La7O6(BO3)(PO4)2:Eu3+/Tb3+荧光材料的制备及其光致发光性能

采用优化的高温固相方法制备了稀土离子Eu³⁺和Tb³⁺掺杂的La₇O₆（BO₃）（PO₄）₂系荧光材料,并对其物相行为、晶体结构、光致发光性能和热稳定性进行了详细研究。结果表明,La₇O₆（BO₃）（PO₄）₂：Eu³⁺材料在紫外光激发下能够发射出红光,发射光谱中最强发射峰位于616 nm处,为⁵D₀→⁷F₂特征能级跃迁,Eu³⁺的最优掺杂浓度为0.08,对应的CIE坐标为（0.610 2,0.382 3）;La₇O₆（BO₃）（PO₄）₂：Tb³⁺材料在紫外光激发下能够发射出绿光,发射光谱中最强发射峰位于544 nm处,对应Tb³⁺的⁵D₄→⁷F₅能级跃迁,Tb³⁺离子的最优掺杂浓度为0.15,对应的CIE坐标为（0.317 7,0.535 2）。此外,对2种材料的变温光谱分析发现Eu³⁺和Tb³⁺掺杂的La₇O₆（BO₃）（PO₄）₂荧光材料均具有良好的热稳定性。     

Photoluminescence properties of a novel phosphor, Na3La9O3(BO3)8:RE(RE=Eu,Tb)

The new oxyborate phosphors, Na₃La₉O₃(BO₃)₈:Eu³⁺ (NLBO:Eu) and Na₃La₉O₃(BO₃)₈:Tb³⁺ (NLBO:Tb) were prepared by solid-state reactions. The photoluminescence characteristics under UV excitation were investigated. The dominated emission of Eu³⁺ corresponding to the electric dipole transition ⁵D₀→⁷F₂ is located at 613 nm and bright green luminescence of NLBO:Tb attributed to the transition ⁵D₄→⁷F₅ is centered at 544 nm. The concentration dependence of the emission intensity showed that the optimum doping concentration of Eu and Tb is 30% and 10%, respectively.     

La_7O_6(BO_3)(PO_4)_2∶Eu~(3+)/Tb~(3+)荧光材料的制备及其光致发光性能

采用优化的高温固相方法制备了稀土离子Eu~(3+)和Tb~(3+)掺杂的La_7O_6(BO_3)(PO_4)_2系荧光材料,并对其物相行为、晶体结构、光致发光性能和热稳定性进行了详细研究。结果表明,La_7O_6(BO_3)(PO_4)_2∶Eu~(3+)材料在紫外光激发下能够发射出红光,发射光谱中最强发射峰位于616 nm处,为5D0→7F2特征能级跃迁,Eu~(3+)的最优掺杂浓度为0.08,对应的CIE坐标为(0.610 2,0.382 3);La_7O_6(BO_3)(PO_4)_2∶Tb~(3+)材料在紫外光激发下能够发射出绿光,发射光谱中最强发射峰位于544 nm处,对应Tb~(3+)的5D4→7F5能级跃迁,Tb~(3+)离子的最优掺杂浓度为0.15,对应的CIE坐标为(0.317 7,0.535 2)。此外,对2种材料的变温光谱分析发现Eu~(3+)和Tb~(3+)掺杂的La_7O_6(BO_3)(PO_4)_2荧光材料均具有良好的热稳定性。     

Hydrolysis of ammonium oxofluorotungstates: A F, O and W NMR study

Fluorine-19 and natural abundance ¹⁷O and ¹⁸³W NMR spectroscopy were employed for the characterization of aqueous solutions of (NH₄)₂WO₂F₄ and (NH₄)₃WO₃F₃. Dissolution of the (NH₄)₂WO₂F₄ complex is accompanied by its partial acid hydrolysis to give the trans(mer)-dimer, [W₂O₅F₆]⁴⁻, and unreacted cis-[WO₂F₄]²⁻. The cis(fac)-[W₂O₅F₆]⁴⁻ anion is the major soluble product resulting from the alkaline hydrolysis of (NH₄)₂WO₂F₄ along with the isolation of the solid (NH₄)₂WO₃F₂. In addition, the edge-bridging dimer, [W₂O₆F₄]⁴⁻, and the cyclic trimer, [W₃O₉F₆]⁶⁻, are also suggested as hydrolysis products. Decomposition of (NH₄)₃WO₃F₃ occurs in aqueous solution to give NH₄WO₃F.     

