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We report an experimental study concerned with the synthesis and luminescence properties of Al5O6N aluminum oxynitride doped with Tb3+ in the concentration range 0.025–0.5 at %. All of the samples, prepared by firing appropriate mixtures in a nitrogen atmosphere at 1600°C, consisted predominantly of phase-pure γ-ALON (Al5O6N), with small amounts of impurity phases: Al7O3N5 aluminum oxynitride and Tb3Al5O12 terbium aluminate. Their pulsed cathodoluminescence and photoluminescence spectra contain emission bands typical of Tb3+ ions. The concentration threshold for luminescence quenching corresponds to a Tb3+ concentration at a level of 0.4 at %. A Tb3+ cross relaxation effect found in Al5O6N:Tb3+ is discussed and photoluminescence spectra are shown to be inhomogeneous at low Tb3+ concentrations in Al5O6N.

Polycrystalline Al5O6N samples have been prepared by sol–gel synthesis followed by carbothermal reduction and nitridation. X-ray luminescence (XRL) spectra and thermoluminescence (TL) curves of Ce3+- and Eu2+-doped aluminum oxynitride have been measured in the temperature range 5–380 K and analyzed. Working TL peaks have been detected in the range 150–250 K for the Al5O6N:Ce3+ sample and in the range 140–200 K for the Al5O6N:Eu2+ samples. There are also lower temperature peaks: in the ranges 10–60 and 20–100 K. The XRL spectra of the samples have been measured at temperatures of 8 (for the first time) and 300 K.

Herein we report the synthesis of aluminum oxynitride (Al5O6N) doped with Eu2+ and Ce3+ and examine the effects of the dopant concentration and the nature of the rare-earth-containing precursor (europium and cerium oxides, Eu(acac)3, and Ce(acac)3) on its properties. At dopant concentrations above the solubility limit of rare-earth aluminates (EuAl12O19 and CeAl11O18) in aluminum oxynitride, we observed the formation of aluminum nitride and aluminum oxide (α-Al2O3) as individual phases. The concentration of the latter phase was higher when the rare-earth oxides were used. The emission intensity in the cathodoluminescence spectra of the samples was shown to have a maximum at Eu2+ and Ce3+ concentrations from 0.1 to 0.5 at %. Concentration quenching of luminescence was observed.

The X-ray luminescence (XRL) properties of γ-AlON (γ-Al5O6N), β-SiAlON (Si6–nAlnOnN8–n, where n = 2 and 3) and Ca-α-SiAlON (Cam/2Si12−(m+n)Alm+nOnN16−n) oxynitride samples doped by Eu2+ were investigated. The strong correlation of luminescence spectra parameters of Eu2+ luminescence centers in dependence of oxynitride samples composition is observed. With fitting procedure the composition of XRL spectra with complex profile of investigated oxynitride samples of γ-AlON, β-SiAlON and Ca-α-SiAlON was identified and discussed.

Ce3+-doped borate crystal fibers of Li6Gd(BO 3)3 (LGBO) and Li6Y(BO3)3 (LYBO) compositions are grown by the micro-pulling down (μ-PD) method for potential application in developing new neutron detectors. The ternary equilibrium diagram of Li2O-Gd2O3-B 2O3 is drawn and the preparations of homogeneous mixed LGBO and LYBO powders and growth conditions for single crystal fibers are discussed. Absorption, excitation and X-ray luminescence spectra are investigated. Absolute light yield derived from energy spectra and kinetic decay curves measured under α- and γ-scintillations of Ce 3+-doped LGBO and LYBO single crystal fibers is provided. © 2012 Elsevier B.V. All rights reserved.

