Optical and Photo-stimulated EPR Studies on Intrinsic and Mn-doped Zinc Germinates Phosphors

Intrinsic zinc germinates (Zn2GeO4) and Mn-doped Zn2GeO4 phosphors have been prepared using solid state reaction and their photoluminescence and phosphorescence studied. Phosphorescence from both the Mn2$+$ ions and host defects in Zn2GeO4 has observed upon UV excitation, while the Mn2$+$ ions present a longer persistent time than the defects. The charging process has also been studied and different behaviors of Mn2$+$ and defects observed. Electron paramagnetic resonance (EPR) and photo (UV)-stimulated EPR spectra have been collected for both host defects and Mn dopants from 20 K to room temperature. UV-induced EPR signal and the decay processes have been analyzed and provided a better understanding of the trapping mechanism for the phosphorescence. EPR signal from Mn2$+$ has been found decreasing after the UV excitation, indicating that the population of Mn2$+$ ions decreases in the trapping state and the valence change from Mn2$+$ to Mn3$+$ when hole trapping occurred.