Blue and green upconversion luminescence modification of Tb<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript> co-doped Ca<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>F inverse opal

Tb³⁺–Yb³⁺ co-doped Ca₅(PO₄)₃F inverse opal photonic crystals were prepared by a self-assembly technique in combination with a sol–gel method. Upconversion luminescence characteristics of the inverse opals were investigated. The results indicate that photonic band gap has a significant effect on upconversion luminescence of Tb³⁺–Yb³⁺ co-doped Ca₅(PO₄)₃F inverse opal. Significant inhibition of the green or blue upconversion luminescence was inspected if the photonic band gap overlapped with the emission band of Tb³⁺ ions.     

Flame synthesized Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Tb<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript> phosphors as spectral convertors for solar cells

Near-infrared (NIR) quantum cutting phosphors serve as a potential material for fabricating photovoltaic spectral convertors. In many cases, quantum cutting phosphors are obtained via a wet chemical method coupled with a post-annealing treatment—a very costly process. In this report, we used continuous flame spray pyrolysis (FSP) for fabricating Y₂O₃:Tb³⁺–Yb³⁺ quantum-cutting phosphors without any post-treatment. Based on characterizations by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, we found that as-synthesized Y₂O₃:Tb³⁺–Yb³⁺ phosphors exhibit hollow and shell-like micro-structures composed of highly crystalline and pure cubic-phase nanoparticles (< 50 nm). Photoluminescence studies of the phosphors revealed that NIR emissions appeared with the introduction of Yb to Y₂O₃:Tb³⁺. Phosphor size was successfully controlled by managing the concentration of the metal precursor solution for FSP. The Y₂O₃:Tb³⁺–Yb³⁺ phosphors were then embedded into transparent poly-ethylene-co-vinyl acetate (EVA) film to form a spectral convertor. The composite films of Y₂O₃:Tb³⁺–Yb³⁺ phosphors and poly-EVA were found to be highly transparent in the visible range (> 500 nm), making them suitable as spectral photovoltaic convertors.     

Yb<Superscript>3+</Superscript> → Er<Superscript>3+</Superscript> energy transfer in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and temperature characteristic of near-infrared photoluminescence

For the Er³⁺–Yb³⁺ codoped Al₂O₃ powders, the strong near-infrared photoluminescence (PL) centered at 1.535 μm derived from the energy transfer (ET) from Yb³⁺ to Er³⁺ was detected by a 978 nm laser diode excitation. Compared with that of Er³⁺ doped Al₂O₃ powders, the PL intensity enhanced about 9 times, the full width at half maximum (FWHM) extended from 82 to 90 nm, and the lifetime increased from 3.22 to 4.17 ms for Er³⁺–Yb³⁺ codoped Al₂O₃ powders at room temperature. The ET coefficient of 2.18 × 10⁻¹⁸ cm³ s⁻¹ from Yb³⁺ to Er³⁺ was obtained based on the rate equations. The decrease of PL intensity with increasing temperature in the range of 298–733 K was observed, due to thermally enhanced nonradiative relaxation ⁴I_13/2 → ⁴I_15/2 dominated over thermally enhanced phonon-assisted ET in the Er³⁺–Yb³⁺ codoped Al₂O₃.     

Synthesis of Ca<Subscript>3</Subscript>Al<Subscript>6</Subscript>Si<Subscript>2</Subscript>O<Subscript>16</Subscript>: Ce<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript> phosphors by sol–gel method and optical properties

Ca₃Al₆Si₂O₁₆: Ce³⁺, Tb³⁺ phosphors have been prepared by sol–gel method. The structure and photoluminescence properties were studied with careful. The results indicated that the single-phased Ca₃Al₆Si₂O₁₆ phosphors crystallize at 1,000 °C for 2 h in conventional furnace. With appropriate concentrations of Ce³⁺ and Tb³⁺ ions into Ca₃Al₆Si₂O₁₆ matrix, these materials exhibit blue phosphors and white light under ultraviolet radiation. White-light emission can be achieved because of a 400 nm emission ascribed to transitions of Ce³⁺ ions and three sharp peaks at 487, 543, 585 nm, respectively, resulting from transitions of Tb³⁺ ions.     

