Nitridosilicates and Oxonitridosilicates: From Ceramic Materials to Structural and Functional Diversity

A New Family of High Oxidation State Antiperovskite Nitrides: La3MN5 (M=Cr, Mn and Mo)

Three new nitrides La3MN5 (M=Cr, Mn, and Mo) have been synthesized using a high pressure azide route. These are the first examples of ternary Cs3CoCl5-type nitrides, and show that this (MN4)NLa3 antiperovskite structure type may be used to stabilise high oxidation-state transition metals in tetrahedral molecular [MN4]n- nitridometallate anions. Magnetic measurements confirm that Cr and Mo are in the M6+ state, but the M=Mn phase has an anomalously small paramagnetic moment and large cell volume. Neutron powder diffraction data are fitted using an anion-excess La3MnN5.30 model (space group I4/mcm, a=6.81587(9) Å and c=11.22664(18) Å at 200 K) in which Mn is close to the +7 state. Excess-anion incorporation into Cs3CoCl5-type materials has not been previously reported, and this or other substitution mechanisms may enable many other high oxidation state transition metal nitrides to be prepared.

Ammonothermal Synthesis and Solid-State NMR Study of the Imidonitridosilicate Rb3Si6N5(NH)6

The imidonitridosilicate Rb3Si6N5(NH)6, being only the second representative of this compound class, was synthesized ammonothermally at 870 K and 230 MPa. Its crystal structure was solved from single-crystal X-ray diffraction data. The imidonitridosilicate crystallizes isotypically with the respective potassium compound in space group P4132 with the lattice parameter a=10.9422(4) Å forming a three-dimensional imidonitridosilicate tetrahedra network with voids for the rubidium ions. The structure model and the presence of the imide groups were verified by Fourier-Transform infrared (FTIR) and magic-angle spinning (MAS) NMR spectroscopy, using cross polarization 15N{1H} and 29Si{1H} MAS NMR experiments. Rb3Si6N5(NH)6 represents a possible intermediate during the ammonothermal synthesis of nitridosilicates. The characterization of such intermediates improves the understanding of the reaction pathway from ammonothermal solutions to nitrides. Thus, the ammonothermal synthesis is an alternative approach to the well-established high-temperature synthesis leading to the compound class of nitridosilicates.

A brief review of characteristic luminescence properties of Eu3+ in mixed-anion compounds

Trivalent europium (Eu3+) ions show red luminescence with sharp spectral lines owing to the intraconfigurational 4f-4f transitions. Because of their characteristic luminescence properties, various Eu3+-doped inorganic compounds have been developed to meet the demands of optoelectronic devices. Regardless of shielding by the outer 5s and 5p orbitals, the properties of the Eu3+:4f-4f transition depend on the local environment, such as the shapes of the coordination polyhedra, site symmetry, nephelauxetic effects, crystal field effects, and bonding character. Mixed-anion coordination, where multiple types of anions surround a single Eu3+ ion, can directly affect the optical properties of Eu3+. We review the luminescence properties of Eu3+ ions in mixed-anion compounds of the oxynitride YSiO2N and oxyhalides YOX (X = Cl or Br). Oxynitride and oxyhalide coordination results in characteristic transition probabilities and branching ratios of the 5D0 → 7F0-6 transitions due to distorted structural environments and red-shifted charge transfer excitation bands due to an upward shift of the valence band. The expected and experimentally observed features of Eu3+ luminescence in mixed-anion compounds are outlined based on band and Judd-Ofelt theories. Future applications of the intense red luminescence at ∼620 nm under near-ultraviolet light illumination in Eu3+-doped mixed-anion compounds are introduced, and material design guidelines for new functional Eu3+-doped phosphors are presented.

A novel n-UV convertible colour-tunable emitting oxynitride phosphor: Realization based on Ce3+ -Tb3+ energy transfer

In the present work, a novel n-UV convertible colour-tunable emitting phosphor was obtained based on the efficient Ce3+ -Tb3+ energy transfer in the Y10 Al2 Si3 O18 N4 host. By properly controlling the ratio of Ce3+ /Tb3+ , the colour hue of the obtained powder covered the blue and green regions, under excitation of 365 nm. The steady-state and dynamic-state luminescence measurement was performed to shed light on the related mechanism, which was justified by the electronic dipole-quadrupole dominating the related energy transfer process. Preliminary studies showed that Y10 Al2 Si3 O18 N4 :Ce3+ ,Tb3+ can be promising as an inorganic phosphor for white LED applications.

