Influences of C1-C3 alcohols and purities of TiO2 powders on their photoluminescence properties at room temperature

We have investigated the photoluminescence (PL) of rutile and anatase TiO2 powders at room temperature in vacuum, in air, and in air with one of C-1-C-3 alcohols (methanol, ethanol, 1-propanol, and 2-propanol). For rutile TiO2 powder, we observed that the PL intensities in these atmospheres, except air, increase linearly with the square root of the UV irradiation time (t(0.5)), and found that the time dependence agrees with that of the integrated amount of photo-desorbed O-2 from rutile TiO2 powder. By considering the O-2 photo-desorption and its effect on the surface band bending of the powder, we could explain the time dependence of the PL intensities. This explanation is supported by the experimental results. For anatase TiO2 powder, the PL intensities in air with one of the alcohols, except for methanol, did not increase linearly with t(0.5), although those in vacuum and in air with methanol did increase. This inconsistency is probably due to the difference between the photocatalytic activities of anatase TiO2 powder for the alcohols. In addition, it was found that the difference between the slopes of the PL intensities of the TiO2 powders in vacuum against t(0.5) corresponds to that between the purities of the powders.