Photo-electronic properties and persistent luminescence in Pr3+ doped (Ca,Sr)TiO3 ceramics

We obtained direct evidence of inlet-valence charge transfer (IVCT) in Ca1-xSrxTiO3:Pr3+ (x=0, 0.3, 0.5, 0.8, and 1) by a photocurrent excitation (PCE) measurement, and proposed a mechanism of the persistent luminescence based on the results of the PCE and persistent luminescence measurements. The PCE spectra in all samples showed two bands in the UV range due to the band-to-band and lVCT transitions. With increasing Sr content, x, the host bandgap energy decreased monotonically from 3.59 to 3.23 eV, and the IVCT energy increased from 3.20 to 3.38 eV. PCE bands of the Pr3+:H-3(4) -> P-3(J) transitions in the blue region were observed only in the samples with x=0, 0.3, and 0.5 and the relative intensity decreased with increasing Sr content, x. Based on temperature dependence of the PCE results in the sample with x=0, a thermally assisted photoionization process was indicated under the H-3(4) -> P-3(J) excitation. Red persistent luminescence was observed in the samples with x=0, 0.3 and 0.5, showing trap depth in the range of 0A8-0.35 eV, which was estimated from the thermoluminescence measurement. The afterglow process by the electron moving through the conduction band was evidenced by the similar quenching behavior of the H-3(4) -> P-3(J) band both in the PC[ and afterglow excitation spectra. The difference in the processes of persistent luminescence among the band-to-band, lVCT and H-3(4) -> P-3(J) excitations was discussed. (C) 2013 Elsevier B.V. All rights reserved.