In this study,we investigate the photoluminescence (PL) properties of γ and θ-alumina nanoparticles synthesized by the chemical wet method followed by annealing.The obtained experimental results indicate the presence of some favorable near ultraviolet (NUV)-orange luminescent centers for usage in various luminescence applications,such as oxygen vacancies (F,F2+,F22+,and F2 centers),OH related defects,cation interstitial centers,and some new luminescence bands attributed to trapped-hole centers or donor-acceptor centers.The energy states of each defect are discussed in detail.The defects mentioned could alter the electronic structure by producing some energy states in the band gap that result in the optical absorption in the middle ultraviolet (MUV) region.Spectra show that photoionazation of F and F2 centers plays a crucial role in providing either free electrons for the conduction band,or the photoconversions of aggregated oxygen vacancies into each other,or mobile electrons for electrons-holes recombination process by the Shockley-Read-Hall (SRH) mechanism.