Effect of BiI<Subscript>3</Subscript> doping on the optical properties of CaI<Subscript>2</Subscript>

The effect of BiI₃ doping on the optical absorption spectra and roentgeno-, photo-, and thermoluminescence of CaI₂ scintillator crystals has been studied in the temperature range 90–295 K. The crystals were grown by the Bridgman-Stockbarger method. Doping of CaI₂ with BiI₃ from the melt gives rise to absorption bands centered at 466, 400, and 350 nm, which can be interpreted as the A, B, and C bands due to electronic transitions from the ¹ S ₀ state to the ³ P ₁, ³ P ₂, and ¹ P ₁ levels of a free Bi³⁺ ion. The absorption band at 270–290 nm is assignable to near-activator excitons. Changes in spectral composition and the reduction in luminescence intensity caused by Bi³⁺ doping of CaI₂ are associated mainly with the reabsorption of the emission from centers characteristic of the host by activator centers. Under x-ray excitation, the spectrum of heavily doped crystals shows, in addition, a weak emission centered around 620 nm, which is probably due to an impurity phase. The light sum of CaI₂:Bi³⁺ under x-ray excitation is small and is due to shallow traps. Upon Bi³⁺ substitution on the cation site of CaI₂, the excess charge of the activator is probably compensated by unintentional O^2? impurity and vacancy pairs near Bi³⁺ centers—one vacancy in a neighboring cation site and the other in a neighboring anion site.     

Luminescent properties of Pb<Superscript>2+</Superscript>- and Mn<Superscript>2+</Superscript>-activated CdI<Subscript>2</Subscript> crystals

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.     

Mechanochemical Synthesis of Crystalline Compounds in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–GeO<Subscript>2</Subscript> System

Crystalline mechanochemical synthesis products in the Bi₂O₃–GeO₂ system are studied by x-ray diffraction. The results indicate the formation of sillenite (Bi₁₂GeO₂₀), eulytite (Bi₄Ge₃O₁₂), and Aurivillius (Bi₂GeO₅) phases. The Aurivillius phase is shown to be in mechanochemical equilibrium with the sillenite phase in the 2Bi₂O₃ + GeO₂ system and with the eulytite phase in the Bi₂O 3 + GeO 2 system. The structural parameters of the synthesized metastable solid solutions are determined. The three phases contain high concen-trations of vacancies. In addition, the sillenite and Aurivillius phases are characterized by compositional disordering. Structural and ESR data point to partial reduction of the oxides, which accounts for the formation of the Aurivillius phase. According to x-ray photoelectron spectroscopy results, mechanical activation of bismuth oxide produces reduced binding energy states of Bi and O, which is tentatively attributed to clustering and the formation of complex radicals.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 711–719.Original Russian Text Copyright © 2005 by Zyryanov, Smirnov, Ivanovskaya.     

Co-existence of Bi with multiple valence states in zeolites - Controlling the optical properties by annealing atmosphere

We investigate the effect of annealing atmosphere on the optical properties of Bi doped zeolites by diffuse reflectance, steady state and time-resolved photoluminescence (PL), and PL excitation measurements. The results reveal that zeolites can be used as an excellent host material to stabilize multiple Bi centers (Bi³⁺, Bi²⁺, and Bi-related near-infrared (NIR) active centers) in the framework, which shows ultra-broadband emission from visible to NIR range. Annealing in N₂ leads to the partial conversion of Bi³⁺ ions into Bi²⁺ and Bi-related NIR active centers. Our results demonstrate that the broadband NIR emission may be attributed to the electronic transition of Bi low valence state, rather than a higher valence state.     

The influence of activation of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> polycrystalline matrices by Bi<Superscript>3+</Superscript> ions on the luminescence of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript>

The influence of activation of the Y₂O₃ matrix of the Y₂O₃:Eu³⁺ phosphor by Bi³⁺ ions on the luminescence of Eu³⁺ and Bi³⁺ ions in it and on conditions of the excitation energy transfer to luminescence centers is studied. It is shown that the presence of Bi³⁺ ions leads to the appearance of recombination luminescence with participation of bismuth ions at low concentrations (up to 6–8 at %) of the dominant activator europium and to an increase in the threshold of intrinsic concentration quenching of its luminescence.     

