Luminescent impurity ion probe and low temperature phase of SrTiO 3 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 O_h¹ 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.