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Funding Information: The authors thank Christoph Wallach for Raman measurements and Sabine Zeitz for UV/Vis absorption spectroscopy. A. M. and M. B. thank Leonhard Dorsch for packing of the MAS rotors. Bircan Dilki is thanked gratefully for conducting the elemental analysis. We would like to thank the Institut Laue-Langevin for beam time allocated on D2B; https://doi.org/10.5291/ILL-DATA.5-21-1170 and https://doi.org/10.5291/ILL-DATA.EASY-725 . A. M. and N. K. thank the DFG for funding (project number 245845833) within International Research Training Group IRTG 2022—Alberta Technical University of Munich School for Functional Hybrid Materials (ATUMS). A. M. thanks the International Graduate School for Science and Engineering (IGSSE) for support. A. J. K. thanks Academy of Finland for funding (grant 324973) and CSC, the Finnish IT Center for Science for computational resources. Publisher Copyright: © 2022 The Royal Society of Chemistry The four compounds A3MO4H (A = Rb, Cs; M = Mo, W) are introduced as the first members of the new material class of the transition oxometalate hydrides. The compounds are accessible via a thermal synthesis route with carefully controlled conditions. Their crystal structures were solved by neutron diffraction of the deuterated analogues. Rb3MoO4D, Cs3MoO4D and Cs3WO4D crystallize in the antiperovskite-like K3SO4F-structure type, while Rb3WO4D adopts a different orthorhombic structure. 2H MAS NMR, Raman spectroscopy and elemental analysis prove the abundance of hydride ions next to oxometalate ions and experimental findings are supported by quantum chemical calculations. The tetragonal phases are direct and wide band gap semiconductors arising from hydride states, whereas Rb3WO4H shows a unique, peculiar valence band structure dominated by hydride states.

The first representative of a novel class of mixed-anionic compounds, the sulfate hydride Na3SO4H, and the corresponding deuteride Na3SO4D were obtained from the solid-state reaction of NaH or NaD with dry Na2SO4. 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. 1H and 23Na MAS NMR spectra are consistent with the structure of Na3SO4H: a single 1H peak at 2.9 ppm is observed, while two peaks at 15.0 and 6.2 ppm for the inequivalent 23Na sites are observed. Elemental analysis and quantum chemical calculations further support these results.

Die ersten Vertreter einer neuen Klasse gemischt‐anionischer Verbindungen, das Sulfathydrid Na3SO4H und das entsprechende Deuterid Na3SO4D, werden durch die Festkörperreaktion von NaH bzw. NaD mit trockenem Na2SO4 erhalten. Hierfür wird eine genaue Reaktionskontrolle benötigt, da zu harsche Reaktionsbedingungen zur Reduktion des Sulfats zum Sulfid führen. Eine kombinierte Auswertung von Röntgen‐ und Neutronendiffraktometrie zeigt, dass die Verbindung tetragonal mit der Raumgruppe P4/nmm und den Zellparametern a=7.0034(2) Å and c=4.8569(2) Å kristallisiert. Die alleinige Anwesenheit von Hydridionen und die Abwesenheit von Hydroxidionen wird durch Schwingungsspektroskopie im Vergleich zu Spektren, erhalten durch quantenchemische Berechnungen, bewiesen. 1H‐ und 23Na‐Festkörper‐NMR‐Spektren entsprechen der Struktur von Na3SO4H: ein 1H‐Signal bei 2.9 ppm sowie zwei Signale bei 15.0 und 6.2 ppm für zwei ungleiche 23Na‐Positionen. Zusätzlich stützen Elementaranalyse und quantenchemische Berechnungen die experimentellen Befunde.

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.

The engineering of covalency and crystal field is a key point for the control of the 5d energy level of Eu2+. The hydride ion exhibits strong covalency, which results in a large 5d energy shift by the nephelauxetic effect compared to their fluoride analogues. In this study, the Eu2+-doped K2MgH4 Ruddlesden–Popper (n = 1) perovskite was prepared and its optical properties were investigated. Red luminescence due to the 4f65d1 → 4f7 transition was observed at 670 nm by UV excitation of the K2MgH4:Eu2+ sample. Compared with yellow Eu2+-luminescence at 565 nm of the KMgH3 cubic perovskite, which has almost the same chemical composition as K2MgH4, the additional red-shift of the luminescence in K2MgH4:Eu2+ is caused by the strong crystal field splitting in the unique 9-fold coordinated site in addition to the large nephelauxetic effect by hydride ions. Using a hydride model system that allows for a clear distinction between crystal field splitting and nephelauxetic effect, we successfully demonstrated the design concept for the 5d energy shifting by covalency and crystal field in Eu2+-doped K2MgH4. Also, the thermal quenching process of K2MgH4:Eu2+ by the ionization process was discussed in comparison to KMgH3:Eu2+ on the basis of the energy diagram.

