Zwei neue Silicat-Chloride mit zweiwertigem Europium: LiEu3[SiO4]Cl3 und Li7Eu8[SiO4]4Cl7

Two New Silicate-Chlorides with Divalent Europium: LiEu₃[SiO₄]Cl₃ and Li₇Eu₈[SiO₄]₄Cl₇ LiEu₃[SiO₄]Cl₃ was prepared by reaction of LiCl with Eu₂SiO₄ and Li₇Eu₈[SiO₄]₄Cl₇ from Li with Eu₂O₃, SiO₂ and LiCl. The crystal structures of LiEu₃[SiO₄]Cl₃ (Pmna, a = 946.95(13); b = 699.52(8); c = 1 368.0(2) pm; Z = 4; R1 = 0.0325, R2_w = 0.0642) and Li₇Eu₈[SiO₄]₄Cl₇ (P2₁/c; a = 851.85(5); b = 948.62(7); c = 1 679.0(2) pm; β = 96.221(8)°; Z = 2; R1 = 0.0352, R2_w = 0.0744) were determined from four-circle diffractometer data. LiEu₃[SiO₄]Cl₃ contains [Li(SiO₄)₂] units and LiCl₆ octahedra while in Li₇Eu₈[SiO₄]₄Cl₇ larger ?lithosilicate”? groups are found. In both structures, the Eu²⁺ ions are coordinated mostly eightfold by O^2? and Cl^? ligands.     

Rb[Li5Si2O7] – A Latecomer in the Family of Alkali Lithosilicates Hiding a Green-Emitting Lithosilicate

In order to expand the field of alkali lithosilicates, a new representative of the substance class with a previously unknown structure type was found based on solid-state synthesis. The novel compound with the sum formula Rb[Li₅Si₂O₇] crystallizes in the orthorhombic space group Pbcm (no. 57) with a=7.6269(3), b=9.5415(4), and c=9.4095(3) Å by means of single-crystal X-ray diffraction. The structure consists of a highly condensed lithosilicate framework, built up of corner- and edge-linked [LiO₄]-tetrahedra and [Si₂O₇]-units, and the rubidium ions aligned in channels. Suitable crystals of the material were obtained using sealed tantalum ampoules as reaction tube at a temperature of 750 °C. The new compound was further characterized via powder diffraction, Rietveld analysis, and EDX measurements. At first glance, Eu²⁺-doped Rb[Li₅Si₂O₇] reveals an intense green luminescence. In-depth crystal analysis shows that a core-shell formation is present even for apparently high quality single-crystals. As a minority phase, the known green phosphor RbLi[Li₃SiO₄]₂:Eu²⁺ is the origin of the luminescence, representing a tiny core inside of the particles surrounded by a large matrix of transparent Rb[Li₅Si₂O₇] dominating the single-crystal diffraction pattern.     

A Double-Band Emitter with Ultranarrow-Band Blue and Narrow-Band Green Luminescence

Understanding the origin and mechanisms of luminescence is a crucial point when it comes to the development of new phosphors with targeted luminescence properties. Herein, a new phosphor belonging to the substance class of alkali metal lithosilicates with the generalized sum formula Cs_{4−x−y−z}Rb_xNa_yLi_z[Li₃SiO₄]₄:Eu²⁺ is reported. Single crystals of the cyan-emitting UCr₄C₄-type phosphor show a peculiar double-band luminescence with one ultranarrow emission band at 473 nm and a narrow emission band at 531 nm under excitation with UV light (λ_exc=408 nm). Regarding occupation of the channels by the light metal ions, investigations of single-crystal XRD data led to the assumption that domain formation with distinct lithium- and sodium-filled channels occurs. Depending on which of these channels hosts the activator ion Eu²⁺, a green or blue emission results. The herein-presented results shed new light on the luminescence process in the well-studied UCr₄C₄-type alkali metal lithosilicate phosphors.     

