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Photoluminescence, luminescence excitation spectra, and electrical conductivity of β-Ga2O3-In2O3 solid solutions were studied. For this purpose, polycrystalline samples of unintentionally doped (UID) and doped with Ca or Zr β-Ga2O3-In2O3 solid solution with 20% In were synthesized and characterized. All samples were obtained by the high-temperature solid-phase method from appropriate oxides at 1300 °C at low and high oxygen partial pressure. It was established that UID and doped with Ca2+ or Zr4+ samples synthesized in an oxygen atmosphere were highly resistive, while the samples synthesized in an argon atmosphere had high conductivity. The conductivity was the lowest in the samples doped with Ca2+ and was 10−13 Ω−1 cm−1, while in the samples doped with Zr4+, the electrical conductivity was the highest and reached 10−3 Ω−1 cm−1. The broadband luminescence of β-Ga2O3-In2O3 solid solution is a superposition of three elementary bands with maxima in the violet 3.08 eV, blue 2.73 eV, and green 2.45 eV regions of the spectrum. Doping with Ca2+ or Zr4+ impurities and varying the synthesis atmosphere led mainly to a redistribution of intensities between the elementary luminescence bands. The luminescence arises from the radiative recombination of charge carriers through donor–acceptor pairs and self-localized holes. Donors and acceptors are formed by native defects such as (Gai, VGa, VGaVo) or doping impurities (Zr4+, Ca2+). Unlike the luminescence spectra, the luminescence excitation spectra change significantly when the synthesis conditions vary or when doping with divalent impurities. The excitation band at 4.46 eV is due to electron transitions from the VGa or VGaVO acceptor levels to the conduction band. Electron transitions from acceptor levels of Ca2+ impurities are manifested in the intense excitation band at 4.1 eV. [ABSTRACT FROM AUTHOR]

The effect of the sintering atmosphere on the structural, electrical, and luminescence properties of gallium oxide ceramics was studied using X-ray diffraction, scanning electron microscopy, luminescent spectroscopy, and electrical conductivity methods. A single β-Ga2O3 structure was confirmed by X-ray diffraction. The sintering of ceramics in the argon atmosphere caused structural changes on the surface and an insignificant increase in intrinsic volume. These features were also confirmed by scanning electron microscopy, where a larger number of vacancy-type defects were observed for argon-sintered ceramics rather than in the case of sintering in an oxygen atmosphere. The β-Ga2O3 ceramics exhibited three photoluminescence excitation peaks located at 3.33, 4.52, and 5.3 eV. The emission spectra revealed a broad peak in the 2.0–4.0 eV region, with a maximum at around 3.03 eV. The sintering atmosphere also affected the relative intensity of elementary luminescence bands. The photoluminescence properties are mainly attributed to the radiative recombination of charge carriers through donor–acceptor pairs. It was established that the electrical conductivity of ceramics also strongly depended on the sintering atmosphere. [ABSTRACT FROM AUTHOR]

We have obtained X-ray emission spectra of Ga and Ge in Ca3Ga2Ge4O14, X-ray emission OKα-spectra in Ca3Ga2Ge4O14, Ca3Ga2Ge4O14 + Ce3%, and Ca3Ga2Ge4O14 + Eu4% and Xray photoelectron spectra in Ca3Ga2Ge4O14 . Our X-ray spectral studies of the Ca3Ga2Ge4O14 gallogermanate have shown that the top of the valence band near the Fermi level is formed mainly by p states of gallium and germanium as well as p states of oxygen, whose intensity is sufficiently low. The middle of the valence band is formed by gallium 3d states with oxygen 2s states lying below them. These states are hybridized with 4p states of gallium and germanium because of which there are Kβ′′-satellites in the Kβ2-subbands of gallium and germanium. The bottom of the valence band is formed by 3d states of germanium, whose contribution to chemical bonding is insignificant. The X-ray emission bands of Ga and Ge in Ca3Ga2Ge4O14 and the photoelectron spectrum of the valence electrons of Ca3Ga2Ge4O14 are in good agreement. The OKα-band changes its fine structure only slightly upon doping Ca3Ga2Ge4O14 with Ce or Eu. The investigations of intrinsic luminescence under X-rays excitation of Ca3Ga2Ge4O14 gallogermanate are presented. [ABSTRACT FROM AUTHOR]