Die Quanteninformationstechnik ist ein lebendiges Thema in der Forschung an anorganischen Materialien, beispielsweise bei der Verschlusselung fur Datentransfer oder fur den Traum vom Quantencomputer. Neben supraleitenden Qubits oder Defektzentren in Diamant eignen sich moglicherweise seltenerddotierte Materialien dafur.

Magnetische Werkstoffe sind fundamental fur technische Anwendungen wie Datenspeicher und Windenergie. Magnetische Eigenschaften entstehen durch die relative Ausordnung von magnetischen Momenten auf paramagnetischen Atomen oder Ionen im Festkorper. Um diese Ausordnungen der Spins im Gitter zu verstehen, sind klassische Symmetrieelemente zu erweitern.

Seltenerdelemente finden sich nicht nur in Wohnungs‐, Automobil‐ oder Stadionbeleuchtung, sondern auch im Glasfasernetz fur unsere Telekommunikation, in Detektoren fur die medizinische Bildgebung sowie als kontaktlose und empfindliche Thermometer.

Im Jahr 1932 entdeckt, diente das Neutron schon bald der Untersuchung diverser Verbindungen. Was tut sich derzeit bei der Neutronendiffraktion an den internationalen Grosforschungseinrichtungen?

Werden anorganische Verbindungen in neuen Modifikationen oder metastabilen Zustanden hergestellt, haben sie oft andere Eigenschaften als ihre bekannten Vertreter. Um andere Eigenschaften und Strukturen zu generieren, reicht es sogar schon, die Verbindungen als Filme wachsen zu lassen: Hier entscheidet die Schichtdicke.

The first representative of a novel class of mixed‐anionic compounds, the sulfate hydride Na3SO4H, and the corresponding deuteride Na3SO4D were obtained from the solid‐state reaction of NaH or NaD with dry Na2SO4. 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. 1H and 23Na MAS NMR spectra are consistent with the structure of Na3SO4H: a single 1H peak at 2.9 ppm is observed, while two peaks at 15.0 and 6.2 ppm for the inequivalent 23Na sites are observed. Elemental analysis and quantum chemical calculations further support these results., The novel sulfate hydride—the first representative of a new compound class—has been prepared by precise reaction control. A number of different methods, including neutron and X‐ray powder diffraction, solid state MAS NMR, vibrational spectroscopy, and density functional calculations, were applied.

In the search for novel mixed anionic hydrides, simple and sensitive detection methods can be useful and local probes lead to a better understanding of the materials. In our present study, we show that 5d–4f lanthanide luminescence can serve as a local sensor to verify the presence of hydride and potentially estimate the hydride content. As a model system, the Eu2+-doped hydride fluoride solid solution series of MMgDxF3−x (MMgHxF3−x) with M = K, Rb is used, which were prepared and characterized by a combined X-ray and neutron diffraction approach. At room temperature, the compounds with M = Rb crystallize in a hexagonal perovskite-type structure and those with M = K crystallize in a normal cubic perovskite structure. Their lattice parameters follow Vegard's law. We also reinvestigated the structure and anion distribution in KMgD2F. Bright yellow emission in RbMgH3:Eu2+ is observed for the first time and for both M, the hydride fluoride compounds show Eu2+ emission energies between those of the pure hydrides and fluorides, which can be used for calibration and fast idendification of the hydride content, especially in the region of low hydride content.

A model study on the use of pulsed electron paramagnetic resonance spectroscopy and optical spectroscopy of Eu2+ as a local probe in hydrides is presented for the Eu2+-doped (and codoped) perovskites LiMH3 and LiMD3 (M = Sr or Ba). Two-pulse field-swept electron spin echo, Davies and Mims electron nuclear double resonance, Davies-type difference triple resonance experiments, and thermoluminescence spectroscopy, as well as density functional calculations, were carried out. Electron nuclear double resonance spectroscopy allows for an unambiguous determination of the position occupied by the dopant ion, which is important information necessary for the correct interpretation of optical spectra. With regard to the current importance of hydrides and mixed anionic hydrides, doping with rare-earth or transition-metal ions and the combination of pulsed EPR and optical spectroscopy may serve as a promising and convenient tool for studying such materials.

The apatite family is a mineral class that also contains the biologically very important hydroxyapatite. Here, we are reporting on the synthesis and characterization of a fully hydride-substituted strontium apatite, which could be obtained via mechanochemical synthesis and subsequent annealing treatment. The full substitution by hydride anions is proven by various methods, such as neutron powder diffraction of a deuterated sample Sr5(PO4)3D, as well 1H MAS solid state NMR combined with quantum chemical calculations, vibrational spectroscopy and elemental analysis. The present work expands the apatite family from the known halide and hydroxide apatites to the fully hydride-anion-substituted variant and is expected to open up a new field of materials containing coexistent phosphate and hydride anions.

