Fluorescence of doped nanocrystalline insulating materials: Effects of structural phase transitions

The fluorescence spectra of new doped nanocrystalline materials-SrTiO 3 :Cr 3+ and SrTiO 3 :Eu 3+ produced by the sol-gel process and consisting of the powder clusters built of the 20-50 nm particles are studied. The fluorescence spectroscopy of the probe Cr 3+ and Eu 3+ ions was used to detect the structural phase transition in nanocrystalline SrTiO 3 . The ferroelastic D 4h -O h phase transition, which in the bulk SrTiO 3 occurs at T = 105K, reveals itself in the splitting and shifts of the spectral lines of Cr 3+ 2 E- 4 A 2 and Eu 3+ 5 D 1 - 7 F n transitions. The studies of the fluorescence spectra of Cr 3+ and Eu 3+ in nanocrystalline SrTiO 3 showed that in these samples the phase transition temperature is shifted to the higher temperatures. The lifetimes of Cr 3+ 2 E and Eu 3+ 5 D 0.1 excited levels were measured in the wide temperature range and the effects of size restriction were observed.