Zeolite-like Topology Oxonitridosilicate La3.6Ba1.7Si5N10O2.1 with Potential Applications in Nonlinear Optical Materials

A novel zeolite-like topology oxonitridosilicate La3.6Ba1.7Si5N10O2.1 with the space group Amm2 (no. 38) and lattice parameters a = 9.5193 (3) Å, b = 16.7011 (5) Å, c = 26.0279 (8) Å, and Z = 12 has been synthesized by a high-temperature solid-state reaction. The crystal structure of La3.6Ba1.7Si5N10O2.1 has four different kinds of tiling, and the cages in the structure are filled with La, Ba, and O atoms. The presence of a noncentrosymmetric space group further suggests its potential for nonlinear optical (NLO) applications, and La3.6Ba1.7Si5N10O2.1 demonstrated a stronger second-harmonic generation (SHG) response than that of SiO2.

Defect rocksalt structures in the La-Na-N system

Sodium azide (NaN3) is a versatile nitrogen source that can be used for the synthesis of new nitrides under high-pressure and temperature conditions. Reactions between lanthanum nitride (LaN) and sodium azide (NaN3) at 800°C under 8 GPa pressure have led to the discovery of two defect rocksalt phases which are the first reported ternaries in the La-Na-N system. Preliminary structure assignments have been made based on fits to powder X-ray diffraction profiles. One phase is La1-xNa3xN with vacancies at octahedral La sites and interstitial tetrahedral Na cations. This phase has a tetragonally distorted rocksalt structure (space group I4[Formula: see text]mmm, a = 3.8704(2) and c = 5.2098(3) Å for nominal x = 0.10) and the distortion decreases with increasing Na content (space group I4[Formula: see text]mmm, a = 3.8060(2) Å, c = 5.2470(3) Å for nominal x = 0.14), further giving a cubic phase (a = 5.3055(2) Å) for nominal x = 0.25. This coexists with another cubic [Formula: see text] phase (a = 5.1561 (5) Å), tentatively identified as rocksalt 'NaN1/3' stabilized by a small amount of La; NaLayN(1+3y)/3 with y ≈ 1%. These initial investigations reveal that the high-pressure La-Na-N phase diagram may be rich in defect rocksalt-type materials although further work using neutron diffraction will be needed to confirm the structures. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.

Polymorphism and polymorph-dependent luminescence properties of the first lithium oxonitridolithosilicate Li3SiNO2:Eu2

Building on studies of monoclinic Li₃SiNO₂, a polymorph, β-Li₃SiNO₂, with a previously unknown structure type was synthesized. The β-phase crystallizes in the orthorhombic space group Pbca (no. 61) with lattice parameters of a = 18.736(2), b = 11.1267(5), c = 5.0897(3) Å, and a cell volume of V = 1057.2(1) ų. Using high-temperature solid-state reactions in sealed tantalum tubes, it was possible to obtain high purity samples (<5 wt% of side phase LiSi₂N₃ according to Rietveld analysis) containing exclusively one or the other polymorph, depending solely on the cooling rate. In contrast to the monoclinic phase, orthorhombic β-Li₃SiNO₂ additionally contains a third layer and shows a layer-sequence of the type ABCB. Doped with the activator ion Eu²⁺, the new polymorph exhibits an intense yellow emission (λ_max = 586 nm, fwhm = 89 nm, 0.33 eV, 2650 cm^-1) under irradiation with UV to blue light. Hence, the structural difference between the two polymorphs goes along with a significant blue-shift of 16 nm. The results from single-crystal diffraction and single-grain luminescence measurements were confirmed by Rietveld analysis of bulk samples and powder luminescence data.

