Institute for Scintillation Materials of Ukraine

Kharkov, Ukraine

Institute for Scintillation Materials of Ukraine

Kharkov, Ukraine
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Gektin A.V.,Institute for Scintillation Materials of Ukraine | Belsky A.N.,University Claude Bernard Lyon 1 | Vasil'Ev A.N.,Moscow State University
IEEE Transactions on Nuclear Science | Year: 2014

Analysis of the last years theoretical studies and track simulations to conclusion that primary stages (electron scattering and e-h thermalization) play the key role in the following scintillator efficiency. The long thermalization length comparing to Onsager radius is the main reason for geminate pair concentration decrease and later luminescence losses. The easiest way for thermalization length decrease is the scintillation crystal doping or even transfer to the mixed crystals (solid solution). The simple model of modification of electrons scattering and e-h pairs thermalization for the mixed crystals is proposed. It is shown that solid solutions have higher light output independently on the crystal type. Analysis of experimental data confirmed this conclusion. This phenomenon is found for halide, oxide and sulfates scintillators. The similar behavior is typical for mixed anion and/or cation systems. The key role of initial track formation stages is illustrated by the same trend for activated scintillators and pure crystal with intrinsic luminescence. These estimations and experimental data lead to the conclusion that the scintillation efficiency improvement by mixed crystal use can play an important role in the search and development of new scintillators. © 2013 IEEE.

Gektin A.,Institute for Scintillation Materials of Ukraine | Shiran N.,Institute for Scintillation Materials of Ukraine | Belsky A.,University Claude Bernard Lyon 1 | Vasyukov S.,Institute for Scintillation Materials of Ukraine
Optical Materials | Year: 2012

The work is aimed to research of CsI:Eu single crystals' luminescence at different excitations in the wide temperature range (from 8 to 300 K) and admixture concentration from 10 -4% up to 10 -1% of Eu 2+ ions. This study was directed to separation of different luminescence mechanisms and luminescence quenching explore. It is found that due to the temperature quenching the room temperature yield is decreased in order of magnitude even for heavy Eu doped CsI crystals. Intense low temperature luminescence band at 441-448 nm connected with Eu 2+ 4f 6 5d → 4f 7 radiative transition is observed. The results obtained show that the excitonic mechanism plays the main role in energy transfer process to Eu 2+ ions and this is the reason for relatively low light yield of this emission at RT. The nature of the additional emission bands (410, 450, 480 and 500 nm) are apparently caused by the significant non-isomorphism of cations and/or by the presence of oxygen-containing admixtures. © 2012 Elsevier Ltd. All rights reserved.

Sidletskiy O.,Institute for Scintillation Materials of Ukraine | Gektin A.,Institute for Scintillation Materials of Ukraine | Belsky A.,University Claude Bernard Lyon 1
Physica Status Solidi (A) Applications and Materials Science | Year: 2014

The behavior of light yield in a wide range of inorganic scintillation crystals formed by isovalent substitution of anions or cations was investigated. The correlation between improvement of light yield in mixed crystals, and the ratios of volumes occupied by the competing atoms (ions) has been analyzed. A phenomenological approach to the prediction of light yield in mixed scintillation crystals allows us to predict the optimal combination of mixing components to reach the best scintillation performance. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dekaliuk M.O.,Palladin Institute of Biochemistry | Viagin O.,Institute for Scintillation Materials of Ukraine | Malyukin Y.V.,Institute for Scintillation Materials of Ukraine | Demchenko A.P.,Palladin Institute of Biochemistry
Physical Chemistry Chemical Physics | Year: 2014

Despite many efforts, the mechanisms of light absorption and emission of small fluorescent carbon nanoparticles (C-dots) are still unresolved and are a subject of active discussion. In this work we address the question as to whether the fluorescence is a collective property of these nanoparticles or they are composed of assembled individual emitters. Selecting three types of C-dots with "violet", "blue" and "green" emissions and performing a detailed study of fluorescence intensity, lifetime and time-resolved anisotropy as a function of excitation and emission wavelengths together with the effect of viscogen and dynamic fluorescence quencher, we demonstrate that the C-dots represent assemblies of surface-exposed fluorophores. They behave as individual emitters, display electronic anisotropy, do not exchange their excited-state energies via homo-FRET and possibly display sub-nanosecond intra-particle mobility. This journal is © the Partner Organisations 2014.

Vasil'Ev A.N.,Moscow State University | Gektin A.V.,Institute for Scintillation Materials of Ukraine
IEEE Transactions on Nuclear Science | Year: 2014

This work is directed to analysis and description of the factors which determine the efficiency of inorganic scintillators. The interconnection of different stages of track formation and relaxation is analyzed. The hierarchy of the scales of different processes in scintillators is discussed. The main attention is paid on the evolution of energy and spatial distribution of excitations in the excited region in scintillators. Different types of recombination - geminate and stochastic - and their features are considered, both in cases of low and high concentration of excitations and impurities. The spatial structure of the track after thermalization is discussed, with discriminating high-energy and low-energy part of the track of ionizing particle. Main features of thermalization and formation of thermalization length in different types of crystals with simple and complex structure and with different phonon spectrum are considered. The peculiarities of these processes in binary and complex halides and the estimation of limits of scintillator efficiency in these crystals are reviewed. Possible mechanism based on Auger relaxation of core hole which enhances the yield in CsI is proposed. The estimations of limiting factors for traditional alkali halide crystals and the perspectives of complex halides are discussed. © 2013 IEEE.