Synthesis and photoluminescence properties of LiEu(W,Mo)<Subscript>2</Subscript>O<Subscript>8</Subscript>:Bi<Superscript>3+</Superscript> red-emitting phosphor for white-LEDs

LiEu_1−x (W_2−y Mo _y )O₈:xBi³⁺ series red-emitting phosphors were synthesized by solid state reaction. The structure, morphology, and photoluminescent properties of phosphors were studied by X-ray powder diffraction, scanning electron microscopy, and photoluminescence spectrum, respectively. X-ray powder diffraction analysis showed that the as-obtained phosphors belong to the scheelite structure. The average particle size of the investigated phosphor was about 8 μm. The excitation spectrum exhibits a charge-transfer broad band along with some sharp peaks from the typical 4f–4f transitions of Eu³⁺. Under excitation of UV, near-UV, or blue light, these phosphors showed strong red emission at 615 nm due to ⁵D₀–⁷F₂ transition of Eu³⁺. The incorporation of Mo⁶⁺ into LiEuW₂O₈:Bi³⁺ could induce red-shift of the charge-transfer broad band and a remarkable increase of photoluminescence. The highest red-emission intensity was observed with LiEu_0.80Mo₂O₈:0.20Bi³⁺. Compared with the commercial red-emitting phosphor, Y₂O₂S:Eu³⁺, the emission intensity of LiEu_0.80Mo₂O₈:0.20Bi³⁺ phosphor is much stronger than that of Y₂O₂S:Eu³⁺ and its chromaticity coordinates are closer to the standard values than that of the commercial phosphor. The optical properties of LiEu_0.80Mo₂O₈:0.20Bi³⁺ phosphor make it attractive for the application in white-light-emitting diodes (LEDs), in particular for near-UV InGaN-based white-LEDs.     

Luminescence properties of Bi codoped and P codoped Ca<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Eu<Superscript>3+</Superscript>

New red emitting phosphors, Ca₃(VO₄)₂:Eu³⁺,Bi³⁺, Ca₃((P,V)O₄)₂:Eu³⁺ were synthesized by low temperature solid-state reaction and characterized by X-ray diffraction, scanning electron microscopy, photoluminescence spectra and Fourier transform infrared spectroscopy. The results show that the red emission located at about 613 nm was ascribed to ⁵ D ₀-⁷ F ₂ transition of Eu³⁺. The effect of by Bi doping and by P doping was also investigated systematically.     

Electrical Conductivity of Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript> Crystals Doped with Ca<Superscript>2+</Superscript>, Pb<Superscript>2+</Superscript>, Sr<Superscript>2+</Superscript>, and Ba<Superscript>2+</Superscript>

Single crystals of Bi₂WO₆ (a layered perovskite-like compound) doped with Ca²⁺, Pb²⁺, Sr²⁺, and Ba²⁺ on the Bi³⁺ site are grown, and their oxygen ionic conductivity is measured along the polar axis. The intrinsic conductivity of the doped crystals differs insignificantly from the conductivity of undoped Bi₂WO₆, indicating that the oxygen ions in the Bi₂O₂ layers contribute little to the oxygen ionic conductivity of the crystals. The sharp change in the activation energy for conduction at 600°C attests to a transition from one conduction mechanism to another in going from low to high temperatures.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 863–865.Original Russian Text Copyright © 2005 by Kharitonova, Voronkova, Yanovskii.     

Luminescence Study of LiY<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript>x</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The luminescence spectra of LiY_{1 − x} Eu_x(MoO₄)₂ (x = 0.0005, 0.001, 0.01, 0.05, 0.1, 0.5, 1) scheelite solid solutions are measured under laser excitation at 337.1 nm. The effect of Eu³⁺ concentration on the luminescence behavior of the solid solutions is examined. The highest integrated emission intensity is offered by LiY_0.5Eu_0.5(MoO₄)₂. Eu³⁺ substitution for Y³⁺ has no effect on the symmetry of the emission centers involved. Eu³⁺ is shown to occupy only one site in the structure of the solid solutions. X-ray diffraction and luminescence data indicate that all of the solid solutions have an undistorted scheelite structure.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 871–875.Original Russian Text Copyright © 2005 by Zaushitsyn, Mikhailin, Romanenko, Khaikina, Basovich, Morozov, Lazoryak.     

