Anomalous size dependence of the luminescence in reconstructed silicon nanoparticles

Abstract

Using a time-dependent density-functional method, we investigated the effect of surface reconstruction in a series of hydrogen-capped silicon nanoparticles of sizes up to 2 nm with different coverage ratios of Si–Si dimers. For the models ranging from perfect bulklike to fully reconstructed configurations, changes in structural stability and optical absorption and luminescence properties were systematically studied. Excited state relaxation is sizable in these systems and gives rise to huge Stokes shifts of several eV. Contrary to the trend observed for II-VI quantum dots, luminescence energies of reconstructed Si dots increase with increasing system size, showing an “inverse quantum confinement effect.”