Eu luminescence—a structural probe in BiCa4(PO4)3O, an apatite related phosphate

Eu³⁺ luminescence is studied in apatite-related phosphate BiCa₄(PO₄)₃O. Compositions of the formula Bi_1−xEu_xCa₄(PO₄)₃O [x=0.05, 0.1, 0.3, 0.5, 0.8 and 1.0] are synthesized and they are isostructural with parent BiCa₄(PO₄)₃O. Room temperature photoluminescence shows the various transitions ⁵D₀→⁷F_J(=0,1,2) of Eu³⁺. The emission results of compositions with different Eu³⁺ content show the difference in site occupancy of Eu³⁺ in Bi_1−xEu_xCa₄(PO₄)₃O. The intense ⁵D₀-⁷F₀ line at 574 nm for higher Eu³⁺ content is attributed to the presence of strongly covalent Eu-O bond that is possible by substituting Bi³⁺ in the Ca(2) site. This shows the preferential occupancy of Bi³⁺ in Ca(2) site and this has been attributed to the 6s² lone pair electrons of Bi³⁺. This is further confirmed by comparing the emission results with La_0.95Eu_0.05Ca₄(PO₄)₃O.     

Photoluminescence properties of La(PO3)3:Tb under VUV excitation

La_1−x(PO₃)₃:Tb_x³⁺ (0<x0.6) were prepared using solid-state reaction. The vacuum ultraviolet (VUV) excitation spectrum of La_0.55(PO₃)₃:Tb_0.45³⁺ indicates that the absorption of (PO₃)₃³⁻ groups locates at about 163 and 174 nm and the absorption bands of (PO₃)₃³⁻ groups (174 nm) and La³⁺–O²⁻ (200 nm) and Tb³⁺ (213 nm) overlap each other. These results imply that the (PO₃)₃³⁻ groups can efficiently absorb the excited energy around 172 nm and transfer the energy to Tb³⁺. Under 172 nm excitation, the optimal photoluminescence (PL) intensity is obtained when Tb concentration reaches 0.45 and is about 71% of commercial phosphor Zn_1.96SiO₄:0.04 Mn²⁺ with chromaticity coordinates of (0.343, 0.578) and the decay time of about 4.47 ms.     

Electron-irradiation induced phase transformation in La1/3Zr2(PO4)3: La displacement in a preserved NASICON framework

The La_1/3Zr₂(PO₄)₃ NASICON-type compound (S.G. - neutron and X-ray diffraction experiments) is investigated by transmission electron microscopy (TEM) technique, selected area electron diffraction (SAED) and high-resolution electron microscopy (HREM), in order to study locally the lanthanum distribution. An irreversible structural transformation is observed, without modification of the atomic content and cell size, as soon as the phase is illuminated by the electron beam. The progressive disappearance of the spots which do not check the R conditions on the SAED patterns is clearly shown along two zone axis, [001] and [100]. This transformation implies the displacement of the two La³⁺ cations in a preserved classical [Zr₂(PO₄)₃]⁻ network. This interesting behavior is in good agreement with the La³⁺ ionic conductivity observed in La_1/3Zr₂(PO₄)₃ (4.09×10⁻⁷ S cm⁻¹ at 700 °C). To our knowledge, this is the first time that a complete TEM study is done on a NASICON-type phase.     

