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

The fluorescence spectra of new doped nanocrystalline materials—SrTiO3:Cr3+ and SrTiO3:Eu3+ 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 Cr3+ and Eu3+ ions was used to detect the structural phase transition in nanocrystalline SrTiO3. The ferroelastic D4h–Oh phase transition, which in the bulk SrTiO3 occurs at image, reveals itself in the splitting and shifts of the spectral lines of Cr3+ 2E– 4A2 and Eu3+ 5D1–7Fn transitions. The studies of the fluorescence spectra of Cr3+ and Eu3+ in nanocrystalline SrTiO3 showed that in these samples the phase transition temperature is shifted to the higher temperatures. The lifetimes of Cr3+ 2E and Eu3+ 5D0,1 excited levels were measured in the wide temperature range and the effects of size restriction were observed.