Synthesis and luminescent properties of Tb3+-activated yttrium indium germanate phosphor

An yttrium indium germanate YInGe2O7 and YInGe2O7:Tb3+ was synthesized using a vibrating milled solid-state reaction with metal oxides. The structure was characterized by its X-ray powder diffraction pattern. All of the peaks can be attributed to the monoclinic YInGe2O7 phase, as increasing the Tb3+ ion concentrations and the full-width of the half-maximum (fwhm) of these peaks did not cause any obvious differences in the increase in Tb3+ concentration. The CIE color coordinates were all in the green region. The phosphor exhibited a bright green emission at 542 nm under excitation at 378 and 258 nm, which belongs to the 5D4→7F5 transition of Tb3+ ions. There were two kinds of emission mechanism in YInGe2O7:Tb3+: (1) under excitation at 378 nm, time-resolved 5D4→7F5 transition shows a single exponential decay even when all sites are occupied by Tb3+ ions; (2) under excitation at 258 nm, the excited energy was absorbed by the host crystal then transferred effectively to the Tb3+ ion which caused the decay curves for the 5D4→7F5 transition to show non-exponential behavior. There is a maximum value for photoluminescence intensity when the Tb3+ concentration is 100 mol% with CIE color coordinates of x=0.252; y=0.595. The concentration quenching effect was not observed, because the YInGe2O7:Tb3+ structure gradually changed to a thortveitite-like structure with increasing Tb3+ concentration.