Optical properties of Nd-doped Ca3(VO4)2 single crystal fiber

Optical absorption and photoluminescence of Ca₃(VO₄)₂ single crystal grown by a floating-zone technique and containing Nd³⁺ ions were investigated. High absorption coefficients and broadening of most absorption bands are present at 300 K, while substructures in some of the same bands can be evidenced at 12 K. Most features of measured spectra are characteristic of random occupation of more than a single Ca²⁺ site by the Nd³⁺ ion and of distortions provoked by different charge compensation mechanisms involving oxygen vacancies promotion in the crystal lattice. Nd³⁺ optical properties were studied by using the Judd-Ofelt theory to calculate the spectral parameters relevant for laser applications.     

Structure and phase relations in the 2(CuInS2)-Cu2ZnSnS4 solid solution system

The intermixing of roquesite (CuInS₂) and kesterite (Cu₂ZnSnS₄), i. e. Cu(In_x(ZnSn)_1−xS₂ was investigated by a combination of neutron and X-ray powder diffraction. Samples with 0 ≤ × ≤ 1 were synthesized by a solid state reaction of the pure elements in evacuated silica tubes at 800 °C and cooled with a 10 K/h rate after the final annealing. The structural parameters of CuIn_x(ZnSn)_1−xS₂ were determined by simultaneous Rietveld refinement of neutron and X-ray diffraction data. The microstructure and chemical composition of the samples were investigated by electron microprobe analysis. A broad miscibility gap exists in the region 0.4 ≤ × < 0.8 indicated by the coexistence of two phases, an In-rich (x ~ 0.77) and a Zn-Sn-rich (x ~ 0.33) phase. Cu(In_x(ZnSn)_1−xS₂ mixed crystals with 0 ≤ x < 0.4 crystallize in the kesterite type structure, and with 0.8 ≤ × ≤ 1.0 in the chalcopyrite type structure. In the latter In, Zn and Sn are disordered on the In site. In the mixed crystals the lattice constant a and c show a linear dependence on chemical composition, whereas the tetragonal deformation Δ = 1−c/2a varies nonlinearly. Moreover in the mixed crystal with x ~ 0.15 the tetragonal deformation is equal zero and thus its structure is characterized by a pseudo-cubic unit cell.     

含钛磷酸盐玻璃NaTi2(PO4)3-0.9Ca3(PO4)2的析晶行为

利用差热分析、X射线衍射仪、液氮吸附BET孔经测试仪对组成为NaTi2(PO4)3-0.9 Ca3(PO4)2的含钛磷酸盐玻璃的析晶行为进行了研究.通过对该玻璃相继进行成核、析晶和酸浸泡处理制备了NaTi2(PO4)3骨架多孔微晶玻璃.证明该玻璃在646℃8h成核处理过程中产生了旋节分解特征的成分偏聚,形成了富TiO2玻璃相和富CaO玻璃相交错生长的连通结构,成核处理后的玻璃在738℃析晶过程中依次在富钛相和富钙相中析出NaTi2(PO4)3和β-Ca3(PO4)2.成核过程对析晶的促进作用是通过促进NaTi2(PO4)3的析出而实现的.     

Preparation and properties of the Pb3(VO4)2Pb3(PO4)2 system

Single crystals of the pseudobinary system Pb₃(V_1?xP_xO₄)₂ were grown via the Czochralski technique and were studied over wide ranges of x, particularly with regard to the influence of substitution on the $\text{3}\text{?}\text{mF}\text{2}\text{m}$ transition as a function of temperature.     

Enhanced luminescence by charge compensation in red-emitting Eu-activated Ca3Sr3(VO4)4

The effects of charge compensation on the luminescence behavior of a red-emitting phosphor, Ca₃Sr₃(VO₄)₄:Eu³⁺, were investigated. It has been observed that charge compensated by monovalent ions, especially Na⁺, shows greatly enhanced red emission under ultraviolet excitation. It is found that Na₂CO₃ addition acts as a fluxing agent and plays a role in charge compensation, which clearly improves the emission intensity of Eu³⁺-activated Ca₃Sr₃(VO₄)₄. Enhanced emission intensity of the corresponding charge compensated phosphors under ultraviolet radiation may find application in the production of red phosphors for white light-emitting diodes.     

