Tunable full-color-emitting Ca3Sc2Si3O12:Ce3+, Mn2+ phosphor via charge compensation and energy transfer

A tunable full-color-emitting Ca(3)Sc(2)Si(3)O(12):Ce(3+), Mn(2+) (CSS:Ce(3+),Mn(2+)) phosphor is obtained by addition of doped ions as charge compensation. White LEDs with high R(a) (> 90) are achieved using the single CSS:Ce(3+),Mn(2+) phosphor.     

Neuartige Polyanionen in Zintlphasen. Zur Kenntnis von Ca3Si2As4, Ca3Ge2As4, Sr3Si2As4 und Sr3Ge2As4

New Polyanions in Zintl Phases. On Ca₃Si₂As₄, Ca₃Ge₂As₄, Sr₃Si₂As₄, and Sr₃Ge₂As₄ The new compounds Ca₃Si₂As₄, Ca₃Ge₂As₄, Sr₃Si₂As₄ and Sr₃Ge₂As₄ crystallize in the monoclinic system with lattice constants see “Inhaltsübersicht”. There are two new structure types. Both contain Si₂As₆ or Ge₂As₆ groups connected to chains in different ways. These chains are ordered parallel to each other to sheets with the alkaline-earth atoms between them.     

High-Temperature Synthesis of the Mg2-x Ca xP4O12 and Cd2-x CaxP4O12

Abstract

The cyclo-tetraphosphates of the M^II _2-xCa_xP₄O₁₂ type (MI^II = Mg, Cd) have been synthetized as new binary compounds, and their existence for x ε (0; 1 > (Mg) or for x ε (0; 0.7 > (Cd) has been proved. The synthesis is based on a two-step thermal process. The first step starts from pure cyclo-tetraphosphates of the two divalent metals and Ca(PO₃)₂ which are melted in normal atmosphere and then abruptly cooled to give a vitreous amorphous product composed of higher linear phosphates of the summary formula (M^II _2-x Ca_x)_n/4H₂P_nO_3n+1 · In the second step, this product is repeatedly heated to a suitable temperature and recrystallized to give microcrystalline product M^II _2-x Ca_xP₄O₁₂ · The colourless (white) products crystallize in the monoclinic aystem, C2c group. Their structural parameters have the values for Mg_2-x Ca_xP₄O₁₂: a = 11.749(5) to 12.063(4) Å, b = 8.278(4) to 8.635(4) Å c = 9.905(4) to 9.875(3) Å and β = 118.92(2)° to 118.03(2)°; or for Cd_2-x Ca_xP₄O₁₂: a = 12.328(4) to 12.457(5) Å b = 8.639(3) to 8.732(4) Å c = 10.388(3) to 10.443(4) Å and β = 119.33(2)° to 119.45(2)°.     

The gas-phase equilibrium structures of Si8O12(OSiMe3)8 and Si8O12(CHCH2)8

The equilibrium molecular structure of Si(8)O(12)(OSiMe(3))(8) has been determined in the gas phase by electron diffraction (GED). With OSi-containing substituents on the cage silicon atoms, this molecule contains a moiety, which would, if reproduced in a periodic manner, yield a zeolite-type structure. Extensive ab initio calculations were used to identify two conformers of this molecule, with D(4) and D(2) point-group symmetries; the D(4)-symmetric conformer was approximately 1.2 kJ mol(-1) lower in energy. With 132 atoms in each conformer, this is one of the largest studies to be undertaken using gas electron diffraction. Semiempirical molecular-dynamics (SE-MD) calculations were used to give amplitudes of vibration, vibrational distance corrections (differences between interatomic distances in the equilibrium structure and the vibrationally averaged distances that are given directly by the diffraction data), and anharmonic constants. The structure of Si(8)O(12)(CHCH(2))(8) has also been determined by GED. Calculations showed that the vinyl groups are fairly unhindered and rotate between three minimum-energy positions. Ultimately, all possible combinations of the vinyl groups in these low-energy positions were accounted for in the GED model.     

New garnet compounds A 3 2+ B 2 2+ C4+V 2 5+ O12(A = Ca,Cd; B = Mg,Zn, Co,Ni, Cu,Mn, Cd; C = Ge,Si)

Garnet compounds A ₃ ²⁺ B ₂ ²⁺ C⁴⁺V ₂ ⁵⁺ O₁₂ (A = Ca, Cd; B = Mg, Zn, Co, Ni, Cu, Mn, Cd; C = Ge, Si) (space group \(Ia\bar 3d\) , Z = 8) have been prepared by solid-phase synthesis in air at 900–1250°C. Most of these compounds melt incongruently or decompose in the solid phase. The isomorphic capacity of garnets and their homogeneity fields are discussed. The structures of Ca₃Zn₂GeV₂O₁₂ and Ca₃Cu₂GeV₂O₁₂ have been refined by the Rietveld method.     

Sodium scandium arsenate,Na3Sc2(AsO4)3

Nasicon-type trisodium discandium tris­(arsenate), Na₃Sc₂(AsO₄)₃, contains a polyhedral network of vertex-sharing octahedral ScO₆ and tetrahedral AsO₄ units [d_av(Sc—O) = 2.089 (2) Å and d_av(As—O) = 1.672 (2) Å] encapsulating two types of Na⁺ species. The sodium site occupancies are similar to those of the equivalent species in β-Na₃Sc₂(PO₄)₃.     

