Tuning photoluminescence of Ge/GeO₂ core/shell nanoparticles by strain

The distribution of strain field plays an important role in deciding the physical properties of nanocrystals. The growth strain of Ge/GeO₂ core/shell nanoparticles embedded in a regular array of Al₂O ₃ nanoparticles and its resulting effect on the optical properties are investigated. Two-dimensional finite element calculations clearly demonstrate that Ge/GeO₂ nanoparticles certainly experienced greater compressive strain in Al₂O₃ nanoparticles than in Al ₂O₃ thin film, especially at the GeO₂ shell area. This may lead to much more strainrelaxing defects produced at the GeO ₂ shell in Al₂O₃ nanoparticles. Meanwhile, the photogenerated excitons/ electron-hole pairs are localized by defects located at the GeO₂ shell and are forced to recombine while being spatially confined in the Al₂O₃ nanoparticles. These effects might contribute to the observed intensity enhancement and blue shift of the photoluminescence peaks for the sample with Ge/GeO₂ core/shell nanoparticles embedded in Al₂O₃ nanoparticles. The findings presented here provide physical insight and offer useful guidelines to controllably modify the optical properties of semiconductor nanoparticles through strain engineering.