Origin of Blue Emission from Silicon Nanoparticles: Direct Transition and Interface Recombination

Abstract

Blue light luminescent Si nanoparticles (NPs) have many potential applications in optoelectronics. However, blue light emission from Si is not stable in many cases, which severely hinders their real applications. Here, it is found that Si NPs prepared by laser ablation have strong and aging-enhancement blue light emissions. Subsequent annealing treatment of the aged Si NPs will weaken the blue emission dramatically. Through monitoring the photoluminescence (PL) evolutions (including the peak position and intensity) during different treatments of the Si NPs, we studied the origin of the blue light emission. In this case, such blue light emission cannot be simply ascribed to the quantum confinement effect of Si nanocrystals or surface states. The most plausible luminescent mechanism is that excitons first formed within Si nanocrystals by direct transitions at Γ or X point, then some of the formed excitons are trapped by nonradiative Pb centers, and the others transfer to and recombine at near-interface traps located at the interface areas between Si and the surrounding SiOx (0 < x < 2) layer, giving rise to the strong blue light emission. According to this scenario, aging enhancement and annealing reduction of the blue emission could be satisfactorily explained. On the basis of the understanding of the blue light emission mechanism, a time-saving hydrothermal approach is supplied to generate Si NPs with strong blue light emission instead of a time-consuming aging process. This investigation deepens the insight into the mechanism of the blue light emission from Si NPs prepared by laser ablation.