Abstract
In this article, I will discuss the optical properties of SiO2-nanoparticles that we have investigated recently by photoluminescence (PL) spectroscopy. In particular, I will show the blue-shifts of PL, originating from the electron-hole recombination of the self-trapped exciton (STE), observed in smaller-sized SiO2-nanoparticles. To explain the size effect in relating to the STE PL shift, a question has been raised on whether it is appropriate to apply the quantum confinement (QC) theory usually used for the Mott-Wannier type excitons in semiconductors to wide band-gap material, such as silica. In this study, a laser-heating model of free excitons (FEs) to activate lattice phonons has been developed, rather than the QC effect, to interpret the blue-shifts of STE PL in smaller-sized SiO2-nanoparticles. The blue-shift of STE PL is actually resulted from phonon-assisted PL due to the thermalization of the SiO2-nanoparticle system during laser irradiation.
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