Energy Levels in the Forbidden Band of the Bi4Ge3O12 Ceramics

Thermally stimulated luminescence in the Bi₄Ge₃O₁₂ ceramics and also in the ceramics of the parent components Bi₂O₃ and GeO₂ is investigated. The similarity of the curves of the thermally stimulated luminescence in bismuth germanate with the structure of eulytine Bi₄Ge₃O₁₂ and sillenite Bi₁₂GeO₂₀ is explained. The relation of the thermally stimulated luminescence band in Bi₄Ge₃O₁₂ (with a maximum at 143 K) to the disruptions in the germanium sublattice and of the thermally stimulated band (with a maximum at 187 K) to the recombination processes in the bismuth sublattice is shown. It has been established that the light sum in the Bi₄Ge₃O₁₂ ceramics is stored most effectively upon excitation by light in an energy region of 4.4 eV.     

Luminescence of Thin Bismuth Germanate Films Having the Structure of Eulitine and Benitoite

The luminescence and luminescence excitation spectra of thin films of Bi₄Ge₃O₁₂ and Bi₂Ge₃O₉ were investigated. The spectra were decomposed into elementary components by the Alentsev-Fok method. It has been established that the luminescence spectra of thin Bi₄Ge₃O₁₂ and Bi₂Ge₃O₉ films have a similar structure and that each contains three luminescence bands with maxima at 2.70, 2.40, and 2.05 eV and at 2.73, 2.40, and 1.95 eV, respectively. Comparison of the results obtained with the well-known results of investigation of the luminescence of Bi₁₂GeO₂₀ and Bi₂O₃ suggests that the luminescence in the compounds considered is caused by the radiation processes that proceed in structural complexes of similar configuration that contain the bismuth ion in the nearest oxygen environment. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 377–380, May–June, 2005.     

Local Trapping Centers in the Ceramics of Eulytines

Thermally stimulated luminescence (TSL) of ceramics having the structure of eulytine Bi₄X₃O₁₂ (X = Si, Ge, Zr) on exposure to x-ray irradiation in the temperature region 80–400 K is studied. An analysis of the forms of the TSL curves implies that the recombination processes in the TSL peaks at 149 and 212 K in Bi₄Si₃O₁₂ ceramics and at 143 and 230 K in Bi₄Ge₃O₁₂ ceramics can be described by the linear kinetics. The spectral composition of TSL of the ceramics obtained is investigated, and the activation energy and frequency factors which correspond to the TSL maxima are determined by various methods. Based on common spectral and energy characteristics of TSL, a conclusion concerning the connection of TSL with recombination processes in common structural complexes of BiO₆ ^9– is drawn.     

Luminescence centers in Pb2Bi6O11 and Sn2Bi6O11 ceramics

We have studied the luminescence spectra and luminescence excitation spectra of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ ceramics at 80 K. We have used the Alentsev-Fock to decompose the spectra into elementary components. We have established that the luminescence spectra of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ ceramics contain three elementary bands each with maxima at 2.60, 2.32, 12.93 eV and 2.62, 2.30, 2.00 eV. Comparison of the data obtained with the results of a study of the luminescence spectra for a series of bismuth-containing oxide compounds suggest that luminescence of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ is due to radiative processes in structural complexes containing a bismuth ion in a nearest-neighbor oxygen environment. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 597–600, September–October, 2006.     

Luminescence centers in bismuth-containing oxytungstate ceramics

We have studied the photoexcitation and luminescence spectra of Bi₂WO₆, Y₂WO₆ and Y₂WO₆:Bi ceramics. We used the Alentsev-Fock method to decompose the spectra into elementary components. The emission bands with maximum at 2.93 eV in the luminescence spectrum of Bi₂WO₆, 3.02 eV in the luminescence spectrum of Y₂WO₆, and 2.95 eV in the luminescence spectrum of Y₂WO₆:Bi are assigned to luminescence of self-localized Frenkel excitons. The bands with maxima at 2.35 eV and 1.90 eV in the spectrum of Bi₂WO₆, 2.25 eV and 1.75 eV in the spectrum of Y₂WO₆, and 2.35 eV and 1.85 eV in the spectrum of Y₂WO₆:Bi are connected with oxygen vacancies. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 688–691, September–October, 2007.     

Influence of Oxygen Vacancies on the Luminescence Spectra of Thin Bi4Ge3O12 Films

Luminescence spectra of thin Bi₄Ge₃O₁₂ films annealed in air and in vacuum have been investigated. It has been established that the luminescence spectra for different forms of excitation consist of three bands with maxima at 2.70, 2.40, and 2.05 eV. The relation of the bands with maxima at 2.40 and 2.05 eV to the centers that incorporate an oxygen vacancy has been shown. The separated emission bands have been interpreted.     

