Optical energy storage properties of Sr2MgSi2O7:Eu2+,R3+ persistent luminescence materials
The details of the mechanism of persistent luminescence were probed by investigating the trap level structure of Sr2MgSi2O7:Eu2+,R3+ materials (R: Y, La-Lu, excluding Pm and Eu) with thermoluminescence (TL) measurements and Density Functional Theory (DFT) calculations. The TL results indicated that the shallowest traps for each Sr2MgSi2O7:Eu2+,R3+ material above room temperature were always ca. 0.7 eV corresponding to a strong TL maximum at ca. 90 °C. This main trap energy was only slightly modified by the different co-dopants, which, in contrast, had a significant effect on the depths of the deeper traps. The combined results of the trap level energies obtained from the experimental data and DFT calculations suggest that the main trap responsible for the persistent luminescence of the Sr2MgSi2O7:Eu2+,R3+ materials is created by charge compensation lattice defects, identified tentatively as oxygen vacancies, induced by the R3+ co-dopants.
KeywordsThermoluminescence Persistent luminescence DFT Disilicate Trapping
Financial support is acknowledged from the Turku University Foundation, Jenny and Antti Wihuri Foundation (Finland) and the Academy of Finland (contracts #117057/2000, #123976/2006, and #134459/2009). The DFT calculations were carried out using the supercomputing resources of the CSC IT Center for Science (Espoo, Finland). The study was supported by the research mobility agreements (112816/2006/JH and 116142/2006/JH, 123976/2007/TL) between the Academy of Finland and the Academy of Sciences of the Czech Republic, as well as the Czech research project AVOZ10100521.
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