Luminescence Properties of Ca2Ga2SiO7:RE Phosphors for UV White‐Light‐Emitting Diodes

A series of Eu²⁺‐, Ce³⁺‐, and Tb³⁺‐doped Ca₂Ga₂SiO₇ phosphors is synthesized by using a high‐temperature solid‐state reaction. The powder X‐ray diffraction and structure refinement data indicate that our prepared phosphors are single phased and the phosphor crystalizes in a tetrahedral system with the ${P\bar 42m}$ (113) space group. The Eu²⁺‐ and Ce³⁺‐doped phosphors both have broad excitation bands, which match well with the UV light‐emitting diodes chips. Under irradiation of λ=350 nm, Ca₂Ga₂SiO₇:Eu²⁺ and Ca₂Ga₂SiO₇:Ce³⁺, Li⁺ have green and blue emissions, respectively. Luminescence of Ca₂Ga₂SiO₇:Tb³⁺, Li⁺ phosphor varies with the different Tb³⁺ contents. The thermal stability and energy‐migration mechanism of Ca₂Ga₂SiO₇:Eu²⁺ are also studied. The investigation results indicate that the prepared Ca₂Ga₂SiO₇:Eu²⁺ and Ca₂Ga₂SiO₇:Ce³⁺, Li⁺ samples show potential as green and blue phosphors, respectively, for UV‐excited white‐light‐emitting diodes.     

Vibrational Spectra and Magnetic Properties of Eu3[BN2]2 and LiEu4[BN2]3

Eu₃[BN₂]₂ and LiEu₄[BN₂]₃ were synthesized from a stoichiometric mixture of EuN, BN, europium metal and Li₃N, EuN and BN (ratio: 1:4:3) in sealed niobium ampoules at 1475 and 1275 K, respectively. Temperature dependent susceptibility measurements of Eu₃[BN₂]₂ and LiEu₄[BN₂]₃ show Curie‐Weiss behavior with experimental magnetic moments of 8.03(5) and 8.5(1) μ_B/Eu atom, respectively, compatible with divalent europium. Both nitridoborates order ferromagnetically at T_C = 32.0(5) K (Eu₃[BN₂]₂) and 22.0(5) K (LiEu₄[BN₂]₃). The saturation magnetizations of 5.73(5) μ_B/Eu atom at 5 K and 7 T for Eu₃[BN₂]₂ and 4.2 μ_B/Eu atom at 5 K and 2 T for LiEu₄(BN₂)₃ are smaller than the maximum value of 7 μ_B. ¹⁵¹Eu Mössbauer data of Eu₃[BN₂]₂ at 4.2 K show an isomer shift of —11.4(1) mm/s and an experimental line width of 3.1(2) mm/s. Full magnetic hyperfine field splitting with 26.2(3) T at the europium nuclei is detected. Vibrational spectra of Eu₃[BN₂]₂ are interpreted on the basis of discrete [BN₂]^3— units with symmetry D_∞h by taking into account the existence of two crystallographically independent [BN₂]^3— anions and their dynamic coupling in the unit cell (factor group splitting).     

Mixed‐Valent Europium in the Cubic Thiosilicate Li3Eu6[SiS4]4

In an attempt to synthesize LiEu₃S₃[SiS₄] utilizing elemental europium and sulfur as well as SiS₂ and an excess of LiCl as flux and lithium source, dark red, platelet‐shaped single crystals of Li₃Eu₆[SiS₄]₄ were obtained. This new compound crystallizes in the cubic space group I4 3d (a = 1369.22(5) pm) with four formula units per unit cell. Both the Li⁺ and the Si⁴⁺ cations are surrounded by four sulfide anions. The [SiS₄]^4– tetrahedra show merely a slight trigonal distortion, while the [LiS₄]^7– units are best described as flattened bisphenoids. The europium cations exhibit an eightfold, rather irregular coordination environment by eight S^2– anions and have to be regarded mixed‐valent with a +2:+3 charge‐ratio of 5:1 in order to gain electroneutrality. The lack of an inversion center is caused by the [SiS₄]^4– tetrahedra being stacked exclusively top up along [111] in this acentric crystal structure.     

