Role of Ti4+ in the luminescence process of Al2O3:Si,Ti

Al2O3:Si,Ti, prepared under oxidizing condition at high temperature, gives PL emission around 430 nm when excited with 240 nm. The Al2O3:C, TL/OSL phosphor, also shows emission around 430 nm, which corresponds to characteristic emission of F-center. Thus, to identify the exact nature of luminescent center in Al2O3:Si,Ti, fluorescence lifetime measurement studies were carried out along with the PL,TL and OSL studies. The PL and TL in Al2O3:Si,Ti show emission around 430 nm and the time-resolved fluorescence studies show lifetime of about 43 μs for the 430 nm emission, which is much smaller than the reported lifetime of ∼35 ms for the 430 nm emission (F-center emission) in Al2O3:C phosphor. Therefore, the emission observed in Al2O3:Si,Ti phosphor was assigned to Ti4+ charge transfer transition. Fluorescence studies of Al2O3:Si,Ti do not show any traces of F and F+ centers. Also, Ti4+ does not show any change in the charge state after gamma-irradiation. On the basis of the above studies, a mechanism for TSL/OSL process in Al2O3:Si,Ti is proposed.