Anatase titanium dioxide (A-TiO 2) with a wide band-gap energy of 3.2 eV can be used as a host semiconductor of rare-earth dopants for optical devices. However, the chemical activity of A-TiO 2 strongly affects the luminescence properties of the devices. In this study, we analyzed oxidized and deoxidized samarium (Sm)-doped A-TiO 2 (TiO 2:Sm) by impedance spectroscopy and microscopic photoluminescence. Charge propagation analyses using dielectric relaxation (DR) revealed that different kinds of charge-trapping centers were formed by the oxidization and deoxidization. For oxidization, Sm-oxygen complexes incorporated in the A-TiO 2 formed a trapping level that contributed to Sm excitation, while defective complexes at the A-TiO 2 boundary formed other levels that dissipated the charges. For deoxidization using thermal treatment in a hydrogen (H) atmosphere, the number of profitable trapping centers in A-TiO 2 was reduced but the remainder maintained the property of Sm excitation. It was also found that H adsorption on the A-TiO 2 boundary delocalized the electrons. Photoexcited dielectric relaxation (PEDR) studies confirmed the charge recombination at the profitable traps, and the peak height of the spectra corresponded to the luminescence intensity. Microscopic photoluminescence studies provided results consistent with DR and PEDR measurements and also revealed another quenching factor, i.e., Ti 2O 3 microcrystal formation on the TiO 2:Sm surface.