Excitation-dependent variation in local symmetry in Ba2Mg(BO3)2 evidenced by Eu3+ luminescent structural probe

Eu³⁺ luminescence was studied in Ba₂Mg(BO₃)₂ by selectively substituting at Mg site. The parent host Ba₂Mg(BO₃)₂ and Ba₂Mg_0.9Eu_0.05Li_0.05(BO₃)₂ were synthesized by conventional solid state reaction method. Their isostructural nature was confirmed using powder X-ray diffraction technique. The photoluminescence excitation spectrum of Eu³⁺ exhibited a broad Eu³⁺O²⁻ charge transfer band with a maximum at 253 nm along with other excitation transitions. The emission characteristics of Eu³⁺ were found to be excitation wavelength-dependent. The equally intense magnetic and electric dipole transitions for excitation under longer wavelengths showed the presence of Eu³⁺ at a site with non-inversion symmetry. Excitation using 253 nm resulted in the predominant magnetic dipole transition revealing Eu³⁺ at a site with inversion symmetry. The difference in the relative intensities of magnetic and electric dipole transitions originates from the change in symmetry around Eu³⁺ in Ba₂Mg(BO₃)₂ under different excitations.     

Yellow-green luminescence and extreme thermal quenching in the Sr6M2Al4O15:Eu2+ (M = Y,Lu, Sc) phosphor series

A series of Eu²⁺-substituted yellow-green emitting phosphors based on the compound, Sr₆M₂Al₄O₁₅ (M = Y, Lu, Sc) were identified as potential efficient phosphors based on their high calculated Debye temperatures (Θ_D > 450 K), which acts as a proxy for photoluminescent quantum yield (PLQY). The crystal structure contains corner-sharing [MO₆] octahedra and [AlO₄] tetrahedra leading to a highly connected, densely packed crystal structure. However, contrary to prediction, these compounds all showed a low PLQY (<6.5%) at room temperature. Temperature dependent luminescence measurements indicate that the photoluminescence is intense at 80 K but loses ≈90% of the emission intensity by room temperature, with the thermal quenching temperature (T₅₀) occurring well below room temperature. These results suggest that even though Debye temperature (Θ_D) is a valid proxy for PLQY, it does not describe thermal quenching.     

Structure determination and relative properties of novel cubic borates MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba)

A series of novel borates, MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba), have been successfully synthesized by standard solid-state reaction. The crystal structures have been determined from powder X-ray diffraction data. They crystallize in the cubic space group Iad with large lattice parameters: a = 14.95066(5) A for LiSr4(BO3)3, a = 15.14629(6) A for NaSr4(BO3)3, and a = 15.80719(8) A for NaBa4(BO3)3. The structure was built up from 64 small cubic grids, in which the M' atoms took up the corner angle and the BO3 triangles or MO6 cubic octahedra filled in the interspaces. The isolated [BO3]3- anionic groups are perpendicular to each other, distributed along three 100 directions. The anisotropic polarizations were counteracting, forming an isotropic crystal. Sr and Ba atoms were found to be completely soluble in the solid solution NaSr(4-)xBax(BO3)3 (0 < or = x < or = 4). The photoluminescence of samples doped with the ions Eu2+ and Eu3+ was studied, and effective yellow and red emission was detected, respectively. The results are consistent with the crystallographic study. The DTA and TGA curves of them show that they are chemically stable and congruent melting compounds.     

Photocatalytic properties of CoOx-loaded nano-crystalline perovskite oxynitrides ABO2N (A = Ca,Sr, Ba,La; B = Nb,Ta)

Highly crystalline niobium- and tantalum-based oxynitride perovskite nanoparticles were obtained from hydrothermally synthesized oxide precursors by thermal ammonolysis at different temperatures. The samples were studied with respect to their morphological, optical and thermal properties as well as their photocatalytic activity in the decomposition of methyl orange. Phase pure oxynitrides were obtained at rather low ammonolysis temperatures between 740 °C (CaNbO₂N) and 1000 °C (BaTaO₂N). Particle sizes were found to be in the range 27 nm–146 nm and large specific surface areas up to 37 m² g⁻¹ were observed. High photocatalytic activities were found for CaNbO₂N and SrNbO₂N prepared at low ammonolysis temperatures. CoO_x as co-catalyst was loaded on the oxynitride particles resulting in a strong increase of the photocatalytic activities up to 30% methyl orange degradation within 3 h for SrNbO₂N:CoO_x.     

