Recombination luminescence of CaI<Subscript>2</Subscript> crystals activated with Eu<Superscript>2+</Superscript>, Gd<Superscript>2+</Superscript>, Tl<Superscript>+</Superscript>, Pb<Superscript>2+</Superscript>, and Mn<Superscript>2+</Superscript>

The spectral characteristics of thermostimulated luminescence, steady-state roentgenoluminescence and photostimulated luminescence (PSL) buildup and decay kinetics, and the effect of IR irradiation on the roentgenoluminescence yield and glow curves of CaI₂:Eu²⁺, CaI₂:Gd²⁺, CaI₂:Tl⁺, CaI₂:Pb²⁺, CaI₂:Mn²⁺, and CaI₂: Pb²⁺, Mn²⁺ crystals grown by the Bridgman-Stockbarger method have been studied in the temperature range 90–295 K. Coupled with earlier data, the present results on the influence of oxygen and hydrogen impurities on the spectral characteristics of CaI₂ indicate that the activation of calcium iodide with Eu²⁺, Gd²⁺, Tl⁺, Pb²⁺, and Mn²⁺ leads to the formation of cation impurity-native defect complexes, which act as carrier traps and are responsible for the thermostimulated luminescence in the range 150–295 K. IR exposure after 90-K x-ray excitation gives rise to flash PSL and influences the thermostimulated luminescence light sum. The nature of the emission and trapping centers involved and the mechanisms of recombination luminescence excitation in the crystals are discussed.     

Superionic Conductors in the Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>-Bi<Subscript>2</Subscript>VO<Subscript>5.5</Subscript> System

Bi₂V_xW_{1 − x} O_{6 − y} ceramics are synthesized, and their structure and electrical properties are studied. The results indicate that the Bi₂WO₆-Bi₂VO_5.5 system contains Bi₂WO₆- and Bi₂VO_5.5-based solid solutions in the ranges 0 < x ≤ 0.2 and 0.75 ≤ x < 1, respectively. Tungsten stabilizes the high-temperature, tetragonal phase γ-Bi₂VO_5.5, which persists down to room temperature at 0.75 ≤ x ≤ 0.84. In the range 350–550°C, the electrical conductivity of the bismuth-vanadate-based solid solutions exceeds that of Bi₂VO_5.5 by about one order of magnitude. The conductivity of the Bi₂WO₆-based solid solutions is also higher than that of the host phase.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 866–870.Original Russian Text Copyright © 2005 by Voronkova, Yanovskii, Kharitonova, Rudnitskaya.     

Synthesis and properties of AgTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-based NASICON-type phosphates doped with Nb<Superscript>5+</Superscript>, Zr<Superscript>4+</Superscript>, and Ga<Superscript>3+</Superscript>

We have synthesized materials based on a silver titanium phosphate with partial substitution of tri-, tetra-, or pentavalent cations for titanium: Ag_1±x Ti_2−x M _x (PO₄)₃ (M = Nb⁵⁺, Ga³⁺) and AgTi_2−x Zr _x (PO₄)₃. The materials have been characterized by X-ray diffraction and impedance spectroscopy and have been shown to have small thermal expansion coefficients. Their ionic conductivity has been determined. Silver ions in these materials are difficult to replace with protons.     

Morphology and luminescent properties of Al<Superscript>3+</Superscript>/Mg<Superscript>2+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor

Al³⁺/Mg²⁺ doped Y₂O₃:Eu phosphor was synthesized by the glycine-nitrate solution combustion method. In contrast to Y₂O₃:Eu which showed an irregular shape of agglomerated particles (the mean particle size >10 μm), the morphology of Al³⁺/Mg²⁺ doped Y₂O₃:Eu crystals was quite regular. Al³⁺/Mg²⁺ substituting Y³⁺ in Y₂O₃:Eu resulted in an obvious decrease of the particle size. Meanwhile, higher the Al³⁺/Mg²⁺ concentration, smaller the particle size. In particular, the introduction of Al³⁺ ion into Y₂O₃ lattice induced a remarkable increase of PL and CL intensity. While, for Mg²⁺ doped Y₂O₃:Eu samples, their PL and CL intensities decreased. The reason that causes the variation of PL and CL properties for Al³⁺ and Mg²⁺ doped Y₂O₃:Eu crystals was concluded to be related to sites of Al³⁺ and Mg²⁺ ions inclined to take and the difference of ion charge.     

