A mixed indium–iron lithium diphosphate, In0.51Fe0.49LiP2O7

The structure of In0.51Fe0.49LiP2O7 consists of a three-dimensional network constructed from (InIII/FeIII)O6 octa­hedra and P2O7 groups. Each M IIIO6 octa­hedron is linked to six PO4 tetra­hedra belonging to five different P2O7 groups and shares two corners with the same P2O7 group so as to build infinite chains or rather parallel colums of [M IIIP2O11] running along the a axis. The linkage between these chains or columns defines hepta­gonal tunnels parallel to [100] in which the Li+ ions are located in off-centred positions. The In0.51Fe0.49LiP2O7 compound can be regarded as one composition of the continuous solid solution between LiFeP2O7 and LiInP2O7 whose structure is isotypic with the A IFeP2O7 (A I = Na, K, Rb, Cs and Ag) diphosphate family

Silver indium diphosphate, AgInP2O7

Polycrystalline material of the title compound, AgInP2O7, was synthesized by traditional high-temperature solid-state methods and single crystals were grown from the melt of a mixture of AgInP2O7 and B2O3 as flux in a platinium crucible. The structure consists of InO6 octa­hedra, which are corner-shared to PO4 tetra­hedra into a three-dimensional network with hexa­gonal channels running parallel to the c axis. The silver cation, located in the channel, is bonded to seven O atoms of the [InP2O7] framework with Ag–O distances ranging from 2.370 (2) to 3.015 (2) Å. The P2O7 diphosphate anion is characterized by a P—O—P angle of 137.27 (9) and a nearly eclipsed conformation. AgInP2O7 is isotypic with the M IFeP2O7 (M I = Na, K, Rb, Cs and Ag) diphosphate family

Band Gap Engineering and Trap Depths of Intrinsic Point Defects in RAlO3 (R = Y, La, Gd, Yb, Lu) Perovskites

The work was supported by the Polish National Science Centre (Project No. 2018/31/B/ST8/00774), by the NATO SPS Project G5647, and by the Ministry of Education and Science of Ukraine (Project DB/Kinetyka no. 0119U002249). L.V. acknowledges support of the National Research Foundation of Ukraine under Grant No. 2020.02/0373 “Crystalline phosphors’ engineering for biomedical applications, energy saving lighting and contactless thermometry”. Researchers from Tartu were supported by the ERDF fundings in Estonia granted to the Centre of Excellence TK141 “Advanced materials and high-technology devices for sustainable energetics, sensorics and nanoelectronics (HiTechDevices)” (Grant No. 2014-2020.4.01.15-0011) and Estonian Research Council Grant PRG-629. The Institute of Solid State Physics, University of Latvia as the Center of Excellence acknowledges funding from the H2020-WIDESPREAD-01-2016-2017-Teaming Phase2 under Grant Agreement No. 739508, Project CAMART2. N.K. was supported by the National long-term project No. WQ20142200205 (Recruitment Program of Global Experts, PRC). Authors are thankful to George Loutts from Norfolk State University, United States, and Dorota Pawlak from Institute of Electronic Materials Technology, Poland for providing some single crystals studied in the work, as well as to Kirill Chernenko from FinEstBeAMS of MAX IV for his assistance with synchrotron experiments.The possibility of band gap engineering (BGE) in RAlO3(R = Y, La, Gd, Yb, Lu) perovskites in the context of trap depths of intrinsic point defects was investigated comprehensively using experimental and theoretical approaches. The optical band gap of the materials,Eg, was determined via both the absorption measurements in the VUV spectral range and the spectra of recombination luminescence excitation by synchrotron radiation. The experimentally observed effect ofEgreduction from ∼8.5 to ∼5.5 eV in RAlO3perovskites with increasing R3+ionic radius was confirmed by the DFT electronic structure calculations performed for RMIIIO3crystals (R = Lu, Y, La; MIII= Al, Ga, In). The possibility of BGE was also proved by the analysis of thermally stimulated luminescence (TSL) measured above room temperature for the far-red emitting (Y/Gd/La)AlO3:Mn4+phosphors, which confirmed decreasing of the trap depths in the cation sequence Y → Gd → La. Calculations of the trap depths performed within the super cell approach for a number of intrinsic point defects and their complexes allowed recognizing specific trapping centers that can be responsible for the observed TSL. In particular, the electron traps of 1.33 and 1.43 eV (in YAlO3) were considered to be formed by the energy level of oxygen vacancy (VO) with different arrangement of neighboring YAland VY, while shallower electron traps of 0.9-1.0 eV were related to the energy level of YAlantisite complexes with neighboring VOor (VO+ VY). The effect of the lowering of electron trap depths in RAlO3was demonstrated for the VO-related level of the (YAl+ VO+ VY) complex defect for the particular case of La substituting Y. © 2021 The Authors. Published by American Chemical SocietyNATO SPS G5647; National Research Foundation of Ukraine 2020.02/0373; Polish National Science Centre 2018/31/B/ST8/00774; Eesti Teadusagentuur PRG-629; Latvijas Universitate 739508, WQ20142200205; Institute of Solid State Physics, Chinese Academy of Sciences; Ministry of Education and Science of Ukraine 0119U002249; European Regional Development Fund 2014-2020.4.01.15-0011, TK14

