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Low-temperature In2O3 nanowire luminescence properties as a function of oxidizing thermal treatments

In the present work the optical properties of In2O3 nanowires, grown by the vapour transport process, have been investigated by means of photo- (PL) and cathodo-luminescence (CL), applied in the ultraviolet (UV)–visible range. Although In2O3 is expected not to emit light at room temperature, a complex photo-luminescence emission spectrum has been revealed and its temperature dependence has been carefully analysed by varying the temperature from 20 to 300 K. The influence of the substrate on the photo-luminescence spectra has been studied by performing low-temperature measurements on In2O3 nanowires deposited both on alumina and silicon substrates. Some samples have been submitted to suitable thermal treatments (in oxygen-rich atmosphere at 1000 °C), whose effects on the In2O3 nanowires’ emission have been put in evidence. When performed with low magnification, cathodo-luminescence has revealed the same features as photo-luminescence spectroscopy. When applied with high magnification, cathodo-luminescence can provide the emission spectra of a single nanostructure. The CL spectra have been measured for the first time on a single In2O3 nanowire, before and after in situ electron-beam irradiation. Thanks to this comparative analysis, the effectiveness of the growth procedure in obtaining good-quality materials has been demonstrated and the unexpected bands exhibited by In2O3 nanowires have been tentatively attributed to specific defects. In particular, an orange emission, whose amplitude can be increased by submitting the sample to appropriate thermal treatments, has been revealed (both with PL and CL spectroscopy) and might be exploited for visible laser applications.