THE LUMINESCENCE OF EUROPIUM(III) AND CERIUM(III) IN CALCIUM-SULFATE - ACTIVATORS WITH AN EFFECTIVE CHARGE

The luminescence and the quantum efficiency of the phosphors CaSO4:Eu3+ and CaSO4:Ce3+ are reported. The Eu3+ phosphor shows a very weak luminescence under charge-transfer excitation, the quantum efficiency amounting to about 10%. Codoping of the Eu3+ phosphor with P5+ or Na+ as charge compensators enhances the luminescence efficiency. This is ascribed to a decrease of the concentration of vacancies in the lattice. The phosphor CaSO4:Ce3+ shows a very efficient ultraviolet luminescence. The Stokes shift of the d-f emission amounts to about 800 cm-1. Vibrational structure is observed in the emission and excitation spectra. It is shown that the effective charge on the activator ion has a different influence on the relaxation of the opposite-parity excited states of Eu3+ and Ce3+. © 1990.