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28. New ultrafast scintillators with core valence luminescence: Cs2MgCl4 and Cs3MgCl5.

Author

Rutstrom, Daniel, Stand, Luis, Windsor, Dylan, Xu, Haixuan, Kapusta, Maciej, Melcher, Charles L., and Zhuravleva, Mariya

Abstract

Future experiments in high energy physics and medical imaging require radiation detectors having properties which are not presently available. The main limitations arise from a lack of suitable scintillation crystals. This dilemma prompts the need for research leading to the discovery of new fast and bright scintillator materials that combine unique properties to fulfil modern experiment requirements without compromises. In this work, single crystals of Cs2MgCl4 and Cs3MgCl5 up to 12 mm in diameter are grown via the vertical Bridgman method. Scintillation properties are reported for the first time, and core valence luminescence is observed for both compounds. X-ray excited radioluminescence emission of Cs2MgCl4 is centered at 295 nm, with a scintillation decay time of 2.25 ± 0.05 ns and relatively high core-valence light yield of 2200 ± 110 ph per MeV. Cs3MgCl5 has two main emission peaks centered at 242 nm and 302 nm, a decay time of 1.46 ± 0.05 ns, and a light yield of 1340 ± 70 ph per MeV. The better coincidence time resolution (CTR) is obtained with Cs2MgCl4, which is measured to be 129 ± 4 ps FWHM. Density functional theory (DFT) calculations are also performed and provide supporting evidence that the observed scintillation originates from core valence luminescence. The combination of speed and brightness of these new scintillators could be useful for fast timing applications in which moderately dense materials are required. [ABSTRACT FROM AUTHOR]

Published
2024
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40. Crystal growth and phase formation of high‐entropy rare‐earth monoclinic aluminates.

Author

Pianassola, Matheus, Loveday, Madeline, Lalk, Rebecca, Pestovich, Kimberly, Melcher, Charles L., and Zhuravleva, Mariya

Subjects
CRYSTAL growth, PHASE transitions, RARE earth metals, ELECTRON probe microanalysis, ALUMINATES, X-ray powder diffraction
Abstract

For the first time, high‐entropy rare‐earth monoclinic aluminate crystals were grown via directional solidification using the micro‐pulling‐down method. Five high‐entropy compositions were formulated with a general formula RE4Al2O9, where RE is an equiatomic mixture of five rare‐earth elements. The rare‐earth elements included were Lu, Yb, Er, Y, Ho, Dy, Tb, Gd, Eu, Sm, Nd, and La. High‐temperature powder X‐ray diffraction and Rietveld structure refinement indicated that all crystals were a single monoclinic phase and that rare‐earth average ionic radius did not affect phase purity. At room temperature, the refined lattice parameters increased consistently with increasing average ionic radii of the five compositions. One of the crystals had a typical high‐temperature phase transition of single‐RE RE4Al2O9 in the range of 1100–1150°C, which consisted of a lattice contraction upon heating. Differential scanning calorimetry indicated a thermal event corresponding to that phase transition. Electron probe microanalysis revealed Al‐rich inclusions on the surface of the crystals. Crystals containing Tb had dark surface features that became lighter after annealing in a reducing atmosphere, which indicated that Tb4+ may be responsible for the dark features. [ABSTRACT FROM AUTHOR]

Published
2023
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