Photoluminescence spectral dispersion as a probe of structural inhomogeneity insilica

Abstract

We perform time-resolved photoluminescence measurements on point defects inamorphous silicon dioxide (silica). In particular, we report data on the decaykinetics of the emission signals of extrinsic oxygen deficient centres of thesecond type from singlet and directly excited triplet states, and we use themas a probe of structural inhomogeneity. Luminescence activity in sapphire(α-Al2O3) is studied as well and used as a model system to compare the optical properties ofdefects in silica with those of defects embedded in a crystalline matrix. Only fordefects in silica did we observe a variation of the decay lifetimes with emissionenergy and a time dependence of the first moment of the emission bands. Thesefeatures are analysed within a theoretical model, previously proposed in D’Amico et al (2008 Phys. Rev. B 78 014203), with an explicit hypothesis about the effect introduced bythe disorder of vitreous systems. Separate estimations of the homogeneous andinhomogeneous contributions to the measured emission linewidth are obtained.It is found that inhomogeneous effects strongly condition both the triplet andsinglet luminescence activities of oxygen deficient centres in silica, although thedegree of inhomogeneity of the triplet emission turns out to be lower than that ofthe singlet emission. Inhomogeneous effects appear to be negligible in sapphire.