Luminescence in trilanthanumtrichlorotungstate (La3WO6Cl3)

The luminescence properties of La₃WO₆Cl₃ are reported and discussed. The tungstate group occurs as a trigonal prismatic WO^6?₆ complex. The blue luminescence is, for the greater part, quenched at room temperature. No energy migration occurs in this lattice. The decay times are discussed in terms of a simple molecular-orbital (MO) scheme. The luminescence of the following activating ions was studied: Mo⁶⁺, Bi³⁺, Eu³⁺, Sm³⁺, Ce³⁺, and Tb³⁺. The molybdate group produces a red emission with low efficiency. The Bi³⁺ ion induces a narrow band emission with small Stokes shift. This is interpreted using a Bi³⁺O^2?W⁶⁺ charge-transfer state. Except for Ce³⁺, the rare earth activators show luminescence, but the total transfer efficiency from tungstate to the rare-earth ions is low. This is not due to the one-step tungstate-rare-earth transfer (which is efficient), but to the localized nature of the tungstate excitation. The Eu³⁺ charge-transfer band is at very low energies.     

Thermochemical studies of group iiib borates and mixed borates

The changes in energy, mass and structure of Sc, Y, La and In borate were studied at temperatures up to 1400°C with and without the solid diluents, alumina and magnesia. These compounds did not decompose, but based on the energetics of solid state transitions, the stability of the crystal lattice was found to be: ScBO₃ ～- LaBO₃ ～- InBO₃ > YBO₃. YBO₃ was found to be dimorphic. The high temperature form being the pseudohexagonal vaterite structure. LaBO₃ formed a solid solution with this structure. The reverse transition took place with considerable hysteresis.     

Synthesis of nanocrystalline REBO3 (RE=Y, Nd, Sm, Eu, Gd, Ho) and YBO3:Eu using a borohydride-based solution precursor route

A solution precursor route has been used to synthesize a series of nanocrystalline rare-earth borates. Amorphous precursor powders are precipitated during an aqueous reaction between RE³⁺ and NaBH₄, and the isolated powders can be annealed in air at 700 °C to form YBO₃, NdBO₃, SmBO₃, EuBO₃, GdBO₃, and HoBO₃. YBO₃:Eu formed using this strategy shows red-orange emission properties that are similar to high-quality nanocrystals prepared by other methods. The materials have been characterized by FTIR spectroscopy, powder XRD, SEM, DSC, UV-Vis fluorimetry, and TEM with EDS and element mapping.     

Influence of crystal structure on the luminescence of ions with s2 configuration

It is shown that the Stokes shift and thermal quenching temperature of the luminescence of Pb²⁺ and Bi³⁺ depend strongly on the stiffness of the host lattice, as is to be expected from the configurational coordinate diagram.     

Li2O-Ln2O3-SiO2:Eu3+,Bi3+体系的结构

采用ｓｏｌ－ｇｅｌ法合成了系列发光体Ｌｉ２Ｏ－Ｌｎ２Ｏ３－ＳｉＯ２：Ｅｕ＾３＾＋，Ｂｉ＾３＾＋，并确定了发光体的物相结构。当Ｌｎ＾３＾＋＝Ｙ＾３＾＋和Ｌｎ＾３＾＋＝Ｌａ＾３＾＋时，紫外光激发下Ｅｕ＾３＾＋的发射分别以红光和橙光为主，只存在一种Ｅｕ＾３＾＋发光中心；Ｌｎ＾３＾＋＝Ｇｄ＾３＾＋时，至少存在两种Ｅｕ＾３＾＋发光中心和两种Ｂｉ＾３＾＋发光中心（共掺杂Ｅｕ＾３＾＋，Ｂｉ＾３＾＋的吸收和发射所     

The luminescence of some oxidic bismuth and lead compounds

The luminescence properties of the bismuth compounds Bi₂Ge₃O₉, Bi₁₂MO₂₀ (M = Ge, Ti), and Bi₂Al₄O₉ and of the lead compounds PbGe₃O₇ and PbM₂O₄ (M = Al, Ga) are reported and discussed. Bi₁₂MO₂₀ and probably PbGe₃O₇ show semiconductor-type luminescence. For Bi₁₂MO₂₀ blue and red emission bands are reported which both are ascribed to radiative recombination at (deep) defect centre levels in the band gap. The blue emission originates probably from surface defects. The other compounds show broad emission and excitation bands with large Stokes shifts. The transitions occur on one and the same Bi³⁺(Pb²⁺) ion. From decay time measurements it is found that the energy difference between the two lowest excited levels is very small for all compounds. The large Stokes shifts and small trap depths are discussed in terms of the asymmetrical coordination of the 6s² ions in the compounds under discussion. It is concluded that asymmetrically surrounded Bi³⁺ ions give rise to luminescence which is characterized by a broad emission band which shows a very large Stokes shift (?2 eV).     

