Structural study and luminescence of TlSrLa(AsO4)2

This work presents the crystal structure and luminescent properties of TlSrLa(AsO₄)₂. In this phase Tl⁺ ions are located in large tunnels delimited by chains of alternating (AsO₄) and (Sr,La)O₈ polyhedra. Thallium atoms are eightfold coordinated with C₁ symmetry. Large TlO distances are observed revealing a low stereochemical activity of the 6s² lone pair. Excitation and emission spectra of Tl⁺ in TlSrLa(AsO₄)₂ showed broad bands at lower energy than those observed in previous works. Excitation spectra are decomposed into multiple Gaussian bands and a theoretical analysis is made to explain the number of observed components. Two Gaussian components are revealed for emission spectra.     

Raman and infrared spectra of SmAsO4

SmAsO₄ crystals were grown by the high-temperature flux method. Raman and infrared spectra of the crystals have been taken in the frequency region of 20–4000 and 300–4000 cm⁻¹ respectively. Assignments and correlations have been made for the observed bands. The results obtained were compared with those of some other compounds of the rare-earth arsenates.     

Crystal data for two new phosphate-tellurates : Te(OH)6·2TlH2PO4·Tl2HPO4 and Te(OH)6·2TlH2PO4. Crystal structure of Te(OH)6·2TlH2PO4

We describe chemical preparations and give crystal data for two new phosphate-tellurates : Te(OH)₆·2TlH₂PO₄·Tl₂HPO₄ and Te(OH)₆·2TlH₂PO₄. Both are monoclinic with the following unit cell dimensions : a = 13.68(1), b = 6.317(5), $\text{c}\text{= 11.36(1)}\text{A}\text{?}$, β = 110.18(1)°, Z = 2, D_x = 4.82, S.G. = Cm for the first one, a = 6.285(5), b = 14.74(1), $\text{c}\text{= 7.844(5)}\text{A}\text{?}$, β = 113.38(1)°, Z = 2, D_x = 4.14, S.G. = P2₁/n for the second one. Crystal structure of the second salt shows, as in the already described phosphate-tellurates, the coexistence of independent TeO₆ octahedra and PO₄ tetrahedra in the atomic arrangement.     

Growth and Raman spectra of doped ZnO single crystals

ZnO:M ⁿ⁺(M ⁿ⁺ = Cd²⁺, Co²⁺, Ni²⁺, Sc³⁺, In³⁺, Ga³⁺, Fe³⁺, Te⁴⁺, V⁵⁺) single crystals have been grown under hydrothermal conditions in ZnO-M _x O _y -KOH-LiOH-H₂O systems, and their Raman spectra have been measured under visible (514.5 nm) and near-IR (1064 nm) excitation. The anomalous band between 500 and 600 cm⁻¹ in the Raman spectra of ZnO:Mn²⁺ has A ₁ symmetry and is due to vibrations involving Mn²⁺.     

Low temperature synthesis and characterisation of lecontite, (NH4)Na(SO4)·2H20

Lecontite, (NH₄)Na(SO₄).2H₂O, was synthesised at room temperature in high purity compared to earlier work with a minor impurity of mascagnite, (NH₄)₂SO₄. Rietveld refinement of the XRD results confirmed the crystal structure and unit cell dimensions as published earlier. Raman and Infrared spectroscopy, in conjunction with factor group analysis, resulted in a complex pattern of overlapping sulphate, NH and OH modes. The NH modes υ₁ was observed around 2880 cm⁻¹, υ₂ around 1700 cm⁻¹ overlapping with water OH-bending modes, υ₃ around 3300 cm⁻¹ overlapping with water OH-stretching modes around 3023, 3185 and 3422 cm⁻¹, and υ₄ around 1432, 1447 and 1462 cm⁻¹. The sulphate group in the crystal structure displays a decrease in symmetry from T_d as evidenced by the activation of the ν₁ mode at 982 cm⁻¹ and the ν₂ mode around 452 cm⁻¹ in the Infrared spectrum. The υ₃ mode shows clear splitting in the infrared spectra with a strong band at 1064 cm⁻¹ accompanied by two shoulders at 1107 and 1139 cm⁻¹. The Raman spectra show three weak bands at 1068, 1109 and 1135 cm⁻¹ with a shoulder at 1155 cm⁻¹. Similar splitting was observed for the υ₄ mode around 611 and 632 cm⁻¹ in the Infrared and Raman spectra, respectively.     