Local density calculation of structural and electronic properties for Ca10(PO4)6F2

The local-density-functional pseudopotential approach is applied to the calculation of the lattice properties and electronic structure of the fluoroapatite Ca₁₀(PO₄)₆F₂ which is one of the simplest apatites. The calculated lattice parameters agree well with the experiment. Valence charge density and Mulliken population are analysed to understand the nature of the bond between the different atoms.     

Preparation of (NH4)Zr2(PO4)3 and HZr2(PO4)3

(NH₄)Zr₂(PO₄)₃ has been prepared, hydrothermally, from α-zirconium phosphate in three different ways; (1) from amine intercalates at 300°C, (2) from mixtures of ZrOCl₂·8H₂O in excess (NH₄)H₂PO₄ and (3) reaction of NH₄Cl with Zr(NaPO₄)₂. Ammonium dizirconium triphosphate is rhombohedral with a = 8.676(1) and $\text{c}\text{= 24.288(5)}\text{A}\text{?}$. It decomposed on heating to HZr₂(PO₄)₃. Below 600°C a complex, as yet unindexed, X-ray pattern was obtained. A very similar X-ray pattern was obtained by washing LiTi_0.1Zr_1.9(PO₄)₃ with 0.3N HCl. Heating this phase or NH₄Zr₂(PO₄)₃, above 600°C resulted in the appearance of a rhombohedral phase of HZr₂(PO₄)₃ with cell dimensions a = 8.803(5) and $\text{c}\text{= 23.23(1)}\text{A}\text{?}$. The protons were not completely removed until about 1150°C. Decomposition of (NH₄)Zr₂(PO₄)₃ at 450°C yielded an acidic gas whereas at 700°C NH₃ was evolved. A possible explanation for this behavior is presented.     

Multi-wavelength continuous-wave laser operation of Yb:Ca3Gd2(BO3)4 disordered crystal

The diode-pumped multi-wavelength continuous-wave laser operation of the disordered Yb:Ca₃Gd₂(BO₃)₄ crystal was firstly investigated in this paper. The simultaneous emission wavelengths varied from 2 to 5 in the range from 1045.4 to 1063.6 nm with the change of the absorbed pump power and crystal length. An output power of 1.4 W was obtained with four-wavelength emission, corresponding to an optical-optical slope efficiency of 23.7%. Five-wavelength emission at 1049.4, 1051.3, 1053.4, 1055.6 and 1057.4 nm was realized under the output power of 1.0 W. The absorption behavior of Yb:Ca₃Gd₂(BO₃)₄ have also been measured.     

Syntheses and structures of Ta2(WO2)0.87H0.26(PO4)4 and Ta2(MoO2)(PO4)4

Tantalum hydrogen phosphate, β-TaH(PO₄)₂, has a three-dimensional structure that is stable to remarkably high temperature (∼600 °C) presumably due to the presence of strong hydrogen bonds. Impedance measurements indicate a low conductivity, 2.0 × 10⁻⁶ S/cm at 200 °C in 5% H₂. In further studies aimed at enhancing the conductivity by aliovalent doping, we have investigated systematically the synthesis of compounds in the TaH(PO₄)₂-W₂P₂O₁₁ system at 380 °C. As a result, a new phase, Ta₂(WO₂)_0.87H_0.26(PO₄)₄, was identified and subsequently the molybdenum analog Ta₂(MoO₂)(PO₄)₄ was also prepared. The structures were determined by single crystal X-ray diffraction techniques. The structures of Ta₂(WO₂)_0.87H_0.26(PO₄)₄ and Ta₂(MoO₂)(PO₄)₄ can be formally derived from the structure of β-TaH(PO₄)₂ by the replacement of two P-OH protons with an MO₂²⁺ (M = Mo and W) group together with a change in the orientation of some phosphate tetrahedra.     

Self-activated afterglow luminescence of un-doped Ca2ZrSi4O12 material and explorations of new afterglow phosphors in a rare earth element-doped Ca2ZrSi4O12 system

Un-doped Ca₂ZrSi₄O₁₂ material is prepared using a solid state reaction and it emits intense green afterglow luminescence peaking at 490 nm. The afterglow luminescence can be recorded for about 4800 s (0.32 mcd m⁻²). The thermoluminescence revealed that at least four types of traps existed in the Ca₂ZrSi₄O₁₂ material and the depths of these traps were calculated. The contributions of these traps on the afterglow luminescence were also investigated in detail. Accordingly, a possible afterglow mechanism of Ca₂ZrSi₄O₁₂ was proposed. Moreover, Ca₂ZrSi₄O₁₂ was also doped by rare earth or metal ions for developmental purpose and we arrived at some useful conclusions according to the experimental results.     

