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101. Self-assembled natLiCl–CeCl3 directionally solidified eutectics for thermal neutron detection.

Author

huangliang Cheng, Hunneke, Rachel E., Tian, Mengkun, Lukosi, Eric, Zhuravleva, Mariya, Melcher, Charles L., and Yuntao Wu

Subjects
NEUTRON counters, EUTECTICS, THERMAL neutrons, SCINTILLATORS, NEUTRON irradiation, OPTICAL properties, X-rays, SOLIDIFICATION
Abstract

Novel natLiCl–CeCl3 eutectic scintillators for thermal neutron detection were synthesized by using the vertical Bridgman method. The eutectic molar ratio of LiCl and CeCl3 is 0.75/0.25. The effects of solidification speed on the microstructure, optical properties, and scintillation properties under γ and neutron irradiation were studied. The grown natLiCl–CeCl3 eutectics have a lamellar structure. Excited by X-rays, the scintillation emission of the natLiCl–CeCl3 eutectics peaks at 365 nm, which is related to the Ce3+ 5d–4f emission, and a broad and weak emission appears at 526 nm. The scintillation decay time of the natLiCl–CeCl3 eutectics under γ irradiation is about 20 ns. The energy spectra under Pu/Be source irradiation indicate that the synthesized natLiCl–CeCl3 is capable of detecting thermal neutrons. [ABSTRACT FROM AUTHOR]

Published
2020
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107. Excitation Transfer Engineering in Ce‐Doped Oxide Crystalline Scintillators by Codoping with Alkali‐Earth Ions

Author

Auffray, Etiennette, primary, Augulis, Ramūnas, additional, Fedorov, Andrei, additional, Dosovitskiy, Georgy, additional, Grigorjeva, Larisa, additional, Gulbinas, Vidmantas, additional, Koschan, Merry, additional, Lucchini, Marco, additional, Melcher, Charles, additional, Nargelas, Saulius, additional, Tamulaitis, Gintautas, additional, Vaitkevičius, Augustas, additional, Zolotarjovs, Aleksejs, additional, and Korzhik, Mikhail, additional

Published
2018
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109. Spectroscopic refractive indices of monoclinic single crystal and ceramic lutetium oxyorthosilicate from 200 to 850 nm.

Author

Jellison, Gerald E., Specht, Eliot D., Boatner, Lynn A., Singh, David J., and Melcher, Charles L.

Subjects
REFRACTIVE index, SINGLE crystals, CERAMICS, ELECTRONIC structure, THIN films, BAND gaps
Abstract

The four real values of the dielectric function tensor of the monoclinic crystal Lu2SiO5 or lutetium oxyorthosilicate (LSO) have been determined using generalized ellipsometry from 200 to 850 nm. The three principal values are fit to the Sellmeier model and they indicate that the band gap of LSO is less than ∼9 eV. The off-diagonal element [variant_greek_epsilon]12 is non-zero over the entire spectrum, but it is very close to zero for wavelengths longer than ∼400 nm, indicating that structurally monoclinic LSO is nearly optically orthorhombic in this wavelength region. The spectroscopic dielectric functions of three isotropic ceramic LSO samples are presented, which are consistent with the dielectric functions of single-crystal LSO when the effects of optical density are included. As a comparison, the dielectric functions are also determined using relativistic electronic structure and optical calculations based on the recently developed potential functional of Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)]. [ABSTRACT FROM AUTHOR]

Published
2012
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110. Investigating the luminescence properties as a function of activator concentration in single crystal cerium doped Lu2SiO5: Determination of the configuration coordinate model.

Author

Peak, Jonathan D., Melcher, Charles L., and Rack, Philip D.

Subjects
*CRYSTALS, *CERIUM, *SILICON oxide, *LUMINESCENCE, *LUTETIUM
Abstract

The effect of cerium concentration on single crystal lutetium orthosilicate (Lu2SiO5, LSO) was investigated with temperature-dependent steady state and time resolved luminescence spectroscopy. The results were used to determine the thermal quenching activation energies and the phonon energies responsible for the thermal broadening of the luminescence spectra. The measured phonon values were used to calculate configuration coordinate (CC) diagrams of the luminescence centers. The nature of single crystal LSO:Ce concentration quenching was determined to be due to radiative energy transfer by self-absorption. The observed broadening of the excitation spectra and narrowing of the emission spectra with increasing cerium was explained via a CC model. A combination of the CC model and concentration quenching explained the measured thermal quenching activation energies. [ABSTRACT FROM AUTHOR]

Published
2011
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112. Defect Engineering by Codoping in KCaI3:Eu2+ Single-Crystalline Scintillators

Author

Wu, Yuntao, primary, Li, Qi, additional, Jones, Steven, additional, Dun, Chaochao, additional, Hu, Sheng, additional, Zhuravleva, Mariya, additional, Lindsey, Adam C., additional, Stand, Luis, additional, Loyd, Matthew, additional, Koschan, Merry, additional, Auxier, John, additional, Hall, Howard L., additional, and Melcher, Charles L., additional