Raman study of ACu3Fe4O12 (A = Ca,Sr, Y and Eu)

A vibrational study of ACu₃Fe₄O₁₂ (A = Ca, Sr, Y and Eu) compounds was carried out by means of micro-Raman scattering and lattice dynamics calculations. Polarized Raman scattering measurements were performed on rectangular microcrystals, with sizes close to 7 μm, and six Raman active modes were observed among the eight expected. It was then possible to assign the observed modes to the correct symmetry. Moreover, lattice dynamics calculations led to determine the main atomic displacements and a good agreement was found between experimental and theoretical wavenumbers. Furthermore, wavenumbers evolution versus A cation showed two behaviors separating the samples into two groups.     

Structure-dependent luminescence properties of Eu3+-doped CsBPO4 (B = Mg,Zn)

Eu³⁺-doped monophosphate CsBPO₄ (B = Mg, Zn) was synthesized by conventional solid state reaction. The crystal phase formations and morphology of the phosphates were analyzed by X-ray powder diffraction (XRD) and scanning electron microscope (SEM) measurements, respectively. The luminescence properties, including the photoluminescence excitation and emission spectra, decay curve (lifetime), the color coordinates and the internal quantum efficiency were investigated. Two Eu³⁺-doped monophosphates display very distinct luminescence properties. CsMgPO₄:Eu³⁺ presents the dominant reddish-orange emission from magnetic dipole transition ⁵D₀ → ⁷F₁ and a long luminescence lifetime. In contrast, CsZnPO₄:Eu³⁺ has a pure red color with the dominant induced electric-dipole transition ⁵D₀ → ⁷F₂ and a fast decay. Different results on the luminescence features of CsBPO₄ (B = Mg, Zn):Eu³⁺ were discussed on the base of crystal structure. Eu³⁺ has structure-dependent transitions due to the special microstructure occupied in a given host.     

Mechanochemical synthesis,structure and properties of lead containing alkaline earth metal fluoride solid solutions MxPb1-xF2 (M = Ca,Sr, Ba)

The paper deals with the mechanochemical synthesis of lead containing alkaline earth metal fluoride solid solutions M_xPb_1-xF₂ (M = Ca, Sr, Ba) by high-energy ball milling. Several metal precursors and fluorinating agents were tested for synthesizing M_0.5Pb_0.5F₂. Metal acetates and ammonium fluoride as precursors show the most promising results and were therefore used for the formation of M_xPb_1-xF₂ with different metal cationic ratios. The characterization of the local fluorine coordination and the crystal structure was performed by ¹⁹F MAS NMR spectroscopy and X-ray diffraction. Additional calculations of ¹⁹F chemical shifts using the superposition model allow a deeper insight into the local structure of the compounds. The fluoride ion conductivity was followed by temperature dependent DC conductivity measurements. Significantly higher conductivities were found in comparison with those of the corresponding binary fluorides. The highest values were observed for samples with high lead content M_0.25Pb_0.75F₂, bearing in mind the much higher conductivity of PbF₂ compared to MF₂.     

碱土金属铝酸盐系列长余辉磷光体的制备研究

研究了MAl2O4∶Eu2+(M=Ca,Sr,Ba)磷光体的制备过程,通过向磷光体中引入微量Dy3+,B3+等添加剂离子,得到了发绿色光的超长余辉磷光体,余辉发光初始亮度达4.8cd·m-2,激发停止50h后,其余辉发光仍清晰可见。制备出发紫色光、蓝色光及黄色光的碱土金属铝酸盐系列长余辉磷光体。分析了各磷光体发射光谱、激发光谱及余辉发光,讨论了磷光体的光谱移动以及Eu2+在碱土金属铝酸盐中的发光。     

Synthesis and Structure of Ba3La2（BO3）4 Crystal

1 INTRODUCTION At present the researches on more efficient solid-state laser materials become more important for the rapid development of diode-laser pumped solid-state laser. More researches have been devoted to the double borate compounds RX3(BO3)4 (R = Y, La, Gd and X = Y, Al, Sc), some of which exhibit good chemical and physical properties[1～10]. The rare earth and alkali-halide double borates M3Ln2(BO3)4 (M = Ca, Sr, Ba and Ln = LaLu and Y) were reported in literatures[11…     

K3Eu5(PO4)6: hydrothermal synthesis,crystal structure and photoluminescence properties

