Origin of resolution enhancement by co-doping of scintillators: Insight from electronic structure calculations

It was recently shown that the energy resolution of Ce-doped LaBr$_3$ scintillator radiation detectors can be crucially improved by co-doping with Sr, Ca, or Ba. Here we outline a mechanism for this enhancement on the basis of electronic structure calculations. We show that (i) Br vacancies are the primary electron traps during the initial stage of thermalization of hot carriers, prior to hole capture by Ce dopants; (ii) isolated Br vacancies are associated with deep levels; (iii) Sr doping increases the Br vacancy concentration by several orders of magnitude; (iv) $\text{Sr}_\text{La}$ binds to $V_\text{Br}$ resulting in a stable neutral complex; and (v) association with Sr causes the deep vacancy level to move toward the conduction band edge. The latter is essential for reducing the effective carrier density available for Auger quenching during thermalization of hot carriers. Subsequent de-trapping of electrons from $\text{Sr}_\text{La}-V_\text{La}$ complexes then can activate Ce dopants that have previously captured a hole leading to luminescence. This mechanism implies an overall reduction of Auger quenching of free carriers, which is expected to improve the linearity of the photon light yield with respect to the energy of incident electron or photon

ІЛОСОФСЬКА ТАКСОНОМІЯ КЛАСИЧНИХ ЗАХІДНИХ ТЕОРІЙ СМІХУ

Розглядаються основні теорії комічного, що належать до класичної парадигми філософствування (Т.Гоббса, І.Канта, Г.Гегеля, З.Фройда та ін.), розкривається їх взаємозв’язок та еволюція поглядів на проблему комічного. Комічне сформувало особливий культурний пласт – світ сміху, який постійно протиставляється світу серйозному. Мета цієї статті – дати загальний огляд основних теорій комічного в західній філософській думці. Розгалужена культура сміху, заснована на комічному в житті та мистецтві, має глибоке історичне коріння. У класичній західній філософії існують три види традиційних теорій сміху: переваги, невідповідності, розрядки. Основні положення теорії переваги були викладені Аристотелем і Платоном і домінували у західному мисленні про сміх протягом двох тисячоліть. Вважалось, що сміх виражає почуття переваги над іншими людьми або над нашим колишнім станом. Другим підходом до вивчення проблеми гумору була теорія невідповідності яка виникла у 18 столітті, щоб кинути виклик теорії переваги,. У той час як теорія переваги стверджує, що причиною сміху є почуття переваги, то теорія невідповідності вважає, що причина сміху –це сприйняття чогось невідповідного, чогось, що порушує наші розумові моделі та очікування. Зараз це домінуюча теорія гумору у філософії та психології. Теорія розрядки стверджує, що сміх позбавляє від накопиченої нервової енергії. Засновниками цієї теорії є Герберт Спенсер і Зигмунд Фройд. У статті зазначається, що кожна з теорій гумору здатна пояснити лише деякі з комічних проявів. Проте кожен тип теорії висвітлює певний аспект гумору. А тому ведеться подальший пошук філософського обґрунтування такого складного поняття, як сміх

Interpretation of Light-Quenching Factor Measurements

We observe that the pattern of the quenching factors for scintillation light from various ions, recently studied in $CaWO_4$ in connection with dark matter detectors, can be understood as a saturation phenomenon in which the light output is simply proportional to track length, independent of the ion and its energy. This observation is in accord with the high dE/dx limit of Birks' law. It suggests a simple model for the intrinsic resolution of light detectors for low energy ions, which we briefly discuss.Comment: Seven pages, seven figures, some with colo

Ultrafast luminescence of Ga- and In-doped ZnO ceramics

The work of authors (a-c) was financially supported by Russian Foundation for Basic Research (RFBR, Russia) and the work of the last author (d) had financial support from State Education Development Agency (VIAA, Latvia) . All of that was approved as a result of ERA.Net RUS PLUS 2017 joint call for proposals. Here is the link for the joint call for reference: https://www.eranet-rus.eu/en/196.php .In the presented work we compare luminescence characteristics of ZnO:Ga and ZnO:In ceramics prepared by hot uniaxial pressing method. Two types of initial powders were used. The first one was nanosized powder prepared by precipitation method. In the second case we used microsized powders and mechanical admixturing the oxides of intended dopant. In both cases doping by the trivalent ions lead to a significant quenching of ZnO visible emission and an increase in near-band-edge luminescence. The study has shown that the type of dopant greatly affects the transmittance of ceramics prepared from nano- and micro sized powders. Several reasons for the specific effect of powder preparation process and a type of introduced dopant, including changes in dopant solubility, their interaction with the grain boundaries, etc., were considered. © 2021 The Author(s). Published under the CC-BY-NC-ND license.Russian Foundation for Basic Research (RFBR, Russia); State Education Development Agency (VIAA, Latvia); ERA.Net RUS PLUS 2017 joint call for proposals; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2