Rhombohedral hexametavanadates K4Sr(VO3)6, K4Ba(VO3)6, Rb4 Ba(VO3)6, and Cs4Ba(VO3)6 melt incongruently in the temperature range of 491 to 600°C. Cooling of peritectic melts yields mixtures of compounds typical of M2+O-M2+O-V2O5 systems, far from equilibrium and depending on the cooling kinetics. The vanadate Cs4Ba(VO3)6 undergoes reversible polymorphic transformation at 360°C. All compounds show broad-band luminescence with a maximum of the luminescence spectrum at 490–590 nm with three types of excitation. The vanadates K4Sr(VO3)6 and Rb4Ba(VO3)6 show the highest luminescence intensity at room temperature. The latter is also most efficient at liquid nitrogen temperatures. The luminescence spectra depend on the excitation of vanadates. Three hypotheses were put forward to interpret this finding. The nature of luminescence is attributed to the relaxation of electronic excitation in [VO4]3− structural tetrahedra present in the vanadates. The performance characteristics of luminophores were determined. These luminophores may be promising as X-ray luminescent screens, radioluminescence indicators, and light-emitting diode devices.

Optical absorption and luminescence of synthetic initial and neutron irradiated Gd2SiO5–Ce (0.5 mol.%) crystals was studied. Optical absorption spectra (1–6 eV) were measured using UV-Visible Helios Alpha spectrophotometer at T = 300 K . Time-resolved luminescence spectra (1.5–6 eV), luminescence excitation spectra (4–20 eV) and decay kinetics were recorded at SUPERLUMI station (DESY, Hamburg). Reactor neutron’s irradiation (fluence of 4⋅1018 cm−2) leads to the effective production of defects. There were not registered any new luminescence bands in the irradiated samples, but radiation defects take significant part in the processes of energy transfer to luminescence centers.

The luminescence spectra of bulk and fiber sodium fluoride crystals activated with uranium ions have been analyzed. Luminescence of uranium centers at temperatures of 8.5 and 300 K is considered and the features of the luminescence spectra of these centers in crystals of different dimension are analyzed. The luminescence spectra are simulated with allowance for the spectral-line profiles. Possible models of uranium centers are considered.

X-ray luminescence (XRL) and pulsed cathodoluminescence (PCL) spectra of Eu2+-doped aluminum oxynitride Al5O6N (prepared using the standard sol-gel technique) have been investigated. The radioluminescence spectra, concentration dependences of light yield and time parameters of luminescence process have been measured and discussed. Some peculiarities of luminescence spectra as well as the possible excitation mechanism of AL5O6N with Eu2+ dopants are discussed too.

The thermostimulated exoelectron emission (TSEE) of NaF:(U,Me) compounds after electron beam irradiation in the 300–800 K temperature range has been investigated. For NaF:(U,Me) bulk, fiber and nanocrystals several regular peaks of TSEE have been found. Additional effects with the sign of thermostimulated explosive electron emission have been found too. The nature of TSEE process is discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A study of transient optical absorption of the ADP (NH4H2PO4) and KDP (KH2PO4) nonlinear crystals in the visible and UV spectral regions is reported. Measurements made by absorption optical spectroscopy with nanosecond-time resolution established that the transient optical absorption (TOA) of these crystals originates from optical transitions in the hole A and B radicals and the optical-density relaxation kinetics is rate-controlled by interdefect tunneling recombination, which involves these hole centers and the electronic H0 centers representing neutral hydrogen atoms. At 290 K, hole polarons and the H0 centers undergo thermally stimulated migration, which is not accompanied by carrier ejection into the conduction or valence band. The slow components of the TOA kinetics with characteristic times from a few tens of milliseconds to a few seconds can be assigned to diffusion-controlled annihilation of hydrogen vacancies associated with impurity or structural defects.

Low-temperature photoluminescence (PL) of unactivated KDP crystals under selective synchrotron excitation is for the first time measured with subnanosecond time resolution. Time-resolved PL (2–6 eV) and PL excitation (4–35 eV) spectra, as well as PL kinetics, are measured at 7 K. From the acquired experimental data, luminescent bands related to intrinsic defects of the KDP lattice are identified; in particular, the long-wave band at 2.6 eV is assigned to L defects, and the band at 3.5–3.6 eV is attributed to D defects. An efficient energy transfer over the hydrogen sublattice is shown to take place in KDP at low temperatures. It results in the efficient excitation of L and D center photoluminescence in the fundamental absorption region, at electron transitions to the bottom levels of the conduction band, corresponding to the states of the hydrogen atom. The band gap E g is evaluated to be 8.0–8.8 eV.