An anhydrous orthophosphate, K₃Eu₅(PO₄)₆ (tripotassium pentaeuropium hexaphosphate), has been prepared by a high‐temperature solid‐state reaction combined with hydrothermal synthesis, and its crystal structure was determined by single‐crystal X‐ray diffraction analysis (SC‐XRD). The results show that the compound crystallizes in the monoclinic space group C2/c and the structure features a three‐dimensional framework of [Eu₅(PO₄)₆]_∞, with the tunnel filled by K⁺ ions. The IR spectrum, UV–Vis spectrum and luminescence properties of polycrystalline samples of K₃Eu₅(PO₄)₆, annealed at temperatures of 650, 700, 750, 800 and 850 °C, were investigated. Although with a full Eu³⁺ concentration (9.96 × 10²¹ ions cm^?3), the self‐activated phosphor K₃Eu₅(PO₄)₆ shows s strong luminescence emission intensity with a quantum yield of 37%. Under near‐UV light excitation (393 nm), the series of samples shows the characteristic emissions of Eu³⁺ ions in the visible region from 575 to 715 nm. The sample sintered at 800 °C gives the strongest emission and its lifetime sintered at 800 °C (1.88 ms) is also the longest of all.     

Rapid synthesis of A2(MoO4)3 (A = Y3+ and La3+)with a CO2 laser

Negative thermal expansion material of yttrium molybdate and positive thermal expansion material of lanthanum molybdate have been successfully synthesized by rapid solidification with a CO₂ laser. Both materials were solidified in densely packed blocks with smooth surface and glazing color. They have similar microstructures consisting of nano-particles or nano-dendrites with grain sizes around 20–30 nm. Raman spectroscopic and XRD analyses reveal that lanthanum molybdate crystallized in a high temperature phase of tetrahedral La₂Mo₃O₁₂, whereas yttrium molybdate crystallized in an orthorhombic Y₂Mo₃O₁₂. This synthetic route is a very rapid process with which a sample can be synthesized within a few seconds and holds prospect for the synthesis of other rare earth molybdates and tungstates.     

Mild hydrothermal synthesis,isomorphous substitution,crystal structure characterization and magnetic properties of BaMP2O7 (M = Mn,Cu)

At mild hydrothermal conditions triclinic modifications of BaMP₂O₇ (M = Mn and/or Cu) have been succeeded. The method offers cheap, one step, impurity free and chemical flexible fabrication of family of metal phosphates that are potential low-dimensional quantum magnets. Partial isomorphous substitution of the Mn²⁺ by Cu²⁺ resulted into mixed-metal solid that has been structurally and magnetically characterized. Rietveld refinement study confirmed the structures and revealed the influence of transition metal substitution. The temperature-dependent magnetic measurements revealed that the system is paramagnetic in almost all temperature range and an apparent antiferromagnetic phase transition occurs around 5 K. Using the Curie–Weiss law, a Curie–Weiss temperature, θ_P = −11.0 K, and a Curie constant C = 3.39 emu K mol⁻¹ was obtained. The small negative θ_P value and the χT behavior as a function of temperature reveal a weak antiferromagnetic interaction between the Cu²⁺/Mn²⁺magnetic centers.     

Crystal growth,structures, magnetic and photoluminescent properties of NaLnGeO4 (Ln = Sm,Eu, Gd,Tb)

Single crystals of NaLnGeO₄ (Ln = Sm, Eu, Gd) were grown out of a molten sodium hydroxide flux, and their crystal structures were determined by single crystal X-ray diffraction. The lanthanide containing germanates crystallize in the orthorhombic space group of Pnma, and exhibit a complex three-dimensional structure consisting of corner- or edge-shared LnO₆, GeO₄, and NaO₆ polyhedra. UV–vis diffuse reflectance spectra indicated that the reported oxides are insulating materials with wide band gaps. The magnetic susceptibility data shows paramagnetic behavior. For the NaEuGeO₄ and NaTbGeO₄ compositions intense room temperature photoluminescence was observed.     

Er^3＋／Yb^3＋：Sr3Y2（BO3）4晶体的光谱和激光性质

采用提拉法生长了双掺Yb3+和Er3+离子浓度分别为18.63%和0.87%(原子分数)的Sr3Y2(BO3)4晶体.利用测量的偏振吸收谱结合Judd-Ofeh理论,拟合得到了该晶体中Er3+离子的偏振和有效J-O参数.测量了Er3+离子4I13/2能级和Yb3+离子2F5/2能级的荧光衰减曲线,并计算了4I13/2能级的荧光量子效率和Yb3+到Er3+的能量传递效率.利用Fuchtbauer-Ladenberg公式计算了Er3+离子4I13/2→4I15/2跃迁的偏振受激发射截面.在平-凹谐振腔中,利用97nm波长光纤耦合准连续半导体激光端面泵浦1.12mm厚的该晶体,当输出镜透过率为1.5%时,获得了最大输出功率为1.3 w和斜率效率为20%的1560 nm附近的激光输出.结果表明,Er3+/Yb3+:Sr3+Y2+(BO3)4晶体是一种优良的1.5～1.6 μm波段激光的增益介质.     