Hydrothermal synthesis of NaLa(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Eu<Superscript>3+</Superscript> octahedrons and tunable luminescence by changing Eu<Superscript>3+</Superscript> concentration and excitation wavelength

NaLa(WO₄)₂:Eu³⁺ phosphors with different Eu³⁺ concentrations have been synthesized by a hydrothermal method. The phase is confirmed by XRD analysis, which shows a pure-phase NaLa(WO₄)₂ XRD pattern for all of NaLa(WO₄)₂:Eu³⁺ phosphors. The SEM and TEM images indicate that all of NaLa(WO₄)₂:Eu³⁺ phosphors have a octahedral morphology. These suggest that the Eu³⁺ doping has no influence on the structure and growth of NaLa(WO₄)₄ particles. By monitoring the emission of Eu³⁺ at 615 nm, NaLa(WO₄)₂:Eu³⁺ phosphors show excitation bands originating from both host and Eu³⁺ ions. Under the excitation at 271 nm corresponding to WO₄ ^2? groups, emission bands coming from the ¹A₁ → ³T₁ transition with the WO₄ ^2? groups and the ⁵D₀ → ⁷F_j (j = 0, 1, 2, 3 and 4) transitions of Eu³⁺ are observed. The emission intensity relating to WO₄ ^2? groups decreases with increasing Eu³⁺ concentration. But emission intensities of Eu³⁺ increase firstly and then decreases because of concentration quenching effect. Under the excitation at 395 nm corresponding to ⁷F₀ → ⁵L₆ transition of Eu³⁺, only characteristic Eu³⁺ emission bands can be observed. The results of this work suggest that tunable luminescence can be obtained for Eu³⁺ doped NaLa(WO₄)₂ phosphors by changing Eu³⁺ concentration and excitation wavelength.     

Ultraviolet upconversion luminescence in Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Yb<Superscript>3+</Superscript>,Tm<Superscript>3+</Superscript> nanocrystals and its application in photocatalysis

Infrared-to-ultraviolet upconversion luminescence agent Y₂O₃:Yb³⁺,Tm³⁺ was prepared by a combustion method using citrate as a fuel/reductant. The prepared sample was characterized by X-ray diffraction, SEM, and fluorescence spectrophotometer. Two unusual ¹I₆ → ³H₆ (~297 nm) and ¹D₂ → ³H₆ (~363 nm) emissions from Tm³⁺ ions were observed at room temperature under 980-nm laser excitation. The change of upconversion emission intensity depending on the Yb³⁺ concentrations was discussed. The results showed that modest Yb³⁺ doping could make the upconversion emission of Tm³⁺ intense, and high Yb³⁺ concentrations might lead to fluorescence quenching. Moreover, the influence of ultraviolet upconversion luminescence on the photodegradation of methyl orange aqueous solution under solar light irradiation in the presence of TiO₂ catalyst doped with Y₂O₃:Yb³⁺,Tm³⁺ was also investigated. It was concluded from the experiment of this study that TiO₂/Y₂O₃:Yb³⁺,Tm³⁺ composite had higher photocatalytic activity than pure TiO₂ under solar light. This study would make TiO₂ utilize sunlight more efficiently and accelerate the practical application of photocatalytic technology in water treatment region.     

Influence of Mn<Superscript>2+</Superscript> on the up-conversion emission performance of Mn<Superscript>2+</Superscript>, Yb<Superscript>3+</Superscript>, Er<Superscript>3+</Superscript>: ZnWO<Subscript>4</Subscript> green phosphors

The Mn²⁺, Yb³⁺, Er³⁺: ZnWO₄ green phosphors are synthesized successfully through the high temperature solid state reaction method. The micro-structure and morphology have been investigated by means of XRD and EDS. The doped concentrations of Mn²⁺, Yb³⁺, Er³⁺ are measured by ICP. The absorption spectra and emission spectra with different doped concentrations of Mn²⁺ are presented to reveal the influence of Mn²⁺ on the green up-conversion performance. Excited with 970 nm LED, the up-conversion emission peak at 547 nm is obtained and the CIE spectra as well as the green light photo are also presented. The results indicate that the Mn²⁺ ions play the role of the luminescence adjustment in the up-conversion process, which can improve the up-conversion green emission intensity effectively. The luminescence adjustment mechanism of Mn²⁺ ions in Mn²⁺, Yb³⁺, Er³⁺: ZnWO₄ green phosphors has been discussed. The crystal parameters of Dq, B and C are calculated to evaluate the energy level split effect.     