Li2 Ba4 Al2 Ta2 N8 O, the First Barium Nitridoalumotantalate with BCT-Zeolite Type Structure

Single-crystals of Li₂ Ba₄ Al₂ Ta₂ N₈ O:Eu²⁺ were synthesized from Ba₃ N₂ , Al₂ O₃ , Li₃ N, Eu₂ O₃ , and lithium metal by a high-temperature solid-state reaction in a weld shut tantalum ampule. The crystal structure of Li₂ Ba₄ Al₂ Ta₂ N₈ O was determined by single-crystal X-ray diffraction and it crystallizes in the orthorhombic space group Pnnm (no. 58) with the lattice parameters a=1006.71(3), b=1026.58(3), c=607.10(2) pm, and a volume of V=0.62742(3) nm³ . The compound is built up from AlN₄ and TaN₄ tetrahedra, which form a three-dimensional network corresponding to the BCT-zeolite type structure. Li₂ Ba₄ Al₂ Ta₂ N₈ O is homeotypic to Li₂ Sr₄ Si₄ N₈ O and Li₂ Sr₄ Al₂ Ta₂ N₈ O but, additionally, it could be successfully doped with the activator ion Eu²⁺ and hence features an experimental observed overall emission at λ_max =565 nm (fwhm=89 nm) consisting of a superposition of two adjusted emission bands at λ_max =557 nm (fwhm=69 nm) and at λ_max =604 nm (fwhm=102 nm).

A novel color-tunable nitride phosphor for near ultraviolet excitation of WLED

Due to the diversity of structure and composition and the unique coordination environment, nitride materials enable the doped activator ions to possess compelling luminescence characteristics, such as rich emission colors, favorable stability and tunable emission spectra. Here, novel SrLuSi 4 N 7 :Ce 3+ ,Tb 3+ nitride phosphors were successfully synthesized by a modified carbothermal reduction and nitridation method at atmospheric pressure. SrLuSi 4 N 7 (SLSN) belongs to hexagonal symmetry, with space group P6 3 mc, and its crystal structure is composed of the basic building block with corner-sharing [SiN 4 ] tetrahedron. Under 365 nm excitation, SLSN:Ce 3+ exhibits a broad emission band peaking at 450 nm with a full width at half-maximum (FWHM) of 92 nm and the most forceful intensity obtained at the Ce 3+ concentration amount of 0.04. On the basis of the efficient energy transfer, SLSN:Ce 3+ ,Tb 3+ exhibits color-tunable emission from blue (450 nm) to green (545 nm). Our results indicate SLSN nitride phosphor is a promising candidate for use in near-ultraviolet (n-UV) based white LEDs.

Synthesis and Luminescence Properties of Amber Emitting La 7 Sr[Si 10 N 19 O 3 ] : Eu 2+ and Syntheses of the Substitutional Variants RE 8‐ x AE x [Si 10 N 20‐ x O 2+ x ] : Eu 2+ with RE =La, Ce; AE =Ca, Sr, Ba; 0≤ x ≤2

The oxonitridosilicate La₇Sr[Si₁₀N₁₉O₃] : Eu²⁺ and its substitutional variants RE_8‐xAE_x[Si₁₀N_20‐xO_2+x] : Eu²⁺ with RE=La, Ce; AE=Ca, Sr, Ba and 0≤x≤2 were synthesized starting from REN, SrN/Ca₃N₂/Ba₂N, SiO₂, amorphous Si₃N₄ and Eu₂O₃ as doping agent at 1600 °C in a radiofrequency furnace. The crystal structure of La₇Sr[Si₁₀N₁₉O₃] was solved and refined based on single‐crystal X‐ray diffraction data. La₇Sr[Si₁₀N₁₉O₃] crystallizes in the orthorhombic space group Pmn2₁ (no. 31). The crystal structures of the isotypic compounds RE_8‐xAE_x[Si₁₀N_20‐xO_2+x] were confirmed by Rietveld refinements based on powder X‐ray diffraction data using the single‐crystal data of La₇Sr[Si₁₀N₁₉O₃] as starting point. Crystal structure elucidation reveals a 3D network of vertex sharing SiN₄ and SiN₂(N_1/2‐x/4O_1/2+x/4)₂ (0≤x≤2) tetrahedra. When excited with UV to blue light, La₇Sr[Si₁₀N₁₉O₃] : Eu²⁺ shows amber luminescence with λ_em=612 nm and fwhm=84 nm/2194 cm⁻¹, which makes it interesting for application in amber phosphor‐converted light emitting diodes.

