Absorption spectra of Er3+ ions in Li6Y(BO3)3 crystals

The optical absorption spectra of Li₆Y(BO₃)₃:Er³⁺ crystals have been studied. The absorption lines corresponding to intraconfiguration electronic transitions from the ⁴I_15/2 ground state to the levels of excited states of Er³⁺ ions have been found in the spectral range of 370–700 nm. The transitions to the ⁴F_9/2, ⁴S_3/2, ²H_11/2, ⁴F_7/2, ⁴F_5/2, ⁴F_3/2, ²H_9/2, and ⁴G_11/2 levels have been investigated in detail at 2 K. The number of lines observed for these transitions corresponds to the theoretical maximum for the f-f electronic transitions in Er³⁺ ions located in the noncubic crystal field. The narrowness of the lines observed and their number indicate that erbium occupies one regular position (specifically, the yttrium position). The energy levels of the excited states have been determined for the transitions under study.     

Ce<Superscript>3+</Superscript> and Eu<Superscript>2+</Superscript> luminescence in calcium and strontium aluminates

Compound CaAl₄O₇ (CA4), SrAl₄O₇ (SA4), CaAl₁₂O₁₉ (CA12) and SrAl₁₂O₁₉ (SA12) have been synthesized by using single step combustion method. The phosphors have been characterized by XRD, SEM and PL techniques. Both CA4 and SA4 possess monoclinic crystal structure whereas CA12 and SA12 possess hexagonal structure. Effects of crystal symmetry on the emission spectrum have been studied by doping the samples with Ce³⁺ and Eu²⁺ ions. The luminescence properties of Ce³⁺ and Eu²⁺ in these hosts is discussed on the basis of their covalent character and the crystal field splitting of the d-orbital of dopant ions. The spectroscopic properties, crystal field splitting, centroid shift, red shift and stokes shift have been studied. Spectroscopic properties of Eu²⁺ ions have been accurately predicted from those of Ce³⁺ ions in the same host. Most importantly experimental results were matched excellently with the calculated results. The preferential substitution of Ce³⁺ and Eu²⁺ at different Ca²⁺, Sr²⁺ crystallographic sites have been discussed. The dependence of emission wavelengths of Ce³⁺ and Eu²⁺ on the local symmetry of different crystallographic sites was also studied by using Van Uitert’s empirical relation. Differences in the emission spectrum of these samples have been observed despite their similar crystal structures and space group. Possible reasons have been discussed.     

Luminescence of 60B2O3-32CaF2-8Bi2O3 glasses codoped with chromium and neodymium

60B₂O₃-32CaF₂-8Bi₂O₃ glasses codoped with chromium and neodymium have been prepared for the first time, and their luminescence properties have been studied. The glasses have been shown to contain chromium in two oxidation states. We have obtained luminescence spectra of Cr³⁺ in octahedral coordination and Cr⁴⁺ in tetrahedral coordination. Energy transfer from Bi³⁺ to Nd³⁺ and Cr³⁺ has been demonstrated.     

Coordination of Ti4+ and Ge4+ ions in Na2O-TiO2-GeO2 glasses—an approach based on crystallization behaviour,X-ray absorption and IR spectroscopy

The coordination state of Ti⁴⁺ and Ge⁴⁺ ions in Na₂O-TiO₂-GeO₂ glasses has been investigated. Upon crystallization of the glasses, the thermodynamically metastable hexagonal GeO₂ crystals containing 4-fold coordinated Ti⁴⁺ ions together with stable Na₄Ge₉O₂₀ crystals containing 6-fold coordinated Ti⁴⁺ ions were precipitated. The distribution of Ti⁴⁺ ions between these two crystalline phases is a reflection of the coordination state of Ti⁴⁺ ions in the starting glass. The majority of Ti⁴⁺ ions are in 6-fold coordination at a small TiO₂/Na₂O ratio and they are contained in Na₂Ge₉O₂₀, while the majority of Ti⁴⁺ ions are in 4-fold coordination at a large TiO₂/Na₂O ratio and they are contained in GeO₂ crystals. Concentrations of 4- and 6-fold coordinated Ti⁴⁺ ions have been confirmed to be similar to that in Na₂O-TiO₂-SiO₂ glasses as measured by the X-ray absorption spectrometry of Ti⁴⁺ ions. The coordination state of Ge⁴⁺ ions in the glasses have been examined by infrared (IR) spectrometry. It is found that in Na₂O-TiO₂-GeO₂ glasses Ge⁴⁺ ions have 6-fold coordination preferentially, while Ti⁴⁺ ions have 4-fold coordination except at small contents of TiO₂, indicating that the addition of TiO₂ to Na₂O-GeO₂ glasses leads to the replacement of 4-fold coordinated Ge⁴⁺ ions by 4-fold coordinated Ti⁴⁺ ions.     