Synthesis,Structural Characterization,Electronic Structure,and Magnetic Properties of the Zintl Phase Eu10Cd6Bi12

A new transition‐metal‐containing Zintl phase, Eu₁₀Cd₆Bi₁₂, was synthesized by combining the elements in excess molten Cd. Single‐crystal X‐ray diffraction studies indicated that this compound crystallizes in the orthorhombic space group Cmmm (No. 65) with a=7.840(2), b=24.060(7), and c=4.7809(14) Å. The crystal structure of Eu₁₀Cd₆Bi₁₂ can be viewed as a stacking of a series of [Cd₆Bi₁₂] double layers, which are arranged alternately along the b axial direction. The layers are composed of corner‐ and edge‐shared CdBi₄ tetrahedra, a common feature in the crystal chemistry of many transition‐metal Zintl phases. Electronic‐band‐structure calculations confirm the closed‐shell configuration of all constituent elements and corroborate the electron count inferred by the Zintl formalism, that is, [Eu²⁺]₁₀[Cd²⁺]₆[Bi^3?]₈[Bi^2?]₄. Magnetic‐susceptibility measurements confirm the divalency of europium and show the existence of a long‐range antiferromagnetic order of the Eu spins below 12.3 K.     

Er4F2[Si2O7][SiO4]: Das erste Selten‐Erd‐Fluoridsilicat mit zwei verschiedenen Silicat‐Anionen

Er₄F₂[Si₂O₇][SiO₄]: The First Rare‐Earth Fluoride Silicate with Two Different Silicate Anions By the reaction of Er₂O₃ with ErF₃ and SiO₂ at 700 °C in sealed tantalum capsules using CsCl as flux (molar ratio 5 : 2 : 3 : 20), the compound Er₄F₂[Si₂O₇][SiO₄] (triclinic, P 1; a = 648.51(5), b = 660.34(5), c = 1324.43(9) pm, α = 87.449(8), β = 85.793(8), γ = 60.816(7)°; V_m = 148.69(1) cm³/mol, Z = 2) is obtained as pale pink platelets or lath‐shaped single crystals. It consists of disilicate anions [Si₂O₇]^6– in eclipsed conformation, ortho‐silicate anions [SiO₄]^4– and isolated [Er₄F₂]¹⁰⁺ units comprising two edge‐shared [Er₃F] triangles. Er³⁺ is surrounded by 7 + 1 (Er1) or 7 (Er2–Er4) anionic neighbors, respectively, of which two are F^– in the case of Er1 and Er4 but only one for Er2 and Er3. The other ligands recruit from oxygen atoms of the different oxosilicate groups. The crystal structure can be described as simple rowing up of the three building groups ([SiO₄]^4–, [Er₄F₂]¹⁰⁺, and [Si₂O₇]^6–) along [001]. The necessity of a large excess of fluoride for a successful synthesis of Er₄F₂[Si₂O₇][SiO₄] will be discussed.     

