Energy transfer to luminescent impurity by thermally quenching excitons in CdWO₄:Sm

CdWO₄:Sm single crystals were studied by optical, electron-paramagnetic and thermoluminescence spectroscopy in the temperature range of 4–750 K. A hopping diffusion of self-trapped excitons and energy transfer to Sm³⁺ centres is demonstrated. The mechanism of energy transfer includes the formation of a Sm³⁺ bound exciton either by direct excitation or in the result of a thermally stimulated hopping diffusion of self-trapped excitons as well as a sequential trapping of charge carriers near the Sm³⁺ ions. The energy transfer from the perturbed excitons to Sm³⁺ ions is controlled by an electric dipole-dipole or exchange interaction and it is terminated in the temperature range of 450–650 K due to the thermal destruction of Sm³⁺-perturbed excitons. In the case of near-surface excitations created in the energy region of high absorption coefficients by 5-eV photons, the Sm³⁺ emission is additionally quenched by surface-induced quenching centres.