Effect of synthesis conditions on the preparation of BiFeO<Subscript>3</Subscript> nanopowders using two different methods

Bismuth orthoferrite (BiFeO₃) nanoparticles have been synthesized via the co-precipitation and the oxalate precursor methods. Effects of Bi source, annealing temperature, Bi/Fe molar ratio, oxalic acid ratio and Mn²⁺ ion on the crystal structure, crystallite size, microstructure and magnetic properties of the produced powders were systematically studied. The results revealed that bismuth oxychloride and iron oxide were formed using chlorides sources. A single phase of BiFeO₃ was formed from as-made samples with Bi/Fe molar ratio 1.1 using nitrate sources and annealed at 500 and 600 °C for 2 h via the two pathways. The pure BiFeO₃ phase appeared as spherical and pseudocubic-like structure using the co-precipitation and the oxalic acid precursor routes, respectively. A high saturation magnetization (3.94 emu/g) was achieved for powder formed from the oxalate precursor route with Bi/Fe molar ratio 1.0 annealed at 600 °C for 2 h as the result of the formation of Bi₂₅FeO₃₉. Moreover, Mn²⁺ ion addition affected BiFeO₃ properties due to the formation of Bi₂Fe₂Mn₂O₁₀. Hence, the saturation magnetization and the coercive force of BiFeO₃ were improved substantially by substitution of Mn²⁺ ions (BiFe_1-XMn_XO₃, X = 0.1–0.2).     

Effect of iodine doping on the luminescent properties of the photochromic material CdBr<Subscript>2</Subscript>:Cu<Superscript>+</Superscript>

The effect of iodine doping on the roentgenoluminescence (RL) and thermoluminescence (TL) of CdBr₂:Cu⁺ is studied using CdBr₂:(Cu⁺ ,I^-) crystals grown by the Bridgman-Stockbarger method from melts containing 0.5 wt % CuBr and 0.15, 0.5, or 5.0 wt % CdI₂. The results demonstrate that, with increasing iodine content, the RL intensity first rises and then drops; in addition, the RL band shifts from 560 to 490–510 nm. At low CdI₂ levels, the TL curve shows peaks at 110, 130, 152, and 168 K, characteristic of CdBr₂:Cu⁺. At the maximum iodine concentration, the TL curve shows a weak peak at 115 K. The TL spectrum of lightly iodine-doped crystals is dominated by the 490-nm emission, which is attributable to heteronuclear anion excitons. The formation of nI^- clusters in heavily doped CdBr₂:(Cu⁺,I^-) crystals reduces the concentration of (BrI)^- hetero-nuclear centers. The nature of the trapping levels responsible for the TL of the crystals is discussed.Translated from Neorganicheskie Materialy, Vol. 41, No. 2, 2005, pp. 235–239.Original Russian Text Copyright © 2005 by S. Novosad, I. Novosad, Borodchuk.     

Formation of microtubes in CdI2 crystals doped with BiI3

The formation of microtubes (MTs) with rectangular cross section in the volume of CdI₂ layered crystals doped with Bi³⁺ trivalent impurity ions has been observed for the first time by scanning electron microscopy. The MTs grow predominantly in pores that appear in the volume of CdI₂-BiI₃ crystals as a result of a difference in the valence of host Cd²⁺ ions and guest Bi³⁺ ions substituted into regular crystal lattice sites. The formation of MT structures is related to the rolling of I-Cd-I trilayers containing impurity ions, which takes place as a result of the presence of uncompensated charges at the edges. Deviation of the MT cross section from circular is explained by nonuniformity of the elastic properties of I-Cd-I trilayers with Bi impurity, which is related to the appearance of vacancies in the cation subsystem upon replacement of Cd²⁺ ions by Bi³⁺ ions.     

