Knowledge Bank

Dispersed photoluminescence (PL) spectra of silica $(SiO2)$ nanoparticles induced by ArF (193 nm) and Nd:YAG (266 nm) lasers have been $observed.a$ PL measurements from the composites of silica nanoparticles (the primary pasticle size 7 and 15 nm) as a function of heat-treatment temperature show that the PL results from hydrogen-related species and thermally produced structural defects. The green PL exhibits a progression with spacings of $\Delta \nu \sim 630cm-1$ assigned to the bending vibration of $\equiv Si-H$ on the surface of particles. The spacings increase up to $\Delta \nu \sim 1200cm-1$ when $\equiv Si-H$ and non-bridging oxygen $(\equiv Si-O\bullet )$ form interfacial water species. The two-photon (TP) induced PL with an ArF laser excitation has also been studied. The TP-produced excitons can result in a self-trapped exciton recombination (blue band), surface hydrogen-related centers (green band) and bulk non-bridging oxygen hole centers (red band). Relaxation of free TP-produced excitons and energy transfer of the excitons to the surface and bulk defects will be discussed.