Synthesis And Optical Properties Of Multi-color Long Persistent Iuminescence Materlals

A series of long persistent phosphor with different color were synthesized by solid-state reaction method and their multiple color change in visible region was studied. Emphases were placed on the afterglow properties and the mechanism of the tricolor phosphoresce materials.Blue long persistent phosphor:CaAl2O4:Eu2+, Nd3+, Pr3+and CaAl2O4:Eu2+,Nd3+,Mn2+have been prepared by solid-state synthesis method, respectively. Based on the energy transfer between Pr3+and Eu2+in the CaAl2O4host, it was observed that the presence of Pr3+modifies the shape of emission spectra and produces an enhancement of photoluminescence intensity. Thermoluminescence measurement has been performed. The results revealed that the concentration of efficient traps decreased with the increase of Pr3+. As Pr3+and Nd3+have occupied the different Ca sites, a competition between Nd'Ca and Pr'Ca exists in the process of arresting Ca2+vacancies. The CaAl2O4:Eu2+,Nd3+,Mn2+phosphors show two emission bands peaking at around440nm and545nm, originating from the allowed f-d transition of Eu2+and the forbidden4T1-6A1transition of Mn2+respectively, under ultraviolet excitation at340nm. Spectroscopy and afterglow decay time measurements demonstrate that energy transfer from Eu2+to Mn2+. The different color between photoluminescence and afterglow was analysised and observed based on energy transfer. Moreover, effects of Mn2+doping on the afterglow properties of CaAl2O4:Eu2+,Nd3+are explored and explained by thermoluminescence technique.Green long persistent phosphor:Ce3+and Mn2+singly doped and codoped SrAl2O4phosphors were prepared by solid state reaction. Ce3+and Mn2+co-doped SrAl2O4phosphor shows tunable blue to green emission. Apart from the emission band of Ce3+at374nm, which ascribes to the site of Sr2+occupied by Ce3+, the emission of Mn2+located at515nm was also observed for the energy transferred from Ce3+to Mn2+in SrAl2O4:Ce3+,Mn2+. By appropriately tuning the activator content, the developed phosphors can generate lights from blue to green region. In addition, green phosphorescence from Mn2+was observed in the co-doped system, which was due to the persistent energy transfer between Ce3+and Mn2+. The finding suggests a promising approach to controlling the color of the photoluminescence and phosphorescence of persistent phosphors.Red long persistent phosphor:The thermoluminescence, persistent luminescence and storage properties of Sm-doped alkaline-earth stannates, A2SnO4:Sm3+(A=Ca, Sr, Ba), are studied above room temperature. Different characteristic features of the thermoluminescence glow curves of A2SnO4:Sm+are observed, which implicates A2Sn04:Sm3+could provide different potential applications. Ca2SnO4:Sm3+with suitable traps shows efficient persistent luminescence, the red persistent luminescence could be observed in the dark for about several hours. Sr2SnO4:Sm3+possesses relative deep traps fulfill the requirement of a good storage phosphor, and the different amount of the stored energy could be released under the various treatments (the excitation with980nm/680nm light or heating at200℃). The extremely weak PL intensity of Ba2SnO4:Sm3+implies that it is inadequate applied as storage phosphor or afterglow phosphor. The decay time of afterglow increase in the order of Ba2SnO4:Sm3+<Sr2SnO4:Sm3+<Ca2SnO4:Sm3+. Our analysis indicates that the persistent luminescence properties of A2Sn04:Sm3+are governed by the cation vacancy, serve as the hole trap, which accept one hole to get stabilized. For Sr2Sn04:Sm3+, comparing with the air-sintered sample, a significant enhancement in both the fluorescence and phosphorescence for the vacuum-sintered sample was observed. This improvement could be attributed to the increase of oxygen vacancies which act as the sensitizer and the electron traps for the effective energy transfer from Sr2Sn04host to Sn3+Other color long persistent phosphor:Without doping any rare earth ions, Ca3SnSi2O9emits blue light and exhibits weak long-lasting phosphorescence. By selecting appropriate rare earth ions doped into the host, multicolor phosphorescence can be obtained from Ca3SnSi2O9):Re3+(Re=Pr, Tb, Sm) after excitation at316nm, which is due to the persistent energy transfer between the host and rare earth ions. The thermoluminescence results indicate that the introduction of Re3+(Re=Pr, Tb, Sm) produces more suitable traps (VCa) depth at360K, which make an important contribution to the more excellent long persistent luminescence phenomena.