Synthesis and structural study of the new rare earth magnesium borates LnMgB5O10 (Ln = La, …, Er)

To obtain rare earth luminescent materials with weak concentration quenching, the B₂O₃-rich portion of the ternary diagram Ln₂O₃MgOB₂O₃ (Ln = rare earth) has been investigated. A ternary phase of composition LnMgB₅O₁₀ has been found for Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er. These compounds all crystallize in the monoclinic space group $\text{P2}{}_1\text{c}$. The structure has been determined on a LaMgB₅O₁₀ crystal. A full-matrix least-squares refinement leads to R = 0.039. The structure can be described as being made of (B₅O₁₀^5?)_n two-dimensional layers linked together by the lanthanum and magnesium ions. The rare earth atom coordination polyhedra form isolated chains. These borates are isostructural with some rare earth cobalt borates.     

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.     

The luminescence of Cs3Bi2Cl9 and Cs3Sb2Cl9

The luminescence properties of Cs₃Bi₂Cl₉, α-Cs₃Sb₂Cl₉, and β-Cs₃Sb₂Cl₉ are reported and compared with those of Cs₃Bi₂Br₉. The first two compounds have comparable luminescence properties which can be described in terms of a band model. Deep center emission is observed for both compounds, whereas edge emission is observed only for Cs₃Bi₂Cl₉. The optical transitions of β-Cs₃Sb₂Cl₉ are localized on the Sb³⁺ ion. The orientation of the lone-pair orbitals of the ns² ions seems to play an important role in the formation of the cationic valence band. The α-β transformation must therefore have a considerable influence on the spectral properties of Cs₃Sb₂Cl₉.     

Vacuum Ultraviolet Excited Photoluminescence Properties of Y2O2S：Eu^3＋,Bi^3＋ Phosphor

As an Hg-free lamp using phosphor, the Bi^3＋ and EH^3＋ co-doped Y2O2S phosphors were prepared and their luminescence properties under vacuum ultraviolet（VUV） excitation were investigated. The VUV photoluminescent intensity of Y2O2S：Eu^3＋ was weak, however, considerably stronger red emission at 626 nm with good color purity was observed in Y2O2S：Eu^3＋,Bi^3＋ systems. Investigation on the photoluminescence reveals that the strong VUV luminescence of Y2O2S：Eu^3＋,Bi^3＋ at 147 nm is mainly because the Bi^3＋ acts as a medium and effectively performs the energy transfer process： Y^3＋-O^2-→Bi^3＋→Eu^3＋, while the intense emission band at 172 nm is attributed to the absorption of the characteristic ^1So-^1P1 transition of Bi^3＋ and the direct energy transfer from Bi^3＋ to Eu^3＋. The Y2O2S：Eu^3＋,Bi^3＋ shows excellent VUV optical properties compared with the commercial （Y,Gd）BO3：Eu^3＋. Thus, the Y2O2S：Eu^3＋,Bi^3＋ can be a potential red VUV-excited candidate applied in Hg-free lamps for backlight of liquid crystal display.     

The luminescence of mercury-like ions in and the crystal structure of SrLaBO4

The crystal structure of SrLaBO₄ contains triangular borate groups. The luminescence of mercury-like ions (Sn²⁺, Sb³⁺, Tl⁺, Pb²⁺, Bi³⁺) in this host lattice is characterized by a large Stokes shift. The Pb²⁺ is a very efficient activator at room temperature. The luminescent properties are discussed in terms of earlier models related to an off-center position of the metal ion. The emission of Eu³⁺ shows that the crystal structure has a disordered nature and confirms an off-center position. Energy transfer from Pb²⁺ to Eu³⁺ and Tb³⁺ was studied and found to be inefficient.     