Closing the yellow gap with Eu- and Tb-doped GaN: one luminescent host resulting in three colours

Gallium nitride (GaN) is a key material when it comes to light-emitting diodes (LEDs) and has pushed the LED revolution in lighting and displays. The concept of down-conversion of a GaN-based blue LED offers the possibility to provide efficient generation of monochromatic, high-color purity light resulting in a highly efficient warm-white all-nitride phosphor-converted light emitting diode (pc-LED). Although the down conversion of blue light from InGaN LEDs has become a dominant technique for producing white light, there are still some technical challenges, e.g. the immiscibility of GaN and InN and the lattice mismatch between the substrate and InGaN, that have to be overcome. Here we demonstrate the doping of bulk GaN with europium, terbium and the combination of both resulting in intriguing luminescence properties, pushing the role of GaN:Eu,Tb as a chief component in future light emitting diodes. This colour tuning proves that one luminescence host can provide three colours (red, green and orange) and that even the so called “yellow gap” could be closed with a III-nitride. By using one material for all colours, it will be possible to overcome the technical challenges in building up LED devices, which will open up new capabilities for modern highly efficient phosphors.

Mitigating Interfacial Mismatch between Lithium Metal and Garnet-Type Solid Electrolyte by Depositing Metal Nitride Lithiophilic Interlayer

Solid-state lithium batteries are generally considered as the next-generation battery technology that benefits from inherent nonflammable solid electrolytes and safe harnessing of high-capacity lithium metal. Among various solid-electrolyte candidates, cubic garnet-type Li7La3Zr2O12 ceramics hold superiority due to their high ionic conductivity (10-3 to 10-4 S cm-1) and good chemical stability against lithium metal. However, practical deployment of solid-state batteries based on such garnet-type materials has been constrained by poor interfacing between lithium and garnet that displays high impedance and uneven current distribution. Herein, we propose a facile and effective strategy to significantly reduce this interfacial mismatch by modifying the surface of such garnet-type solid electrolyte with a thin layer of silicon nitride (Si3N4). This interfacial layer ensures an intimate contact with lithium due to its lithiophilic nature and formation of an intermediate lithium-metal alloy. The interfacial resistance experiences an exponential drop from 1197 to 84.5 Ω cm2. Lithium symmetrical cells with Si3N4-modified garnet exhibited low overpotential and long-term stable plating/stripping cycles at room temperature compared to bare garnet. Furthermore, a hybrid solid-state battery with Si3N4-modified garnet sandwiched between lithium metal anode and LiFePO4 cathode was demonstrated to operate with high cycling efficiency, excellent rate capability, and good electrochemical stability. This work represents a significant advancement toward use of garnet solid electrolytes in lithium metal batteries for the next-generation energy storage devices.

Design of a nitridoalumosilicate red phosphor synthesized under mild conditions

A nitridoalumosilicate red phosphor Ca4SiAl3N7:Eu2+ was successfully synthesized at normal pressure and a low temperature (1350 °C).

The crystal structure and luminescence properties of the first lithium oxonitridolithosilicate Li3SiNO2:Eu2+

Obtained by a high temperature solid-state synthesis, the compound Li3SiNO2:Eu2+ was characterized via SCXRD, PXRD, and luminescence spectroscopy. This revealed a new structure type and interesting luminescence properties.

Synthesis and luminescence properties of new nitridolithosilicate phosphor La4Ba3Li3Si9N19: Pr3+ grown in Li flux

Flux synthesis is an effective method to discover large crystals of new compounds. In this paper, the solid-state reaction in Li flux produced a new nitridolithosilicate La4Ba3Li3Si9N19 in orthorhombic space...