Sm4S3[Si2O7] und NaSm9S2[SiO4]6: Zwei Sulfidsilicate mit dreiwertigem Samarium

Sm₄S₃[Si₂O₇] and NaSm₉S₂[SiO₄]₆: Two Sulfide Silicates with Trivalent Samarium The sulfide silicates Sm₄S₃[Si₂O₇] and NaSm₉S₂[SiO₄]₆ are obtained as light yellow transparent crystals by the reaction of Sm, Sm₂O₃, S, and SiO₂ with fluxing SmCl₃ or NaCl, respectively, in suitable molar ratios in fused evacuated silica tubes (850 °C, 7 d). Tetragonal crystals of Sm₄S₃[Si₂O₇] (I4₁/amd; Z = 8; a = 1186.4(1); c = 1387.0(2) pm) with ecliptically conformed [Si₂O₇]^6–‐groups of corner sharing [SiO₄]‐tetrahedra are formed. These double tetrahedra as well the sulfide anions (S^2–) coordinate two crystallographically independent metal cations. They provide coordination numbers of 8 + 1 (5 S^2– and 3 + 1 O^2–) for Sm1 and 9 (3 S^2– and 6 O^2–) for Sm2. NaSm₉S₂[SiO₄]₆ crystallizes hexagonally (P6₃/m; Z = 1; a = 975.32(9); c = 676.46(7) pm) in a modified bromapatite‐type structure. The coordination spheres about the two crystallographically different Sm³⁺ cations are built up by oxygen atoms of the orthosilicate units ([SiO₄]^4–) and sulfide anions (S^2–). As a result, Sm1 and Sm2 have coordination numbers of 9 and 8, respectively. Na⁺ and (Sm1)³⁺ occupy the position 4 f in a molar ratio of 1 : 3 whereas the lower coordinated (Sm2)³⁺ occupies the 6 h position.     

Li2EuSiO4, ein Europium(II)-dilithosilicat: Eu[(Li2Si)O4]

Li₂EuSiO₄, an Europium(II) Litho-Silicate: Eu[(Li₂Si)O₄] Single crystals of Li₂EuSiO₄ were first obtained by reaction of Eu₂SiO₄ with a melt of LiCl at 800 °C in a sealed tantalum tube. It crystallizes with the trigonal space group P3₁21, Z = 3, with a = 502.70(5), c = 1247.0(2) pm. The tetrahedra [LiO₄] and [SiO₄] are connected via common corners and thereby build up a three-dimensional network that leaves space for Eu²⁺ which is in an eightfold coordination. Li₂SrSiO₄ is isotypic with a = 502.59(4) and c = 1247.1(1) pm.     

Learning from a Mineral Structure toward an Ultra‐Narrow‐Band Blue‐Emitting Silicate Phosphor RbNa3(Li3SiO4)4:Eu2+

Learning from natural mineral structures is an efficient way to develop potential host lattices for applications in phosphor converted (pc)LEDs. A narrow‐band blue‐emitting silicate phosphor, RbNa₃(Li₃SiO₄)₄:Eu²⁺ (RNLSO:Eu²⁺), was derived from the UCr₄C₄‐type mineral model. The broad excitation spectrum (320–440 nm) indicates this phosphor can be well matched with the near ultraviolet (n‐UV) LED chip. Owing to the UCr₄C₄‐type highly condensed and rigid framework, RNLSO:Eu²⁺ exhibits an extremely small Stokes shift and an unprecedented ultra‐narrow (full‐width at half‐maximum, FWHM=22.4 nm) blue emission band (λ_em=471 nm) as well as excellent thermal stability (96 %@150 °C of the initial integrated intensity at 25 °C). The color gamut of the as‐fabricated (pc)LEDs is 75 % NTSC for the application in liquid crystal displays from the prototype design of an n‐UV LED chip and the narrow‐band RNLSO:Eu²⁺ (blue), β‐SiAlON:Eu²⁺ (green), and K₂SiF₆:Mn⁴⁺ (red) components as RGB emitters.     

Eu5F[SiO4]3 und Yb5S[SiO4]3: Gemischtvalente Lanthanoid‐Silicate mit Apatit‐Struktur

