Formation and Photoluminescence Characterization of Transparent Silica Glass Prepared by Solid-Phase Reaction of Nanometer-Sized Silica Particles

We investigate the structural transformations of nanometer-sized silica particles during the solid-phase sintering process using infrared and Raman spectroscopy and field emission scanning electron microscopy (FESEM). We also carry out detailed time-resolved photoluminescence (PL) measurements for the fully sintered transparent sample, which has recently been shown to exhibit a unique white PL emission under ultraviolet excitation (Uchino, T.; Yamada, T. Appl. Phys. Lett. 2004, 85, 1164). We show that the macroscopic enclosed-pore formation and elimination processes are occurring during sintering and are closely correlated to the condensation reaction of surface silanol groups. The structure and bulk density of the fully sintered samples are analogous to those of normal bulk silica glass although the structure of the non-heat-treated sample is rather different. FESEM measurements reveal a particulate morphology even in the thoroughly sintered and apparently transparent sample. As for the fully sintered sample, we observe three distinguishable PL bands with different decay kinetics ranging from nanosecond to millisecond time regions. These versatile PL characteristics probably result from the interfacial highly constrained structures created during the present solid-phase sintering process.