Unique photoluminescence degradation/recovery phenomena in trivalent ion-activated phosphors

Photo-induced luminescence intensity degradation in red-emitting Tb₃Ga₅O₁₂:Eu³⁺ (TGG:Eu³⁺) phosphor is observed and studied using x-ray diffraction measurement, photoluminescence (PL) analysis, PL excitation spectroscopy, and PL decay analysis. The red-emitting TGG:Eu³⁺ phosphor exhibits remarkable degradation in the PL intensity under weak UV light (λ < 350 nm) exposure in the seconds time scale. The PL degradation characteristics can be well expressed by the exponential formulation with respect to exposure time. Interestingly, the PL intensity recovers after a few minutes when the phosphor is stored in a dark room or exposed to the long-wavelength (λ > 350 nm) light. The luminescence decay dynamics measured by excitation at λ_ex = 355 and 266 nm suggest that the present degradation/recovery processes are caused by the electron traps formed in the TGG:Eu³⁺ phosphor. The Tb³⁺ emission in TGG shows the essentially same degradation characteristics as those observed in the TGG:Eu³⁺ phosphor. The present luminescence degradation/recovery phenomena of the trivalent ions (4f → 4f transitions) may universally occur in various oxide phosphors such as TGG (Tb³⁺ emission) and CaTiO₃:Eu³⁺.