The crystal structures of Mn3Ni2Si,V3Ni2Si,Nb3Ni2Si and related Cr and Ta compounds

Journal of Structural Chemistry -     

Ca10Ge16B6O51 and Cd12Ge17B8O58: two types of new 3D frameworks based on BO4 tetrahedra and 1D [Ge4O12]n chains

Two new acentric borogermanates, Ca(10)Ge(16)B(6)O(51) (Pba2) and Cd(12)Ge(17)B(8)O(58) (P4), have been successfully synthesized by high-temperature solid-state reactions of CaCO(3) (or CdCO(3)), GeO(2), and H(3)BO(3). Both structures display the same one-dimensional (1D) [Ge(4)O(12)](n) chains composed of GeO(4) tetrahedra and GeO(6) octahedra. In Ca(10)Ge(16)B(6)O(51), neighboring 1D [Ge(4)O(12)](n) chains are condensed into a two-dimensional (2D) [Ge(4)O(10.75)](n) layer via corner sharing, and such layers are further interconnected by "isolated" BO(4) tetrahedra and B(2)O(7) dimers into a three-dimensional (3D) framework, forming 1D tunnels of 5-, 6-, and 7-MRs along the c axis that are occupied by Ca(2+) cations. In Cd(12)Ge(17)B(8)O(58), neighboring 1D [Ge(4)O(12)](n) chains are interconnected into a [Ge(4)O(10.5)](n) open framework via corner sharing with large pores filled by big [Ge(B(2)O(7))(4)](28-) clusters, leading to formation of three types of 1D tunnels of 5-, 6-, and 7-membered rings (MRs) along the c axis which are occupied by the Cd(2+) cations. Both compounds are transparent in the range of 0.3-6.67 μm and exhibit very weak SHG responses.     

Vanadate garnet,Ca2NaMg2V3O12

The vanadate garnet Ca₂NaMg₂V₃O₁₂ (dicalcium sodium dimagnesium trivanadium dodecaoxide), synthesized by a floating zone method, has a notable structural feature in that the dodecahedral–dodecahedral shared edge length is longer than the unshared dodecahedral edge length. It is also noteworthy that the octahedral–dodecahedral shared edge length is as long as the unshared octahedral edge length. These unusual structural features are closely related to the weak repulsions between dodecahedral cations and between dodecahedral and octahedral cations.     

Cluster self-organization of silicate and germanate systems: Suprapolyhedral precursor nanoclusters and self-assembly of tetrahedral structures of the family A2T2O5 (A = Li, Na; T = Si, Ge): Li2T2O5, Li4Ge3SiO10, Li2Si2O5, and A2Si2O5

Modeling of atomic species (An clusters in the form of atoms or Kn polyhedra, where n is the number of atoms or polyhedra) corresponding to the initial stage of evolution of a chemical system has been carried out. Three series of K4 clusters built of different T tetrahedra (L and T) have been recognized. For L₂T₂ clusters, six geometrically and symmetrically different types of suprapolyhedral clusters have been discovered. The model has been used to identify precursor clusters in A₂T₂O₅ (A = Li, Na; T = Si, Ge) framework structures: A-type Li₂T₂O₅ with space group Cc, B-type Li₄Ge₃SiO₁₀ with space group Abm2, C-type Li₂Si₂O₅ with space group Ccc2, and D-type A₂Si₂O₅ with space group Pbcn. Three (of the six possible) types of suprapolyhedral precursor nanoclusters K4 in the four structures have been identified. The full 3D reconstruction of the self-assembly scenario of crystal structures is as follows: precursor nanocluster ?? primary chain ?? microlayer ?? microframework ?? ?? framework. The bifurcation of structural evolution pathways (structural branching points) at the suprapolyhedral level for type A and B structures is found to occur only when a microframework is formed of equivalent microlayers.     

Magnetic properties of the layered compounds Ca2Mn3O8 and Cd2Mn3O8

Ca₂Mn₃O₈ and Cd₂Mn₃O₈, which contain Mn⁴⁺ monolayers, have been prepared and characterized. Their magnetic susceptibility and electron paramagnetic resonance (EPR) behavior have been examined in detail. The Mn⁴⁺ moments in both Ca₂Mn₃O₈ and Cd₂Mn₃O₈ order antiferromagnetically near 60 and 10°K, respectively. Although the Néel temperature in Ca₂Mn₃O₈ is in reasonable agreement with molecular-field theory, that in Cd₂Mn₃O₈ is well below its expected value. It is proposed that these results, as well as those in the calcium manganite series CaMnO₃ → Ca₂MnO₄, may reflect the chemical influence of the divalent cation in modifying the MnO covalent mixing.     

Ca3Al2Ge3O12:Cr3+的光谱性质及晶场参数计算

为了解Cr3 离子在钙铝锗酸盐Ca3Al2Ge3O12石榴石中的光谱性质,合成了Ca3Al2Ge3O12:Cr3 多晶材料;测量了其X射线衍射图,漫反射光谱,激发、发射光谱等;分析了Cr3 离子在钙铝锗酸盐中的发光特性;计算了其晶场强度(Dq/B),Stokes位移(ΔEs)及黄昆-里斯因子(S)等.在450nm激发下,Ca3Al2Ge3O12:Cr3 室温发射光谱主要由三个宽带及附加其上的弱R线构成,分别对应于Cr3 离子的4T1、4T2、2T2到4A2能级跃迁.低温时R线变得强而锐.通过计算,Dq/B=2.43,ΔEs=1884cm-1,S=5.21.表明在Ca3Al2Ge3O12中Cr3 离子处于较弱的晶场强度,电子-声子耦合较强,为发展可调谐激光材料提供重要线索.