758 ISSN 1063-7834, Physics of the Solid State, 2019, Vol. 61, No. 5, pp. 758–762. © Pleiades Publishing, Ltd., 2019. Russian Text © The Author(s), 2019, published in Fizika Tverdogo Tela, 2019, Vol. 61, No. 5, pp. 867–871. Luminescence of Pr 3+ Impurity Centers and Defects in Sr 9 Sc (PO 4 ) 7 :Pr 3+ V. A. Pustovarov a , K. V. Ivanovskikh a, *, Yu. E. Khatchenko a , V. Yu. Ivanov a , M. Bettinelli b , and Q. Shi c a Ural Federal University, Ekaterinburg, Russia b University of Verona and INSTM, Verona, Italy c Taiyuan University of Technology, Taiyuan, P.R. China *e-mail: k.v.ivanovskikh@urfu.ru Received December 4, 2018; accepted December 5, 2018 Abstract—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 intercon- figurational 5d → 4f 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 → 4f transitions in Pr 3+ ions. When excited by an electron beam (5 Hz), the main component with a decay time τ ∼ 17 ns dominates in the decay kinetics of the 5d → 4f luminescence. The decay kinetics of 5d → 4f luminescence upon excitation with high- frequency (τ ∼ 8 MHz) synchrotron radiation of the X-ray range contains a fast component (τ ∼ 15 ns) against the background of the slow component of the μs-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. DOI: 10.1134/S1063783419050275 1. INTRODUCTION It is well known that wide-bandgap materials, in particular, complex silicates, phosphates, binary rare- earth metal (RE) halides doped with Ce 3+ or Pr 3+ ions are used as fast scintillation detectors due to their high light output and fast nanosecond luminescence decay kinetics [1–5]. In complex phosphates Sr 9 Sc (PO 4 ) 7 the d–f luminescence of Ce 3+ or Eu 2+ impurity ions were proposed to be used to increase the efficiency of energy transport between impurity centers in order to obtain efficient “white” light-emitting diodes WLED [6]. In this work, with the use of a complex of various techniques, the excitation processes of impurity and defect-related luminescence of the complex phos- phate Sr 9 Sc (PO 4 ) 7 :Pr 3+ are investigated in a wide spectral range. The possibility of using the observed fast 5d → 4f luminescence for energy conversion, in particular, for scintillator applications, has been studied. 2. OBJECTS AND EXPERIMENTAL PROCEDURE 2.1. Objects of Research Polycrystalline Sr 9 Sc(PO 4 ) 7 samples doped with Pr 3+ ions (1%) were synthesized through the solid state reaction the Laboratory of Luminescent Materials (University of Verona, Italy). Phase purity was exam- ined by X-ray diffraction (XRD) method. All observed peaks in the XRD spectrum are consistent with stan- dard data for the Sr 9 Sc(PO 4 ) 7 compound (JPCDS card no. 54-1186). This confirms that the synthesized samples are single phase. 2.2. Photoluminescence Spectroscopy The photoluminescence (PL) spectra and PL exci- tation in the UV and VUV ranges (3.5–9.5 eV) were recorded upon excitation with synchrotron radiation at the 4B8 channel of the Beijing Synchrotron Radia- tion Facility, China. To detect the luminescence, an Acton SP308 monochromator (spectral resolution 0.2 nm) and a Hamamatsu H6241 photon counting detector were used. The PL and excitation PL spectra in the UV range (3.5–5.8 eV) were measured at the Department of Experimental Physics of the Ural Fed- eral University. The corresponding setup included a 400 W deuterium lamp, two double prism monochro- mators of the DMR-4 type and a Hamamatsu R6358- 10 photomultiplier tube [7]. IMPURITY CENTERS