Luminescence and scintillation characteristics of four selected material systems, namely CsI:Tl(Na), CeF 3 , PbWO 4 and Ce-doped aluminium perovskites XAIO 3 :Ce (X=Y, Lu, Y-Lu) are reviewed. The progress in their physical understanding and related optimisation of their characteristics and technology are demonstrated. The important role of various defect states in the scintillator performance of these materials is stressed, which has led to the need for a deeper study of the processes of energy transfer and storage to achieve their intrinsic limits and full exploitation in scintillation detectors.

Wide Band Gap Scintillation Materials: Progress in the Technology and Material Understanding

The luminescence spectra of CaWO4, CaMoO4, and ZnWO4 scintillating crystals were investigated in the temperature range 8–400K The excitation photon energy was varied from the ultraviolet (45eV) to the hard x-ray region (35keV) It is found that as the excitation energy decreases the relative intensity of the low-energy luminescence band, attributed to the extrinsic emission of defect centers in CaWO4 and CaMoO4 crystals, increases This observation is interpreted in terms of the total absorption of incident radiation, ie, the variation of the mean penetration depth of the photons with their energy It indicates that the centers responsible for the extrinsic emission in the crystals with scheelite structure are mainly localized in a thin (∼100nm) surface layer On the other hand no noticeable changes with the excitation energy were found in the emission spectra of ZnWO4 crystals with wolframite structure The possible implication of this finding is discussed The light yield of the crystals is compared

Luminescence of CaWO4, CaMoO4, and ZnWO4 scintillating crystals under different excitations

Inorganic scintillators are important elements of a new type of cryogenic phonon scintillation detector (CPSD) being developed for single particle detection. These detectors, exhibiting superior energy resolution and the ability to identify the type of interaction in an event, are considered to be the next generation of instrumentation in the search for extremely rare events. This paper presents the latest results of our research on cryogenic scintillators for CPSD applications in the search for dark matter. The paper gives a description of the concept of direct dark matter detection and the operation principles of CPSD, discusses the major material requirements and summarizes the results of investigations over a wide temperature range of the luminescence and scintillation properties of tungstates (CaWO4 and ZnWO4), molybdates (CaMoO4, MgMoO4 and CdMoO4) and Ti-doped Al2O3.

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Cryogenic scintillators in searches for extremely rare events

Features of the reflectivity spectra in the fundamental absorption region were analysed for a series of tungstates. The contribution of electronic states of cations to the formation of the bottom of the conduction band and the top of the valence band is demonstrated. Its relation with the dominant mechanism of the energy transfer to the emission centres and the nature of these centres is discussed.

Optical and luminescent properties of anisotropic tungstate crystals

The colloidal synthesis of ZnO−WO3 heteroaggregates composed of 3−5 nm particles is presented. These sols can be used to prepare nanocrystalline ZnWO4 xerogels, powders, and thin films with strong blue fluorescence (quantum yield between 25 and 50% at room temperature). The conversion of the precursor aggregates into nano- and microcrystalline monoclinic ZnWO4 Sanmartinite has been followed by XRD, DTA−TG−MS, SEM, FTIR, optical absorption, and fluorescence methods. The ZnWO4 crystallites start to develop at 350 °C, and their mean crystal size increases with temperature to 35 nm at 400 °C and 120 nm at 600 °C. At the same time, the fluorescence intensity increases by 3 orders of magnitude within the aforementioned temperature regime, no matter whether X-rays or UV photons are used to excite the samples. In complementary time-resolved X-ray fluorescence investigations, two recombination processes in the micro- and millisecond range were detected. In weakly fluorescing ZnO−WO3 aggregate samples at sizes betw...

Conversion of Colloidal ZnO-WO3 Heteroaggregates into Strongly Blue Luminescing ZnWO4 Xerogels and Films

The spectra of luminescence and photoexcitation as well as emission decay kinetics in various parts of spectra are investigated in ZnWO4 and CdWO4 crystals in a wide temperature range (4.2 to 300 K). The bands of red afterglow and of rapidly decaying violet luminescence are observed for the first time. The likeness of the emission properties of ZnWO4 and CdWO4 allows the explanation of the luminescence in these tungstenite type crystals in terms of configurational coordinate diagrams of self-activated radiation centre and of self-trapped exciton.



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Luminescence of ZnWO4 and CdWO4 Crystals

The kinetics of luminescence of PbWO 4 single crystals is investigated by utilizing synchrotron radiation and selective photoexcitation of intrinsic luminescence. The dynamics of excitation is interpreted in terms of thermally activated depletion of radiative centers and their repopulation from trapping centers resulting in slow components of luminescence decay. The contributions of the luminescence bands in the blue and green regions to the total dynamics of luminescence decay are discussed.

Luminescence Kinetics of PbWO4 Scintillator Crystals

Spectral, temporal, and intensity characteristics of bismuth orthogermanate luminescence are investigated under photoexcitation with various photon quantum energies in the temperature range of 6 to 300 K. Besides the usually observed band peaked at ≈2.5 eV, two fast decaying emission components are studied. The mechanisms of luminescence are accounted for in terms of self-trapped excition recombination and of hot luminescence of selectively excited bismuth ions.



[Russian Text Ignored].

V. D. Ryzhikov

Papers

Luminescence of ZnWO4 and CdWO4 Crystals

Luminescence Kinetics of PbWO4 Scintillator Crystals

Photoluminescence of bismuth orthogermanate single crystals

Luminescence kinetics of pbwo4 scintillation crystals