Luminescence properties of long-lasting phosphor SrMg2(PO4)2:Eu2+, Ho3+, Zr4+

Novel long lasting phosphors SrMg₂(PO₄)₂:Eu²⁺, SrMg₂(PO₄)₂:Eu²⁺, Zr⁴⁺, SrMg₂(PO₄)₂:Eu²⁺, Ho³⁺ and SrMg₂(PO₄)₂:Eu²⁺, Ho³⁺, Zr⁴⁺ were synthesized by conventional solid-state reaction method. The luminescent properties were systematically characterized by X-ray diffraction, photoluminescent excitation and emission spectra, as well as thermoluminescence spectrum and decay curves. The XRD patterns indicated that the samples belonged to monoclinic phase and co-doping Eu²⁺, Ho³⁺ and Zr⁴⁺ ions had no effect on the basic crystal structure. These phosphors emitting purplish blue light is related to the characteristic emission of Eu²⁺. The afterglow time of Eu²⁺ activated SrMg₂(PO₄)₂ can be greatly enhanced by the co-doping of Ho³⁺, Zr⁴⁺. After the 365 nm UV light excitation source switching off, the Sr_0.92Mg_1.95(PO₄)₂:Eu²⁺_0.01, Zr⁴⁺_0.05, Ho³⁺_0.07 phosphorescence can be observed for more than 1013 s in the limit of light perception of dark-adapted human eyes (0.32 mcd/m²). Different kinds of TL peaks at 423, 448 and 473 K have appeared, and traps densities have increased compared with the Eu²⁺ single doped SrMg₂(PO₄)₂ phosphor. By analyzing the TL curve the depths of traps were calculated to be 0.846, 0.896 and 0.946 eV, respectively, which suggested that the co-doping of Ho³⁺, Zr⁴⁺ improved the electron storage ability of material. Besides, the mechanism was discussed in this report.     

Vibrational studies of the oxysulphide (LaO)4GaS4.5

Far-infrared and Raman spectra of the oxysulphide (LaO)₄GaS_4.5 single crystal were measured and analysed. The interpretation of the observed spectra is based on the existence of (S-S)^2– disulphur groups which are responsible for the high-frequency features. Most of the frequencies are assigned in terms of internal and external vibrations of tetrahedral La₄O groups, GaS₄ units and (S-S)^2– disulphur groups. Spectroscopy measurements are in good agreement with the recent structure determination.     

Sr3Bi(PO4)3:Eu2+, Mn2+: Single-phase and color-tunable phosphors for white-light LEDs

Sr₃Bi(PO₄)₃:Eu²⁺, Sr₃Bi(PO₄)₃:Mn²⁺, and Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ phosphors were synthesized by solid state reaction. The structure and luminescent characteristics were investigated by X-ray powder diffraction and fluorescent spectrophotometer. All samples have the structural type of eulytine. The excitation and emission spectra of Sr₃Bi(PO₄)₃:0.01Eu²⁺ sample show characteristic bands of Eu²⁺ ions. Also, the excitation and emission spectra of Sr₃Bi(PO₄)₃:0.06Mn²⁺ sample show characteristic bands of Mn²⁺ ions. The emission color of Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ sample could be tuned through tuning the co-dopant concentration of Mn²⁺ ions. The decay times for the Eu²⁺ ions decrease with the increase of Mn²⁺ dopant concentration, but the energy transfer efficiency increases with the increase of Mn²⁺ dopant concentration. On the basis of the luminescent spectra and fluorescence decay curves, we confirm that the energy transfer process from the Eu²⁺ to Mn²⁺ ions takes place in the co-doped Sr₃Bi(PO₄)₃ phosphor. Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ sample shows the good thermostability. The emission intensity of the sample at 400 K is about 60% of the value at 300 K. These results show Sr₃Bi(PO₄)₃:Eu²⁺, Mn²⁺ phosphors could be anticipated for UV-pumped white-light-emitting diodes.     