Performance of scintillation materials at cryogenic temperatures

An increasing number of applications of scintillators at low temperatures, particularly in cryogenic experiments searching for rare events, has motivated the investigation of scintillation properties of materials over a wide temperature range. This paper provides an overview of the latest results on the study of luminescence, absorption and scintillation properties of materials selected for rare event searches so far. These include CaWO4, ZnWO4, CdWO4, MgWO4, CaMoO4, CdMoO4, Bi4Ge3O12, CaF2, MgF2, ZnSe and AL2O3-Ti. We discuss the progress achieved in research and development of these scintillators, both in material preparation and in the understanding of scintillation mechanisms, as well as the underlying physics. To understand the origin of the performance limitation of self-activated scintillators we employed a semi-empirical model of conversion of high energy radiation into light and made appropriate provision for effects of temperature and energy transfer. We conclude that the low-temperature value of the light yield of some modern scintillators, namely CaWO4, CdWO4 and Bi4Ge3O12, is close to the theoretical limit. Finally, we discuss the advantages and limitations of different materials with emphasis on their application as cryogenic phonon-scintillation detectors (CPSD) in rare event search experiments

Origin of intrinsic luminescence in oxide crystals containing Bi cations and XO₄(X = P, Mo, W) molecular anionic groups

Intrinsic photoluminescence (PL) of BiPO₄, K₃Bi₅(PO₄)₆, K₂Bi(PO₄)(MoO₄), KBi(MoO₄)₂, K₅Bi(MoO₄)₄, K₂Bi(PO₄)(WO₄) and K₆.₅Bi₂.₅W₄P₆O₃₄ crystals is studied in 2.8-14 eV range of excitation photon energies. The electronic band structures of the crystals are calculated by the Full-Potential Linear Augmented Plane Wave Method. Origin of intrinsic luminescence in studied compounds is analyzed on the ground of obtained experimental and computational results. It is found that PL emission components of BiPO₄,K₃Bi₅(PO₄)₆, K₂Bi(PO₄)(MoO₄) and KBi(MoO₄)₂ in the violet-green spectral region are related to radiative transitions in Bi³⁺ ions. The red PL components of K₂Bi(PO₄)(MoO₄), KBi(MoO₄)₂ and K₅Bi(MoO₄)₄ have MoO₄₂--related origin. The red PL component of K₂Bi(PO₄)(WO₄) luminescence is presumably related to the molybdenum impurities. The intrinsic PL emission band of K₆.₅Bi₂.₅W₄P₆O₃₄ is probably not related to Bi³⁺ ions