Ultrapurification of iron pentacarbonyl by distillation techniques

Volatile impurities have been removed from iron pentacarbonyl of natural isotopic composition by vacuum pumping. We have examined the behavior of impurities in the course of fractional distillation of iron pentacarbonyl. As a result of simple distillation, we have obtained an iron pentacarbonyl sample containing on the order of 10^–4 mol % C₃–C₆ hydrocarbon impurities, 10^–3 mol % C₇–C₈ hydrocarbons, and 10^–8 to 10^–6 wt % metallic impurities. We have estimated the effective separation factor at a distillation rate of 0.021 kg/(m² s) for a number of impurities in Fe(CO)₅.     

Absorption and emission spectral analysis of Pr<Superscript>3+</Superscript>: tellurite glasses

This paper reports on the results concerning optical absorption and fluorescence properties of 60TeO₂–25ZnO–10BaO–4.5La₂O₃–0.5Pr₂O₃ (Pr³⁺: TZBL) glass. Both electronic (α_e) and vibrational (α_v) band edge cut-off wavelengths of the host glass (TZBL) have been evaluated from the measurement of its UV–Vis and IR transmission spectra. The glass studied has shown 80% transmittance throughout its optical window from 0.366 μm (α_e = 3.39 eV) to 6.30 μm (α_v = 0.197 eV). The FT-IR transmission spectra of Pr³⁺ doped and also reference tellurite glasses have demonstrated the presence of TeO₄ and TeO₃₊₁ or TeO₃ structural units. The thermal properties of this glass have been investigated from the study of DTA profile. The recorded optical absorption spectra of Pr³⁺: TZBL glass have shown eight absorption bands from 300 nm to 2,500 nm. The fluorescence emission has been observed mainly from ³P₁, ³P₀ and ¹D₂ states to the lower lying states and which are assigned to the transitions of ³P₀→ ³H_4,5,6; ³P₀→ ³F_2,3,4; ³P₁→³H₅ & ¹D₂→³H_4,5 upon excitations at three excitation states of ³P_0,1,2. From the time resolved spectra, it is found that ³P₀ level decays faster than ¹D₂ level. The fluorescence decay kinetics of ³P₀ and ¹D₂ levels have been measured and the lifetimes are found to be 21 and 39 μs, respectively.     

High-pressure investigations of positive ion-molecule reactions in a mixtureof H2S and CH4

The positive ion-molecule reactions in the mixtures of hydrogen sulfide and methane have been examined by means of quadrupole mass spectrometer with the high-pressure ion source. The concentration of hydrogen sulfide in mixtures ranged from 10% to 90% with 10% increment. For each mixture major bimolecular ion-molecule reactions have been identified in the total pressure range from 0.7 to 33.3 Pa. The electron energy for all measurements was fixed at 300 eV and the repeller potential was maintained at 5 V. Relative intensities of ion currents for the observed ions C⁺, CH⁺, CH₂⁺, CH₃⁺, CH₄⁺, CH₅⁺, C₂H₃⁺, C₂H₄⁺, C₂H₅⁺, S⁺, HS⁺, H₂S⁺, H₃S⁺, H₃³⁴S⁺, CHS⁺, CH₃S⁺, S₂⁺, HS₂⁺ and H₂S₂⁺ were determined as a function of total gas pressure inside the ion source collision chamber, repeller potential and concentration of methane in the mixture.     

Thermodynamic and quasi-chemical modeling of point defects in CdTe〈I〉

The carrier concentration and the densities of predominant point defects in CdTe〈I〉 crystals have been calculated as functions of two-step annealing parameters using quasi-chemical and thermodynamic modeling. We have identified the dominant native and impurity defect species, which govern the electrical properties of the material, and proposed a compensation model that takes into account not only native defects, I_Te⁺ substitutional defects, and their complexes with native point defects, such as (V _Cd²⁻I_Te⁺)⁻, and (V _Cd²⁻2I_Te⁺)⁰, but also DX ⁻ centers. The equilibrium constants of formation of the V _Cd²⁻I_Te⁺)⁻, defect complex and center have been evaluated.     

Thermally stable luminescence and energy transfer in Ce, Mn doped Sr2Mg(BO3)2 phosphor

Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺ and Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺,Mn²⁺ phosphors have been synthesized by conventional solid state reaction technology at 900 °C for 12 h in reducing atmosphere. The phase purity, photoluminescence (PL) properties, thermal stability, energy transfer and luminescent decay curves have been investigated. Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺,Mn²⁺ phosphors show blue and deep-red¹ emission bands. The deep-red emission band is attributed to the energy transfer from Ce³⁺ to Mn²⁺. The fluorescence lifetimes of Ce³⁺ in co-doped sample are shorter than that in single doped one, which confirms that the energy transfer takes place. The phosphors have weak thermal quenching. The luminescence properties of Sr₂Mg(BO₃)₂:Ce³⁺,Li⁺,Mn²⁺ make the phosphor a new bicolor emitting material.     

