Concentration Quenching of Infrared Stimulated Luminescence in CaS:Eu,Sm

Concentration quenching of infrared stimulated luminescence (ISL) in CaS:Eu,Sm phosphors with various dopant concentrations is discussed. The discussion is based on experimental results on the dopant concentration dependence of ISL intensity and that of the intensity of the emission from a symmetric-site Sm (s-Sm) and from a defect-related asymmetric-site Sm (a-Sm). The excitation and emission spectra of s-Sm and a-Sm are revealed by site-selective photoluminescence measurements. The relationship between the concentration dependence of ISL intensity and that of both the s-Sm and a-Sm emission intensities is clarified. The s-Sm is shown to be the active center for ISL. Concentration quenching of ISL intensity is caused by a decrease in the s-Sm concentration resulting from excess doping of Sm and Eu.