Tunable luminescence and energy transfer properties in YVO<Subscript>4</Subscript>:Bi<Superscript>3+</Superscript>,Ln<Superscript>3+</Superscript> (Ln = Dy,Sm, Eu) phosphors prepared by microwave sintering method

YVO₄:Bi³⁺,Ln³⁺ (Ln?=?Dy, Sm, Eu) phosphors were successful synthesized by microwave sintering method, and characterized by X-ray powder diffraction, scanning electron microscope, photoluminescence spectra, lifetime, quantum efficiency and general structure analysis system structure refinement. Refinement results indicated that the introduced ions occupy the sites of Y³⁺. Under 275 nm excitation, the luminescent intensity of YVO₄:Bi³⁺ samples reach the maximum when Bi³⁺ concentration is 0.02, the broad excitation spectrum of YVO₄:Bi³⁺ has a strongest peak at near 343 nm. Doped Bi³⁺ can effectively improve the emission intensity of YVO₄:Ln³⁺. The energy transfer mechanism of Bi³⁺?→?Ln³⁺ was dipole-quadrupole mechanism of electric multipole interaction. The critical distance (R_c) between Ln³⁺ and Bi³⁺ were calculated by concentration quenching method. Emitting color of YVO₄:Bi³⁺,Ln³⁺ phosphors were tunable by adjusting Ln³⁺ content. In a word, the material has a good application prospects on light emitting diodes.     

Color tunable luminescence from LaAlO<Subscript>3</Subscript>:Bi<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript> doped phosphors for field emission displays

Bi³⁺-activated LaAlO₃:Ho³⁺ Phosphor, was prepared by Polyol method, and its photoluminescent properties were investigated under (UV) light excitation. Luminescence studies indicated that optimum concentration of Bi³⁺ and Ho³⁺ in LaAlO₃ was found to be 1 and 1.5 at.%. The luminescent intensity of Ho³⁺ emission lines was remarkably enhanced on exciting with 272 nm, which suggested that efficient energy transfer from Bi³⁺ ions to Ho³⁺ ions takes place. There is significant energy overlap between the emission band of Bi³⁺ ions and the excitation band of Ho³⁺ ions.The ET efficiency has been calculated and found to be 69%. The critical ET distance has been calculated by the concentration–quenching method. The enhanced intensity and tuned luminous color of LaAlO₃: Bi³⁺/Ho³⁺ phosphors from blue to cyan provides a promising material for field emission display devices.     

Synthesis of new (Bi,La)<Subscript>3</Subscript>MSb<Subscript>2</Subscript>O<Subscript>11</Subscript> phases (M = Cr,Mn, Fe) with KSbO<Subscript>3</Subscript>-type structure and their magnetic and photocatalytic properties

Synthesis and structure of new (Bi, La)₃MSb₂O₁₁ phases (M = Cr, Mn, Fe) are reported in conjunction with their magnetic and photocatalytic properties. XRD refinements reflect that Bi₃CrSb₂O₁₁, Bi₂LaCrSb₂O₁₁, Bi₂LaMnSb₂O₁₁ and Bi₂LaFeSb₂O₁₁ adopt KSbO₃-type structure (space group, Pn[`3])Pn\overline{3}). The structure can be described through three interpenetrating networks where the first is the (M/Sb)O₆ octahedral network and other two are the identical networks having Bi₆O₄ composition. The magnetic measurements on Bi₂LaCrSb₂O₁₁ and Bi₂LaMnSb₂O₁₁ show paramagnetic behaviour with magnetic moments close to the expected spin only magnetic moments of Cr^+ 3 and Mn^+ 3. The UV-Visible diffuse reflectance spectra are broad and indicate that these materials possess a bandgap of ∼ 2 eV. The photocatalytic activity of these materials has been investigated by degrading Malachite Green (MG) under exposure to UV light.     

Synthesis,crystal structure and luminescence in Ca<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>6</Subscript>

Bluish green emitting phosphor, Ca₃Al₂O₆:Ce³⁺, is prepared by low-temperature combustion method. X-ray diffraction, photoluminescence, scanning electron microscopy techniques are used to characterize the synthesized phosphor. The most efficient bluish green (483 nm) emission is observed under the excitation by near UV light. The emission characteristics are credited to 5d → 4f type transitions in Ce³⁺. The luminescence properties of Eu²⁺ are predicted for the first time from those of Ce³⁺. Also, photoluminescence of Eu³⁺ is studied in the same host. The emission spectrum of Ca₃Al₂O₆:Eu³⁺ shows the peak at 592 (orange) and 614 nm (red) wavelengths. Ca₃Al₂O₆:Ce³⁺phosphor can be a potential blue phosphor for field emission display, solid-state lighting and LED.     