Thermostimulated Luminescence of PbWO4, Bi2WO6, and Y2WO6 Ceramics

Thermostimulated luminescence (TSL) of PbWO₄, Bi₂WO₆, and Y₂WO₆ ceramics on x-ray excitation is investigated. The spectral luminosity of the thermostimulated luminescence is analyzed. The thermal activation energies conforming to the corresponding thermostimulated luminescence peaks are determined. It is established that on emptying trapping centers radiative recombination occurs at the intrinsic-luminescence centers associated with tungsten-oxygen complexes WO₄ ^2–.     

Luminescence spectroscopy of the Bi single and dimer centers in Y3Al5O12:Bi single crystalline films

Luminescence of the Bi³⁺ single and dimer centers in UV and visible ranges is studied in YAG:Bi (0.13 and 0.27 at% of Bi, respectively) single crystalline films (SCFs), grown by liquid phase epitaxy from a Bi₂O₃ flux. The cathodoluminescence spectra, photoluminescence decays, and time-resolved spectra are measured under the excitation by accelerated electrons and synchrotron radiation with energies of 3.7 and 12 eV, respectively. The energy level structure of the Bi³⁺ single and dimer centers was determined. The UV luminescence of YAG:Bi SCF in the bands that peaked at 4.045 and 3.995 eV at 300 K is caused by radiative transitions of Bi³⁺ single and dimer centers, respectively. The excitation spectra of UV luminescence of Bi³⁺ single and dimer centers consist of two dominant bands, peaked at 4.7/4.315 and 5.7/6.15 eV, related to the ¹S₀→³P₁ (A band) and ¹S₀→ ¹P₁ (C-band) transitions of Bi³⁺ ions, respectively. The excitation bands that peaked at 7.0 and 7.09 eV are ascribed to excitons bound with the Bi³⁺ single and dimer centers, respectively. The visible luminescence of YAG:Bi SCF presents superposition of several wide emission bands peaking within the 3.125-2.57 eV range and is ascribed to different types of excitons localized around the Bi³⁺ single and dimer centers. Apart from the above mentioned A and C bands the excitation spectra of visible luminescence contain wide bands at 5.25, 5.93, and 6.85 eV ascribed to the O²⁻→Bi³⁺ and Bi³⁺→Bi⁴⁺ + e charge transfer transition (CTT) in Bi³⁺ single and dimer centers. The observed significant differences in the decay kinetics of visible luminescence under excitation in A and C bands of Bi³⁺ ions, CTT bands, and in the exciton and interband transitions confirm the radiative decay of different types of excitons localized around Bi³⁺ ions in the single and dimer centers.     

Luminescence centers in yttrium silicate and germanate

Luminescence spectra for isostructural Y₂SiO₅ and Y₂GeO₅ are investigated. The spectra are resolved into elementary components by the Alentsev—Fock method. Bands with maxima in regions of 2.6, 2.3, and 2.05 eV in the spectra of Y₂SiO₅ luminescence and in regions of 2.55, 2.25, and 2.0 eV in the spectra of Y₂GeO₅ luminescence are considered as radiative recombination of excited associative donor-acceptor Y³⁺−O²⁻ pairs. The indicated bands are related to certain distances between yttrium (the donor) and oxygen (the acceptor). A band with a maximum of 2.95 eV in Y₂SiO₅ and 3.0 eV in Y₂GeO₅ occurs in recombination of electrons with holes trapped by an anionic sublattice. I. Franko L’vov State University, 50, Dragomanov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 528–531, July–August, 1998.     

Luminescence centers in ceramics of yttrium, scandium, and bismuth oxytungstates

An investigation is made of the luminescence spectra of Me₂WO₆ ceramics (Me=Y, Sc, Bi). The spectra were decomposed into elementary components by the Alentsev—Fock method. Radiation hands with a maximum at 3.02 eV in the Y₂WO₆ luminescence spectrum, at 2.8 eV in the ScWO₆ spectrum, and at 2.93 eV in the Bi₂WO₆ spectrum are assigned to the light emission of self-localized Frenkel excitons. The bands with maxima at 2.25 and 1.75 eV in the Y₂WO₆ spectrum, at 2.36 and 1.9 eV in the Sc₂WO₆ spectrum, and at 2.35 and 1.9 eV in the Bi₂WO₆ spectrum are related to oxygen vacancies. Translated from Zhurnal Prikladnoi Spektroskopii, Vol 67, No. 2, pp. 273–275, March–April, 2000.     