Eu- and Tb-adsorbed Si3N4 and Ge3N4: tuning the colours with one luminescent host

The adsorption of europium and terbium at the grain boundaries of bulk β-Si3N4 and β-Ge3N4 and the synergic combination of both results in intriguing luminescence properties of all compounds (red, green, orange and yellow).

Nitridic Analogs of Micas AESi3 P4 N10 (NH)2 (AE=Mg, Mg0.94 Ca0.06 , Ca, Sr)

We present the first nitridic analogs of micas, namely AESi₃P₄N₁₀(NH)₂ (AE=Mg, Mg_0.94Ca_0.06, Ca, Sr), which were synthesized under high‐pressure high‐temperature conditions at 1400 °C and 8 GPa from the refractory nitrides P₃N₅ and Si₃N₄, the respective alkaline earth amides, implementing NH₄F as a mineralizer. The crystal structure was elucidated by single‐crystal diffraction with microfocused synchrotron radiation, energy‐dispersive X‐ray spectroscopic (EDX) mapping with atomic resolution, powder X‐ray diffraction, and solid‐state NMR. The structures consist of typical tetrahedra–octahedra–tetrahedra (T‐O‐T) layers with P occupying T and Si occupying O layers, realizing the rare motif of sixfold coordinated silicon atoms in nitrides. The presence of H, as an imide group forming the SiN₄(NH)₂ octahedra, is confirmed by SCXRD, MAS‐NMR, and IR spectroscopy. Eu²⁺‐doped samples show tunable narrow‐band emission from deep blue to cyan (451–492 nm).

Structure Elucidation of Complex Endotaxially Intergrown Lanthanum Barium Oxonitridosilicate Oxides by Combination of Microfocused Synchrotron Radiation and Transmission Electron Microscopy

Single‐crystalline domains in intergrown microcrystalline material of the new compounds Ba_22.5+xLa_55−x[Si₁₂₉N_240−xO_x]O₃:Ce³⁺ and Ba_25.5+xLa_77−x[Si₁₇₀N_312−xO_9+x]O₄:Ce³⁺ were identified by transmission electron microscopy (TEM). Precise diffraction data from these domains were collected with microfocused synchrotron radiation so that crystal structure elucidation of the complex disordered networks became possible. They are composed of two different interconnected slabs of which one is similar in both compounds, which explains their notorious intergrowth. The distribution of Ba and La is indicated by the analysis of bond‐valence sums and by comparison with isostructural Sr_28.5+xLa_75−x[Si₁₇₀N_312−xO_9+x]O₄. Ce³⁺ doping leads to yellow luminescence. This is a showcase that highlights the discovery and accurate characterization of new compounds relevant for luminescence applications from heterogeneous microcrystalline samples by exploiting the capability of the combination of TEM and diffraction using the latest focusing techniques for synchrotron radiation.

Narrow-band red emitting oxonitridosilicate phosphor La4-xSr2+xSi5N12-xOx:Pr3+ (x≈ 1.69)

The new oxonitridosilicates Ln_4-xSr_2+xSi₅N_12-xO_x (Ln = La, Ce) were synthesized by high temperature solid-state reactions. The crystal structures were solved and refined from both single-crystal and powder X-ray diffraction data. These oxonitridosilicate compounds crystallize in the monoclinic space group P2₁/n (no. 14) and exhibit a double-layer structure made up of corner-sharing Si(O/N)₄ tetrahedra. When excited with near-UV and blue light, the Pr³⁺ doped La_2.31Sr_3.69Si₅N_10.31O_1.69 phosphor shows a narrow-band red emission peaking at 625 nm with a full width at half-maximum of 40 nm.

The Reduced Nitridogermanates(III) Ca6 [Ge2 N6 ] and Sr6 [Ge2 N6 ] with Ge-Ge Bonds

The first nitridogermanates(III) Ca₆[Ge₂N₆] and Sr₆[Ge₂N₆] were synthesized from sodium flux and structurally characterized by powder and single crystal X‐ray diffraction, respectively. They crystallize isostructurally to each other and homeotypic to Ca₆[Cr₂N₆]H in space group R3‾ . They feature unprecedented, mutually isolated, ethane‐like [Ge^III₂N₆]¹²⁻ anions in a staggered conformation. The compounds are semiconductors according to resistivity measurements and electronic structure calculations, yielding band gaps of 1.1 eV for Ca₆[Ge₂N₆] and 0.2 eV for Sr₆[Ge₂N₆].