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.     

Pulsed cathodoluminescence of single-crystalline and pressed CaF<Subscript>2</Subscript>:Yb<Superscript>2+</Superscript>,Yb<Superscript>3+</Superscript>

We have studied the pulsed cathodoluminescence spectra and kinetics of CaF₂:Yb²⁺,Yb³⁺ (3 mol % YbF₃) single crystals and pressed samples under excitation with nanosecond electron pulses and determined the characteristic times and intensities of nanosecond and microsecond emission decay components at temperatures from 15 to 300 K. The results demonstrate that deformation pressing in vacuum at 1150°C followed by annealing in a CF₄ atmosphere at 1180°C has an insignificant effect on the emissive properties of CaF₂:Yb²⁺,Yb³⁺.     

Roles of doping ions in persistent luminescence of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>, RE<Superscript>3+</Superscript> phosphors

The polycrystalline Eu²⁺ and RE³⁺ co-doped strontium aluminates SrAl₂O₄:Eu²⁺, RE³⁺ were prepared by solid state reactions. The UV-excited photoluminescence, persistent luminescence and thermo-luminescence of the SrAl₂O₄:Eu²⁺, RE³⁺ phosphors with different composition and doping ions were studied and compared. The results showed that the doped Eu²⁺ ion in SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors works as not only the UV-excited luminescent center but also the persistent luminescent center. The doped Dy³⁺ ion can hardly yield any luminescence under UV-excitation, but can form a electron trap with appropriate depth and greatly enhance the persistent luminescence and thermo-luminescence of SrAl₂O₄:Eu²⁺. Different co-doping RE³⁺ ions showed different effects on persistent luminescence. Only the RE³⁺ ion (e.g. Dy³⁺, Nd³⁺), which has a suitable optical electro-negativity, can form the appropriate electron trap and greatly improve the persistent luminescence of SrAl₂O₄:Eu²⁺. Based on above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated.     

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.     

Spectroscopy and Structure of Nd<Superscript>3+</Superscript> Activator Centers in Stabilized Cubic ZrO<Subscript>2</Subscript>

The nonuniformly broadened spectra of Nd³⁺ in ZrO₂-Y₂O₃-Nd₂O₃ crystals are studied using selective excitation, different time delays, and measurements of the excited-state lifetime at 77 K. Three basic types of optical spectra are identified and are assigned to three basic configurations of the nearest neighbor environment of Nd³⁺: sevenfold coordination and eightfold coordination with and without an oxygen vacancy among its second neighbors.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 955–959.Original Russian Text Copyright © 2005 by Voron’ko, Lomonova, Popov, Sobol’, Ushakov.     

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.     

Crystallization from high-temperature solutions in the Na<Subscript>2</Subscript>O-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript>-M<Superscript>VI</Superscript>O<Subscript>3</Subscript> (M = Mo,W) systems

We have studied the crystallization behavior of Na₂O-NaPO₃-M^VIO₃(M^VI = Mo, W) high-temperature solutions containing 15 mol % Bi₂O₃ in the pseudoquaternary systems Na₂O-Bi₂O₃-P₂O₅-M^VIO₃ and have established the conditions for the formation of Na₃Bi(PO₄)₂, high-temperature BiPO₄, NaBi(MoO₄)₂, Bi₂WO₆, and NaMoO₂PO₄. The compounds identified have been characterized by powder x-ray diffraction and IR spectroscopy.     

Spectral parameters of Er<Superscript>3+</Superscript> ion in Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>:KY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

The spectral parameters of Er³⁺ in Yb³⁺/Er³⁺:KY(WO₄)₂ crystal with space group C2/c have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the intensity parameters are: ₂ = 6.33 × 10^–20 cm², ₄ = 1.35 × 10^–20 cm², ₆ = 1.90 × 10^–20 cm². The radiative lifetime and the fluorescence branch ratios were calculated. The emission cross section _e (at 1536 nm) is 2.0 × 10^–21 cm².     