Published
2017
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117. Scintillators: Quaternary Iodide K(Ca,Sr)I 3 :Eu 2+ Single‐Crystal Scintillators for Radiation Detection: Crystal Structure, Electronic Structure, and Optical and Scintillation Properties (Advanced Optical Materials 10/2016)

Author

Wu, Yuntao, primary, Li, Qi, additional, Chakoumakos, Bryan C., additional, Zhuravleva, Mariya, additional, Lindsey, Adam C., additional, Johnson, Jesse Ashby, additional, Stand, Luis, additional, Koschan, Merry, additional, and Melcher, Charles L., additional

Published
2016
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123. Conference Comments by the Editors

Author

Dorenbos, Pieter, primary, Auffray, Ettienette, additional, Cherepy, Nerine, additional, Fasoli, Mauro, additional, Glodo, Jarek, additional, Kim, Hongjoo, additional, Melcher, Charles L., additional, and Payne, Steve, additional

Published
2016
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128. Improvements in Light Yield and Energy Resolution by Li+ Codoping (Lu0.75Y0.25)3Al5O12:Pr3+ Single Crystal Scintillators.

Author

Foster, Camera, Wu, Yuntao, Koschan, Merry, and Melcher, Charles L.

Subjects
SCINTILLATORS, PHOTOMULTIPLIERS, PHOTOELECTRONS, QUANTUM efficiency, CHARGE carriers
Abstract

In this study, we demonstrated a drastic improvement in energy resolution of (Lu0.75Y0.25)3Al5O12:Pr (LuYAG) single crystal scintillators from 4.8% to 4.1% at 662 keV upon Li+ codoping, which is the best value ever reported in the class of oxide single crystal scintillators. Li+ codoping can also significantly enhance its scintillation yield from 16 000 to 25 000 photons MeV−1, but slightly prolong the scintillation decay time. As Li+ codoping was found to have a negligible effect on the light yield non‐proportionality, we attributed the significant improvement in energy resolution to the reduced statistical variance in the number of photoelectrons produced in the photomultiplier tube (Rstat). [ABSTRACT FROM AUTHOR]

Published
2018
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129. Zero-dimensional Cs4EuX6 (X = Br, I) all-inorganic perovskite single crystals for gamma-ray spectroscopy.

Author

Koschan, Merry, Wu, Yuntao, Greeley, Ian, Loyd, Matthew, Rutstrom, Daniel J., Melcher, Charles L., Stand, Luis, Chen, Shiyou, Han, Dan, Du, Mao-Hua, Chakoumakos, Bryan C., and Shi, Hongliang

Abstract

Organic–inorganic and all-inorganic halide perovskites have become leading candidates toward high-performance optoelectronic devices and radiation detectors. In this work, we report novel zero-dimensional Cs4EuX6 (X = Br, I) perovskite single crystals as self-activated scintillators with superior performance for gamma-ray spectroscopy. Both Cs4EuBr6 and Cs4EuI6 single crystals grown by the Bridgman method were determined to have the trigonal crystal structure with the R3̅c space group, and have a melting point of approximately 540 °C. Cs4EuBr6 and Cs4EuI6 exhibit blue emission under UV excitation and high light yields of 78 000 ± 4000 photons per MeV and 53 000 ± 3000 photons per MeV under 137Cs gamma-ray irradiation, respectively. In particular, the former represents the best result achieved for self-activated scintillators thus far. Thermally stimulated luminescence studies and density functional theory calculations elucidate the correlation between halogen vacancies and long-lived emission (afterglow) at room temperature in Cs4EuX6 (X = Br, I) single crystals. Our findings not only demonstrate the high gamma-ray detection efficiency in Cs4EuX6 (X = Br, I), but will further promote the development of 0D metal halide-based novel luminescent and radiation detection materials. [ABSTRACT FROM AUTHOR]

Published
2018
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130. Tailoring the Properties of Europium‐Doped Potassium Calcium Iodide Scintillators Through Defect Engineering.

Author

Wu, Yuntao, Li, Qi, Rutstrom, Daniel J., Zhuravleva, Mariya, Loyd, Matthew, Stand, Luis, Koschan, Merry, and Melcher, Charles L.

Subjects
SCINTILLATION spectrometry, EUROPIUM isotopes, METAL halides, DENSITY functional theory, THERMODYNAMICS
Abstract

Codoping is an effective approach for precise control of point defects in many advanced materials, and can be used to optimize their function. This paper reports an effort toward tailoring the scintillation properties of metal halides through defect engineering. A study of aliovalent codoping of the KCaI3:Eu2+ single‐crystalline scintillators is performed, through which it is discovered that a simultaneous suppression of X‐ray induced afterglow and improvement of gamma‐ray energy resolution can be successfully achieved via Zr4+ codoping. The afterglow level is reduced by more than twofold with Zr4+ codoping. The energy resolution of a 5 mm cubic KCaI3:Eu2+ sample is improved from 3.25 to 2.7% at 662 keV, and 6.5 to 5.73% at 122 keV upon Zr4+ codoping. Physical explanations for the improvements are revealed from our investigations into both the electronic structure and thermodynamics of the defects by using thermoluminescence techniques and density functional theory calculations. The codoped Zr4+ ions prefer to form interstitials acting as shallow electron traps. The {ZrCa+VCa} complex can co‐exist with Zri interstitials as shallow hole traps under certain condition, which are able to trap holes temporarily. [ABSTRACT FROM AUTHOR]

Published
2018
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131. Czochralski Growth, Optical, Scintillation, and Defect Properties of Cu2+Codoped Lu2SiO5:Ce3+Single Crystals

Author

Wu, Yuntao, Koschan, Merry, Foster, Camera, and Melcher, Charles L.