Luminescence and excitation spectra of doped LiF and NaF crystals are studied by time-resolved optical and luminescent vacuum ultraviolet (VUV) spectroscopy (2–40 eV energy range, T=10–295 K) with the use of synchrotron radiation of the X-ray and the VUV ranges and pulsed electron beams. Spectral kinetic parameters of luminescence and energies of excited states of U6+ ions are determined. The dominant role of the electron-hole mechanism for energy transfer to impurity centers is established. The effect of multiplication of electronic excitations is clearly manifested for E > 25 eV in NaF:U, Cu crystals and determines their high scintillation yield (137% relative to Tl:CsI when detected in the current regime).

Electronic excitations and the processes of their radiative relaxation are studied in pure and Ce3+ ion-doped crystals of lanthanum beryllate excited by synchrotron radiation in the x-ray and VUV ranges by methods of optical and luminescent vacuum ultraviolet time-resolved spectroscopy. Manifestations of excitons of the valence band are absent in the reflection spectra. However, a fast (τ=1.7 ns) and a slow (microsecond range) channel corresponding to two possible types of self-trapped excitons (STE) are found in radiative relaxation of intrinsic electronic excitations at T=10 K. The slow channel corresponds to emission of STE formed through recombination, the fast channel corresponds to emission of relaxed metastable excitons from the STE state. In the energy region higher than 14 eV (E>2Eg), the effect of multiplication of electronic excitations due to generation of secondary electron-hole pairs resulting from inelastic scattering of both hot photoelectrons and hot photoholes is exhibited.

Luminescence spectroscopy with subnanosecond time resolution is used to study features of nonequilibrium processes excited in several broad-zone dielectrics (mainly inorganic scintillators) by pulses of synchrotron radiation (SR). When excitation density exceeds a certain level, which is different for each material, there is an abrupt change in the kinetics of relaxation of the nonequilibrium states. This change is accompanied by nonuniform broadening or shortwave shifting of the luminescence spectrum and a drop in quantum light yield. The decay time for natural luminescence decreases by 1–3 orders, to nanoseconds, and is independent of temperature within the range 80–450 K. The build-up stage disappears in the kinetics of luminescence of Ce3+-centers and decay time is reduced by a factor of 2–4. Density effects are found to be independent of the conditions under which the material is exposed to SR. A model is proposed in which density effects are related to nonradiative energy transfer from the upper excited states of the luminescence centers to external quenching centers. The contribution of the space charge induced by SR is also examined.

Using solid-state reactions and a combination of carbothermal reduction-nitridation with sol- gel processing, we have synthesized a number of oxynitride phases: Eu 2+-doped Ca-sialons. We have mea- sured the pulsed cathodoluminescence spectra of the synthesized powders under pulsed electron beam exci- tation and determined their emission parameters, including temporal emission characteristics.. © Pleiades Publishing, Ltd., 2012.

Kyropoulos method in an inert atmosphere; - Stockbarger method in an inert atmosphere. The doping with uranium impurity was accomplished in the course of crystal growth by adding UO2(NO3) 2 to the charge in amount of 0.01 mole %. Activation with the lead impurity was accomplished by several methods: doping in the course of crystal growth (PbF 2 in amount of 0.5 mole %); thermal diffusion in an inert atmosphere at a temperature close to the melting point of the matrix, for a period of 50 h; and by implanting lead ions (implantation performed in a DIANA-2 unit [7]). The surface density of the implanted lead ions was determined by backscattering of He + ions (1.65 MeV) in a cyclotron; the surface density proved to be (4.5-6.3)'i0 Is ions/cm 2 [7]. The depth of localization of lead ions in this case was no greater than 0.4 nm. Thermostimulated luminescence was studied in an automatic unit [9] operating in a loop with an Elektronika 0585 microcomputer. By means of a low-inertia nitrogen cryostat, the temperature was varied in the 80-550 K interval with a linear heating rate of 0.i or 0.3 K/ sec. Excitation was accomplished at 80 K by x-ray radiation from a BSV2:Cu tube (30 kV, i0 mA) with an exposure of 5 min. A vacuum better than 10 -4 Pa was obtained by pumping down with a nonoily medium. TSL was registered by means of an FEU-106 photomultiplier, and in the photon count mode an MDR-2 monochromator.