Sorokin A.V.,Institute for Scintillation Materials of Ukraine | Zabolotskii A.A.,Russian Academy of Sciences | Pereverzev N.V.,Institute for Scintillation Materials of Ukraine | Yefimova S.L.,Institute for Scintillation Materials of Ukraine | And 2 more authors.
Journal of Physical Chemistry C | Year: 2014

In the present work controlled plasmon enhanced fluorescence of thiacyanine dye J-aggregates in water solution has been demonstrated. To control a distance between J-aggregates and silver nanoparticles the latter have been covered by a polymer shell of variable thickness using the layer-by-layer assembly method. The best 2-fold fluorescence enhancement has been observed for the 16 nm thick polymer shell. Transmission electron microscopy (TEM) images have revealed an insufficient contact between J-aggregates and NPs that could be the main reason for the small fluorescence enhancement. Experimental results have been described using a model of two-level system affected by the local plasmon resonances field. According to the model more than 20-fold enhancement of J-aggregates fluorescence could be expected under optimal conditions. Besides, strong fluorescence enhancement dependence on an exciton coherence length has been predicted. According to it, significant fluorescence response should be observed for metal nanoparticles interacting J-aggregates with large exciton coherence length such as pseudoisocyanine J-aggregates and some others. © 2014 American Chemical Society.

Galunov N.,Institute for Scintillation Materials of Ukraine | Tarasenko O.,Institute for Scintillation Materials of Ukraine
Radiation Measurements | Year: 2010

The primary quenching in a track of a recoil proton or an alpha particle was studied on the base of "one step" model for molecular crystals of stilbene and doped p-terphenyl as well as for composite scintillators based on the grains of these single crystals. This approach is the first, which takes into account the influence the effect of polarization on recombination of polarons those are generated by ionizing radiation. It was shown that the primary quenching has to be concentration controlled process, which is faster than the track formation along it full length. Results obtained are in good agreement with results of studies of organic crystals as organic semiconductor materials. © 2009 Elsevier Ltd. All rights reserved.

Klochkov V.,Institute for Scintillation Materials of Ukraine
Journal of Photochemistry and Photobiology A: Chemistry | Year: 2015

Photocatalytic activity of aqueous colloidal solutions of nanoparticles of different nature at UV-irradiation was determined. 2 nm GdYVO4:Eu, 8 × 25 nm GdVO4:Eu, 6 × 40 nm LaVO4:Eu, 2 and 9 nm CeO2, 5 × 10 nm CePO4:Tb and 62 nm C60 nanoparticles were used. Rare earth orthovanadate nanoparticles as well as fullerenes induce radical formation in water. It was shown that intensity of photocatalytic process increases with increase of the linear sizes of orthovanadate nanocrystals. Rare earth orthophosphate nanoparticles do not participate in photocatalytic processes at all. Cerium dioxide nanocrystals inactivate radicals in the water playing a role of a radical sponge. ©2015 Elsevier B.V. All rights reserved.

Ucer K.B.,Wake forest University | Bizarri G.,Lawrence Berkeley National Laboratory | Burger A.,Fisk University | Gektin A.,Institute for Scintillation Materials of Ukraine | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

Although light continues to be emitted from insulating crystals used as scintillators over a period of nanoseconds to microseconds after stopping of an energetic particle, much of what determines the nonlinearity of response goes on in the first picoseconds. On this time scale, free carriers and excitons are at high density near the track core and thus are subject to nonlinear quenching. The hot (free) electrons eventually cool to low enough energy that trapping on holes, dopants, or defects can commence. In the track environment, spatial distributions of trapped carriers determined on the picosecond time scale can influence the proportionality between light yield and the initial particle energy throughout the whole light pulse. Picosecond spectroscopy of optical absorption induced by a short pulse of above-gap excitation provides a useful window on what occurs during the crucial early evolution of excited populations. The laser excitation can be tuned to excite carriers that are initially very hot (∼3 eV) relative to the band edges, or that are almost thermalized (∼0.1 eV excess energy) at the outset. Undoped and doped samples of NaI:Tl(0%, 0.1%), CsI:Tl(0%, 0.01%, 0.04%, 0.3%), and SrI2:Eu(0%, 0.2%, 0.5%, 3%) are studied in this work. © 2014 American Physical Society.

Malyukin Y.V.,Institute for Scintillation Materials of Ukraine
International Conference on Oxide Materials for Electronic Engineering - Fabrication, Properties and Applications, OMEE 2014 - Book of Conference Proceedings | Year: 2014

Luminescence and scintillation processes in nanomaterials can differ sufficiently from the same processes in bulk crystals. A range of effects providing such a difference (confinement of electronic and phonon states, Purcell's effect, migration of defects to the surface) are discussed in the paper. © 2014 IEEE.

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