LiBa0.95-yBO3:0.05Tb3+,yBi3+荧光粉的制备及荧光性质

以硼酸和碳酸盐为原料,用高温固相法制备了可被（近）紫外光（369、254 nm）有效激发的Tb³⁺单掺杂LiBa_1-xBO₃：xTb³⁺（物质的量分数x=0.02、0.03、0.04、0.05、0.06、0.07）及Bi³⁺和Tb³⁺共掺杂LiBa_0.95-yBO₃：0.05Tb³⁺,yBi³⁺（物质的量分数y=0.02、0.03、0.04、0.05、0.06、0.07）的2个系列荧光粉,产物的结构和形貌分别用粉末X射线衍射（PXRD）和扫描电子显微镜进行表征。PXRD测定结果表明2个系列的产物均为纯相LiBaBO₃。通过对第一系列产物荧光光谱的测定,筛选出发光强度最好的产物,据此确定铽离子的最佳掺杂量;在此基础上制备出铋离子掺杂量不同的第二系列荧光粉。荧光光谱测定的实验结果表明,Tb³⁺/Bi³⁺共掺杂的荧光粉的发光强度好于Tb³⁺单掺杂的荧光粉,这说明Bi³⁺对Tb³⁺有敏化作用;而且随着Bi³⁺掺杂量的增加,产物的荧光强度表现出先增加后减小的趋势,当Bi³⁺的掺杂量y=0.03时,产物的荧光强度达到最大。Bi³⁺和Tb³⁺之间存在偶极-四极相互作用而进行能量传递。系列荧光粉的CIE坐标显示其发光颜色在一定程度上呈现出由绿色光到白光的渐变趋势。     

Structure, 31P and 13C chemical shift anisotrophy of (CH3)3P, (CH3)3PO, (CH3)3PS and (CH3)3PSe as determined by liquid crystal NMR spectroscopy

The ¹³P and ¹³C spectra of the triply ¹³C labelled molecules (CH₃)₃P, (CH₃)₃PO, (CH₃)₃PS and (CH₃)₃PSe oriented in a nematic phase are reported. The CPC bond angles have been measured. The ¹³P chemical shift tensor shows a large anisotropy except in the case of (CH₃)₃P. The abnormal large value observed for the PSe bond length suggests a large anisotropy of the ¹J(PSe) spin coupling.     

Magnetic and calorimetric studies on rare-earth iron borates LnFe3(BO3)4 (Ln=Y, La-Nd, Sm-Ho)

A series of rare-earth iron borates having general formula LnFe₃(BO₃)₄ (Ln=Y, La-Nd, Sm-Ho) were prepared and their magnetic properties have been investigated by the magnetic susceptibility, specific heat, and ⁵⁷Fe Mössbauer spectrum measurements. These borates show antiferromagnetic transitions at low temperatures and their magnetic transition temperatures increase with decreasing Ln³⁺ ionic radius from 22 K for LaFe₃(BO₃)₄ to 40 K for TbFe₃(BO₃)₄. In addition, X-ray diffraction, specific heat, and differential thermal analysis (DTA) measurements indicate that the phase transition occurs for the LnFe₃(BO₃)₄ compounds with Ln=Eu-Ho, Y, and its transition temperature increases remarkably with decreasing Ln³⁺ ionic radius from 88 K for Ln=Eu to 445 K for Ln=Y.     

A kinetic study of proton transfer reactions of NH+4, CH3NH+3, and PH+4 with calcium atoms

Cross section measurements for the proton transfer reactions of NH⁺₄, CH₃NH⁺₃, and PH⁺₄ with Ca(g) have been obtained over a range of low ion kinetic energies. For all reactions studied the cross sections drop sharply with increase in ion kinetic energy, indicating exothermic behavior. The results show that Ca(g) is an unusually strong base with a proton affinity in excess of 9.2 eV. Cross sections for the PH⁺₄Ca reaction are an order to magnitude higher than those for the NH⁺₄Ca reaction for ion energies between one and three eV. This effect is not explained by simple theories of ion-induced dipole interactions. It is suggested that the enhanced rate of the PH⁺₄Ca reaction may be due to d-orbital participation.     

Optical properties of CeBO3 and CeB3O6 compounds: first-principles calculations and experimental results

The cerium borates o-CeBO₃, m-CeBO₃ and CeB₃O₆ have been shown to be isostructural to their lanthanum derivatives. From diffuse reflectance, electron energy loss spectroscopy (EELS) and band structure calculations, it has been evidenced that a Ce³⁺ 4f-5d transition is responsible for weak absorption peaks around 3.5 eV while the O2p-Ce5d charge transfer gives rise to a strong absorption around 7 eV. Starting from self-consistent full potential LAPW calculations, the dielectric tensors of the three compounds were computed and compared to experimental data. It results in a satisfactory fit between the observed and the calculated extinction coefficient k and the index of refraction n.     

Luminescence properties of efficient X-ray phosphors of YBa3B9O18, LuBa3(BO3)3, α-YBa3(BO3)3 and LuBO3

The samples of YBa₃B₉O₁₈, LuBa₃(BO₃)₃, α-YBa₃(BO₃)₃ and LuBO₃ powders have been synthesized by the solid-state reaction methods at high temperature and their X-ray excited luminescent properties were investigated. All the studied materials show a broad emission band in the wavelength range of 300-550 nm with the peak centers at about 385 nm for YBa₃B₉O₁₈ and LuBa₃(BO₃)₃, 415 nm for α-YBa₃(BO₃)₃ and 360 nm for LuBO₃ powders, respectively. Even though those compounds have the different atomic structures, they have the common structural feature of each yttrium or lutetium ion bonded to six separate BO₃ groups, i.e., octahedral RE(BO₃)₆ (RE=Lu or Y) moiety. This octahedral RE(BO₃)₆(RE=Lu or Y) moiety seems to be an important structural element for efficient X-ray excited luminescence of those compounds, as are the edge-sharing octahedral TaO₆ chains for tantalate emission.     