Influence of isovalent and heterovalent substitution for Bi<Superscript>3+</Superscript> and Fe<Superscript>3+</Superscript> on the properties of Bi<Subscript>2</Subscript>Fe<Subscript>4</Subscript>O<Subscript>9</Subscript>-based solid solutions

Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites have been prepared by solid-state reactions at a temperature of 1073 K. X-ray diffraction data indicate that, in the Bi_2–хLa_хFe₄O₉ system, the limiting degree of La³⁺ substitution for Bi³⁺ ions in Bi₂Fe₄O₉ does not exceed 0.05 and that the limiting degree of substitution in the Bi₂Fe_4–2xTi_xCo_xO₉ system lies in the range 0.05 < x < 0.1. The specific magnetization and specific magnetic susceptibility of the samples have been measured at temperatures from 5 to 300 K in a magnetic field of 0.86 T. The field dependences of magnetization obtained for the Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites at temperatures of 300 and 5 K demonstrate that partial isovalent substitution of La³⁺ for Bi³⁺ ions in Bi₂Fe₄O₉ and heterovalent substitution of Ti⁴⁺ and Co²⁺ ions for two Fe³⁺ ions leads to partial breakdown of the antiferromagnetic state and nucleation of a ferromagnetic state.     

Growth of Rare-Earth-Doped K<Subscript>2</Subscript>LaCl<Subscript>5</Subscript>, K<Subscript>2</Subscript>BaCl<Subscript>4</Subscript>, and K<Subscript>2</Subscript>SrCl<Subscript>4</Subscript> Single Crystals

Processes are described for the synthesis and melt growth of rare-earth-doped K₂LaCl₅, K₂BaCl₄, and K₂SrCl₄, using rare-earth oxides as starting materials. The solubility of rare-earth activators in Bridgman-grown crystals are determined, and the spectroscopic properties of K₂LaCl₅〈Nd〉 crystals are investigated.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 748–752.Original Russian Text Copyright © 2005 by Vinogradova, Galagan, Dmitruk, Moiseeva, Osiko, Sviridova, Brekhovskikh, Fedorov.     

Ionic conductivity in the Lu<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> system

Nanocrystalline Lu₂O₃-TiO₂ (33.3–44 mol % Lu₂O₃) materials with a partially disordered pyrochlore structure, prepared via heat treatment in the range 1400–1750°C, are found to possess high oxygen ionic conductivity. Their 740°C conductivity is 10^-3 to 10^-2 S/cm, depending on the heat-treatment temperature and composition, which is comparable to that of the well-known fluorite solid electrolyte ZrO₂-9 mol % Y₂O₃.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 324–331.Original Russian Text Copyright © 2005 by Shlyakhtina, Mosunov, Stefanovich, Knotko, Karyagina, Shcherbakova.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Tunable luminescence properties and energy transfer of single-phase Ca<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>O: Dy<Superscript>3+</Superscript>, Eu<Superscript>2+</Superscript> multi-color phosphors for warm white light

The novel Ca_4?x(PO₄)₂O: xDy³⁺ and Ca_4?x?y(PO₄)₂O: xDy³⁺, yEu²⁺ multi-color phosphors were synthesized by traditional solid-state reaction. The crystal structure, particle morphology, photoluminescence properties and energy transfer process were investigated in detail. The X-ray diffraction (XRD) results demonstrate that the products showed pure monoclinic phase of Ca₄(PO₄)₂O when x < 0.1. The scanning electron microscopy (SEM) indicated that the phosphors were grain-like morphologies with diameters of ~ 3.7–7.0 μm. Under excitation of 345 nm, Dy³⁺-doped Ca₄(PO₄)₂O phosphors showed multi-color emission bands at 410, 481 and 580 nm originated from oxygen vacancies and Dy³⁺. Interestingly, Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors exhibited blue emission band at 481 nm and broad emission band from 530 to 670 nm covering green to red regions. The energy transfer process from Dy³⁺ to Eu²⁺ was observed for the co-doped samples, and the energy transfer efficiency reached to 60% when Eu²⁺ molar concentration was 8%. In particular, warm/cool/day white light with adjustable CCT (2800–6700 K) and high CRI (R_a > 85) can be obtained by changing the Eu²⁺ co-doping contents in Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors. The optimized Ca_3.952(PO₄)₂O: 0.04Dy³⁺, 0.008Eu²⁺ phosphor can achieve the typical white light with CCT of 4735 K and CRI of 87.