Luminescent impurity ion probe and low temperature phase of SrTiO3 nanoparticles

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-h(1) 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.