Long-lasting phosphorescence in Mn²⁺:Zn₂GeO₄crystallites precipitated in transparent GeO₂–B₂O₃–ZnO glass-ceramics

Mn2+-doped GeO2–B2O3–ZnO (GBZ) glasses were investigated and developed as long-lasting phosphorescence host materials. Transparent glass-ceramics were obtained after heat-treated at the first crystallization temperature for 20 min. By X-ray diffraction measurement and SEM observation, it is clarified that Zn2GeO4 crystallites with a diameter of about 1 μm precipitate on the sample's surface after heat-treatment. An orange long-lasting phosphorescence from Mn2+ was observed in the 25GeO2–25B2O3–50ZnO glass matrix, however, a stronger long-lasting green phosphorescence was observed in the phase of Zn2GeO4 crystallites. This phenomenon is considered to be due to the different ligand field environment surrounding Mn2+ ions in the glass and the glass-ceramics. A possible mechanism for the long-lasting phosphorescence in the Mn2+-doped glass was discussed.