Photoluminescence and structural studies on Na2O–PbO–SiO2 glasses

PbOx[(Na2O)0.25(SiO2)0.75]1−x glasses (with x = 0.1–0.30) were prepared by a conventional melt-quench method and characterized by UV–visible optical absorption, photoluminescence and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) studies. It has been confirmed that the increased number of non-bridging oxygen atoms brought about by the increase in Q2 structural units of silicon is responsible for the shifting of the wavelength corresponding to the onset of absorption, as PbO concentration increases in the glass. Emission in the visible region (400–450 nm), from these glasses has been attributed to the presence of L-centers, whose the peak maxima and line widths systematically shift to higher values by incorporating Pb2+ along with Na+ in the network modifying positions. All the Pb2+ ions in these glasses occupy only the network modifying positions, as revealed by the identical chemical shift values of Qn structural units of silicon with increase in PbO concentration. In contrast to binary lead silicate glasses, no luminescence has been observed for comparable concentration of PbO, possibly due to the significant quenching of Pb2+ ions in the excited state.