Synthesis and properties of LiZr2(AsO4)3 and LiZr2(AsO4) x (PO4)3 − x

The LiZr₂(AsO₄)₃ arsenate and LiZr₂(AsO₄) _x (PO₄)_{3 ? x} solid solutions have been prepared through precipitation followed by heat treatment, and characterized by X-ray diffraction, X-ray structure analysis, IR spectroscopy, and impedance spectroscopy. We have established conditions for the crystallization of the arsenate and a continuous series of arsenate phosphate solid solutions (0 ≤ x ≤ 3), which have been obtained as two polymorphs: monoclinic and hexagonal. Using the Rietveld method, we have refined the crystal structures of the polymorphs of LiZr₂(AsO₄)₃ (sp. gr. P2₁/n, a = 9.1064(2), b = 9.1906(2), c = 12.7269(3) Å, β = 90.844(2)°, V =1065.03(5) ų, Z = 4; sp. gr. R $\bar 3$ c, a = 9.1600(4), c = 22.9059(13) Å, V = 1664.44(14) Å, Z = 6) and LiZr₂(AsO₄)_1.5(PO₄)_1.5. Their structural frameworks are built up of AsO₄ tetrahedra—or (As,P)O₄ tetrahedra occupied by arsenic and phosphorus atoms at random—and ZrO₆ octahedra, with the lithium atoms in between. The ionic conductivity of the materials has been measured. The cation conductivity of monoclinic LiZr₂(AsO₄) _x (PO₄)_{3 ? x} with 0 ≤ x ≤ 1 has been shown to exceed the conductivity of lithium zirconium phosphate.     

Phosphors based on NaZr2(PO4)3-type calcium and strontium phosphates activated with Eu2+ and Sm3+

Ca_0.5Zr₂(PO₄)₃:Eu²⁺, Sr_0.5Zr₂(PO₄)₃:Eu²⁺, and Ca_0.5Zr₂(PO₄)₃:Eu²⁺, Sm³⁺ orthophosphates prepared through precipitation using sol-gel processes are analogs of NaZr₂(PO₄)₃ (NZP) and crystallize in space group R $\bar 3$ . Their crystallographic parameters determined by X-ray diffraction are consistent with the interatomic distances extracted from EXAFS data. Their luminescence spectra obtained under excitation in the range 300?C400 nm contain emission bands between 425 and 525 nm. Substitution of the larger sized cations Eu²⁺ and Sm³⁺ for Ca²⁺ shifts the emission bands to shorter wavelengths and reduces their width because of the decrease in the effect of the crystal field. Analysis of the spectra indicates that Eu²⁺ occupies two types of crystallographic sites (independent interstitial sites of different sizes and shapes in the NZP framework structure). Codoping with Eu and Sm has ensured luminescence with chromaticity coordinates approaching those of white light: (x = 0.27, y = 0.34).     

Crystal-field analyis of Mn (3d) in Sr5 (PO4)3Cl

The absorption and emission spectra of Mn⁵⁺ (3d²) in Sr₅(PO₄)₃Cl are analyzed using a C₄ crystal-field hamiltonian. The descent in symmetry from cubic was guided by a point-charge calculation of the crystal-field componensts. The calculated energy levels are in excellent agreement with those obtained experimentally. The resulting crystal-field parameters, B_nm, represent very well the crystal-field interactions of Mn⁵⁺ in Sr₅(PO₄)₃Cl.     