Eu₅F[SiO₄]₃ and Yb₅S[SiO₄]₃: Mixed‐Valent Lanthanoid Silicates with Apatite‐Type of Structure By the reaction of Eu, EuF₃, Eu₂O₃ with SiO₂ in evacuated gold ampoules, using NaF as flux, at a temperature of 1000 °C for ten hours, dark‐red, platelet‐shaped single crystals of Eu₅F[SiO₄]₃ are obtained. Similarly dark‐red, but pillar‐shaped single crystals of Yb₅S[SiO₄]₃ are obtained by the reaction of Yb, Yb₂O₃ and S with SiO₂ in the presence CsBr as flux in evacuated silica ampoules at 850 °C and an annealing time of seven days. Both compounds crystallize hexagonally (P6₃/m, Z = 2; Eu₅F[SiO₄]₃: a = 954.79(9), c = 704.16(6) pm; Yb₅S[SiO₄]₃: a = 972.36(9), c = 648.49(6) pm) in the case of Eu₅F[SiO₄]₃ analogous to the mineral fluorapatite and for Yb₅S[SiO₄]₃ as a bromapatite—type variety. The crystal structure containing isolated [SiO₄]^4— tetrahedra distinguishes two rare‐earth cation positions with coordination numbers of nine (M1) and seven (M2), in which the position M1 of the europium fluoride silicate is almost exclusively occupied by Eu²⁺ cations, whereas in ytterbium sulfide silicate it contains di‐ and trivalent Yb cations in the ratio 1 : 1. In both cases, however, the M2 position is only populated with M³⁺.     

La2Si2O7 im I—Typ: Gemäß La6[Si4O13][SiO4]2 kein echtes Lanthandisilicat

I‐Type La₂Si₂O₇: According to La₆[Si₄O₁₃][SiO₄]₂ not a Real Lanthanum Disilicate In attempts to synthesize lanthanum telluride silicate La₂Te[SiO₄] (from La, TeO₂, SiO₂ and CsCl, molar ratio: 1 : 1: 1 : 20, 950 °C, 7 d) or fluoride‐rich lanthanum fluoride silicates (from LaF₃, La₂O₃, SiO₂ and CsCl, molar ratio: 5 : 2 : 3 : 17, 700 °C, 7 d) in evacuated silica tubes, colourless lath‐shaped single crystals of hitherto unknown I‐type La₂Si₂O₇ (monoclinic, P2₁/c; a = 726.14(5), b = 2353.2(2), c = 1013.11(8) pm, β = 90.159(7)°) were found in the CsCl‐flux melts. Nevertheless, this new modification of lanthanum disilicate does not contain any discrete disilicate groups [Si₂O₇]^6‐ but formally three of them are dismutated into one catena‐tetrasilicate ([Si₄O₁₃]^10‐ unit of four vertex‐linked [SiO₄]^4‐ tetrahedra) and two ortho‐silicate anions (isolated [SiO₄]^4‐ tetrahedra) according to La₆[Si₄O₁₃][SiO₄]₂. This compound can be described as built up of alternating layers of these [SiO₄]^4‐ and the horseshoe‐shaped [Si₄O₁₃]^10‐ anions along [010]. Between and within the layers the high‐coordinated La ³⁺ cations (CN = 9 ‐ 11) are localized. The close structural relationship to the borosilicates M₃[BSiO₆][SiO₄](M = Ce ‐ Eu) is discussed and structural comparisons with other catena‐tetrasilicates are presented.     

Einkristalle des Cer(III)‐Borosilicats Ce3[BSiO6][SiO4]

Single Crystals of the Cerium(III) Borosilicate Ce₃[BSiO₆][SiO₄] Colorless, lath‐shaped single crystals of Ce₃[BSiO₆]‐ [SiO₄] (orthorhombic, Pbca; a = 990.07(6), b = 720.36(4), c = 2329.2(2) pm, Z = 8) were obtained in attempts to synthesize fluoride borates with trivalent cerium in evacuated silica tubes by reaction of educt mixtures of elemental cerium, cerium dioxide, cerium trifluoride, and boron sesquioxide (Ce, CeO₂, CeF₃, B₂O₃; molar ratio 3 : 1 : 3 : 3) in fluxing CsCl (700 °C, 7 d) with the glass wall. The crystal structure contains eight‐ (Ce1) and ninefold coordinated Ce³⁺ cations (Ce2 and Ce3) surrounded by oxygen atoms. Charge balance is achieved by both discrete borosilicate ([BSiO₆]^5– ≡ [O₂BOSiO₃]^5–) and ortho‐silicate anions ([SiO₄]^4–). The former consists of a [BO₃] triangle linked to a [SiO₄] tetrahedron by a single vertex. The anions form layers in [001] direction alternatingly built up from [BSiO₆]^5– and [SiO₄]^4– groups while Ce³⁺ cations are located in between.     

