Critical points in photoluminescence spectra and their relation with phase transition in Nb-doped SrTiO3

Luminescence spectra are extremely sensitive to variations in structural environment; thus, result of structural change, such as phase transition, can be observed via luminescence intensity. The temperature dynamic of photoluminescence in the Nb-doped SrTiO3 demonstrates two critical points at 115 and 160 K, which correspond to temperatures of structural phase transitions for the bulk and the surface of SrTiO3, respectively. The absence of a hysteresis effect in the photoluminescence emission points out the correspondence of the critical points to a second-order phase transition. Similar critical behaviours were also observed in oxygen-deficient SrTiO3, confirming a relationship between the PL and phase transition. The existence of peaks in the temperature coefficient of resistivity at the same temperatures also confirms the correlation between photoluminescence and phase transition in the Nb-doped SrTiO3, providing a simple non-contact method to detect phase transitions in luminescence materials.