Phase Transition, Radio- and Photoluminescence of K3Lu(PO4)2 Doped with Pr3+ Ions

Luminescent characteristics of K3Lu(PO4)2:Pr3+ (1 and 5 mol.%) microcrystalline powders, a promising optical material for scintillation applications, were investigated using various experimental techniques. The material shows emission features connected with both high intensity interconfigurational 4f15d→4f2 transitions (broad UV emission bands) and intraconfigurational 4f2→4f2 transitions (weak emission lines in the visible range). The output of X-ray excited 4f15d→4f2 emission of Pr3+ increases with a temperature rise from 90 K to room temperature and higher depending on the Pr3+ ions concentration. The high 5% concentration of Pr3+ ions is found to be favourable for the stabilization of a monoclinic phase (P21/m space group) over a trigonal one (P3‾ space group) while emission properties of the material reveal that a phase transition occurs at higher temperatures. Decay kinetics of Pr3+ 4f15d→4f2 emission are recorded upon excitation with high repetition rate X-ray synchrotron excitation and pulse cathode ray excitation. Issues related to a non-exponential decay of luminescence and presence of slow decay components are discussed in terms of energy transfer dynamics. The presence of defects was revealed with thermoluminescence measurements and these are suggested to be the mainly responsible for delayed recombination of charge carriers on the Pr3+ 4f15d states. Some peculiarities of host-to-impurity energy transfer are discussed. © 2020 Elsevier B.V.The work was partially supported by the Ministry of Science and Higher Education of the Russian Federation (through the basic part of the government mandate, project No. FEUZ-2020-0060), Act 211 Government of the Russian Federation (contract № 02.A03.21.0006), STSM grant from COST Action TD1401 ″FAST” as well as by Estonian Research Council (project PRG629) and Estonian Center of Excellence in Research “Advanced materials and high-technology devices for sustainable energetics, sensorics and nanoelectronics” TK141 (project No. 2014-2020.4.01.15-0011) by the ERDF funding in Estonia. The time-resolved X-ray excited measurements were performed at the Shared research center SSTRC based on the NovoFEL/VEPP-4 - VEPP-2000 facilities at Budker Institute of Nuclear Physics (Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia) while using experimental equipment funded by RFMEFI62119X0022 project. Authors thank Erica Viviani (University of Verona) for assistance in the synthesis of the samples and Yulya Khatchenko (UrFU, Ekaterinburg) for assistance in the processing the experimental data. F. P. and M. B. thank the Facility “Centro Piattaforme Tecnologiche” of the University of Verona for access to the Thermo ARL X’TRA powder diffractometer