New high-temperature peaks of thermostimulated exoelectron emission (TSEE) from uranium-activated LiF and NaF Crystals were observed. TSEE parameters for various (Li,Na)-(U+Me) systems were determined.

The physical properties of the family of cyclotetravanadates A(2)M(VO3)(4), where A=Na,Ag and M=Ca,Sr, have been studied by means of x-ray powder diffraction, neutron diffraction, electron diffract ...

The spectra and decay kinetics of luminescence and the excitation and reflection spectra of the luminescence of orthosilicates A2SiO5 (A = Y, Lu, Sc, Gd), both nominally pure and doped with cerium, are measured using time-resolved VUV spectroscopy in the ranges of energies ħν = 1.5–16 eV and temperatures T = 8–3000 K. The band structure of the crystals is calculated in the local electron density approximation (LDA). The origin of the intrinsic luminescence in the crystals studied is established, and the assumption regarding the existence of self-trapped excitons and their structure is made.

Structural, luminescence, and electronic properties of the family of alkaline metal-strontium cyclotetravanadates M{sub 2}Sr(VO{sub 3}){sub 4}, M=Na, K, Rb, and Cs have been characterized by means of elemental analyses, x-ray powder diffraction, neutron diffraction, electron diffraction, infrared, Raman, photo, x rays, pulse cathode beam excitation, x-ray photoelectron spectroscopy and band structure calculations. The M{sub 2}Sr(VO{sub 3}){sub 4} system have tetragonal structures Na-, K-, Rb-P4/nbm and Cs-P4/mmm, with a=10.63449(4), 10.94106(6), 11.08889(8), 7.9183(3) and c=4.96205(4), 5.31600(4), 5.46682(8), 5.5778(3) A, respectively. The main structural feature of M{sub 2}Sr(VO{sub 3}){sub 4} is tetracyclic [V{sub 4}O{sub 12}] units. When going from Na{sub 2}Sr(VO{sub 3}){sub 4} to Cs{sub 2}Sr(VO{sub 3}){sub 4} do the coordination polyhedron around the alkaline metal change continuously from an octahedron to a hexagonal prism and that around the strontium from a square antiprism to a square prism. The hybridized O 2p-V 3d states of tetracyclic [V{sub 4}O{sub 12}] units have a dominant influence on the electronic structure of these compounds. All M{sub 2}Sr(VO{sub 3}){sub 4} are semiconducting with a decreasing LDA band gap (E{sub a}) from 2.02 for Na{sub 2}Sr(VO{sub 3}){sub 4} to 1.56 eV for Cs{sub 2}Sr(VO{sub 3}){sub 4}.

The photoexcitation spectra (70-280 nm) of the Eu 3+, Tb 3+, Dy 3+, Er 3+, and Tm 3+ ion luminescence in strontium fluoride crystals are studied at 8 and 295 K by vacuum ultraviolet spectroscopy using synchrotron-radiation excitation. The processes of transfer of the excitation energy to the impurity centers as well as the relaxation mechanisms of the excited high-energy states of the rare-earth ions are analyzed. The bands corresponding to the interconfiguration 4f-5d transitions and the charge-transfer bands are identified in the photoexcitation luminescence spectra. ©2005 Springer Science+Business Media, Inc. The present work was supported in part by the Russian Foundation for Basic Research (Grant 05-02-16530), by the Program “Russian Universities” (Grant UR.02.01.433), by REC-005 (ЕК-005-XI), and BMBF (05KS8GMD/1).

The results of comparative investigations into the scintillation and optical properties of bulk, fiber, and nanosized NaF-U crystals are presented. Fiber and nanosized samples of the NaF-U crystals are prepared for the first time and show considerable promise for practical applications in radiation technology.

The photoluminescence (PL), PL excitation, and PL decay kinetics of 6Li2O-MgO-SiO2-Ce glasses were studied using time-resolved VUV spectroscopy. The Ce3+ ion PL excitation spectrum contains a known group of structural bands at 4.4–5.2 eV caused by 4f → 5d transitions. Moreover, features at 6.4–7.7 eV were detected and their nature is discussed. At an exciting photon energy E exc > 25 eV, the photon multiplication effect manifests itself. Based on 6Li-silica glasses, a scintillation neutron detector with improved parameters was developed and produced.

