Energy transfer in CaSiO_3 phosphors doped with Ce~(3+) and Tb~(3+)

摘要

Calcium metasilicate phosphors activated by Ce~(3+) and Tb~(3+) have been studied for their emission characteristics. In two series of phosphors, one activator was kept at its optimum value while the other was varied. In another two series, one activator was kept below its optimum value and the other was varied. Concentration quenching effects start when each activator gives its maximum emission. There is clear evidence of an energy transfer from Ce~(3+) to Tb~(3+) because the ~5D_3 lines appear on addition of Ce~(3+) while they were conspicuously absent when Tb~(3+) alone was present. Their absence in singly activated phosphors could not have been due to cross-relaxation. Obviously X-ray excitation does not lead to ~5D_3 transitions which are achieved only by energy transfer. Further, considering the features of the emission spectra and the concentrations of activators used, the transfer could only be of the dipole-dipole type.