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We have studied SnOx nanoparticles fabricated by gas-phase condensation and in-flight sintering using Raman and photoluminescence (PL) spectroscopy. We are able to identify various vibrational states of the rutile phase of the SnOx crystal. By thorough analysis of the vibrational modes, we are able to determine the bond lengths of the O–O and Sn–O bonds for the substoichiometric SnO1.5, leading, together with x-ray diffraction data, to a full characterization of the SnO1.5 lattice. In absorption and photoluminescence spectra, we observe a finite density of states inside the band gap due to oxygen vacancies, giving rise to a midgap luminescence peak. Our results suggest that the defect related luminescence efficiency is limited by nonradiative recombination processes and by the oxygen vacancy density. We therefore conclude that the PL intensity has a maximum around a stoichiometry of SnO1.7.
Meier et al. (Thu,) studied this question.