In this review, the photo luminescence (PL) performance and mechanism of nano-sized semiconductor materials, such as TiO2 and ZnO, are introduced, together with their attributes and affecting factors. Moreover, the applications of PL spectra in environmental photocatalysis are discussed in detail, viz. the inherent relationships between the PL intensity and photocatalytic activity are revealed on the basis of PL attributes, demonstrating that the PL spectra can reflect some important information such as surface defects and oxygen vacancies, surface states, photo-induced charge carrier separation and recombination processes in nano-sized semiconductor materials. Thus, the PL spectrum can provide a firm foundation in theory for designing and synthesizing new semiconductor photocatalysts with high activity, as well as quickly evaluating the photocatalytic activity of semiconductor samples. (c) 2005 Elsevier B.V. All rights reserved.