Thiosilicate der Selten‐Erd‐Elemente: I. Die isotypen Verbindungen KCe[SiS4] und Eu2[SiS4]

Thiosili‐Thiosilicates of the Rare‐Earth Elements: I. The Isotypic Compounds KCe[SiS₄] and Eu₂[SiS₄] Both isotypic thiosilicates KCe[SiS₄] (a = 649.15(6), b = 656.18(6), c = 863.96(8) pm, β = 107.531(9)°) and Eu₂[SiS₄] (a = 651.71(6), b = 659.54(6), c = 821.93(8) pm, β = 108.437(9)°) crystallize monoclinically in the space group P2₁/m and Z = 2. By the reaction of KCl, Ce₂S₃ and SiS₂ in the ratio 1 : 1 : 1 using a sixfold molar amount of KCl as flux in evacuated silica tubes (7 d, 850°C) brownish yellow, plate‐shaped single crystals, resistant both to air and water are obtained. The conversion of Eu, S and SiS₂ in molar ratios of 2 : 2 : 1 with an excess of CsCl as flux in evacuated silica tubes (7 d, 850°C) leads to deep red, plate‐shaped single crystals, which remain air‐ and water‐stable for a few days. The crystal structure contains isolated ortho‐thiosilicate units, that together with the Ce³⁺ or (Eu2)²⁺ cations build corrugated anionic layers parallel (001) according to {(Ce[SiS₄])^—} and {(Eu2[SiS₄])^2—}, respectively. These layers are alternatingly piled with cationic layers consisting solely of K⁺ or (Eu1)²⁺ cations. The latter show coordination numbers of eight in the shape of a bicapped trigonal prism, whereas the cations of the position Ce³⁺ and (Eu2)²⁺ have a (2+1)‐fold capped trigonal prismatic environment with a coordination number of 8+1. The comparison of both compounds KCe[SiS₄] and Eu₂[SiS₄] (≡ EuEu[SiS₄]) demonstrates, that Eu²⁺ is able to substitute both K⁺ and Ce³⁺ isomorphically.     

Zwei Chloridsilicate des Yttriums: Y3Cl[SiO4]2 und Y6Cl10[Si4O12]

