Luminescence of Rare-Earth-Activated Cadmium Sulfide

The narrow emission lines of Nd3+, Er3+, and Yb3+ have been observed from rare-earth doped CdS. These activators formed the principal radiative recombination centers in selected crystals. Decay-time measurements gave fluorescent lifetimes of ∼100 μsec for CdS:Yb, ∼300 μsec for CdS:Nd and ∼3000 μsec for CdS:Er. Both the emission spectra and lifetime measurements showed that the rare-earth ions occupied more than one type of site in the CdS lattice. No emission was observed from a rare-earth ion metastable level greater than 1.53 eV above the ground state, even though the CdS band gap was 2.43 to 2.52 eV in the temperature range of the experiments. This is taken as evidence for rare-earth-ion-acceptor-type defect pairing.