Na3 SO4 H-The First Representative of the Material Class of Sulfate Hydrides

The first representative of a novel class of mixed-anionic compounds, the sulfate hydride Na3 SO4 H, and the corresponding deuteride Na3 SO4 D were obtained from the solid-state reaction of NaH or NaD with dry Na2 SO4 . Precise reaction control is required, because too harsh conditions lead to the reduction of sulfate to sulfide. A combined X-ray and neutron diffraction study revealed that the compound crystallizes in the tetragonal space group P4/nmm with the lattice parameters a=7.0034(2) Å and c=4.8569(2) Å. The sole presence of hydride and absence of hydroxide ions is proven by vibrational spectroscopy and comparison with spectra predicted from quantum chemical calculations. 1 H and 23 Na MAS NMR spectra are consistent with the structure of Na3 SO4 H: a single 1 H peak at 2.9 ppm is observed, while two peaks at 15.0 and 6.2 ppm for the inequivalent 23 Na sites are observed. Elemental analysis and quantum chemical calculations further support these results.

High-Pressure High-Temperature Synthesis of Mixed Nitridosilicatephosphates and Luminescence of AESiP3 N7 :Eu2+ (AE=Sr, Ba)

Tetrahedra-based nitrides with network structures have emerged as versatile materials with a broad spectrum of properties and applications. Both nitridosilicates and nitridophosphates are well-known examples of such nitrides that upon doping with Eu²⁺ exhibit intriguing luminescence properties, which makes them attractive for applications. Nitridosilicates and nitridophosphates show manifold structural variability; however, no mixed nitridosilicatephosphates except SiPN₃ and SiP2N4NH have been described so far. The compounds AESiP₃ N₇ (AE=Sr, Ba) were synthesized by a high-pressure high-temperature approach using the multianvil technique (8 GPa, 1400-1700 °C) starting from the respective alkaline earth azides and the binary nitrides P₃ N₅ and Si₃ N₄ . The latter were activated by NH₄ F, probably acting as a mineralizing agent. SrSiP₃ N₇ and BaSiP₃ N₇ were obtained as single crystals. They crystallized in the barylite-1O (M=Sr) and barylite-2O structure types (M=Ba), respectively, with P and Si being occupationally disordered. Cation disorder was further supported by solid-state NMR spectroscopy and energy-dispersive X-ray spectroscopy (EDX) mapping of BaSiP₃ N₇ with atomic resolution. Upon doping with Eu²⁺ , both compounds showed blue emission under UV excitation.

On the crystal chemistry of inorganic nitrides: crystal-chemical parameters, bonding behavior, and opportunities in the exploration of their compositional space

The scarcity of nitrogen in Earth's crust, combined with challenging synthesis, have made inorganic nitrides a relatively unexplored class of compounds compared to their naturally abundant oxide counterparts. To facilitate exploration of their compositional space via a priori modeling, and to help a posteriori structure verification not limited to inferring the oxidation state of redox-active cations, we derive a suite of bond-valence parameters and Lewis acid strength values for 76 cations observed bonding to N3-, and further outline a baseline statistical knowledge of bond lengths for these compounds. Examination of structural and electronic effects responsible for the functional properties and anomalous bonding behavior of inorganic nitrides shows that many mechanisms of bond-length variation ubiquitous to oxide and oxysalt compounds (e.g., lone-pair stereoactivity, the Jahn-Teller and pseudo Jahn-Teller effects) are similarly pervasive in inorganic nitrides, and are occasionally observed to result in greater distortion magnitude than their oxide counterparts. We identify promising functional units for exploring uncharted chemical spaces of inorganic nitrides, e.g. multiple-bond metal centers with promise regarding the development of a post-Haber-Bosch process proceeding at milder reaction conditions, and promote an atomistic understanding of chemical bonding in nitrides relevant to such pursuits as the development of a model of ion substitution in solids, a problem of great relevance to semiconductor doping whose solution would fast-track the development of compound solar cells, battery materials, electronics, and more.

