Probing metastable Sm2+ and optically stimulated tunnelling emission in YPO4: Ce, Sm

When the model dosimetry system YPO4: Ce3+, Sm3+ is exposed to X-rays, the charge state of the dopants changes, becoming Ce4+ and Sm2+ via hole and electron trapping, respectively which are metastable; the original charge states can be achieved through electron transfer back from Sm2+ to Ce4+ via optical stimulation. The work presented here adds further details to the energy levels of the metastable Sm2+ defect and the electron transfer processes by undertaking measurements of a) Sm2+ excitation spectrum through the internal D-5(0) -> F-7(2) emission at 7 K, b) relaxation lifetime of Sm2+ (D-5(0) state) and its temperature dependence to provide insights into thermal quenching, and c) the kinetics of localised recombination from Sm2+ to Ce4+ on nanoseconds to seconds time scales using sub-band-edge excitation. (C) 2016 Elsevier Ltd. All rights reserved.