Structural investigation of salts containing ions [Pd(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>]<Superscript>2+</Superscript> and [IrF<Subscript>6</Subscript>]<Superscript>2–</Superscript>

Double complex salts (DCS) α-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/m, a = 6.3181(3) Å, b = 10.8718(5) Å, с = 7.4526(4) Å, β = 103.568(2)°), β-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/с, a = 8.5773(3) Å, b = 10.8791(4) Å, с = = 12.6741(3) Å, β = 122.497(2)°), [Pd(NH₃)₄]₃[IrF₆]₂Cl₂·H₂O (P-1, a = 7.6080(2) Å, b = 7.6274(2) Å, с = 11.8070(3) Å, β = 122.497(2)°), and [Pd(NH₃)₄]₂[IrF₆]NO₃ (Fm-3m, a = 11.21210(10) Å) have been synthesized and structurally characterized for the first time. The existence of polymorphs for the DCS has been revealed. The influence of the chemical composition of the initial reagents on the reaction course and, respectively, the products, has been demonstrated. A hypothesis on the influence of the second coordination sphere on the formation of one or the other polymorph of the DCS has been suggested. It has been shown that the series α-[Pd(NH₃)₄][МF₆]·H₂O (M = Pt, Pd) exhibits isostructurality.     

Strong visible up-conversion emissions and thermometric applications of Er<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript> codoped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> prepared by the sol–gel method

The Er³⁺–Yb³⁺ codoped Al₂O₃ has been prepared by the sol–gel method using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived Al₂O₃ sols with addition of the erbium nitrate [Er(NO₃)₃ · 5H₂O] and ytterbium nitrate [Yb(NO₃)₃ · 5H₂O]. The phase structure, including only two crystalline types of doped Al₂O₃ phases, θ and γ, was obtained for the 1 mol% Er³⁺ and 5 mol% Yb³⁺ codoped Al₂O₃ at the sintering temperature of 1,273 K. By a 978 nm semiconductor laser diodes excitation, the visible up-conversion emissions centered at about 523, 545, and 660 nm were obtained. The temperature dependence of the green up-conversion emissions was studied over a wide temperature range of 300–825 K, and the reasonable agreement between the calculated temperature by the fluorescence intensity ratio (FIR) theory and the measured temperature proved that Er³⁺–Yb³⁺ codoped Al₂O₃ plays an important role in the application of high temperature sensor.     

Sol–gel synthesis of Eu<Superscript>3+</Superscript>: Tb<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> nanophosphor

Eu (0.1, 0.5 and 1.0 mol%) doped Tb₃Al₅O₁₂ (TAG) was prepared by sol–gel technique through nitrate-citrate route followed by sintering in air (1,100 °C maximum temperature). XRD analysis showed that Eu³⁺ enters the TAG lattice substitutionally replacing the Tb³⁺ ion. Both XRD as well as FTIR investigation showed improvement in crystalline phase with the increase in the sintering temperature. SEM and TEM analysis showed that the powder contains the particles in 5–20 nm size with almost spherical morphology. The excitation spectrum recorded in 300–500 nm showed dominant absorption due to Tb³⁺ while the emission spectra recorded with 380 nm excitation had strong red emission characteristic of Eu³⁺. The intensity of this emission increases with the increase of the Eu concentration from 0.1 to 0.5 mol%. However, the emission intensity decreased on further increase in Eu concentration to 1.0 mol%. This intensity variation with dopant concentration is attributed to well-known “concentration quenching” observed in rare-earth doped materials. Reasonably strong red emission due to Eu was observed when excited with the blue (480 nm) radiation of a Xe lamp indicating the usefulness of the material for the realization of white light LED.     

Framework coordination polymer based on the [Re<Subscript>3</Subscript>Mo<Subscript>3</Subscript>S<Subscript>8</Subscript>(CN)<Subscript>6</Subscript>]<Superscript>6–</Superscript>heterometallic cluster anions and Cd<Superscript>2+</Superscript> cations

A new coordination polymer, [Cd(NH₃)₄]₂{Cd[Re₃Mo₃S₈(CN)₆]}·1.5H₂O (I), was prepared by the reaction between solutions of Cd(CH₃COO)₂ · 2H₂O in aqueous ammonia and CaK₄[Re₃Mo₃S₈(CN)₆] · 8H₂O in water. The crystals are cubic, space group Fm3m (Prussian blue structural type); a = 15.0268(4) Å (CIF file CSD no. 431555). According to ESR data, compound I is paramagnetic, g-factor is 2.298. Thermal stability investigation by TGA and powder X-ray diffraction showed that elimination of coordinated NH₃ molecules is accompanied by sample amorphization.     

Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript>,Tb<Superscript>3+</Superscript> thin films prepared by sol–gel method: structural and optical studies

Y₂O₃: Eu³⁺,Tb³⁺ transparent, high density and optical quality thin films were prepared by the sol–gel dip-coating technique. Yttrium (III) 2,4-pentadionate was used as a precursor by its hydrolysis in ethanol. The doping agents were incorporated in the form of europium and terbium nitrate. Structural, morphological and optical properties of prepared films were investigated for different annealing temperatures in order to establish the ideal processing route that enhances the luminescent properties. X-ray diffraction (XRD) analysis shows the cubic phase for 10-layer films and annealing temperatures higher than 500°C. At 700°C, highly densified (4.52 g cm⁻³) and very smooth films (1.4 nm at 700°C) are produced, composed of crystallites with a grain size of 11 nm. The film thickness, refractive index and porosity, as well as the luminescent properties, were found to vary with treatment temperature.     

Interaction of [В<Subscript>10</Subscript>H<Subscript>10</Subscript>]<Superscript>2–</Superscript> and [В<Subscript>12</Subscript>H<Subscript>12</Subscript>]<Superscript>2–</Superscript> with nitro compounds

The interaction of the [B₁₀H₁₀]^2– and [B₁₂H₁₂]^2– anions with aliphatic and aromatic nitro compounds (RNO₂, where R = Et, n-Pr, i-Pr, tert-Bu, Ph) has been studied under irradiation with visible and UV light. It has been shown that, depending on the reaction conditions, both mono- and disubstituted nitro-closo-decaborates can be selectively obtained in yields up to 50%.     

Preparation and Characteristics of Nb<Superscript>5+</Superscript>, Ta<Superscript>5+</Superscript>/TiO<Subscript>2</Subscript> Nanoscale Powders by Sol–Gel Process Using TiCl<Subscript>3</Subscript>

Nanoscale TiO₂ powders doping with niobium and tantalum were prepared using TiCl₃ as a source matter. Characterization of the materials was performed by Thermoanalys, particle size, XRD, BET, FTIR, Magnetic Susceptibility. The influence of niobium and tantalum ions on the phase transition was studied, the changes in the crystal size and microstain distributions obtained at 400C were analyzed. The results show that the substitutes of Nb^{5 +}, Ta^{5 +} for Ti⁴⁺ in the anatase structure cause distortions and improve to form rutile. When the dopant content is over certain molar percent, biphase reappears. The IR spectra and magnetic susceptibility indicate the Nb–Nb (or Ta–Ta) bonds along c-axis in rutile by two Nb^{5 +} (Ta^{5 +}) ions located in sites adjacent along the c-axis appear with the dopant content. The magnetic characteristics at rutile showed a weak paramagnetism.     

Mercury complex [(HOCH<Subscript>2</Subscript>)<Subscript>3</Subscript>CNH<Subscript>3</Subscript>]<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> [HgI<Subscript>4</Subscript>]<Superscript>2−</Superscript>: Synthesis and structure

The complex [(HOCH₂)₃CNH₃] ₂ ⁺ [HgI₄]^2? (I) was synthesized by reacting (trioxymethyl)methylammonium iodide with mercury dioide (2: 1 mol/mol) in acetone. X-ray crystallography shows that the complex consists of two types of crystallographically independent [(HOCH₂)₃CNH₃]⁺ cations and tetrahedral anions [HgI₄]^2? (IHgI, 106.49(2)°–113.99(4)°; Hg-I, 2.7849(8)-2.8105(8) Å. [(HOCH₂)₃CNH₃]⁺ cations are linked via hydrogen bonds O…H-N and O-H…N (O…N, 2.84–2.92 Å) to form polymer chains, which are cross-linked with one another via anions (I…H, 2.81, 2.82 Å).     