Substitutions in the Ca2Na6Al6Si6O24(SO4)2 haüyne structure

Four new haüynes having the chemical formula Ca₂Na₆Al₆Si₆O₂₄(XO₄)₂, X = Se, Te, Mo and W, were synthesized by solid-state reaction. Various substitutions were then attempted for Ca, Na, Al and Si. The replacement of Ca²⁺ by Sr²⁺ or Cd²⁺ was successful in Ca₂Na₆Al₆Si₆O₂₄(XO₄)₂, when X = S, Cr, Mo or W, except for Cd, when X = Cr. The synthesis of Mn₂Na₆Al₆Si₆O₂₄(XO₄)₂ could be made when X was Mo or W, and, among the Pb substitutions tried, Pb₂Na₆Al₆Si₆O₂₄(SO₄)₂ was successful. The solubility of Li, K and Ag was partial and was different in different haüynes. Maximum solubility of Li for Na was three atoms in Ca₂Na₆Al₆Si₆O₂₄(SO₄)₂ and the minimum was half an atom in Ca₂Na₆Al₆Si₆O₂₄(XO₄)₂, X = Mo or W. Maximum replacement of K or Ag for Na was two atoms in Ca₂Na₆Al₆Si₆O₂₄(XO₄)₂, X = Mo or W and the minimum was 0.5 in Ca₂Na₆Al₆Si₆O₂₄(SO₄)₂. The solubility of Li, K and Ag was 1.5 atoms in Ca₂Na₆Al₆Si₆O₂₄(CrO₄)₂. The solubility of Ga³⁺ or Fe³⁺ for Al³⁺ was partial. A maximum of 0.5, 3 and 4 atoms of Ga³⁺ can be substituted for Al³⁺ in sulfate, chromate and molybdate or tungstate haüynes, respectively. The solubility of Fe³⁺ was one atom in all haüynes. The complete replacement of Si⁴⁺ by Ge⁴⁺ was possible in M²⁺₂Na₆Al₆Si₆O₂₄(XO₄)₂, when M = Ca, Cd or Sr, and X = Mo or W.     

Novel Dy-doped Ca2Gd8(SiO4)6O2 white light phosphors for Hg-free lamps application

The luminescent properties of Ca₂Gd_8(1−x)(SiO₄)₆O₂:xDy³⁺ (1% ≤ x ≤ 5%) powder crystals with oxyapatite structure were investigated under vacuum ultraviolet excitation. In the excitation spectrum, the peaks at 166 nm and 191 nm of the vacuum ultraviolet region can be assigned to the O²⁻ → Gd³⁺, and O²⁻ → Dy³⁺ charge transfer band respectively, which is consistent with the theoretical calculated value using Jφrgensen's empirical formula. While the peaks at 183 nm and 289 nm are attributed to the f-d spin-allowed transitions and the f-d spin-forbidden transitions of Dy³⁺ in the host lattice with Dorenbos's expression. According to the emission spectra, all the samples exhibited excellent white emission under 172 nm excitation and the best calculated chromaticity coordinate was 0.335, 0.338, which indicates that the Ca₂Gd₈(SiO₄)₆O₂:Dy³⁺ phosphor could be considered as a potential candidate for Hg-free lamps application.     

Temperature dependence of critical stress and phase diagram of ferroelastic Pb3 (PO4)2 Pb3 (VO4)2

The temperature dependence of the critical stress in ferroelastic Pb₃ (PO₄)₂ reveals a Curie-Weiß law ($\text{ß =}\text{1}\text{2}$) up to 145°C. Between 160°C and the transition point at 180°C a crossover to a $\text{ß =}\text{1}\text{3}$ regime was found. For mixed crystals Pb₃ (PO₄)₂ ? Pb₃ (VO₄)₂ a phase diagram is suggested from optical, dielectric and Raman spectroscopical experiments.     

Superconductivity at 103 K in CdBa2(Ca0.7Y0.3)Cu2Oy

A cadmium analogue of the mercury system with nominal composition CdBa₂(Ca_1–xY_x)Cu₂O_y has been synthesized. Thex=0 samples contain about 12 vol.% of the 1212 phase but are not superconducting. Thex=0.3 samples are superconducting atT _on = 103 K. The EDX analysis of 18 microcrystals shows a broad cationic distribution of the different components. The observed broad superconducting transition is attributed to the variousT _c of the different microcrystals.     

