Photoluminescence dispersion as a probe of structural inhomogeneity in silica

TL;DR

This study uses time-resolved photoluminescence spectra to investigate structural inhomogeneity in silica by analyzing defect emission decay, revealing significant inhomogeneous effects in silica but not in sapphire.

Contribution

It introduces a method to quantify inhomogeneous effects on defect luminescence in silica, comparing with sapphire as a crystalline reference.

Findings

Inhomogeneous effects dominate the emission linewidth in silica.

Triplet emission shows less inhomogeneity than singlet emission.

Sapphire exhibits negligible inhomogeneous effects.

Abstract

We report time-resolved photoluminescence spectra of point defects in amorphous silicon dioxide (silica), in particular the decay kinetics of the emission signals of extrinsic Oxygen Deficient Centres of the second type from singlet and directly-excited triplet states are measured and used as a probe of structural inhomogeneity. Luminescence activity in sapphire ($\alpha$-Al$_2$O$_3$) 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, 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 analyzed within a theoretical model with explicit hypothesis about the effect introduced by the disorder of vitreous systems. Separate estimations of the homogenous 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.