Two Chloride Silicates of Yttrium: Y₃Cl[SiO₄]₂ and Y₆Cl₁₀[Si₄O₁₂] The chloride‐poor yttrium(III) chloride silicate Y₃Cl[SiO₄]₂ crystallizes orthorhombically (a = 685.84(4), b = 1775.23(14), c = 618.65(4) pm; Z = 4) in space group Pnma. Single crystals are obtained by the reaction of Y₂O₃, YCl₃ and SiO₂ in the stoichiometric ratio 4 : 1 : 6 with ten times the molar amount of YCl₃ as flux in evacuated silica tubes (7 d, 1000 °C) as colorless, strongly light‐reflecting platelets, insensitive to air and water. The crystal structure contains isolated orthosilicate units [SiO₄]^4– and comprises cationic layers {(Y2)Cl}²⁺ which are alternatingly piled parallel (010) with anionic double layers {(Y1)₂[SiO₄]₂}^2–. Both crystallographic different Y³⁺ cations exhibit coordination numbers of eight. Y1 is surrounded by one Cl^– and 7 O^2– anions as a distorted trigonal dodecahedron, whereas the coordination polyhedra around Y2 show the shape of bicapped trigonal prisms consisting of 2 Cl^– and 6 O^2– anions. The chloride‐rich chloride silicate Y₆Cl₁₀[Si₄O₁₂] crystallizes monoclinically (a = 1061,46(8), b = 1030,91(6), c = 1156,15(9) pm, β = 103,279(8)°; Z = 2) in space group C2/m. By the reaction of Y₂O₃, YCl₃ and SiO₂ in 2 : 5 : 6‐molar ratio with the double amount of YCl₃ as flux in evacuated silica tubes (7 d, 850 °C), colorless, air‐ and water‐resistant, brittle single crystals emerge as pseudo‐octagonal columns. Here also a layered structure parallel (001) with distinguished cationic double‐layers {(Y2)₅Cl₉}⁶⁺ and anionic layers {(Y1)Cl[Si₄O₁₂]}^6– is present. The latter ones contain discrete cyclo‐tetrasilicate units [Si₄O₁₂]^8– of four cyclically corner‐linked [SiO₄] tetrahedra in all‐ecliptical arrangement. The coordination sphere around (Y1)³⁺ (CN = 8) has the shape of a slightly distorted hexagonal bipyramid comprising 2 Cl^– and 6 O^2– anions. The 5 Cl^– and 2 O^2– anions building the coordination polyhedra around (Y2)³⁺ (CN = 7) form a strongly distorted pentagonal bipyramid.     

Synthesis,Luminescence and Nonlinear Optical Properties of Homoleptic Tetracyanamidogermanates ARE[Ge(CN2)4] (A = K,Cs, and RE = La,Ce, Pr,Nd, Sm,Eu, Gd)

Two new series of tetracyanamidogermanates were prepared by solid‐state reaction of appropriate amounts of REF₃ (RE = rare earth), A₂[GeF₆] (A = alkaline), and Li₂(CN₂) in evacuated silica tubes. Powder X‐ray diffraction patterns of crystalline samples of KRE[Ge(CN₂)₄] and CsRE[Ge(CN₂)₄] were indexed isotypically to KRE[Si(CN₂)₄] and RbRE[Ge(CN₂)₄], respectively. Luminescence properties of Ce³⁺, Eu³⁺, and Tb³⁺ doped compounds and non‐linear optical properties (NLO) of KRE[Ge(CN₂)₄] are reported.     

Ultra‐Narrow‐Band Blue‐Emitting Oxoberyllates AELi2[Be4O6]:Eu2+ (AE=Sr,Ba) Paving the Way to Efficient RGB pc‐LEDs

Highly efficient phosphor‐converted light‐emitting diodes (pc‐LEDs) are popular in lighting and high‐tech electronics applications. The main goals of present LED research are increasing light quality, preserving color point stability and reducing energy consumption. For those purposes excellent phosphors in all spectral regions are required. Here, we report on ultra‐narrow band blue emitting oxoberyllates AELi₂[Be₄O₆]:Eu²⁺ (AE=Sr,Ba) exhibiting a rigid covalent network isotypic to the nitridoalumosilicate BaLi₂[(Al₂Si₂)N₆]:Eu²⁺. The oxoberyllates’ extremely small Stokes shift and unprecedented ultra‐narrow band blue emission with fwhm ≈25 nm (≈1200 cm^?1) at λ_em=454–456 nm result from its rigid, highly condensed tetrahedra network. AELi₂[Be₄O₆]:Eu²⁺ allows for using short‐wavelength blue LEDs (λ_em<440 nm) for efficient excitation of the ultra‐narrow band blue phosphor, for application in violet pumped white RGB phosphor LEDs with improved color point stability, excellent color rendering, and high energy efficiency.     

