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.