Luminescence of Pr$^{3+}$ impurity centers and defects in Sr$_{9}$Sc(PO$_{4}$)$_{7}$:Pr$^{3+}$

The spectroscopic characteristics and luminescence decay kinetics of Sr$_{9}$Sc(PO$_{4}$)$_{7}$:Pr$^{3+}$ (1%) were investigated using synchrotron radiation of ultraviolet (UV), vacuum ultraviolet (VUV) and X-ray ranges, as well as pulsed cathodoluminescence (PCL) methods at temperatures of 10, 90, and 295 K. The luminescence spectra contain three groups of bands and lines. In the UV range, the observed bands correspond to interconfigurational $5d\to4f$ transitions in Pr$^{3+}$ ions. In the visible spectrum, the wide luminescence band of defects dominates, as well as narrow lines associated with intraconfigurational $4f\to4f$ transitions in Pr$^{3+}$ ions. When excited by an electron beam (5 Hz), the main component with a decay time $\tau\sim$ 17 ns dominates in the decay kinetics of the $5d\to4f$ luminescence. The decay kinetics of $5d\to4f$ luminescence upon excitation with high-frequency ($\tau\sim$ 8 MHz) synchrotron radiation of the X-ray range contains a fast component ($\tau\sim$ 15 ns) against the background of the slow component of the $\mu$s-range. An effective nonradiative energy transfer is observed from impurity centers to defects, as well as from the host to Pr$^{3+}$ ions and defects.