Synthesis and structural study of a new NASICON-type solid solution: Li1−xLax/3Zr2(PO4)3

A new complete solid solution of NASICON-type compounds between LiZr₂(PO₄)₃ and La_1/3Zr₂(PO₄)₃ was evidenced with the general formula Li_1−xLa_x/3Zr₂(PO₄)₃ (0?x?1). These phases were synthesized by a complex polymerizable method and structurally characterized from Rietveld treatment of their X-ray and neutron powder diffraction data. This solid solution results from the substitution mechanism Li⁺→1/3La³⁺+2/3□ leading to an increase of the vacancies number correlated to an increase of the La content. According to this substitution mechanism, the general formula can then be written Li_1−xLa_x/3□_2x/3Zr₂(PO₄)₃ (0?x?1) in order to underline the correlation between the La content and the vacancies rate. For all the compounds, the structure is clearly related to that of the NASICON family with three crystallographic domains evidenced. For 0?x?0.5, all the members adopt at high temperature the typical NASICON-type structure (s.g. R3¯c), while at lower temperature, their structure distorts to a triclinic form (s.g. C 1¯), as observed for LiZr₂(PO₄)₃ prepared above 1100 °C. Moreover, in this domain, the reversible transition is clearly soft and the transition temperature strongly depends of the x value. For 0.6?x?0.9, the compounds crystallize in a rhombohedral cell (s.g. R3¯), while for x=1, the phase La_1/3Zr₂(PO₄)₃ is obtained (s.g. P3¯, Z=6, a=8.7378(2) Å, c=23.2156(7) Å).This paper is devoted to the structure analysis of the series Li_1−xLa_x/3Zr₂(PO₄)₃ (0?x?1), from X-ray and neutron powder thermo diffraction and transmission electron microscopy (TEM) studies.     

Transport properties and stability of Ni-containing mixed conductors with perovskite- and K2NiF4-type structure

The total conductivity and Seebeck coefficient of a series of Ni-containing phases, including La₂Ni_1−xM_xO_4+δ (M=Co, Cu; x=0.1-0.2) with K₂NiF₄-type structure and perovskite-like La_0.90Sr_0.10Ga_0.65Mg_0.15Ni_0.20O_3−δ and La_0.50Pr_0.50Ga_0.65Mg_0.15Ni_0.20O_3−δ, were studied in the oxygen partial pressure range from 10⁻¹⁸ Pa to 50 kPa at 973-1223 K. Within the phase stability domain, the conductivity of layered nickelates is predominantly p-type electronic and occurs via small-polaron mechanism, indicated by temperature-activated hole mobility and p(O₂) dependencies of electrical properties. In oxidizing conditions similar behavior is characteristic of Ni-containing perovskites, which exhibit, however, significant ionic contribution to the transport processes. The role of ionic conduction increases with decreasing p(O₂) and becomes dominant in reducing atmospheres. All nickelate-based phases decompose at oxygen pressures considerably lower with respect to Ni/NiO boundary. The partial substitution of nickel in La₂Ni(M)O_4+δ has minor effect on the stability limits, which are similar to that of La_0.90Sr_0.10Ga_0.65Mg_0.15Ni_0.20O_3−δ. On the contrary, praseodymium doping enhances the stability of La_0.50Pr_0.50Ga_0.65Mg_0.15Ni_0.20O_3−δ down to p(O₂) values as low as 10⁻¹⁷-10⁻¹⁰ Pa at 1023-1223 K.     

The Crystal Chemistry of Lithium in the Alluaudite Structure: A Study of the (Na1−xLix)CdIn2(PO4)3 Solid Solution (x=0 to 1)

Several compounds of the (Na_1−xLi_x)CdIn₂(PO₄)₃ solid solution were synthesized by a solid-state reaction in air, and pure alluaudite-like compounds were obtained for x=0.00, 0.25, and 0.50. X-ray Rietveld refinements indicate the occurrence of Cd²⁺ in the M(1) site, and of In³⁺ in the M(2) site of the alluaudite structure. This non-disordered cationic distribution is confirmed by the sharpness of the infrared absorption bands. The distribution of Na⁺ and Li⁺ on the A(1) and A(2)′ crystallographic sites cannot be accurately assessed by the Rietvled method, probably because the electronic densities involved in the Na⁺→Li⁺ substitution are very small. A comparison with the synthetic alluaudite-like compounds, (Na_1−xLi_x)MnFe₂(PO₄)₃, indicates the influence of the cations occupying the M(1) and M(2) sites on the coordination polyhedra morphologies of the A(1) and A(2)′ crystallographic sites.     