18-Crown-6 Coordinated Metal Halides with Bright Luminescence and Nonlinear Optical Effects

The crown-ether coordination compounds ZnX₂(18-crown-6), EuX₂(18-crown-6) (X: Cl, Br, I), MnI₂(18-crown-6), Mn₃Cl₆(18-crown-6)₂, Mn₃I₆(18-crown-6)₂, and Mn₂I₄(18-crown-6) are obtained by ionic-liquid-based synthesis. Whereas MX₂(18-crown-6) (M: Zn, Eu) show conventional structural motives, Mn₃Cl₆(18-crown-6)₂, Mn₃I₆(18-crown-6)₂, and Mn₂I₄(18-crown-6) exhibit unusual single MnX₄ tetrahedra coordinated to the crown-ether complex. Surprisingly, some compounds show outstanding photoluminescence. Thus, rare Zn²⁺-based luminescence is observed and unexpectedly efficient for ZnI₂(18-crown-6) with a quantum yield of 54%. Unprecedented quantum yields are also observed for Mn₃I₆(18-crown-6)₂, EuBr₂(18-crown-6), and EuI₂(18-crown-6) with values of 98, 72, and 82%, respectively, which can be rationalized based on the specific structural features. Most remarkable, however, is Mn₂I₄(18-crown-6). Its specific structural features with finite sensitizer-activator couples result in an extremely strong emission with an outstanding quantum yield of 100%. Consistent with its structural features, moreover, anisotropic angle-dependent emission under polarized light and nonlinear optical (NLO) effects occur, including second-harmonic generation (SHG). The title compounds and their optical properties are characterized by single-crystal structure analysis, X-ray powder diffraction, chemical analysis, density functional theory (DFT) calculations, and advanced spectroscopic methods.

From S-O-S to B-O-S to B-O-B Bridges: Ba[B(S2O7)2]2 as a Model System for the Structural Diversity in Borosulfate Chemistry

Various different possible connection patterns of sulfate and borate tetrahedra enable a vast structural diversity in borosulfates, a rather new class of silicate-analogous compounds. Here we unravel a direct relationship from S-O-S to B-O-S to B-O-B bridges for the first time in borosulfate chemistry. Solvothermal synthesis in pure oleum (65% SO₃) yielded the first alkaline earth metal borosulfate comprising S-O-S bridges: Ba[B(S₂O₇)₂]₂ (I2/a, Z = 4, a = 1160.77(9) pm, b = 891.44(7) pm, c = 2130.26(19) pm, β = 104.0341(17)°) contains molecular [B(S₂O₇)₂]^- anions of a central boron atom and two chelating disulfate groups. By using equal amounts of sulfuric acid and oleum solely B-O-S bridges were obtained in Ba[B₂(SO₄)₄] (Pnna, Z = 4, a = 1279.08(18) pm, b = 1280.0(2) pm, c = 731.70(11) pm) featuring one-dimensional _∞¹[B(SO₄)_4/2]^- chains. The thermal analysis on Ba[B(S₂O₇)₂]₂ revealed the conversion from S-O-S bridges to B-O-S bridges in Ba[B₂(SO₄)₄] and to B-O-B bridges in Ba[B₂O(SO₄)₃] by a successive release of SO₃. Thus, BaO-B₂O₃-SO₃ is the first quaternary system for borosulfates uniting all three possible connection patterns enabling us to understand the fascinating but systematic chemistry in such systems. Both new compounds were also characterized by means of X-ray powder diffraction, electrostatic calculations, and infrared spectroscopy assisted by density functional theory (DFT).

