Fluorescence of rare-earth ions in dirty displacive ferroelectrics

The phase transition of ferroelectric Sr_1?xBa_xNb₂O₆ was studied by measuring the fluorescence emitted from the rare-earth ions doped as a probe. The fluorescence spectral width and the wavelength showed singular behavior around the transition temperature. The samples possess a diffuse transition with characteristic optical properties near the inflection point of the temperature-dependence curve of the spontaneous polarization.