Experimental Determination of the Isotherm at 15°C of the System Mg<Superscript>2+</Superscript>/Cl<Superscript>−</Superscript>, SO<Subscript>4</Subscript><Superscript>2</Superscript>–H<Subscript>2</Subscript>O

Summary.  The diagram of the ternary system Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O was established at 15°C by means of analytical and conductimetric measurements. Three compounds were found in this diagram, which are MgSO₄·6H₂O, MgSO₄·7H₂O, and MgCl₂·6H₂O. The solubility field of MgSO₄·7H₂O is important whereas those of MgSO₄·6H₂O and MgCl₂·6H₂O are small. The compositions (mass-%) of the two invariant points determined by the two methods are: MgSO₄:MgCl₂=2.73:33.80 and MgSO₄: MgCl₂=3.38:28.91. Both the measured and the calculated isotherm at 15°C have been used for modelling of the diagram Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O between 0 and 35°C. The polythermal invariant point was approximately located between 15 and 10°C.  Corresponding author. E-mail: ariguib@planet.tn Received October 16, 2002; accepted (revised) December 3, 2002 Published online April 24, 2003 RID="a" ID="a" Dedicated to Prof. Dr. Heinz Gamsj?ger on the occasion of his 70^th birthday     

Synthesis of Pr<Superscript>3+</Superscript> doped or Tb<Superscript>3+</Superscript>–Mg codoped CaSnO<Subscript>3</Subscript> perovskite phosphor by the polymerized complex method

Pr³⁺ doped or Tb³⁺–Mg codoped CaSnO₃ phosphor powder with perovskite structure was synthesized by the polymerized complex method. Powder samples crystallized into the perovskite phase at approximately 600 °C, which is 400 °C lower than the crystallization temperature for the solid-state reaction method. Uniform-sized powders with average particle sizes of 1–2 μm were obtained after heat treatment at 1,400 °C. Although the samples heat-treated at 600 °C did not exhibit photoluminescence, white photoluminescence of Pr³⁺ doped CaSnO₃ or green photoluminescence of Tb³⁺–Mg codoped CaSnO₃ was observed from the sample heat-treated above 800 °C. The intensity of the photoluminescence increased with increase of the heat-treatment temperature and reached a maximum for heat treatment at 1,400 °C. The maximum photoluminescence intensity for the samples prepared by the polymerized complex method was larger than those prepared by solid-state reaction method, which is probably due to the homogeneous mixing of the doped rare earth ions.     

Single-phased white-light emitting CaAl<Subscript>2</Subscript>Si<Subscript>2</Subscript>O<Subscript>8</Subscript>: Eu<Superscript>2+</Superscript>, Mn<Superscript>2+</Superscript> phosphors prepared by a sol–gel method

CaAl₂Si₂O₈: Eu²⁺, Mn²⁺ phosphors have been prepared by a sol–gel method. X-ray diffractometer, spectrofluorometer and UV–Vis spectrometer were used to characterize structural and optical properties of the samples. The results indicate that anorthite (CaAl₂Si₂O₈) directly crystallizes at 1000 °C in the sol–gel process. CaAl₂Si₂O₈: Eu²⁺, Mn²⁺ phosphors show two emission bands excited by ultraviolet light. Blue (around 415 nm) and yellow (around 575 nm) emissions originate from Eu²⁺ and Mn²⁺, respectively. With appropriate tuning of Mn²⁺ content, CaAl₂Si₂O₈: Eu²⁺, Mn²⁺ phosphors exhibit different hues and relative color temperatures.     

Hydration of CBr<Subscript>3</Subscript>COOH molecules and CBr<Subscript>3</Subscript>CO<Stack><Subscript>2</Subscript><Superscript>–</Superscript></Stack> anions in aqueous solutions

The optimal structures and the vibrational frequencies of H-bonded complexes formed from one-two CBr₃COOH molecules or the CBr₃CO ₂ ^– anion with water molecules are calculated by density functional theory (B3LYP/6-31++G(d,p)). The comparison of the obtained results with the known Raman spectra of the CBr₃COOH–H₂O and NaCBr₃CO ₂ ^– ·H₂O solutions (with component molar ratios of ≤1:16) shows that they include stable hydrates: CBr₃COOH·H₂O and CBr₃CO ₂ ^– ·(H₂O)₆. The first one has a cyclic form, and the second has a cubic globular form. The vibrational band frequencies of the CBr₃COOH molecule and the CBr₃CO ₂ ^– anion in the spectra of both solutions are almost completely determined by the mutual arrangement of units in these hydrates.     