Abstract

Divalent cation codoping, such as with Ca2+and Mg2+, is beneficial for the scintillation performance enhancement of Czochralski-grown Lu2SiO5:Ce (LSO:Ce) single crystals for nuclear medical imaging applications, but with that benefit comes a tendency toward acentric growth due to the reduced surface tension of the melt. Here, we present a divalent Cu codoping strategy to achieve a simultaneous improvement of light yield, energy resolution, scintillation decay, and afterglow in LSO:Ce single crystals without destabilizing the solid–liquid interface or promoting acentric growth. High-quality 32-mm-diameter and 110-mm-long LSO:Ce single crystals codoped with 0.1 and 0.3 atom % Cu2+ions in the melt were successfully grown using the Czochralski method. While the surface tension of the LSO melt does decrease with Cu2+codoping, analogous to the effect of Ca2+codoping, it is not reduced enough to affect the crystal growth stability or diameter control. With 0.1 atom % Cu2+codoping, the scintillation light yield of LSO:Ce can be significantly enhanced from 32 000 to 39 000 photons/MeV with an improved enegy resolution of 9% at 662 keV, and a reduced afterglow at room temperature. A continuous shortening of scintillation decay time with Cu2+codoping is ascribed to the combined effect of enhanced thermal ionization from the Ce3+5d1state and a reduction of the emission contribution from Ce2 centers, i.e., in the site neighboring six oxygens. Thermoluminescence and afterglow measurements are utilized to study the defect structure and explain the variation in scintillation yield.

Published
2019
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132. Unraveling the Critical Role of Site Occupancy of Lithium Codopants in Lu2SiO5:Ce3+Single-Crystalline Scintillators

Author

Wu, Yuntao, Peng, Jing, Rutstrom, Daniel, Koschan, Merry, Foster, Camera, and Melcher, Charles L.

Abstract

Lithium codoping has emerged as an effective strategy to enhance the light yield of oxide scintillators for radiation detection applications, but the understanding of the actual role played by Li+remains unclear. In this work, we comprehensively study the effects of Li codoping on optical and scintillation properties of Lu2SiO5:Ce (LSO:Ce) single crystals and reveal the critical role of site occupancy of Li. High-quality LSO:Ce single crystals codoped with 0.05, 0.1, and 0.3 at. % Li ions were grown by the Czochralski method. The optical absorption spectra confirm nonconversion of stable Ce3+to Ce4+in Li-codoped LSO:Ce regardless of the Li codoping concentration. The photoluminescence decay kinetics suggest an enhanced ionization of the excited 5d1state of Ce3+centers in highly codoped samples. A simultaneous improvement of scintillation light yield, decay time, and afterglow is achieved in LSO:Ce codoped with low concentrations of Li. The preferential occupation of Li at interstitial spaces and lutetium sites is proven to rely on its codoping concentration by using the 7Li nuclear magnetic resonance technique. The concentration-dependent site occupancy of Li alters the defect structures of LSO:Ce, in particular resulting in a distinct change in the number of cerium spatially correlated oxygen vacancies confirmed by thermoluminescence and afterglow measurements.

Published
2019
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148. Discovery of New Compounds and Scintillators of the A4BX6Family: Crystal Structure, Thermal, Optical, and Scintillation Properties

Author

Johnson, Jesse A., Zhuravleva, Mariya, Stand, Luis, Chakoumakos, Bryan C., Wu, Yuntao, Greely, Ian, Rutstrom, Daniel, Koschan, Merry, and Melcher, Charles L.

Abstract

We report the discovery of four new compounds of Eu2+-doped scintillators [Cs3Rb]SrI6, [Cs3K]SrI6, [Cs3Rb]CaI6, and [Cs3K]CaI6. A compositional engineering strategy dictated by the structural systematics of the base compounds Cs4CaI6and Cs4SrI6(space group R3̅c-hexagonal basis) was conducted to confirm an ideal solid solution for this system. Substitution of smaller monovalent cations Rb1+and K1+for Cs1+, maintained the crystal structure, producing an ordered substitution. Crystals were initially grown doped with 0.5% Eu to compare scintillation properties, and a Eu2+optimization study determined that 7% Eu was the ideal concentration. A 56 mm3crystal of composition [Cs3.5Rb0.5]SrI6:Eu 7% gave the best measured scintillation performance with an absolute light yield of 75 000 ph/MeV and energy resolution of 3.3% at 662 keV.

Published
2018
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