New arsenates (V) NaKAl2O[AsO4]2 and Na2KAl3[AsO4]4

The title compounds have been synthesized by a solid state reaction route using a salt flux. Their crystal structures were determined from single crystal X-ray data. NaKAl₂O[AsO₄]₂ crystallizes with the orthorhombic K₂Fe₂O[AsO₄]₂-type, Pnma, a = 8.2368(6) Å, b = 5.5228(3) Å, c = 17.0160(13) Å and Z = 4, whereas Na₂KAl₃[AsO₄]₄ crystallizes with the orthorhombic K₃Fe₃[AsO₄]₄-type, Cmce, a = 10.5049(9), b = 20.482(2), c = 6.3574(6) Å and Z = 4. The NaKAl₂O[AsO₄]₂ structure is built up of [Al₂As₂O₉]²⁻ layers perpendicular to the c-axis which are separated by A⁺ alkali layers. The [Al₂As₂O₉]²⁻ layers consist of ribbons of edge-sharing AlO₆ octahedra, running along the a direction and which are connected through AsO₄ tetrahedra by sharing corners. The Na₂KAl₃[AsO₄]₄ structure contains [Al₃As₄O₁₆]³⁻ layers perpendicular to the b-axis separated by A⁺ alkali layers. The [Al₃As₄O₁₆]³⁻ layer consists of a layer of corner-sharing AlO₆ octahedra which are also connected to the AsO₄ tetrahedra by sharing corners.     

Structural investigations of phosphate glasses: a detailed infrared study of the x(PbO)-(1−x) P2O5 vitreous system

The results and detailed discussion of an extensive experimental study of infrared spectra of the x (PbO)-(1–x)P₂O₅ vitreous system (x=0.3–0.75) together with a brief review of infrared spectra of phosphate compounds, are presented. Theoretical models employed in the interpretation of infrared spectra of glasses have been reviewed. The frequency ranges of various infrared bands belonging to PO ₄ ^3– and P₂O ₇ ^4– , observed in different phosphate compounds, are discussed. The glassy and quenched samples were prepared from PbO and NH₄H₂PO₄ by the rapid quenching technique. The infrared spectra of the constituents of the system, PbO and P₂O₅, in their polycrystalline and glassy forms, have been discussed. The intensity and wavenumbers of the infrared bands around 1600 and 3300 cm^–1, assigned to the bending and stretching modes in H₂O trapped by the hygroscopic glasses, have been followed for different compositions with x<0.5. The changes observed in these infrared bands established the role of water as an additional glass modifier. The intensity and frequency variations of the infrared bands have been followed through all the compositions for characteristic phosphate group frequencies including P=O, P-O-P stretching and bending modes and P-O bending mode. The results clearly suggest that the x(PbO)-(1–x)P₂O₅ system undergoes gradual structural changes from metaphosphate (x=0.5), to pyrophosphate (x=0.66) and to orthophosphate (x=0.75). The continuing presence of the infrared band, in varying intensity, in the region 1200–1280 cm^–1 attributed to P=O, suggests that the glass-forming ability of the binary system is extendable at least up to x=0.66 composition, and that no complete rupture of P=O bond by Pb²⁺ takes place. The ionic character of the phosphate groups, P-O^(–), PO ₄ ^3– is well revealed by significant changes with the PbO content in the spectral features of the infrared bands around 1120 and 980 cm^–1 respectively. The maximum intensity of the P-O^(–) band at 1120 cm^–1 for 55 mol% PbO suggests a partial breakdown of the covalent vitreous network of the phosphates and formation of a crystalline phase consisting of ionic groups PO ₄ ^3– , P₂O ₆ ^2– and P₂O ₇ ^4– for PbO greater than 55 mol%. The observed pattern of variation in the intensity of the infrared bands in the 940–1080 cm^–1 region attributed to the v₃-mode in PO ₄ ^3– , suggests a gradual transformation of PO ₄ ^3– units to PO ₃ ^– groups in lead meta-phosphate glass and then their restoration to PO ₄ ^3– groups of pyro- and ortho-phosphate quenched samples. The results indicate a gradual decrease in the number of bridging oxygens and increase in the resonance behaviour of non-bridging oxygens as the mole percentage of metal oxide (PbO) increases in the glass. The infrared spectra of several binary phosphate glasses have been reviewed in the context of the study of effect of the cation on the infrared spectra. It is found that the influence of the cation on the infrared spectra of phosphate glasses does not show any striking regularity. Theoretical calculations of these band frequencies were found to agree well only in the case of pure stretching (P=O and O-H) vibrations and pure bending (P-O-P and O-H) vibrations. The disagreement in the case of P-O^(–), P-O-H and other modes of P-O-P groups, has been attributed to the mixed nature of modes occurring in glasses. The changes in the positions of the characteristic bands and their relative intensities are strongly dependent on the structural units and PbO content in the phosphate glasses and the results emphasize the role of PbO as a network modifier.     

