Luminescence mechanism of (Pr, Al)-doped SrTiO 3 fine particles investigated by x-ray absorption spectroscopy

The $\text{Ti}\text{ }K$ x-ray absorption spectra of fine particles of the practical luminescence material (Pr, Al)-doped ${\text{SrTiO}}_{3}$ were measured under UV irradiation. Significant changes were induced by the UV irradiation both in the pre-edge region and in the $1s\text{\ensuremath{-}}4p$ main absorption edge. Surprisingly, similar changes were observed for a ${\text{SrTiO}}_{3}$ single crystal in a quantum paraelectric state, which also emits a faint greenish light under strong UV irradiation. High-resolution x-ray diffraction measurements reveal that the electron charge-density distributions in the two samples are identical, which indicates that the photoabsorption mechanism of ${\text{Ti}}^{4+}$ ions in the oxygen octahedra is the same.