Photoluminescence spectral dispersion as a probe of structural inhomogeneity in silica

We perform time-resolved photoluminescence measurements on point defects in amorphous silicon dioxide (silica). In particular, we report data on the decay kinetics of the emission signals of extrinsic oxygen deficient centres of the second type from singlet and directly excited triplet states, and we use them as 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 of defects in silica with those of defects embedded in a crystalline matrix. Only for defects in silica did we observe a variation of the decay lifetimes with emission energy and a time dependence of the first moment of the emission bands. These features 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 by the disorder of vitreous systems. Separate estimations of the homogeneous and inhomogeneous contributions to the measured emission linewidth are obtained. It is found that inhomogeneous effects strongly condition both the triplet and singlet luminescence activities of oxygen deficient centres in silica, although the degree of inhomogeneity of the triplet emission turns out to be lower than that of the singlet emission. Inhomogeneous effects appear to be negligible in sapphire.