Investigation of jarosite process tailing waste by means of raman and infrared spectroscopy

The aim of this work was to identify and characterize three samples of jarosite process tailing waste in Mitrovica, Kosovo, using Raman and Fourier transform infrared (FTIR) spectroscopy. The identification is made based on the assignment of bands in the Raman and FTIR spectra. Both Raman and FTIR spectra show the fundamental stretching and bending vibration mode of SO₄^2–, OH^– and NH₄⁺ groups. The results obtained by the means of Raman and infrared spectroscopy are compared with cited reference data in order to sum the analysis of vibrational spectra.     

Acetone intercalation/de-intercalation processes in the HUP (H3OUO2PO4·3H2O) framework: A model for electrochemical degradation

Intercalation of acetone molecules in the H₃OUO₂PO₄ · 3H₂O framework has been studied by X-ray diffraction, differential scanning calorimetry and IR and Raman spectroscopies. The influence of water traces in acetone is pointed out. Four main phases are observed in the course of the rehydration/de-intercalation process. The nature of proton bonding with the (UO₂PO₄) _n slab and its evolution are discussed (H₃O⁺, PO ₄ ^3– , HPO ₄ ^2– , HPO ₄ ^2– ...). The presence of defects in the sub-stoichiometric HUP is demonstrated. Comparison is made with similar partially dehydrated material obtained under electric field action in electrochemical solid state devices.     

Hydrolysis of tetracalcium phosphate in H3PO4 and KH2PO4

The activity product of tetracalcium phosphate (TTCP, Ca₄(PO₄)₂O), was determined at 37°C, and the hydrolysis of TTCP was investigated in 0.01–0.1 mol l^–1 H₃PO₄ and KH₂PO₄ solutions by means of calcium and phosphorus analyses, X-ray diffraction and infrared analysis. The activity product, defined as K _sp=(Ca²⁺)⁴ (PO ₄ ^3– )² (OH^–)², was 37.36 as pK _sp, which was smaller than that previously reported (42.4). TTCP easily hydrolysed to form calcium-deficient apatite (Ca-def OHAp, Ca_5–x (HPO₄) _x (PO₄)_3–x (OH)_1–x ), or dicalcium phosphate dihydrate (DCPD, CaHPO₄2H₂O), depending on the initial phosphate concentration. With 0.1 mol l^–1 H₃PO₄, TTCP hydrolysed to form DCPD within several minutes. In 0.025 mol l^–1 H₃PO₄ and 0.1 mol l^–1 KH₂PO₄, TTCP hydrolysed to form Ca-def OHAp through DCPD. In the latter solution, a small amount of octacalcium phosphate (OCP, Ca₈(H₂PO₄)₂(PO₄)₄5H₂O), was detected as an intermediate product. In 0.025 mol l^–1 KH₂PO₄, TTCP hydrolysed directly to form Ca-def OHAp. In 0.01 mol l^–1 H₃PO₄, hydrolysis of TTCP was not completed, although Ca-def OHAp was only a product. Thus the final product and the degree of hydrolysis depended on the pH and the overall Ca/P ratio in the reaction system. The rate of Ca-def OHAp formation seemed to be controlled by the dissolution rate of TTCP rather than the crystallization rate of the OHAp.     

