Studies on phosphorescence and trapping effects of Mn-doped and undoped zinc germinates

Photoluminescence and phosphorescence from different recombining centers in the Mn2+-doped and undoped Zn2GeO4 phosphors have been observed. By UV excitation the undoped sample presents a broad band of blue-white emission from the host defects while the Mn-doped samples show both the host and Mn2+ emissions with different phosphorescent durations. At the beginning of UV excitation after the phosphorescence has been exhausted, the fluorescent time dependence of Mn2+ exhibits a fast decay process to a constant intensity, different from the rising or charging process as the typical behavior for the common persistent phosphors. This unusual behavior was studied using electron paramagnetic resonance (EPR) spectroscopy. A decrease of the EPR signal from Mn2+ was found for the sample under UV irradiation, suggesting the occurrence of ionization of Mn2+ to Mn3+. A slow recovering process of the ionization has also been detected, which is consistent with the observation of phosphorescence from Mn2+ doped samples.