We have obtained X-ray emission spectra of Ga and Ge in Ca3Ga2Ge4O14, X-ray emission OKα-spectra in Ca3Ga2Ge4O14, Ca3Ga2Ge4O14 + Ce3%, and Ca3Ga2Ge4O14 + Eu4% and Xray photoelectron spectra in Ca3Ga2Ge4O14 . Our X-ray spectral studies of the Ca3Ga2Ge4O14 gallogermanate have shown that the top of the valence band near the Fermi level is formed mainly by p states of gallium and germanium as well as p states of oxygen, whose intensity is sufficiently low. The middle of the valence band is formed by gallium 3d states with oxygen 2s states lying below them. These states are hybridized with 4p states of gallium and germanium because of which there are Kβ′′-satellites in the Kβ2-subbands of gallium and germanium. The bottom of the valence band is formed by 3d states of germanium, whose contribution to chemical bonding is insignificant. The X-ray emission bands of Ga and Ge in Ca3Ga2Ge4O14 and the photoelectron spectrum of the valence electrons of Ca3Ga2Ge4O14 are in good agreement. The OKα-band changes its fine structure only slightly upon doping Ca3Ga2Ge4O14 with Ce or Eu. The investigations of intrinsic luminescence under X-rays excitation of Ca3Ga2Ge4O14 gallogermanate are presented. [ABSTRACT FROM AUTHOR]

Microdefects in β-Ga2O3 and β-Ga2O3:0.1 % Mg single crystals grown by the method of floating zone technique with radiation heating have been studied. Porous defects with a tube-like shape were found on the (100) surface and in the bulk of undoped β-Ga2O3 crystals. Such defects are up to 1 μm in diameter and up to 100 μm in length, elongated along the [010] axis. Doping of gallium oxide with magnesium ions leads to a decrease in the concentration of defects and changes in their shape. The concentration and mobility of electrical charge carriers in undoped β-Ga2O3 crystals were calculated. The activation energies of the conductivity of the studied crystals were estimated. Some correlations between crystal growing conditions, doping, and the rate of Ga2O evaporation from the melt and defect density were revealed and discussed, providing aspects for further material development. The mechanisms of these defects formation have been also analyzed. [ABSTRACT FROM AUTHOR]

The temperature-dependencies of the X-ray excited luminescence spectra were measured from unintentionally doped, annealed in oxygen and Mg-doped β-Ga2O3 crystals prepared by the floating zone growth method. The crystals exhibited ultraviolet, blue and green luminescence bands. It was established that the luminescence intensity is strongly dependent on resistivity of the crystal. For the as-grown sample with a high electron concentration, the main luminescence band at 300 K was blue. The blue luminescence band was observed over a wide range of temperatures, and the thermal quenching of luminescence was observed only at T > 400 K. The blue luminescence band was suppressed in high-resistance crystals, in particular in oxygen annealed and heavily doped β-Ga2O3 crystals with 1% Mg, while the UV band, on the contrary, increased and prevailed at low temperatures. Activation energies of separate luminescence bands and conductivity in the investigated crystals are calculated. Some correlations between conductivity and luminescence parameters were found and discussed to give hints for the further development of this material. [ABSTRACT FROM AUTHOR]

The paper deals with thermostimulated luminescence (TSL) and thermostimulated conductivity (TSC) of unintentionally doped (UID) -Ga2O3 single crystals. The samples under study were β-Ga2O3 single crystals grown by the floating zone method with radiation heating and then subjected to annealing in an atmosphere of oxygen or argon. The obtained photoluminescence emission spectra are typical for β-Ga2O3 single crystals: they contain the broad emission band of the host at 320-550 nm as well as a weak luminescence with maximum at 700 nm due to the unintentional Cr3+ impurities. After exposure to X-ray radiation, the samples exhibit intense TSL at the temperature range of 85-500 K. Three low-temperature peaks at 116, 147 and 165 K are present in TSL and TSC curves of these crystals. The depths of the traps responsible for these peaks are 0.15, 0.2 and 0.3 eV, respectively. The high-temperature TSL peaks at 354 K, 385 K and 430 K with corresponding activation energies of 0.84, 1.0 and 1.1 eV were observed in samples annealed in argon or oxygen atmospheres. The TSС curves are in good agreement with the results of the TSL study. A correlation between annealing of crystals in oxidizing and inert atmospheres and intrinsic defects in single crystals β-Ga2O3 has been established. [ABSTRACT FROM AUTHOR]