Synthesis and the luminescent properties of europium-activated Ca2SnO4 phosphors

The synthesis and photoluminescent (PL) properties of calcium stannate crystals doped with europium grown by mechanically activated in a high energy vibro-mill have been investigated. The characteristics of Ca₂SnO₄:Eu³⁺ phosphors were found to depend on the amounts of europium ions. The XRD profiles revealed that the system, (Ca_1−xEu_x)₂SnO₄, could form stable solid solutions in the composition range of x = 0–7% after being calcined at 1200 °C. The calcined powders emit bright red luminescence centered at 618 nm due to ⁵D₀ → ⁷F₂ electric dipole transition. Both XRD data and the emission ratio of (⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁) reveal that the site symmetry of Eu³⁺ ions decreases with increasing doping concentration. The maximum PL intensity has been obtained for 7 mol% concentration of Eu³⁺ in Ca₂SnO₄.     

Mössbauer resonance studies in the CaTiO3Ca2Fe2O5 system

A Mössbauer resonance study of the CaTiO₃-Ca₂Fe₂O₅ system - i.e. the Ca₂Fe_2xTi_2?2xO_6?x solid solution (0?x?1) - shows a continuous evolution of the local iron environment over the entire composition range. For 0.50?x?1 the investigation confirms a previous structural model of alterning layers of octahedra and tetrahedra. For lower concentrations of oxygen vacancies, evidence is given of Fe³⁺ ions randomly distributed in octahedral and even in tetrahedral sites. Titanium atoms apparently have only octahedral surroundings. A long range order is detected when $\text{x}\text{? 0.50}$.     

Luminescent properties of Eu-activated nanophosphors Ca3Y0.8Gd0.2(VO4)2.4(PO4)0.6: Eu for light-emitting diodes

Eu³⁺-doped Ca₃Y_0.8Gd_0.2(VO₄)_2.4(PO₄)_0.6 nanophosphors have been prepared by modified solid-state reaction. X-ray powder diffraction, transmission electron microscopy (TEM), photoluminescence excitation and emission spectra were used to characterize the resulting samples. X-ray powder diffraction (XRD) analysis confirmed the formation of YVO₄. Photoluminescence (PL) results showed that the phosphor could be efficiently excited by UV-visible light from 350 to 550 nm, exhibiting bright orange-red emission(excited by 397) and red emission(excited by 467), which has potential application as a phosphor for UV and blue GaN-based light-emitting diodes (LEDs). TEM images show that the grain size of Ca₃Y_0.45Eu_0.35Gd_0.2(VO₄)_2.4(PO₄)_0.6 is about 39 nm, which is in full agreement with the theoretical calculation data from the XRD patterns.     

Waveguiding properties of pulsed-laser deposition Ca4GdO(BO3)3 thin films

Waveguiding properties of stoichiometric Ca₄GdO(BO₃)₃ (GdCOB) thin films deposited on quartz substrates by the pulsed-laser deposition (PLD) technique are reported. The optical properties and the anisotropy of the obtained thin films are investigated using the prism-coupling technique. Refractive indices (n_x=1.666, n_y=1.673 and n_z=1.680 at 632.8 nm) were, respectively, determined from the transverse electric (TE) and the transverse magnetic (TM) mode excitations. These values are found to be 3% lower than those of the bulk material, which is likely due to the structural and morphological features of the deposited GdCOB films.     

Dielectric properties of Pb3 (PO4)2 | Pb3 (AsO4)2

The dielectric constants of Pb₃ (PO₄)₂ | Pb₃ (AsO₄)₂ at room temperature are intrinsic and fulfill the Lyddane - Teller - Sachs relation. At higher temperatures the specific conductivity increases with an activation energy of 0.56 eV leading to Maxwell - Wagner polarization effects thereby increasing the effective dielectric constant. Corresponding peaks in ∈' (T) are extrinsic and not attributed to structural phase transformations.     

Direct observation of ferroelasticity in Pb3(PO4)2  Pb3(VO4)2

Ferroelasticity has been established in the room temperature phase of Pb₃(P_xV_1-xO₄)₂, (x ≥ 0.8). The coercitive stress and the spontaneous strain have been determined and found to be 1.6 bars and ca. 3.5 · 10^?4 respectively. The effect of domain switching on double refraction and Raman spectra is clearly brought out.