Formation and luminescence of nanoterraces and elongated structures in sintered TiO2

Samples of rutile TiO2 have been prepared by sintering compacted powders under argon flow. Long (above 20 h) sintering times at 1500 °C led to the formation of rods with squared cross-sections in a broad range of sizes. A two-step annealing treatment, at two temperatures, was found to favour the growth of low-dimensional elongated structures as well as a terraced structure on the grain surface, producing samples with high surface to volume ratio. The cathodoluminescence (CL) spectrum of the initial powder, shows an emission centred at about 2.40 eV, which can be separated into three Gaussian bands at 2.19, 2.30 and 2.55 eV. The main features of the CL spectra of sintered samples are an infrared band at 1.52 eV and a complex band in the visible range, whose peak position shifts with the annealing temperature. In samples sintered for 30 h an emission at 1.80 eV appears, while the dominant emission at 1.52 eV, due to titanium interstitials, is quenched.