Sol–gel elaboration and structural investigations of Lu<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> planar waveguides

Europium actived Lu₂O₃ sol–gel transparent and crack free films were deposited by dipping on silica substrates. The film microstructure was studied by waveguide Raman spectroscopy (WRS) with annealing temperatures from 400 up to 1,000 °C and X-ray diffraction. The WRS results and TEM observations were correlated and showed that crystallization of the lutetium oxide phase into cubic phase occurs at 600 °C and is stable up to 1,000 °C, the crystallite size increasing between ±38 nm with annealing temperature ranging from 600 to 1,000 °C. Opto-geometrical parameters were determined by m-lines spectroscopy using four different wavelengths of laser sources in order to confirm the step-index profile of the as-prepared waveguides. The Eu³⁺ doped films heat-treated at 1,000 °C presented a constant thickness for the wavelengths 493, 543, 594 and 632.8 nm and a density of 8.4 g cm⁻³. High-resolution X-ray images were obtained.     

UV-sensitized nanomaterial semiconductor catalytic reduction of Co<Superscript>III</Superscript>(N–N)<Subscript>3</Subscript><Superscript>3+</Superscript>/nm-TiO<Subscript>2</Subscript> and Co:TiO<Subscript>2</Subscript> formation: SEM-EDX and HRTEM analyses

Interfacial electron transfer induced by 254 nm light at nanomaterial (nm) titanium dioxide/Co^III(N–N)₃ ³⁺ interface in binary mixed solvent media such as water/methanol (or 1,4-dioxane) has been probed. The distinct photo reduction of cobalt(III) complexes, Co^III(N–N)₃ ³⁺; (N–N)=(NH₃)₂, en (1,2-diamino ethane), pn (1,2-diamino propane), tn (1,3-diamino propane), and bn (1,4-diamino butane), by excited nm-TiO₂ particles: Co^III + nm-TiO₂ + hν → TiO₂ (h⁺;e⁻) + Co^III → nm-TiO₂ (h) + Co^II is solvent controlled. The electron transfer from the conduction band of TiO₂ (e⁻, CB) onto the metal centre of the complex consists of (i) electron transport from CB into surface-adsorbed species A: Co^III(N–N)₃ ³⁺ (ii) solution phase species B: Co^III(N–N)₃ ³⁺ _(sol.), accumulated at the surface of the nanoparticle. In addition, UV irradiation of Co^III(N–N)₃ ³⁺ stimulates generation of \textCo_\textaq^\textII {\text{Co}}_{\text{aq}}^{\text{II}} ion, due to charge transfer transition, in solution phase. After UV irradiation, cobalt-implanted nm-TiO₂ separated as gray ultrafine particles, which were isolated. Photo efficiency of the formation of Co^II ion was estimated and the cobalt implanted nanomaterial crystals isolated from the photolyte solutions were subjected to SEM-EDX, X-ray mapping, and HRTEM-SAED analyses. Solvent medium was found to contribute in both the formation of Co^II ion and interstitial insertion of cobalt into the lattice of nm-TiO₂.     

Platinum–Ruthenium Cluster Complexes from the Reaction of Ru<Subscript>3</Subscript>(CO)<Subscript>12</Subscript> with Pt(PBu<Superscript>t</Superscript><Subscript>3</Subscript>)<Subscript>2</Subscript>

Three new platinum–ruthenium complexes: Pt₃Ru₃(PBu^t ₃)₃(CO)₁₂, 8, Pt₅Ru₃(PBu^t ₃)₃(CO)₁₂, 9 and PtRu₃(PBu^t ₃)₂(CO)₈(μ₃-PBu^t)(μ-H)₂, 10 were obtained from the reaction of Ru₃(CO)₁₂ with Pt(PBu^t ₃)₂. Compound 8 was obtained from this reaction when conducted at 25 °C. Compounds 9 and 10 were obtained when the reaction was conducted at 68 °C. The structure of 8 consists of a central triangular cluster of three ruthenium atoms with one Pt(PBu^t ₃) group bridging each of the three Ru–Ru bonds. The structure of 9 consists of a capped pentagonal bipyramidal cluster of eight metal atoms that is formed formally by the addition of two platinum atoms to 8. The structure of 10 contains a triangular cluster of three ruthenium atoms with a Pt(PBu^t ₃) group bridging one of the Ru–Ru bonds. A t-butyl phosphido ligand formed by degradation of a molecule of PBu^t ₃ bridges the three ruthenium atoms. This report is dedicated to the memory of Professor F. A. Cotton for his many pioneering contributions to inorganic and metal cluster chemistry.