UV-light induced luminescence processes in Al2O3 bulk and nanosize powders

UV-light induced photoluminescence (PL) and thermoluminescence (TL) have been studied in the alumina (Al₂O₃) bulk and nanosize powders. It has been found that luminescence properties of the studied alumina powders are determined mainly by presence of the uncontrolled impurities of titanium, iron and chromium. Despite the general similarity of PL characterized by two main emission band around 400 and 750 nm a number of differences has been observed in relative yield and position of the emission bands as well as in the excitation spectrum of the short wavelength band. Essential differences have been observed also in the intensity of the TL signal, TL curves and TL emission spectra revealed by bulk and nanosize alumina powders. Peculiar properties of nanopowder, such as presence of the 395 nm band excited at 210 and 250 nm and ascribed to intrinsic surface-perturbed defect F_s or F _s⁺, as well as very low intensity of the TL signal due to surface quenching, may be considered as manifestation of the surface effects, characteristic to nanostructures.