The role of quantum-confined excitons vs defects in the visible luminescnence of SiO2 films containing Ge nanocrystals

Synthesis of Ge nanocrystals in SiO₂ films is carried out by precipitation from a supersaturated solid solution of Ge in SiO₂ made by Ge ion implantation. The films exhibit strong room-temperature visible photoluminescence. The measured photoluminescence peak energy and lifetimes show poor correlations with nanocrystal size compared to calculations involving radiative recombination of quantum-confined excitons in Ge quantum dots. In addition, the photoluminescence spectra and lifetime measurements show only a weak temperature dependence. These observations strongly suggest that the observed visible luminescence in our samples is not due to the radiative recombination of quantum-confined excitons in Ge nanocrystals. Instead, observations of similar luminescence in Xe⁺-implanted samples and reversible PL quenching by hydrogen or deuterium suggest that radiative defect centers in the SiO₂ matrix are responsible for the observed luminescence.