Composition/structure relationships in monolithic borophosposilicate glasses obtained by the sol-gel route

Monolithic borophosphosilicate glasses were prepared by the sol-gel route through xerogel densification. Tetramethoxysilane (Si(OCH3)4), trimethylborate (B(OCH3)3), and trimethyl phosphite (P(OCH3)3) were used as source compounds for Si, B, and P, respectively. After drying, samples underwent thermal treatment up to 700 °C with alternating flowing oxygen and reduced pressure steps, resulting in transparent, monolithic glasses. The sample chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS). Densification was investigated by vibrational spectroscopies (FT-IR, micro-Raman). The boron oxygen hole centers (BOHC) and phosphorus oxygen hole centers (POHC) paramagnetic defects generated by X-ray irradiation of glasses were studied by electron paramagnetic resonance (EPR) spectroscopy. The results obtained on borophosphosilicate glasses showed that paramagnetic defects are not created by independent processes, as expected for randomly distributed noninteracting B and P doping elements. Diamagnetic precursors of BOHC and POHC are thus proposed to be spatially close together in the glasses.