Energy transfer and upconversion of Sm 3+ ions in YAlO 3

Abstract Sm 3+ doped YAlO 3 (YAP) single crystals were prepared by the micro-pulling down method. Emission spectra as well as luminescence decay curves for these crystals were recorded at temperatures ranging from 10 K to 300 K. Based on the low temperature spectra the energies of the Stark levels for several multiplets were determined. The fluorescence decay curves have been measured as a function of concentration and temperature and are found to exhibit single exponential nature at lowest concentration of 0.1 at.% but are strongly non-exponential at concentrations above 1 at.%. This concentration quenching of the Sm 3+ ion emission was ascribed to resonant cross-relaxation. The non-exponential decay rates were successfully fitted to Inokuti-Hirayama model for s = 6 indicating that the nature of the energy transfer process among the Sm 3+ ions is of electric dipole-dipole type. Cross-relaxation rates were experimentally determined as a function of activator concentration and used to evaluate and to model the decays. The critical distances and energy transfer microparameter for the transfer processes were given. After pulsed 925–975 nm infra-red excitation upconverted yellow-orange emission has been generated at room temperature in Sm 3+ :YAP crystals. Dynamics of the involved excited states have been analyzed and the responsible upconversion mechanism was proposed to be energy transfer.