Time-resolved excitation and emission spectra of SrF2: Er3+ upon selective excitation with synchrotron radiation in the VUV and ultrasoft x-ray ranges at T = 8 K were studied. The VUV luminescence of SrF2: Er3+ derives from high-energy interconfiguration 4f105d-4f11 transitions in the Er3+ ion. The VUV emission spectrum revealed, in addition to the 164.5-nm band (millisecond-range kinetics), a band at 146.4 nm (with a decay time of less than 600 ps). The formation of excitation spectra for the f-f and f-d transitions in the Er3+ ion is discussed.

The absorption, excitation, and luminescence spectra of vanadates of type M 3 + M3+(VO4)2 and M 2 + M4+(VO4)2 are studied, where M+ is Na, K, Rb, Cs; M3+ is Al, Sc; M4+ is Zr, Sn, Ti. The luminescence spectra maxima are located at 490–510 nm, while those of the excitation spectra are at 360–375 nm. Temperature characteristics of luminescence and thermostimulated luminescence are studied. The question of activation of complex vanadates by rare-earth ions is considered.

This paper presents the results of spectroscopic kinetic investigation of the pulsed cathode luminescence (CL) in the alpha, beta and gamma scintillation of BGO (Bi/sub 4/Ge/sub 3/O/sub 12/) crystals. The single crystals of bismuth orthogermanate were grown according to the Czochralski method in platinum crucibles. The cathode luminescence was studied in the 80-500/sup 0/K range with excitation by a beam of electrons with j = 1 A/cm/sup 2/, a lifetime t/sub 0.5/ = 10nsec., and a maximum energy of 200 keV. Radionuclides were used for the investigation of the scintillation properties. Results include the discovery of broadband short-wavelength luminescence in the 2.5-4-eV range, which makes the main contribution to the fast nanosecond scintillation component. The investigation of the form of the scintillation pulses in BGO revealed protracted fronts for the beginning of luminescence and a characteristic ''rounded'' peak for the scintillation pulse. The UV luminescence band discovered, as well as the features of the kinetics of the pulsed CL, are similar to those in CaWO/sub 4/. Therefore, the excitation model first proposed for calcium tungstate and considered as applied to BGO fairly completely reflects the mechanisms for the transfer of luminescence energy and the act of scintillation.

Large lithium hydride single crystals, having the form of a double cone 80 mm in height and 40 mm in average diameter, have been grown by the modified Bridgman—Stockbarger method using ultrasound. The crystals have a perfect structure and differ from those grown earlier in the absolute absence of a small angle divergence of cleaved planes, the high stoichiometry and the small amount of uncontrolled impurities. To obtain the crystals, the necessary apparatus was designed and manufactured and optimal synthesis regimes have been found out. The quality was discovered to be greatly influenced by ultrasound. The LiH host was activated with various elements. The use of ultrasound gives rise to an almost uniform distribution of the activator over the volume. The X-ray analysis showed the samples to be monocrystalline and allowed the determination of the lattice parameters and the symmetry type of synthesized crystals to be made.

Optical scintillations from single crystals of BeO:Li and BeO:Na have been observed in the temperature interval 15-575 K. These scintillations result from subjecting the crystals to a temperature ramp and do not require previous irradiation. It is suggested that pyroelectricity forms the basis for adequately explaining this phenomenon. The electric field near the surface is related to the surface temperature gradient by E = (lambda/sub T/d/kappa epsilon/sub 0/) ..delta..T/..delta..X, where lambda/sub T/ is the pyroelectric coefficient, d is the charge-separation distance, and kappa is the dielectric constant. For small changes in ..delta..T/..delta..X (perhaps as small as 0.26 K/mm), an electric field of sufficient magnitude to break down air is produced. The optical spectrum of these scintillations corresponds to the second positive system of molecular nitrogen. It is shown that there exists a correlation between the temperature region of maximum scintillation activity and the temperature region where an anomalous heat capacity is observed in these samples. 33 references, 3 figures, 1 table.