Characterization, Luminescence, and Defect Centers of a Ce3+-Doped Li2Si2O5 Phosphor Prepared by a Solution Combustion Reaction

Li2Si2O5 doped with Ce was synthesized by solution combustion. The phosphor was characterized by powder x-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). Photoluminescence was investigated by excitation with UV radiation at 244 nm. An emission peak of the Ce3+ ion was observed at 400 nm. Gamma irradiated phosphor exhibits six thermoluminescence (TL) peaks at 110A degrees C, 160A degrees C, 190A degrees C, 250A degrees C, 320A degrees C, and 370A degrees C. Electron spin resonance (ESR) spectroscopy was used to study the defect centers induced in the phosphor by gamma irradiation and to identify the centers responsible for the TL process. The room-temperature ESR spectrum of the irradiated phosphor seemed to be a superposition of at least four distinct centers. One of the centers (center I) with principal g values and g (aSyen) = 2.0040 was identified as an O-2 (-) ion. Center II, with an isotropic g factor 2.0070, was identified as an F+-type center (singly ionized oxygen vacancy); this center correlates with the main low-temperature TL peak at 110A degrees C. Center III was identified as a Ti3+ center and center IV, with a hyperfine interaction with a Si-29 nucleus, as an intrinsic O--type center with a neighboring silicon ion. A Ti(4+)ion, the precursor of the Ti3+ center, acts as a recombination center for the 110A degrees C TL peak whereas a Ti3+ center relates to the main 250A degrees C TL peak and is also the likely recombination center for this peak. An O- ion is associated with the 110A degrees C TL peak as a possible recombination center. An additional defect center (V) was observed during thermal annealing experiments. This center (identified as an F+ center) seems to originate from an F center (oxygen vacancy with two electrons) and is not related to the any of the observed TL peaks.