Structural studies of some body-centered cubic phases of mixed oxides involving Bi2O3: The structures of Bi25FeO40 and Bi38ZnO60

The structures of the compounds initially reported to be 7·Bi₂O₃·ZnO and 96·Bi₂O₃·4Fe₂O₃, have been determined by X ray methods. Three dimensional, absorption corrected diffractometer data were used and atomic parameters were refined by least-squares procedures. The structures are isomorphous, cubic witha = 10.194(3)and10.179(3)A?, respectively, and space group I23. Each Bi³⁺ ion is surrounded by five oxygen atoms that form an incomplete octahedral arrangement with BiO distances ranging from 2.07–2.60A?. The6s²inert electron pair completes the octahedron. The Bi³⁺ ions are vibrating anisotropically. Tetrahedral sites in the structures contain 61 and 46 electrons, respectively. These values are consistent with a statistical distribution of Zn²⁺ and Bi⁵⁺ ions or Fe³⁺ and Bi⁵⁺ ions on these sites. Molar ratios are derived that agree with the observed distributions of electron density and give rise to perfectly stoichiometric systems, devoid of cationic or anionic vacancies. The compositions studied correspond to Bi³⁺₂₄Bi⁵⁺Fe³⁺O₄₀ and Bi³⁺₃₆Bi⁵⁺₂ZnO₆₀ and they are optical enantiomorphs.It is proposed that a reduction in the percentage composition of Bi₂O₅ leads to metastable phases, in which all atomic positions remain fully occupied but some tetrahedral sites contain Bi³⁺ ions. The end product of the series is γ-Bi₂O₃ in which 50% of these sites contain Bi³⁺ and the remainder Bi⁵⁺ ions. We believe that γ-Bi₂O₃ is Bi³⁺₂₅Bi⁵⁺O₄₀.     

Synthesis and crystal structure of (ThCu3)(Mn3+2Mn4+2)O12, a new ferrimagnetic perovskite-like compound

Single crystals of [ThCu₃](Mn³⁺₂Mn⁴⁺₂]O₁₂, a ferrimagnetic perovskite-like compound, have been synthesized by hydrothermal conditions at 600°C and 2 kbar. They have been found to be cubic, of space group Im3, with a = 7.359 Å, and isostructural with [NaMn₃](Mn³⁺₂Mn⁴⁺₂)O₁₂. The crystal structure has been refined by single-crystal X-ray diffraction data. The Th⁴⁺ cations are surrounded by slightly distorted icosahedra; the ThO distance is 2.556 Å. The Cu²⁺ cations are also surrounded by 12 oxygens, which are arranged as three mutually perpendicular rectangles of different size, the smallest and the largest of which are almost squares. The three sets of CuO distances are 1.973, 2.800, and 3.238 Å. The octahedral MnO distance is 1.950 Å. A test based on neutron diffraction powder data indicated that the square sites are occupied by only the Cu²⁺ cations.     

Exfoliated nanoplatelets of an Aurivillius phase, Bi3.25La0.75Ti3O12: Characterisation by X-ray diffraction and by high-resolution electron microscopy

Nanoparticles of the Aurivillius phase La-substituted BTO (Bi_4−xLa_xTi₃O₁₂, with x=0.75) were obtained through a chemical lithiation process. They have been characterised by X-ray diffraction and transmission electron microscopy (diffraction and imaging at high resolution). The defect-free particles are platelet-shaped with the c large axis perpendicular to the plane. From high-resolution images, it is clear that the delamination process occurs at the level of the (Bi₂O₂)²⁺ intermediate layer and is destructive for this layer. The smallest thickness measured corresponds to one cell parameter (3.3 nm) but a large range of thicknesses have been observed: this suggests that the lithium insertion does not take place in all (Bi₂O₂)²⁺ layers, despite a large excess of lithium and a long reaction time. This is confirmed by ICP analysis, which leads to a formula Li_0.99Bi_3.25La_0.77Ti_3.00O₁₂ for the lithiated compound. This behaviour towards lithium intercalation differs from those observed with BTO in literature, where lithium insertion is reported as occurring in every (Bi₂O₂)²⁺ layer. Possible explanations for this difference are advanced based on microstructural and structural considerations.