Effect of in Doping on the ZnO Powders Morphology and Microstructure Evolution of ZnO:In Ceramics as a Material for Scintillators

Transparent ZnO ceramics are of interest for use as material for high-efficiency fast scintillators. Doping ZnO ceramics in order to improve complex of their properties is a promising direction. In the present research, the role of indium in the ZnO nanopowders surface interactions and in the change of microstructures and photoluminescence (PL) characteristics of sintered cera-mics is considered. Undoped and 0.13 wt% In doped ZnO ceramics are obtained by hot pressing sintering. It has been found that indium leads to the transition of initially faceted ZnO particles to rounded, contributing to good sintering with formation of diffusion active grain boundaries (GBs). Unlike ZnO ceramics, ZnO:In ceramics microstructure is characterised by the trans-crystalline mode of fracture, faceted GBs with places of zig-zag forms and predominant distribution of In at the GBs. Such indium induced modifications of GBs promote removal of point defects and reduce PL parameter α = I def /I exc in comparison with the undoped ceramics. Results characterise ZnO:In cera-mics with improved GBs properties as a prospective material for scintillators.The present research has been supported by the Project ERANET RUS_ ST#2017-051(Latvia) and #18-52-76002 (Russia); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Particle detection through the quantum counter concept in YAG:Er3+^{3+}

We report about a novel scheme for particle detection based on the infrared quantum counter concept. Its operation consists of a two-step excitation process of a four level system, that can be realized in rare earth-doped crystals when a cw pump laser is tuned to the transition from the second to the fourth level. The incident particle raises the atoms of the active material into a low lying, metastable energy state, triggering the absorption of the pump laser to a higher level. Following a rapid non-radiative decay to a fluorescent level, an optical signal is observed with a conventional detectors. In order to demonstrate the feasibility of such a scheme, we have investigated the emission from the fluorescent level $^4$S$_{3/2}$ (540 nm band) in an Er$^{3+}$-doped YAG crystal pumped by a tunable titanium sapphire laser when it is irradiated with 60 keV electrons delivered by an electron gun. We have obtained a clear signature this excitation increases the $^{4}I_{13/2}$ metastable level population that can efficiently be exploited to generate a detectable optical signal

Energy Transport and Scintillation of Cerium Doped Elpasolite Cs2LiYCl6: Hybrid Density Functional Calculations

Elpasolites are a large family of halides which have recently attracted considerable interest for their potential applications in room-temperature radiation detection. Cs2LiYCl6 is one of the most widely studied elpasolite scintillators. In this paper, we will show hybrid density functional calculations on electronic structure, energetics of small electron and hole polarons and self-trapped excitons, and the excitation of luminescence centers (Ce impurities) in Cs2LiYCl6. The results provide important understanding in energy transport and scintillation mechanisms in Cs2LiYCl6 and rare-earth elpasolites in general

Sub-nanosecond excitonic luminescence in ZnO:In nanocrystals

The financial support of research European Union ERA.NET RUS_ST20170-51 . This work was partly supported by Russian Foundation for Basic Research, Russia , project No. 18-52-76002 . The sample preparation was carried out as part of SFERA II project -Transnational Access activities ( European Union 7th Framework Programme Grant Agreement N3126430 ).The effects of indium concentration influence on the morphology, luminescence spectra and luminescence decay kinetics of ZnO:In nanocrystals prepared by the solar physical vapour deposition method are investigated. While undoped ZnO nanocrystals exhibit tetrapod-like morphology, with increasing indium concentration the tetrapods are transformed into particles whose average size decreases with increasing indium concentration. The results of time-resolved luminescence studies of undoped and indium doped ZnO nanocrystals showed that by increasing indium concentration the decay time falls and luminescence intensity decreases.ERA.NET RUS_ST20170-51; Russian Foundation for Basic Research No. 18-52-76002; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART