On the photoluminescence behavior of samarium-doped strontium titanate nanostructures under UV light. A structural and electronic understanding

A combined experimental and theoretical investigation on the photoluminescence properties of SrTiO3 (ST) and SrSm0.01Ti0.99O3 (ST_Sm) nanostructures is presented in this work. The nanocrystalline powders were prepared by the polymeric precursor method, and the order-disorder behavior of this material was investigated by means of X-ray diffraction (XRD), spectral absorbance (UV-vis), transmission electron microscopy (TEM) images, electron paramagnetic resonance (EPR) and photoluminescence (PL) experimental techniques. The decrease in the broad PL emission band of ST and ST_Sm powders measured at room temperature indicates an increase in the structural order as the annealing temperature increases, i.e. characteristic samarium peaks intensify as the structural order increases in ST_Sm samples. The interactions of the network clusters that form the ST and ST_Sm structures were evaluated by means of the ab initio periodic method at the density functional theory (DFT) level with the hybrid nonlocal B3LYP approximation. The symmetry-breaking process that leads to the presence of non-ideal [TiO6] and [SrO12] clusters, as well as the relationship between these clusters, provides favorable structural and electronic conditions for the appearance of PL phenomena.