The results of the investigations of X-ray excitation spectra, thermostimulated luminescence and influence of light illumination on the thermoluminescence glow curves of Eu3+-doped Ca3-xCdxGa2Ge3O12 garnet polycrystalline samples are presented. It is shown that Ca3-xCdxGa2Ge3O12 polycrystalline samples are characterized by intrinsic luminescence, which consists of several components. The nature of intrinsic luminescence is discussed. It is suggested that the nature of thermoluminescence glow peak near 150 K is connected with the [(VGe+VO)--F+] associations formed under X-ray irradiation at 85 K. The influence of light illumination on the TSL intensity of the preliminary X-ray irradiated samples is shown. [ABSTRACT FROM AUTHOR]

Optical absorption and photoconductivity investigations of nominal pure and Mg2+ doped β-Ga2O3 single crystals have been carried out. Additional bands in the UV (3.6-4.6 eV) and near-IR (0.4-1.2 eV) spectral regions were found in optical absorption and photoconductivity spectra. A correlation between Mg2+ doping, annealing in oxygen atmosphere as well as optical absorption and photoconductivity bands were established in gallium oxide. Electronic transitions from shallow traps and F-centers were observed in the IR spectral region (0.4-1.2 eV). Absorption and photoconductivity in the UV region are related to deep acceptor levels created by native defects and impurities. [ABSTRACT FROM AUTHOR]

In this work the researched results of the spectral characteristics of the luminescence and the thermostimulated luminescence curves of Y2O3 and Y2O3:Eu ceramic materials at the X-ray excitation in the 85-295 K range were generalized. Considering the features of Y2O3 crystal structure and the possibility of the formation of the short-lived and stable hole and electron centers of V- and F-type by the ionizing radiation X-ray luminescence spectrum of ceramics at 85 K is fitted into the elementary Gaussian shape bands with the maxima near 3.40, 3.06, 2.67, 2.33, 2.09, and 1.91 eV. The main 3.40 and 3.06 eV bands of the luminescence are caused by the self-trapped excitons of (YO6)9- complex, when the cation is localized in the field of the trigonal (C3i) and monoclinic (C2) symmetries. The emission at 2.67 eV and the weak bands in the 1.65-2.61 eV region are considered as the radiation of excitons localized on the anion vacancies and the electron centers of F-type (F+, F and F-). The thermoluminescence of Y2O3 in the 186 and 204 K main peaks range is connected with the thermal destruction of the self-trapped states of O- ions that located in the field of the trigonal and monoclinic symmetries. The activator bands caused by 5D → 7Fj electronic transitions in Eu3+ are only observed in the X-ray and thermostimulated luminescence spectra of Y2O3:Eu ceramics. It was assumed that both at the X-rays irradiation and an optical excitation in the band of the charge transfer of Y2O3:Eu sample the energy goes to Eu3+ through (Eu2+O-) complexes (states) of the charge transfer. [ABSTRACT FROM AUTHOR]

The luminescent properties of CdWO4:Tb,Li crystals have been investigated at 10 K in the region 4-25 eV using synchrotron excitation. It is shown that besides the intrinsic matrix luminescence the number emission lines due to electron f-f-transitions in Tb3+ ions are eficiently excited at near-edge region of the fundamental absorption (Eexc = 4:1 eV). The weak recombination luminescence of terbium impurity on the background of intensive matrix luminescence is observed under excitation in the region of fundamental absorption (Eexc = 5:4 and 13.8 eV). It is shown that the luminescence spectrum of the matrix is a superposition of three elementary bands 2.07, 2.47, and 2.73 eV. The nature of emission bands is discussed. [ABSTRACT FROM AUTHOR]

