Optimization of persistent luminescence performance of zinc gallogermanates

X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal analysis, and X-ray photoelectron spectroscopy, combined with instrumental analysis, have been employed to identify and characterize the physical differences between Zn₃Ga₂GeO₈ (ZGGO-s, s as in stoichiometric) and Zn₃Ga₂Ge₂O₁₀ (ZGGO-e, e as in excess) solid solutions. The two materials differ in the addition of GeO₂ (in the case of the ZGGO-e sample) to the solid solution of ZnGa₂O₄ and Zn₂GeO₄. The optimum sintering temperature for these materials is 1000 °C. The photoluminescence spectra comprise a broad feature between 400 and 600 nm which is slightly red-shifted in the case of ZGGO-e. Notably, ZGGO-e exhibits superior performance for both the intensity and duration of persistent luminescence at room temperature, with emission maximum at 515–517 nm. The performance of the chromium-doped sample, with persistent luminescence emission at 697 nm, is also superior for ZGGO-e. The reasons behind such a significant enhancement of persistent luminescence performance for ZGGO-e sample were investigated in this paper. We have found out that long persistent luminescence in both samples is governed by trap depth distributions. In the case of ZGGO-e, the addition of GeO₂ promotes the formation of deeper traps changing the shape of the resulting trap distribution and hence improving the room temperature persistent luminescence of this compound.