New,thermally stable Gd<Subscript>11</Subscript>(GeO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>O<Subscript>10</Subscript>-based upconversion phosphors

A series of Gd_11–x–y Yb _x Er _y GeP₃O₂₆ germanate phosphates differing in the ratio of the Yb³⁺ and Er³⁺ active ions have been synthesized, and their luminescence spectra have been measured. According to X-ray diffraction characterization results, all of the synthesized germanate phosphates are single-phase and have a triclinic structure (sp. gr. P1). We have measured upconversion luminescence spectra due to the Er^{3+ 2}H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 radiative transitions in the synthesized gadolinium ytterbium erbium germanate phosphates and determined the luminescence upconversion energy yield (B _en) in Gd_11–x–y Yb _x Er _y GeP₃O₂₆. The effects of the concentrations and ratio of the dopants in the Gd₁₁(GeO₄)(PO₄)₃O₁₀ germanate phosphate host on B _en and the ratio of the luminescence intensities in the red and green spectral regions (R/G) have been assessed.     

Hydrothermal synthesis and luminescent properties of GdVO4 : Eu3+ nanophosphors

Eu³⁺-doped GdVO₄ has been synthesised via hydrothermal method by altering the hydrothermal temperature, reaction time and surfactant. The microstructure and morphology information of the phosphors were investigated via the techniques of X-ray powder diffraction and scanning electronic microscopy, which show that the phosphors wear tetragonal phase and the products present various regular morphologies under different reaction conditions such as bulk and nanoparticle. Moreover, the morphologies of the products have been controlled by altering reaction temperature. In addition, the surfactant was also included to control the morphologies of the products and the phosphors present different morphologies. All the phosphors exhibit the characteristic fluorescence of Eu ion (⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₂). The electric dipole transition ⁵D₀ → ⁷F₂ of Eu³⁺ is dominant indicating that most sites of Eu³⁺ ions in GdVO₄ have no inversion centre. Furthermore, we found that the reaction time and the morphologies have great influence on optical properties.     

Structure and photoluminescence of ZnGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>

The structure of undoped and europium-doped ZnGa₂Se₄ has been studied, and the interplanar spacings, the Miller indices of the observed reflections, and their relative intensities have been determined. The photoluminescence spectra of ZnGa₂Se₄ and ZnGa₂Se₄:Eu²⁺ crystals have been measured at temperatures from 77 to 230 K. The 566-nm band in the spectrum of ZnGa₂Se₄:Eu²⁺ is assigned to the Eu²⁺4f ⁶5d→4f ⁷(⁸ S _7/2) electronic transition, and the bands at 591 and 646 nm are attributed to transitions of donor-acceptor pairs.     

Exchange constants in ferrimagnetic garnets

The exchange constants in the ferrimagnetic garnets R₃ Fe₅ O₁₂ (R=Y³⁺, Gd³⁺ and Dy³⁺) have been obtained from the experimental data on saturation magnetisation and inverse susceptibility. The sign and magnitude of the exchange constants in Y₃Fe₅O₁₂ have been explained on the basis of Anderson’s theory of superexchange. The low temperature magnetisation data in Dy₃Fe₅O₁₂ have been explained by assuming canting on thec sublattice.     

Lithium ion conductivity and mobility in the Li0.12Na0.88Ta0.4Nb0.6O3 solid solution

Lithium ion mobility and the superionic phase transition in the Li_0.12Na_0.88Ta_0.4Nb_0.6O₃ solid solution have been studied using temperature-dependent ionic conductivity measurements and Raman spectroscopy. From the temperature dependences of the conductivity and the width of a Raman line corresponding to Li⁺ and Na⁺ vibrations in the AO _x (A = Na⁺, Li⁺) polyhedra, the average lifetime of the Li⁺ ion in its equilibrium position and the height of the barrier to hopping have been estimated at ?3.9 × 10^?13 s and ?16 kJ/mol, respectively.     

Ln2Os2O7 — A new family of pyrochlores

New compounds of the type Ln₂³⁺Os₂⁴⁺O₇ with the pyrochlore structure have been prepared where Ln is a rare earth cation or Y; Lu₂Ru₂O₇ and Lu₂Ir₂O₇ have also been prepared. Electrical resistivity measurements indicate on metallic conductivity for the new compounds. Os⁴⁺ cation is probably the biggest precious metal cation from a comparison of the unit cell size of similar precious metal pyrochlores. Analogous compound where Ln³⁺ is Sc could not be prepared under similar condition.     

