Red luminescence in MgO-GeO2 gel glasses and glass ceramics doped with Mn ions prepared by sol-gel method

To obtain red luminants, MgO-GeO2 gel glasses and glass ceramics doped with manganese ions were prepared by a sol-gel method and their properties were investigated by measuring X-ray diffraction (XRD), electron spin resonance (ESR), and luminescence and excitation spectra. Under UV irradiation at 254 nm, the gel glasses and glass ceramics showed red luminescence at 620–665 nm, the intensity of which became strong with increasing the heat-treatment temperature. A glass ceramic with the composition 1.0MnO-25MgO-75GeO2 heat treated at 1000°C exhibited the strongest red luminescence at 661 nm. From the results of XRD and ESR, this luminescence is found to be due to the transition from the 4T1g to the 6A1g state of octahedrally coordinated Mn2+ ions located in MgGeO3 polycrystals. The luminescence wavelength of the glass ceramics (∼665 nm) is long compared with Eu3+-containing phosphors (612 nm), therefore the glass ceramics can be expected for red luminants.