Borate Hydrides as a New Material Class: Structure, Computational Studies, and Spectroscopic Investigations on Sr5 (BO3 )3 H and Sr5 (11 BO3 )3 D

The unprecedented borate hydride Sr5 (BO3 )3 H and deuteride Sr5 (11 BO3 )3 D crystallizing in an apatite-related structure are reported. Despite the presence of hydride anions, the compound decomposes only slowly in air. Doped with Eu2+ , it shows broad-band orange-red emission under violet excitation owing to the 4f6 5d-4f7 transition of Eu2+ . The observed 1 H NMR chemical shift is in good agreement with previously reported 1 H chemical shifts of ionic metal hydrides as well as with quantum chemical calculations and very different from 1 H chemical shifts usually found for hydroxide ions in similar materials. FTIR and Raman spectroscopy of different samples containing 1 H, 2 H, nat B, and 11 B combined with calculations unambiguously prove the absence of hydroxide ions and the sole incorporation of hydride ions into the borate. The orange-red emission obtained by doping with Eu2+ shows that the new compound class might be a promising host material for optical applications.

Synthesis, Crystal Structure, and Luminescence Properties of a White-Light-Emitting Nitride Phosphor, Ca0.99Eu0.01AlSi4N7

Colorless transparent single crystals of a new europium-doped calcium aluminum silicon nitride, Ca_0.99Eu_0.01AlSi₄N₇, were synthesized by heating a mixture of binary nitrides (Ca₃N₂, EuN, AlN, Si₃N₄, and Mg₃N₂) at 2150 °C under a nitrogen gas pressure of 0.85 MPa. The X-ray diffraction reflections from a single crystal were indexed with orthorhombic cell parameters a = 11.6819(3) Å, b = 21.0193(6) Å, and c = 4.91770(10) Å. The crystal structure was isomorphic to that of SrAlSi₄N₇:Eu (space group Pna2₁). One of the Ca/Eu sites was split into two sites of 4-fold and 8-fold nitrogen coordination. A white-light emission spectrum with two peaks at wavelengths of 498 and 614 nm was observed from the single crystals under 400 nm near-ultraviolet-light irradiation. The CIE1931 chromaticity of the white light was plotted at x = 0.378 and y = 0.429; the mean color-rendering index Ra was 81.

SrAl2-xLi2+xO2+2xN2-2x:Eu2+ (0.12 ≤ x ≤ 0.66)-Tunable Luminescence in an Oxonitride Phosphor

Starting from the recently published narrow band red phosphor SALON, a tunable oxonitride-phosphor can be derived by introducing disorder into the structure. To achieve this, the oxygen content of the reaction mixture is increased, thereby prohibiting the oxygen/nitrogen ordering observed in SALON. The resulting compound is isotypic to UCr₄C₄ and exhibits mixed oxygen/nitrogen and lithium/aluminum sites. Further variation of the oxygen/nitrogen ratio revealed that the structure remains stable over a wide range of compositions. The compound can therefore be described by the general sum formula SrAl_2-xLi_2+xO_2+2xN_2-2x with x ranging between 0.12 and 0.66. When doped with Eu²⁺, the title compound exhibits an intense luminescence upon excitation with blue light. The maximum of this emission varies depending on the oxygen content and can be tuned to values between 581 nm (x = 0.66) and 672 nm (x = 0.12).

Ab initio exploration and prediction of AE-containing nitrido(litho/magneso)tetrelates (AE = Ca, Sr; Tt = Si, Ge) with [Si2N6]10- or [Ge2N6]10- units

Recently, a number of different structurally related nitrides characterized by pairs of edge-sharing Si-N tetrahedra forming [Si₂N₆]^10- units have emerged via different synthesis methods. Concurrently, upon doping with rare earth elements (e.g. Eu²⁺ and Ce³⁺), numerous applications in the field of luminescent materials were revealed, ranging from the visible spectrum to the near IR. This compound class in turn emphasizes the extraordinary large tuning range with respect to relative composition by formal cation exchange. In this contribution, we study the dynamical stabilities of the existing Si-based nitridotetrelates and hypothetical Ge analogues promising for future synthesis efforts of luminescent materials by means of extensive phonon calculations. Further calculations of electronic and mechanical properties corroborate the fundamental suitability of the predicted compounds for the applications of potential luminescent materials with regard to band gap (E_g) and Debye temperature (Θ_D). Calculated enthalpies of the reaction provide further beneficial insights for future experimental attempts. Our study hence highlights a potential range of novel stable nitridogermanates with isotypic structures and suitable electronic properties for optoelectronic applications.