Microstructures and optical properties of strontium titanate nanocrystals prepared by a stearic-acid gel process

SrTiO3 nanocrystals with grain sizes from 26 to 86 nm were prepared by stearic-acid gel method. The microstructures, lattice vibration and luminescence spectra were examined by X-ray diffraction, infrared, Raman and photoluminescence (PL) spectroscopies. Hydroxyl defects were clearly found by infrared spectroscopy in the SrTiO3 nanocrystals. Raman measurement results showed that internal stress exists in the SrTiO3 nanocrystals, which induces first-order Raman scattering processes. Strong visible PL near 2.82 eV was observed under 3.54 eV light excitation in small SrTiO3 nanocrystals. Grain-size dependence of the PL spectrum is investigated and the origin for the PL is attributed to a charge transfer via intrinsic defects inside an oxygen octahedron.