Broad band (UV-VIS) photoluminescence from carbonized fumed silica: Emission, excitation and kinetic properties

Carbon incorporated silica nano-powder (SiO2:C) has been fabricated by chemical treatment of a fumed silica with tetramethoxysilane and subsequent annealing at 700 °C in pure nitrogen ambient. Upon thermal treatment SiO2:C powder exhibits strong photoluminescence (PL) that spans in the range from near-ultraviolet to visible. Two characteristic broad bands, with their maxima at 2.5 eV (Green-band) and 3.3 eV (Violet-band), contribute to the observed broadband emission spectrum from SiO2:C. PL emission and PL excitation (PLE) studies in the temperature range of 10-300 K revealed a different PL behavior pertaining to the change of the peak position of the green and violet bands with respect to temperature. The low-energy emission band showed a redshift in the peak position with decreasing temperature, in contrast to the blue-shift behavior of the violet-band. The latter PL behavior suggests a different origin for the observed emission bands. Complementary time-resolved PL analysis for both emission bands was carried out and yielded PL transients of a few nanoseconds. On the basis of PL/PLE studies and structural characterization by FTIR it is suggested that the origin of the broad band emission may be attributed to radiative recombination in carbon-related surface sites/clusters.