Nanocrystalline titanium dioxide films: Influence of ambient conditionson surface- and volume-related photoluminescence

We report on systematic study of photoluminescence properties of nanocrystalline titanium dioxide films consisting of predominantly anatase nanoparticles with diameters larger than 13 nm. We measured photoluminescence under two selected excitation wavelengths (325 nm/442 nm, i.e., above/below band gap excitation), under different values of ambient air pressure ( 5 - 10 5 Pa ) , and in the temperature interval 10-300 K. On basis of our results, we are able to distinguish two different processes leading to photoluminescence: the exciton recombination and the recombination of carriers in the energy states related to the surface of nanocrystals. We propose microscopic models describing well the effects of temperature and ambient conditions on photoluminescence of nanocrystalline titanium dioxide films.