Light Dispersion in Bismuth Germanate Crystals and Bismuth Oxide Films

The dispersion of light in Bi₄Ge₃O₁₂ and Bi₁₂GeO₂₀ single crystals and thin Bi₂O₃ films with a monoclinic structure was investigated in the visible spectral region. The parameters of a single-oscillator approximation have been found. It is established that in Bi₄Ge₃O₁₂ crystals the absorption band caused by the O2p–Bi6p transitions makes the main contribution to the dispersion curve in the visible region, whereas in Bi₁₂GeO₂₀ crystals this is made by transitions from the hybrid O2p–Bi6p states to the conduction band. The dispersion energy, the degree of the ionicity of binding, and the coordination number of the first coordination sphere of the Bi³⁺ cation have been determined.     

Luminescence centers in α-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramics

Luminescence photoexcitation spectra of α-Bi₂O₃ ceramics are investigated. Luminescence spectra were deconvoluted into fundamental components using the Alentsev-Fok method. It is established that the luminescence spectra of α-Bi₂O₃ ceramics consist of three fundamental bands with maxima at 2.75, 2.40, and 1.97 eV. A comparison of the results with those from an investigation of luminescence of various modifications of bismuth oxide and bismuth germanates suggests that luminescence of these compounds is caused by radiation processes that occur in structural complexes that contain the bismuth ion in a nearest oxygen environment. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 672–676, September–October, 2008.     

Luminescence of Bismuth‐Activated Ceramics of Yttrium and Scandium Oxides

The luminescence spectra of Y₂O₃:Bi and Sc₂O₃:Bi ceramics have been investigated. The spectra have been resolved into elementary components by the Alentsev–Fock method. It has been established that the luminescence is attributed to emission centers of three types, two of which are due to the replacement of Y³⁺ (or Sc³⁺) by Bi³⁺ at the nodes of the crystal lattice of Y₂O₃ (or Sc₂O₃) with the point symmetry C ₂ and C _3i . The emission center Bi³⁺ in the position C_3i leads to the appearance of blue luminescence with maxima at 3.03 eV for Y₂O₃:Bi and at 3.05 eV for Sc₂O₃:Bi; this luminescence is attributed to the transition ³ P ₁–¹ S ₀. The emission center Bi³⁺ in the position C ₂ initiates green luminescence (which is also related to the ³ P ₁–¹ S ₀ transition in Bi³⁺) with a maximum in the region of 2.40 eV in Y₂O₃:Bi and in the region of 2.46 eV in Sc₂O₃:Bi. The red luminescence band with maxima at 1.85 eV in Y₂O₃:Bi and at 1.95 eV in Sc₂O₃:Bi is related to the presence of structural defects.     

Luminescence and thermally stimulated recombination processes in Li<Subscript>6</Subscript>Gd(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>:Ce<Superscript>3+</Superscript> crystals

The luminescence and thermally stimulated recombination processes in lithium borate crystals Li₆Gd(BO₃)₃ and Li₆Gd(BO₃)₃:Ce have been studied. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence), temperature dependences of the intensity of steady-state X-ray luminescence (XL), and thermally stimulated luminescence (TSL) spectra of these compounds have been investigated in the temperature range of 90–500 K. The intrinsic-luminescence 312-nm band, which is due to the ⁶ P _J → ⁸ S _7/2 transitions in Gd³⁺ matrix ions, dominates in the X-ray luminescence spectra of these crystals; in addition, there is a wide complex band at 400–420 nm, which is due to the d → f transitions in Ce³⁺ impurity ions. It is found that the steady-state XL intensity in these bands increases several times upon heating from 100 to 400 K. The possible mechanisms of the observed temperature dependence of the steady-state XL intensity and their correlation with the features of electronic-excitation energy transfer in these crystals are discussed. The main complex TSL peak at 110–160 K and a number of minor peaks, whose composition and structure depend on the crystal type, have been found in all crystals studied. The nature of the shallow traps that are responsible for TSL at temperatures below room temperature and their relation with defects in the lithium cation sublattice are discussed.     

Luminescence centers in thin films of yttrium oxide and yttrium-aluminum garnet activated with bismuth

Luminescence spectra and photoluminescence excitation spectra of Y₂O₃:Bi and Y₃Al₅O₁₂:Bi thin films were investigated. Luminescence was stimulated by the emission from two types of centers that were associated with the substitution of Bi³⁺ for Y³⁺ in sites of the crystal lattice of Y₂O₃ (Y₃Al₅O₁₂) with point symmetries C₂ and C_3i (D₂ and C_3i). The emission of Bi³⁺ in the site with point symmetry C_3i causes blue luminescence in both Y₂O₃:Bi and Y₃Al₅O₁₂:Bi films with maxima at 3.03 eV and 3.15 eV, respectively, that is related to the ³P₁-¹S₀ transition. The emission of Bi³⁺ in the site with point symmetry C₂ gives green luminescence in Y₂O₃:Bi with the maximum at 2.40 eV that is also related to the ³P₁-¹S₀ transition. The emission of Bi³⁺ in the site with point symmetry D₂ leads to ultraviolet luminescence in Y₃Al₅O₁₂:Bi with the maximum at 3.75 eV that corresponds to the ³P₁-¹S₀ transition. The red luminescence band with the maximum at 1.85 eV in Y₂O₃:Bi is due to the presence of structural defects. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 202–207, March–April, 2008.     