Ho2O[SiO4] und Ho2S[SiO4]: Zwei Chalkogenid‐Derivate von Holmium(III)‐ortho‐ Oxosilicat

Ho₂O[SiO₄] and Ho₂S[SiO₄]: Two Chalcogenide Derivatives of Holmium(III) ortho‐Oxosilicate Ho₂O[SiO₄] crystallizes monoclinically with the space group P2₁/c (a = 904.15(9), b = 688.93(7), c = 667.62(7) pm, β = 106.384(8)°, Z = 4) in the A‐type structure of rare‐earth(III) oxide oxosilicates. Yellow platelet‐shaped single crystals were obtained as by‐product during an experiment to synthesize Ho₃Cl[SiO₄]₂ by reacting Ho₂O₃ and SiO₂ in the ratio 4 : 6 with an excess of HoCl₃ as flux at 1000 °C for seven days in evacuated silica ampoules. Both crystallographically different Ho³⁺ cations show coordination numbers of 8+1 and 7 with coordination figures of 2+1‐fold capped trigonal prisms and octahedra, in which one of the vertices changes to an edge by two instead of one coordinating atoms, respectively. The O^2— anion not linked to silicon is surrounded tetrahedrally by four Ho³⁺ cations which built a layer parallel (100) by vertex‐ and edge‐sharing of the [OHo₄]¹⁰⁺ units according to {[(O5)(Ho1)_1/1(Ho2)_3/3]⁴⁺}. Within rhombic meshes of these layers the isolated oxosilicate tetrahedra [SiO₄]^4— come to lie. Ho₂S[SiO₄] crystallizes orthorhombically in the space group Pbcm (a = 605.87(5), b = 690.41(6), c = 1064.95(9) pm, Z = 4). It also emerged as a single‐crystalline by‐product obtained during the synthesis of Ho₂OS₂ by reaction of a mixture of Ho₂O₃, Ho and S with the wall of the evacuated silica tube used as container with an excess of CsCl as flux at 800 °C. The structure of the yellow platelet‐shaped, air and water resistant crystals also distinguishes two Ho³⁺ cations with bicapped trigonal prisms and trigondodecahedra as coordination polyhedra for CN = 8. The S^2— anions are almost square planar surrounded by four Ho³⁺ cations, but situated completely outside this plane. The [SHo₄]¹⁰⁺ squares form strongly corrugated layers perpendicular to [100] by corner‐sharing according to {[(S)(Ho1)_2/2(Ho2)_2/2]⁴⁺}. Contrary to the oxide oxosilicates the isolated oxosilicate tetrahedra [SiO₄]^4— do not lie within the rhombic meshes of these layers, but above and below the (Ho2)³⁺ cations while viewing along [100].     

Alkali Metal Compounds of Hydroquinone: Synthesis and Crystal Structure

A number of novel routes to the alkali metal compounds of hydroquinone M₂[p‐C₆H₄O₂] (M = Li, Na, K, Rb, Cs) and M[p‐C₆H₄O(OH)] (M = K, Rb, Cs) have been synthetically explored. The selective synthesis of the alkali 4‐hydroxyphenolates and 1, 4‐phenylenediolates is based on optimized reaction conditions (solvents, temperatures). All compounds were structurally characterized by means of powder X‐ray diffraction using Rietveld profile refinement including C—C and C—O bond distance restraints. The atomic arrangement of M₂[p‐C₆H₄O₂](M = Na, K) (tetragonal, space group: P4₂/ncm) is characterized by infinite pillars of [M₂^[3]O₂^[3]]‐units along the c axis connected by [p‐C₆H₄O₂]^2—‐anions with stacking direction along c. The coordinatively unsaturated alkali metals, surrounded by three oxygen atoms, exhibit symmetrical (K) as well as asymmetrical (Na) interactions with the phenylene rings. M[p‐C₆H₄O(OH] (M = K, Rb) (tetragonal, space group: P4/n) forms hydrogen‐bridged linear chains of [p‐C₆H₄O(OH)]^—‐anions along the c direction. The phenylene planes of neighboring chains have an almost orthogonal arrangement while the interchain planes are parallel. K and Rb are fourfold coordinated by two different oxygen coordination spheres.