Solvothermal synthesis and optical properties of Mn2+-doped SrTiO3 powders

Pure SrTiO3 (STO) and Mn2+-doped SrTiO3 powders were synthesized by solvothermal method. The structure, morphology and chemical compositions of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Effect of Mn2+ doping concentration on structure and optical properties of the products were detailedly studied. No phase segregation was observed in XRD patterns even after doping 20 mol% Mn2+ to STO, indicating that Mn2+ ions successfully substituted Sr2+ ions without changing the perovskite structure of STO. Optical absorbance and luminescence properties of STO and Mn2+-doped STO powders were measured by ultraviolet–visible (UV–vis) and photoluminescence (PL) spectra. Color of pure and Mn2+-doped STO with increasing dopant concentration changed from white to dark cyan gradually, indicating that doping of Mn2+ ions shows significant influence on the optical properties of STO powders, while red shift of absorption edge of STO powders can be observed. Due to the doping of Mn2+ ions, two small additional humps were found around 400 nm and 565 nm which were assigned to the 6A1g → 4A1g and 6A1g → 4T2g crystal field transitions, respectively. Two violet-blue luminescence emission bands located at 405 nm and 474 nm under ultraviolet excitation (254 nm) at room temperature were also observed and were ascribed to oxygen vacancies which have some intrinsic defect centers of STO.