Luminescence of Donor‐Acceptor Pairs in Compounds of Yttrium and Scandium Oxides

The luminescence spectra of Sc₂O₃, Y₂O₃, and Y₂GeO₅ ceramics and thin films exposed to laser and cathode excitation were investigated. The investigation of the properties of longwave luminescence bands in Sc₂O₃ with maxima at 2.65, 2.35, and 2.05 eV, in Y₂O₃ with maxima at 2.60, 2.35, and 2.10 eV, and also in Y₂GeO₅ with maxima at 2.55, 2.25, and 2.00 eV point to the fact that they are caused by radiative recombination of the excited donoracceptor pairs Sc³⁺ (or Y³⁺)O^2–.     

Luminescence of aggregate centers in CsBr:Eu2+ single crystals

We have used the Bridgman method to grow CsBr:Eu²⁺ single crystals, adding an activator to the mix in the form of Eu₂O₃ in amounts of 0.0125, 0.0250, and 0.0500 mole %. At T = 300 K, we studied the absorption spectra, the photoluminescence (PL) spectra, and the photostimulated luminescence (PSL) spectra of the grown crystals. We have established that the structure of the photoluminescence and photostimulated luminescence centers in crystals grown from the CsBr:Eu₂O₃ mix includes isolated dipole centers Eu²⁺-V_Cs, emitting in bands with maxima at 432 nm and 455 nm respectively, and in crystals grown at activator concentrations of 0.025 and 0.050 mole % they also include aggregate centers (AC) based on CsEuBr₃ nanocrystals with emission bands at 515 m and 523 nm. We have shown that the maximum concentration of aggregate centers of the CsEuBr₃ nanocrystal type in CsBr:Eu²⁺ crystals is achieved for an activator content in the mix within the range 0.01–0.05 mole %. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 359–362, May–June, 2006.     

Luminescence centers in Sc2O3

Sc₂O₃ luminescence spectra are studied. The spectra are separated into elementary bands by the Alentsev–Fock method. It is established that the luminescence spectra consist of a number of overlapping bands with maxima at 3.5; 3.05; 2.65; 2.35, and 2.05 eV. The band at 3.5 eV is interpreted as emission of self-localized excitons, and the other bands, as defect-center recombination. L’vov State University, 50, Dragomanov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 776–778, November–December, 1997.     

Local ordered magnetic fields in bismuth dielectrics. 209Bi NQR in Bi4Ge3O12 single crystal

The results of the ²⁰⁹Bi NQR experiments carried out on α-Bi₂O₃, Bi₃O₄Br, Bi₂M₄O₉ (M=Al, Ga), Bi₂Ge₃O₉, and Bi₄Ge₃O₁₂ showed that these compounds are not diamagnets in the conventional sense. The Zeeman perturbed zero-field ²⁰⁹Bi NQR spectra gave an indication that local ordered magnetic fields of the order of 30–200 G exist in these substances comprising neither transition nor rare earth elements. Further aspects of this principally new phenomenon of yet unknown nature were studied by the ²⁰⁹Bi NQR experiments on the Bi₄Ge₃O₁₂ single crystal in external magnetic fields below 500 Oe, applied at various orientations with respect to the crystal axes. The spectral patterns of dramatically increased intensity and multiplicity, caused by the unknown magnetism of the compound, were observed in applied fields and modeled. Based on the results of the modeling, the conclusions were made that at least four magnetically non-equivalent Bi sites characterized by antiferromagnetically ordered local fields of the order of 30 G are present in the Bi₄Ge₃O₁₂ crystal; the intensity increase was interpreted to arise from the change in orientation of the electric field gradient axes at the Bi site upon applying an external magnetic field.     

Luminescence of Thin Bi2W2O9 Films

The luminescence spectra of thin Bi₂W₂O₉ films have been investigated. The spectra were separated into elementary components by the Alentsev–Fock method. The radiation band with a maximum at 2.43 eV in the luminescence spectrum of Bi₂W₂O₉ has been assigned to the Frenkel autolocalized excitons. The luminescence bands with maxima at 2.10 and 1.90 eV have been assigned to the emission of the centers whose energy levels are located in the forbidden band. The luminescence of the Bi₂W₂O₉ films is due to the emission of the WO₆ complex.