Ca3Al2(SiO4)3−δCl4δ:Eu, Mn: A potential phosphor with energy transfer for near-UV pumped white-LEDs

A series of Eu²⁺ and Mn²⁺ coactivated Ca₃Al₂(SiO₄)_3−δCl_4δ phosphors have been synthesized by solid state reactions and their luminescence properties have been investigated by means of powder diffuse reflection, photoluminescence excitation and emission spectra, and lifetimes. The phosphor Ca₃Al₂(SiO₄)_3−δCl_4δ:Eu²⁺, Mn²⁺ exhibits two dominating bands situated at 460 and 550 nm, originate from the allowed 5d → 4f transition of the Eu²⁺ ion and the ⁴T_1g(4G) → ⁶A_1g(6S) transition of the Mn²⁺ ion, respectively. We have discovered that energy transfers from Eu²⁺ to Mn²⁺ by directly observing significant overlap of the excitation spectrum of Mn²⁺ and the emission spectrum of Eu²⁺ as well as the decline of lifetimes of Eu²⁺. By utilizing the principle of energy transfer, we have demonstrated that with appropriate tuning of activator content Ca₃Al₂(SiO₄)_3−δCl_4δ:Eu²⁺, Mn²⁺ phosphors exhibit potential to act as a phosphor for near ultraviolet light-emitting diodes.     

Hydrothermal synthesis and optical properties of Eu doped NaREF4 (RE = Y, Gd), LnF3 (Ln = Y, La), and YF3·1.5NH3 micro/nanocrystals

5 mol% Eu³⁺ doped NaYF₄ (α-, β-), YF₃, YF₃·1.5NH₃, NaGdF₄, and LaF₃ micro/nanocrystals have been synthesized by a hydrothermal method. The final products are characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence excitation and emission spectra, and luminescent dynamic decay curves. Due to its sensitivity to local symmetry, Eu³⁺ shows different optical properties in the above samples. It has stronger luminescent intensity in β-NaYF₄ than that in α-NaYF₄ while it exhibits different higher energy ⁵D_1,2 to lower ⁷F_J emissions as well as the asymmetric ratios and the splits of ⁵D₀ → ⁷F₁, ⁷F₄. YF₃, LaF₃, and β-NaGdF₄ have analogous optical intensities to those of β-NaYF₄. However, β-NaGdF₄ has the similar spectral profile to that of β-NaYF₄ while YF₃ and LaF₃ have the opposite cases in the ⁵D₀ → ⁷F₂, ⁷F₁ emissions. Further, Judd-Ofelt calculation has been used to analyze the experimental phenomena.     

Growth and electrical properties of pure and Ni-doped Co3O4 single crystals

Single crystals of pure and Ni-doped Co₃O₄ spinel-type phases have been grown by C.V.T. Electrical conductivity and thermopower measurements have been performed between 25 and 950 K. Ni-doping gives rise to a significant increase of electrical conductivity at room temperature by three orders of magnitude. The obtained results suggest that the Ni atoms are located in the octahedral sites of the spinel lattice with both oxidation states 2+ and 3+, as illustrated by the formula : Co²⁺_1?yCo³⁺_y[Co³⁺_2?xNi²⁺_yNi³⁺_x?y]O₄.     

Cathodic reduction of FeOCl in organic electrolytes

Well defined members of a nonstoichiometric family of intercalation complexes M_x(DMSO)_y(Fe⁺³_1?xFe⁺²_xOCl) have been obtained by cathodic reduction of FeOCl in $\text{DMSO}\text{M}{}^{\mathrm{+}}$ solutions. From galvanostatic measurements upper limits for x have been determined with x ≈ 0.1 for M⁺ = Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, x ≈ 0.5 for H⁺ and x ≈ 0.05 for (CH₃)₄N⁺ and (C₄H₉)₄N⁺. Correlations between degree of reduction (x), ionic radii of M⁺, amount of intercalated DMSO (y), basal spacings and M⁺ coordination are discussed.     

Preparation and properties of heavy-metal halide glasses

We have studied the effect of In³⁺, Pb²⁺, Gd³⁺, and Cl (heavier ions) substitutions for Al³⁺, Ba²⁺, La³⁺, and F^? on the crystallization stability and UV/IR optical properties of HBLAN fluorohafnatc glasses (HfF₄-BaF₂-LaF₃-AlF₃-NaF system). We obtained stable glasses containing InF₃ and BaCl₂ instead of AlF₃ and BaF₂, respectively, and offering increased IR transmission. The presence of CCl₄ in the process atmosphere and the removal of oxygen-containing impurities via directional solidification are shown to have an advantageous effect on the optical quality of the glasses. The fluoride-chloride glasses are capable of accommodating about 1.5 times higher levels of rare-earth activators in comparison with their fluoride analogs.