Crystallization from Na2O-P2O5-Fe2O3-MIIO (MII = Mg, Ni) melts and the structure of Na4MgFe(PO4)3

We have studied general trends of phosphate crystallization from Na₂O-P₂O₅-Fe₂O₃-M^IIO (M^II = Mg, Ni) high-temperature solutions at Na/P = 1.0?1.4, M^II/Fe = 1.0, and Fe/P = 0.15 or 0.3, and identified the stability regions of the phosphates Na₄M^IIFe(PO₄)₃ (M^II = Mg, Ni), NaFeP₂O₇, and Na₂NiP₂O₇. The synthesized compounds have been characterized by X-ray powder diffraction and infrared spectroscopy. The structure of Na₄MgFe(PO₄)₃ (sp. gr. $R\bar 3cWe have studied general trends of phosphate crystallization from Na₂O-P₂O₅-Fe₂O₃-M^IIO (M^II = Mg, Ni) high-temperature solutions at Na/P = 1.0−1.4, M^II/Fe = 1.0, and Fe/P = 0.15 or 0.3, and identified the stability regions of the phosphates Na₄M^IIFe(PO₄)₃ (M^II = Mg, Ni), NaFeP₂O₇, and Na₂NiP₂O₇. The synthesized compounds have been characterized by X-ray powder diffraction and infrared spectroscopy. The structure of Na₄MgFe(PO₄)₃ (sp. gr. R[`3]cR\bar 3c, a = 8.83954(13) ?, c = 21.4683(4) ?) has been determined by Rietveld powder diffraction analysis.     

Simultaneous doping of anodic silicon oxide films with phosphorus and arsenic

It is established that, during the formation of anodic P- or As-doped SiO₂ films on p-Si in an ethylene glycol + 0.13% H₂O solution containing 14.3% H₃PO₄, 0.17% HNO₃, and 0.0193–1.95% H₃AsO₄ additives, the orthophosphoric and orthoarsenic acids do not produce any combined effect upon the process of introduction of the arsenate and phosphate anions into silicon dioxide. It is suggested that the partial anodic reactions of Si with NO ₃ ^? , OH^?, AsO ₄ ^3? , and PO ₄ ^3? proceed with the formation of SiO₂ involving As₂O₃, As, As₂O₅, P₂O₅, and P.     

The sodium ytterbium orthophosphate Na3(1+x)Yb(2-x)(PO4)3

A new sodium ytterbium orthophosphate with general formula Na_3(1+x)Yb_(2-x)(PO₄)₃ (0.07 ? x ? 0.50) has been prepared and characterized. Its crystal structure has been determined from a single crystal for x = 0.50. The space group is R3?c, the lattice constants are : $\text{a}\text{= 9.12(1)}\text{A}\text{?}$, $\text{c}\text{= 21.81(6)}\text{A}\text{?}$. The structure of Na_4.50Yb_1.50(PO₄)₃ is related to that of NaZr₂(PO₄)₃. The PO₄ tetrahedra and the (Yb,Na)O₆ octahedra form a three-dimensional skeleton in which the remaining sodium atoms are inserted. This structural type is also found for the phases Na_4.50Ln_1.50(PO₄)₃ (Ln = Tm, Lu) and Na_4.50Ln_1.50(AsO₄)₃ (Ln = Er, Tm, Yb, Lu).