White-light-emitting long-lasting phosphorescence in Dy-doped SrSiO3

We report on a luminescent phenomenon in Dy³⁺-doped SrSiO₃ long-lasting phosphor. After irradiation by a 254-nm UV lamp for 5 min, the Dy³⁺-doped SrSiO₃ phosphor emits white light-emitting long-lasting phosphorescence for more than 1 h even after the irradiation source has been removed. Photoluminescence, long-lasting phosphorescence and thermoluminescence (TL) spectra are used to explain this phenomenon. Photoluminescence spectra reveal that the white light-emitting long-lasting phosphorescence originated from the two mixtures of Dy³⁺ characteristic luminescence, the 480-nm blue emission (⁴F_9/2→⁶H_15/2) and the 572-nm yellow emission (⁴F_9/2→⁶H_13/2). TL spectra shows that the introduction of Dy³⁺ ions into the SrSiO₃ host produces a highly dense trapping level at 377 K (0.59 eV), which is responsible for the long-lasting phosphorescence at room temperature. A possible mechanism of the long-lasting phosphorescence based on the experimental results is proposed. It is considered that the long-lasting phosphorescence is due to persistent energy transfer from the electron traps to the Dy³⁺ ions, which creates the persistent luminescence of Dy³⁺ to produce the white light-emitting long-lasting phosphorescence.     

Effect of sintering on the ionic conductivity of garnet-related structure Li5La3Nb2O12 and In- and K-doped Li5La3Nb2O12

Garnet-structure related metal oxides with the nominal chemical composition of Li₅La₃Nb₂O₁₂, In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ and K-substituted Li_5.5La_2.75K_0.25Nb₂O₁₂ were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li₅La₃Nb₂O₁₂. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In³⁺(r_CN6: 0.79 Å) for smaller Nb⁵⁺ (r_CN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K⁺ for La³⁺ and In³⁺ for Nb⁵⁺ in Li₅La₃Nb₂O₁₂ exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25-300 °C. Among the compounds investigated, the In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ exhibits the highest bulk lithium ion conductivity of 1.8×10⁻⁴ S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10⁻¹⁰-10⁻⁷ cm²/s over the temperature regime 50-200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li₅La₃Nb₂O₁₂ was found to be unsuccessful under the investigated conditions.     

Novel fluorimetric bulk optode membrane based on 5,8-bis((5′-chloro-8′-hydroxy-7′-quinolinyl)methyl)-2,11-dithia-5,8-diaza-2,6-pyridinophane for selective detection of lead(II) ions

A novel fluorescence chemical sensor for the highly sensitive and selective determination of Pb²⁺ ions in aqueous solutions is described. The preliminary potentiometric and spectrofluorimetric complexation studies in solution revealed that the lipophilic ligand 5,8-bis((5′-chloro-8′-hydroxy-7′-quinolinyl)methyl)-2,11-dithia-5,8-diaza-2,6-pyridinophane (L2) forms a highly stable and selective [PbL2]²⁺ and [Pb(L2)₂]²⁺ complexes which results in a strong fluorescence quenching of the ligand. Thus, a novel fluorescence Pb²⁺ sensing system was prepared by incorporating L2 as a neutral lead-selective fluoroionophore in the plasticized PVC membrane containing tetrakis(p-chlorophenyl) borate as a liphophilic anionic additive. The response of the sensor is based on the strong selective fluorescence quenching of L2 by Pb²⁺ ions. At pH 5.5, the proposed sensor displays a calibration curve over a wide concentration range of 3.0 × 10⁻⁷ to 2.5 × 10⁻² M with a relatively fast response time of less than 5 min. In addition to high stability, reversibility and reproducibility, the sensor shows a unique selectivity towards Pb²⁺ ion with respect to common coexisting cations. The proposed fluorescence optode was successfully applied to the determination of lead in plastic toys and tap water samples.     