Luminescent properties of Ba_3(PO_4)_2:Eu,Tb phosphors

Luminescence of europium (Ⅲ),europium(Ⅱ) and terbium(Ⅲ) has been observed in Bas(PO4)2:Eu,Tb phosphors which are synthesized in air atmosphere.The valence state of europium is influenced by amount of terbium.It is notable that the relative intensity of the emission spectra peaks corresponding to Eu2+ is increased if the amount of Tb3+ is increased.These phenomena can be explained by an electron transfer mechanism.We predict a new kind of two-rare-earth codoped trichromatic phosphors in Ba3(PO4)2 matrix.     

Hydrothermal synthesis, crystal structures and luminescent properties of two new Ln(III)–succinate (Ln=Eu, Tb) complexes exhibiting three dimensional networks

Two new coordination polymers, [Eu₂(L)₃(H₂O)₂]_n 1 and {[Tb₂(L)₃(H₂O)₂]·H₂O}_n 2, (H₂L=succinic acid) have been synthesized by the reaction of H₂L with nitrate salts of Eu(III) or Tb(III) under hydrothermal conditions. The X-ray diffraction analysis reveals that the two complexes are constructed by L bridging the chains of edge-sharing EuO₈(H₂O) or TbO₈(H₂O) polyhedra to form 3D network structure. 1 and 2 possess different topological structures due to the difference in the conformations of L. The solid photoluminescence of 1 and 2 was also investigated in room temperature.     

Spectroscopic properties of RBiBO4 (R = Ca,Sr) glasses doped with TiO2

Transparent glasses, melt quenching derived, containing 10RO·20Bi₂O₃·(70 ? x)B₂O₃·xTiO₂ [R = Ca, Sr] with x = 0, 0.5, 1.0 wt% were characterized by X-ray powder diffraction. Physical and spectroscopic properties viz., density, absorption, emission, electron paramagnetic resonance (EPR) and FTIR were investigated. The absorption band around 823 nm in pure glass samples is attributed to the electronic transition of ³P₀ to ³P₂ of Bi⁺ radicals. A small absorption hump centered around 609 nm is found in all doped glasses due to ²T_2g to ²E_g transition of octahedral Ti³⁺ ions. The emission results revealed that all the samples exhibit a broad emission band covering entire visible-light range, with λ_ex = 360 nm, centered 470–520 nm corresponds to electronic transition of ³P₁ to ¹S₀ of Bi³⁺ ions, therefore the present materials can be potentially used as tunable or full-color display systems. And a strong emission around 706 nm with λ_ex = 514 nm due to transition of ²P_3/2 to ²P_1/2 of Bi²⁺ ions. In SrO mixed glasses Ti⁴⁺ ions effect the environment of Bi³⁺ ion symmetry units from C₂ to C_3i. A small EPR signal (at room temperature) is observed in titanium doped glasses due to Ti³⁺ ions. In both the series with increase of TiO₂ concentration BO₄ units are gradually converted into BO₃ units and new cross linkages are formed, like B–O–Ti, Bi–O–Ti at the expense of B–O–B bonds.     

Synthesis,structure, and optical properties of a series of quaternary oxides,K2Ba(MO4)2 (M = Cr,Mo, W)

Single crystals of a family of quaternary oxides K₂Ba(MO₄)₂ (M = Cr, Mo, W) have been grown for the first time. The crystals were grown in a hydroxide-based hydroflux. The compounds crystallize in space group R $\overline{3}$m and, according to single-crystal X-ray diffraction structure determination, are isostructural with the mineral Palmierite. All compounds show anti-site mixing of the potassium and barium. The degree of mixing appears to be determined indirectly by the M-O bond distance. Diffuse reflectance spectra and room-temperature luminescence were measured for each compound.     

Polyol-mediated low-temperature synthesis of crystalline tungstate nanoparticles MWO4 (M = Mn,Fe, Co,Ni, Cu,Zn)

A polyol-mediated synthesis is presented as a general access to nanoscaled transition-metal tungstates MWO₄ (M = Mn, Fe, Co, Ni, Cu, Zn). Using simple inorganic salts as starting materials, uniform and readily crystalline nanoparticles are prepared under mild conditions (T < 220 °C). The nanoparticles are of high quality in terms of small diameter (<20 nm), high surface area (up to 200 m² g⁻¹), phase purity and yield (>85%). Size, morphology and composition can be adjusted by precise variation of the reaction parameters, including type of starting material, duration and temperature of reaction. The transition-metal tungstate nanoparticles are fully functional, exhibiting typical properties of this class of materials, for instance, superparamagnetism (CoWO₄), luminescence (ZnWO₄) and photocatalytic activity (CuWO₄).