Luminescent spectroscopy of phosphates doped with Pr$^{3+}$ ions, irradiated with fast electrons and reactor neutrons

This paper reports the spectroscopic properties of phosphates KLuP$_2$O$_7$, Sr$_9$Sc(PO$_4$)$_7$, K$_3$Lu(PO$_4$)$_2$, doped with Pr$^{3+}$ ions. Photoluminescence (PL) spectra under selective excitation with UV photons, PL excitation spectra, and decay kinetics of pulsed cathodoluminescence are studied. Recordings of luminescence spectra were done with non-irradiated samples and after their irradiation with fast electrons ($E$ = 10 MeV) or fast reactor neutrons. Three typical channels of electronic excitations radiative relaxation have been identified: interconfigurational $d$-$f$ transitions, intraconfigurational $d$-$f$ transitions in Pr$^{3+}$ ions and luminescence associated with defects. After irradiation, significant changes in the luminescence characteristics were observed: a redistribution of the intensity of the intraconfigurational $f$-$f$ transitions, an increase in the luminescence yield of defects and the manifestation of new emission centers. The formation of radiation-induced defects presumably occurs due to the formation of complexes consisting of phosphorus and oxygen atoms.