Synthesis, structures and electrochemical properties of ruthenium (II) complexes bearing bidentate 1,8-naphthyridine and terpyridine analogous (N,N,C)-tridentate ligands

1,8-Naphthyridine (napy) and terpyridine-analogous (N,N,C) tridentate ligands coordinated ruthenium (II) complexes, [RuL(napy-κ²N,N′) (dmso)](PF₆)₂ (1: L=L¹=N″-methyl-4′-methylthio-2,2′:6′,4″-terpyridinium, 2: L = L² = N″-methyl-4′-methylthio-2,2′:6′,3″-terpyridinium) were prepared and their chemical and electrochemical properties were characterized. The structure of complex 1 was determined by X-ray crystallographic study, showing that it has a distorted octahedral coordination style. The cyclic voltammogram of 1 in DMF exhibited two reversible ligand-localized redox couples. On the other hand, the CV of 2 shows two irreversible cathodic peaks, due to the Ru-C bond of 2 containing the carbenic character. The IR spectra of 1 in CO₂-saturated CH₃CN showed the formation of Ru-(η¹-CO₂) and Ru-CO complexes under the controlled potential electrolysis of the solution at −1.44 V (vs. Fc/Fc⁺). The electrochemical reduction of CO₂ catalyzed by 1 at −1.54 V (vs. Fc/Fc⁺) in DMF-0.1 M Me₄NBF₄ produced CO with a small amount of HCO₂H.     

A Structural Investigation of La2(GeO4)O and Alkaline-Earth-Doped La9.33(GeO4)6O2

The structures of the oxyorthogermanate La₂(GeO₄)O and the apatite-structured La_9.33(GeO₄)₆O₂ have been refined from powder neutron diffraction data. La₂(GeO₄)O crystallizes in a monoclinic unit cell (P2₁/c) and is cation stoichiometric in contrast to previous reports. La_9.33(GeO₄)₆O₂ crystallizes in a hexagonal unit cell (P6₃/m) and the powder diffraction data show anisotropic peak broadening that is observed in electron diffraction patterns as incommensurate diffuse spots at hkq reciprocal planes (with q=1.6-1.7) and can be attributed to a correlated disorder in the “apatite channels”. This compound was doped up to a nominal composition close to M₂La₈(GeO₄)₆O₂ with M=Ca, Sr, Ba. The dopant ions preferentially occupy the 4f sites as the number of La vacancies decreases. The measured ionic conductivity of La_9.33(GeO₄)₆O₂ is about 3 orders of magnitude larger than for La₂(GeO₄)O at high temperatures and decreases with increasing dopant content from the highest value of about 0.16 S cm⁻¹ at 1160 K.     

Solid-state electrochemiluminescence sensor through the electrodeposition of Ru(bpy)3/AuNPs/chitosan composite film onto electrode

Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) has been successfully immobilized onto electrode through the electrodeposition of Ru(bpy)₃²⁺/AuNPs/chitosan composite film. In the experiments, chitosan solution was first mixed with Au nanoparticles (AuNPs) and Ru(bpy)₃²⁺. Then, during chronopotentiometry experiments in this mixed solution, a porous 3D network structured film containing Ru(bpy)₃²⁺, AuNPs and chitosan has been electrodeposited onto cathode due to the deposition of chitosan when pH value is over its pK_a (6.3). The applied current density is crucial to the film thickness and the amount of the entrapped Ru(bpy)₃²⁺. Additionally, these doping Ru(bpy)₃²⁺ in the composite film maintained their intrinsic electrochemical and electrochemiluminescence activities. Consequently, this Ru(bpy)₃²⁺/AuNPs/chitosan modified electrode has been used in ECL to detect tripropylamine, and the detection limit was 5 × 10⁻¹⁰ M.     