Phase Relations and Transport Properties of Alloys in the Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>-TlGaTe<Subscript>2</Subscript> System

Using physicochemical analysis, the Bi₂Te₃-TlGaTe₂ system is shown to contain Bi₂Te³⁻ and TlGaTe₂-based restricted solid-solution series and a liquid-liquid miscibility gap in the composition range ≃12–30 mol % TlGaTe₂. The power factor α²σ of (Bi₂Te₃)_1−x (TlGaTe₂)_x solid solutions with 0.01 ≤ x ≤ 0.02 is suitable for thermoelectric applications.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 785–786.Original Russian Text Copyright © 2005 by Abilov, Seidov.     

Preparation and photoluminescence properties of Y2O3:Eu, Bi phosphors by molten salt synthesis for white light-emitting diodes

Y₂O₃:Eu, Bi red phosphors were first prepared by molten salt synthesis (MSS) method at a low temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM), and fluorescence spectrophotometer were used to characterize the as-synthesized phosphors. The results show that as-obtained Y₂O₃:Eu, Bi phosphors have good cubic crystallinity, presenting octahedral morphology with smooth surface and relatively uniform particle size. Bi³⁺ ion as a sensitizer plays a significant effect on the emission intensity of Y₂O₃:Eu, Bi by energy transfer from Bi³⁺ to Eu³⁺ and the optimal concentration of Bi³⁺ is 1.5 mol%. Y₂O₃:Eu, Bi emits excellent red light as the excitation wavelength is between 330 and 420 nm or excited by 254, 466 nm. Meanwhile, its emission intensity is as strong as that of sample prepared by solid-state reaction. So the as-fabricated red phosphors by MSS method would have a promising application in the area of white light-emitting diodes.     

Studies of the EPR Parameters for Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript><Emphasis Type="Italic">Y</Emphasis>Cu<Subscript>2</Subscript>O<Subscript>8</Subscript>:Er<Superscript>3+</Superscript>

The electron paramagnetic resonance (EPR) parameters (the anisotropic g factors g _x , g _y , g _z , and the hyperfine structure constants A _x , A _y , and A _z ) of the two orthorhombic Er³⁺ centers in Bi₂Sr₂ YCu₂O₈ are theoretically studied from the perturbation formulas of these parameters for a 4f¹¹ ion in orthorhombic symmetry. In these formulas, the contributions due to the admixtures of various states are taken into account, and the orthorhombic field parameters are determined from the superposition model and the local geometry of Bi³⁺ site in Bi₂Sr₂ YCu₂O₈. The calculated EPR parameters show reasonable agreement with the observed values. The anisotropy g _z >g _x (g _y ) for the g factors may be attributed to the compression of the ligand octahedra in the Er³⁺ centers.     

Gamma rays interactions with Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped Na<Subscript>2</Subscript>O–CdO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses assessed by collective optical and FT infrared absorption spectroscopy

Undoped and Bi₂O₃-doped glasses from the system Na₂O–CdO–P₂O₅ were prepared and studied through investigating their optical and FTIR spectra before and after gamma irradiation beside measuring their thermal expansion properties. Optical spectra reveal distinct UV absorption with additional peaks upon introducing Bi₂O₃ added with different concentrations from 1 to 7.5%. The UV absorption of the undoped sample is related to trace iron impurities while the extended UV absorption peaks are correlated with absorption of Bi³⁺ ions. FTIR spectra show condensed phosphate groups (Q², Q³ units) beside the sharing of bismuth ions in their vibrational sites. Gamma irradiation causes limited changes in the UV spectra but involves the generation of an induced visible band in the undoped glass. These changes are assumed to be due to some suggested photochemical reactions on the trace iron impurities and the formation of an induced visible (POHC) band on the phosphate network. Careful inspection of the selected deconvoluted spectra for the undoped glass and doped (7.5 wt%) supports the introduced assumptions. The thermal expansion parameters are correlated with the type of bonding of bismuth ions within the network structure.