Coexistence of Sm^3+ and Sm^2+ ions in amorphous SiO_x: origin, main light emission lines and excitation-recombination mechanisms

Abstract

Looking for new and/or improved optical properties from silicon-based materials, this work reports on the spectroscopic study of a samarium-doped silicon-oxide (SiOx) film. The film was prepared by the sputtering method and used argon ions to bombard a Si solid target partially covered with Sm2O3 powder. In the as-deposited form, the film was amorphous and presented samarium and oxygen contents around 0.6 and 13.8 at.%, respectively. Thermal annealing under a flow of oxygen induced the optical bandgap widening of the film and the development of Sm-related light emission in the visible and near-infrared ranges. The luminescence experiments were obtained at different photon excitation energies and temperatures (10 and 300 K). According to these results it is possible to state that both trivalent and divalent samarium ions are present in the SiOx film, and that their relative luminescence intensity is highly susceptible to the SiOx energy bands and Sm3+/2+ energy levels characteristics. The main aspects leading to the simultaneous presence of Sm3+ and Sm2+ ions in the SiOx host as well as their most probable excitation-recombination mechanisms are presented and discussed to a certain extent.