Hydrolysis of dioxouranium(VI): a calorimetric study in NaClaq and NaClO4 aq, at 25 °C

We report the results of a calorimetric study on the hydrolysis of UO₂²⁺ in different ionic media (NaClO_4 aq, NaCl_aq) at 25 °C. Experiments in NaCl were performed at different ionic strength, at I≤1 mol l⁻¹. The species considered in both ionic media were UO₂(OH)⁺, (UO₂)₂(OH)₂²⁺ and (UO₂)₃(OH)₅⁺, and in addition (UO₂)₃(OH)₄²⁺ and (UO₂)₃(OH)₇⁻ in NaCl_aq. The dependence on ionic strength of enthalpy changes in NaCl_aq was expressed by the simple linear equation ΔH_pq=ΔH°_pq+aI^1/2 (a, empirical parameter). Comparison with literature findings is given and some recommended values are reported.     

Structure and properties of a novel cobaltate La0.30CoO2

The layered cobaltate La_0.30CoO₂ was prepared from Na_xCoO₂ precursor by a solid-state ionic exchange and was characterized by means of X-ray and neutron diffraction, magnetic, thermal and electric transport measurements. The compound consists of hexagonal sheets of edge-sharing CoO₆ octahedra interleaved by lanthanum monolayers. Compared to Na⁺ in the parent system, the La³⁺ ions occupy only one-third of available sites, forming a 2-dimensional superstructure. The deviation from the ideal stoichiometry La_1/3CoO₂ introduces extra hole carriers into the diamagnetic LS Co³⁺ matrix making the sample Pauli paramagnetic. The temperature dependence of the electrical conductivity in La_0.30CoO₂ follows Mott's T^−1/3 law up to about 400 K, which is in contrast with the standard metallic behavior in the Na⁺ homolog possessing the same formal doping. The experiments are complemented by electronic structure calculations for La_0.30CoO₂ and related Na_xCoO₂ systems.     

Synthesis and Eu luminescence in new oxysilicates, ALa3Bi(SiO4)3O and ALa2Bi2(SiO4)3O [ACa, Sr and Ba] with apatite-related structure

New oxysilicates with the general formula ALa₃Bi(SiO₄)₃O and ALa₂Bi₂(SiO₄)₃O [ACa, Sr and Ba] are synthesized and characterized. Powder X-ray diffraction of these silicates show that they are isostructural with BiCa₄(VO₄)₃O which has an apatite-related structure. Eu³⁺ luminescence in the newly synthesized oxysilicates show broad emission lines due to disorder of cations. The relatively high intense magnetic dipole transition ⁵D₀→⁷F₁ points to a more symmetric environment. The photoluminescence results confirm that the compounds have apatite-related crystal structure.     

A new promising phosphor, Na3La2(BO3)3:Ln (Ln=Eu, Tb)

We present an efficient way to search a host for ultraviolet (UV) phosphor from UV nonlinear optical (NLO) materials. With the guidance, Na₃La₂(BO₃)₃ (NLBO), as a promising NLO material with a broad transparency range and high damage threshold, was adopted as a host material for the first time. The lanthanide ions (Tb³⁺ and Eu³⁺)-doped NLBO phosphors have been synthesized by solid-state reaction. Luminescent properties of the Ln-doped (Ln=Tb³⁺, Eu³⁺) sodium lanthanum borate were investigated under UV ray excitation. The emission spectrum was employed to probe the local environments of Eu³⁺ ions in NLBO crystal. For red phosphor, NLBO:Eu, the measured dominating emission peak was at 613 nm, which is attributed to ⁵D₀-⁷F₂ transition of Eu³⁺. The luminescence indicates that the local symmetry of Eu³⁺ in NLBO crystal lattice has no inversion center. Optimum Eu³⁺ concentration of NLBO:Eu³⁺ under UV excitation with 395 nm wavelength is about 30 mol%. The green phosphor, NLBO:Tb, showed bright green emission at 543 with 252 nm excited light. The measured concentration quenching curve demonstrated that the maximum concentration of Tb³⁺ in NLBO was about 20%. The luminescence mechanism of Ln-doped NLBO (Tb³⁺ and Eu³⁺) was analyzed. The relative high quenching concentration was also discussed.