Luminescent impurity ion probe and low temperature phase of SrTiO3 nanoparticles

Abstract

Optical absorption and photoluminescence of Cr3+ impurity ion probe were studied on nanocrystalline SrTiO3/Cr(0·1%) powders with an average particle size between 13 and 100 nm prepared by the Pechini type polymeric sol–gel method. Only Oh1 cubic perovskite phase was revealed in the powders at room temperature. The optical absorption edge and the position of the zero-phonon emission R-line of the octahedral Cr3+ centres shifted to higher energies with decreasing particle size. The temperature shift of the R-line position appeared for all powders nearly the same as the 'dielectric related' one in the bulk crystals, evidencing that SrTiO3 retains quantum paraelectric behaviour down to a particle size of about 10 nm. However, behaviour of the R-line position was unstable at low temperatures in powders with a particle size of about 13 and 20 nm. This instability was speculated as a manifestation of a possible low temperature ferroelectric phase transition in small enough SrTiO3 nanoparticles.