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

CdWO 4 :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. • Energy transfer processes were studied in Sm3+ doped CdWO4 crystals. • Self-trapped excitons are thermally quenched due to hopping diffusion in CdWO 4. • Self-trapped excitons transfer energy to Sm3+ ions via Sm3+-bound excitons. • Sm3+-bound excitons are formed by trapping self-trapped excitons or charge carriers. • Energy transfer is terminated due to the destruction of bound excitons at T > 400 K. [ABSTRACT FROM AUTHOR]