Energetic structure of Sm 3+ luminescence centers in Sr 2 TiO 4 .

A luminescent material based on the strontium orthotitanate (Sr 2 TiO 4 ) matrix doped with 1% of a mole of samarium was obtained using the typical solid-state synthesis method under a neutral atmosphere of nitrogen. The sample was investigated using powder X-ray diffraction (XRD) and several luminescence techniques to study the phase composition, luminescence properties as well as to determine the position of the energetic states of Sm 3+ in relation to the valence and conduction bands of Sr 2 TiO 4 . The XRD result shows that the product of the synthesis is pure Sr 2 TiO 4 . From the PL spectra, it can be seen that the phosphor can be effectively excited at 409 and 342 nm to emit significantly different emission spectra. The luminescence obtained under 409 nm excitation is typical of Sm 3+ in Sr 2 TiO 4 and attributed to the nonsymmetrical luminescent center (A-center). In contrast, the luminescence obtained under excitation at 342 nm originates from the symmetrical center (B-center) and has not been reported in the literature so far. The presence of the two emission centers related to Sm 3+ ions in the Sr 2 TiO 4 matrix characterized by only one crystallographic site of Sr 2+ was explained by considering the different ways of charge compensation: Sm 3+ in the A-center via strontium vacancy (V'' sr ), and Sm 3+ in the B-center via Ti 3+ (Ti' Ti ).