red long-lasting phosphor with a brighter afterglow and longer duration is obtained.Ultimately,possible mechanisms and detailed processes are proposed and explained.