ENERGY-TRANSFER IN CASIO3 PHOSPHORS DOPED WITH CE3+ AND TB3+

Calcium metasilicate phosphors activated by Ce3+ and Tb3+ have been st udied 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 valu e 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 Ce3+ to Tb3+ because the D-5(3) lines appear on addition of Ce3+ while they were conspicuously absent when Tb3+ alo ne was present. Their absence in singly activated phosphors could not have been due to cross-relaxation. Obviously X-ray excitation does not lead to D-5(3) transitions which are achieved only by energy transfer . Further, considering the features of the emission spectra and the co ncentrations of activators used, the transfer could only be of the dip ole-dipole type.