Excitation mechanisms and effects of dopant concentration in Gd2O2S:Tb3+ phosphor

Gadolinium oxysulfide powders doped with different Tb3+ concentrations were prepared from sulfur vaporization on rare earths' basic carbonate precursors. Single-phase Gd2O2S samples were obtained, with Tb3+ doping up to 9 at%. The study of the excitation mechanisms revealed that the Tb3+ emission might occur after the direct Tb3+ excitation either by energy transfer from Gd3+ or from the phosphor host. The characteristic terbium emission lines were observed, resulting from the radiative decay from 5D3 or 5D4 to 7Fj levels. The cross-relaxation phenomenon was observed and its effects on the materials emission color were discussed based on the CIE diagram. By using time-resolved spectroscopy, 5D3→7FJ and 5D4→7FJ transitions were separated.