Radiophotoluminescence of Cu-doped silica glass derived from phase-separated sodium borosilicate glass

Radiophotoluminescence, one of the most interesting phenomena induced in materials by ionizing radiation, is expected to be applied for radiation measurements in various fields. The radiophotoluminescence of silica glasses doped with a small amount of copper was investigated after exposure to x rays and 60Co γ rays. The Cu-doped silica glasses were prepared from porous silica glass, obtained from a phase-separated borosilicate glass, through impregnation of the porous glass in Cu(NO3)2 solutions and sintering it. Among various types of defects generated in the glass by the irradiation, boron oxygen hole centers (BOHCs), i.e., holes trapped in oxygen bonded to fourfold-coordinated boron, were observed in electron spin resonance spectra. Before irradiation, a photoluminescence band attributed to the 3d94s1 → 3d10 transition of Cu+ ions was observed at 2.5 eV. The luminescence intensity increased remarkably after irradiation, and in addition, a new luminescence band at 2.1 eV appeared. The intensities of both bands increased proportionally with the irradiation dose. This was due to the conversion of Cu2+ to Cu+ ions by the capture of electrons generated by the irradiation. The luminescent decay was measured, which revealed that the lifetimes of the 2.5-eV and 2.1-eV emissions were 38 µs and 125 µs, respectively. The induced photoluminescence increased after heat treatment up to a temperature of 300 °C and decreased above 350 °C. The effects of heat treatment on the photoluminescence after irradiation and the thermal stability are discussed for BOHCs. A heat treatment of above 500 °C returned the glass near its initial state before irradiation.