Tb3+as a Recombination Center in ZnS

Abstract

The fluorescence and infrared-stimulated emission of ZnS: Tb has been studied. Excitation of the $4f^8$ electronic system of the ${\mathrm{Tb}}^{3+}$ ion occurs during recombination of a hole-electron pair at the rare-earth site. This is the predominant radiative recombination center in the crystal. Simple rate equations describe the infrared-stimulated release of holes from a trap 1.02 eV above the valence band and their recombination with electrons at the ${\mathrm{Tb}}^{3+}$ site. An estimate of the rate of resonance transfer of energy compared to direct radiative recombination shows the former to be at least 40 times faster.