In this paper spectroscopic investigations of Gd3Ga5O12 (GGG) polycrystals, containing Cr3+ and intentionally doped with Pr3+ of concentrations 0.5, 1 and 1.5 mol% are presented. We have measured the steady state luminescence and luminescence excitation spectra, as well as the time resolved spectra and luminescence kinetics. The main goal was to investigate the excitation energy transfer from lattice to impurity and between impurities. We found that relative intensity of Cr3+ and GGG lattice luminescence decreased when material was doped with Pr3+. On the other hand, time resolved spectroscopy and luminescence decay measurements showed that the Cr3+ and GGG lattice luminescence decays were independent of Pr3+ content. The lifetime of Pr3+ luminescence related to ¹D2→³H4 and ³P0→³H4 transitions decreased with concentration of Pr3+, which was attributed to the concentration luminescence quenching. No energy transfer between GGG lattice defects and Cr3+, and Pr3+ ions was observed. We proposed the model of radiative recombination of electron and hole, which took place through three independent pathways: by GGG host emission that peaked at 12750 cm-1, by Cr3+ luminescence that peaked at 15400 cm-1, and by Pr3+ luminescence. [ABSTRACT FROM AUTHOR]

Abstract: The luminescence excitation spectra, emission spectra under photo- and X-ray excitation, luminescence decay kinetics and thermostimulated luminescence (TSL) of Gd3Ga5O12 garnet (GGG) polycrystalline samples have been investigated. It was established that the spectrum of Cr3+ ion emission were present in all TSL peaks. The activation energies of traps that are responsible for appearance of TSL in the region 295–600K were estimated. It is shown that delocalization of electrons from the Cr3+e traps leads to the appearance of thermoluminescence (TL) glow peak at 390K. The nature of other TSL peaks is discussed. The influence of visible light on the TSL intensity of the preliminary X-ray-irradiated samples is shown. [Copyright &y& Elsevier]

The roentgenoluminescence spectra, temperature-dependent activator luminescence, optically stimulated luminescence, and the effect of IR irradiation on the yield and spectral composition of the low-temperature roentgenoluminescence and thermoluminescence curves of the Y3Al5O12:Ce3+ scintillator have been studied in the temperature range 85–295 K. The results, coupled with earlier data, suggest that the Ce3+ ions in the garnet crystal studied form Ce3+ p hole centers and increase the concentration of electronic F −-centers responsible for the IR stimulation band at 940 nm. The reduction in roentgenoluminescence yield on cooling Y3Al5O12:Ce3+ to below 230 K is due to the significant localization of excited carriers at defects, which show up in thermoluminescence peaks and optical stimulation spectra. The low-temperature Ce3+ luminescence in Y3Al5O12:Ce3+ seems to result from the recombination of activator-bound excitons. [ABSTRACT FROM AUTHOR]

The luminescent properties of CdI2, CdI2:Pb2+, CdI2:Mn2+, and CdI2:Pb2+,Mn2+) crystals have been studied at temperatures from 85 to 295 K under optical and x-ray excitation. Analysis of new and earlier spectroscopic data suggests that the 560-nm luminescence of CdI2:Pb2+ and CdI2:(Pb2+,Mn2+) crystals under excitation on the long-wavelength component of the A absorption band of Pb2+ centers is due to Pb2+-bound anion excitons. The 640-to 660-nm emission of these crystals is attributable to α centers. The manganese luminescence in the codoped material originates from both intracenter Mn2+ excitations and a sensitized process due to energy transfer from the host and Pb2+-related centers. The mechanisms of recombination and energy transfer processes in cadmium iodide crystals codoped with Pb2+ and Mn2+ are discussed. [ABSTRACT FROM AUTHOR]

The thermally stimulated properties of PbWO4 in the temperature range 90–400 K have been investigated on undoped and terbium-doped crystals after X-ray irradiation at 90 K. Doping with terbium changes the concentration of shallow traps, which are responsible for retrapping free electrons and holes. Light illumination can change the distribution of the traps. The optically stimulated luminescence is observed. The influence of light illumination on the TSL curves and emission properties is studied. The possible mechanism of TSL phototransformation is discussed. [Copyright &y& Elsevier]