Temperature-dependent photoluminescence (PL) as well as thermoluminescence (TL) were studied in the Eu2+-doped hydrides LiMH3 (M = Sr, Ba) and the corresponding deuterides. Here, thermally stimulated luminescence was observed for the first time in a Eu2+-doped hydrides and deuterides. The onset temperature of quenching (T95 %) and the quenching temperature (T50 %) were determined from photoluminescence intensities, and the energy barrier for thermal quenching was estimated. Then, a scheme with the localization of divalent and trivalent lanthanide 4f and 5d levels for the example LiSrH3 was proposed. In deuterides, the quenching temperatures are slightly higher than in hydrides, which can be related to the influence of the different phonon frequencies. In the TL measurements we observed very shallow and intense TL glow peaks in all samples. We also used density functional methods in order to show qualitative trends for the stability of possible defects. The model calculation suggest that energetically favo...

In NMR, paramagnetic dopants change the relaxation behavior and the chemical shift of the nuclei in their immediate environment. Based on the concept that the "immediate environment" in a diamagnetic host material can be described as a sphere with radius r0, we developed a function for the fraction of unperturbed nuclei (the fraction of nuclei outside the sphere) which gives a link between the effective radius and the doping concentration. In the case of a homogeneous doping scenario a characteristic dependence is observed in both theory and experiment. We validated the model on a sample series where paramagnetic Eu(II) ions are doped into crystalline SrH2. The fraction of unperturbed nuclei was determined from the (1)H NMR signal and follows the predicted curve for a homogeneous doping scenario where the radius r0 is 17 Å.

Among lightweight materials, magnesium-containing systems are of interest for hydrogen storage. Here, we use an efficient prediction scheme at ab initio level in order to identify new magnesium-based alloys that are stable under elevated pressure. The calculations show that pressure can radically change the minimum energy compositions and various new Mg-rich compounds were found under these conditions. For these Mg-rich compounds, a careful investigation and a search for potential hydrides was carried out and our study on the electronic properties reveals interesting information on the behavior of hydrogen atoms. Our theoretical investigations are in good agreement with very recent experimental results and demonstrate a possibility to identify destabilized metal hydrides. Consequently, the present result encourages the use of similar prediction schemes in order to identify and design destabilized systems for hydrogen storage applications.

We present a case study on the vibrational coupling of lattice phonons to the electronic 4f7 (8S7/2)–4f65d1 (eg) transition of divalent europium in the hydrides and deuterides LiMH3 and LiMD3 (M = Sr and Ba). For low doping concentrations, these compounds show extraordinarily well-resolved vibronic fine structures at low temperatures. Besides luminescence emission spectroscopy of the europium-doped compounds, we carried out inelastic neutron scattering (INS) experiments of the europium-free compounds. The phonons coupling to the electronic transition are identified, and a good agreement between the vibronic and the INS data is found. The frequencies of the low-energy acoustic modes do not significantly change upon replacing hydride by deuteride, whereas a decrease by a factor of approximately 2 can be observed for the higher energy optic modes. Furthermore, we compare these experimental results to density functional calculations performed with the Vienna Ab initio Simulation Package. Knowledge of the phon...

Metal hydrides exhibit interesting properties as hosts for Eu(II) containing luminescent compounds due to the nephelauxetic effect and the strong ligand field of the hydride anion. In order to elucidate the lattice site symmetry of europium dopants, Q-band and X-band electron paramagnetic resonance (EPR) spectra were collected on LiMH3 : Eu2+ and LiMD3 : Eu2+ (M = Sr, Ba) powders with europium concentrations between 0.0037 and 0.27 mol %. They show well resolved hyperfine splitting in the central part of the spectra due to magnetic electron spin-nuclear spin coupling of 151Eu and 153Eu, and are in good agreement with simulated spectra based upon cubic site symmetry. Spin Hamiltonian parameters were extracted by spectral analysis and are reported. Low intensity rhombic spectra contributions could be assigned to small amounts of MH2 : Eu2+ or the respective deuterides as impurities in the samples. The results of this EPR investigation and size considerations suggest that europium is divalent and occupies the alkaline earth metal (M) positions in LiMH3 : Eu2+ and LiMD3 : Eu2+ (M = Sr, Ba).

Luminescence properties of divalent europium in the mixed-anion hydride chloride EuHCl were studied for the first time. Olive-green single crystals of EuHCl (PbFCl-type structure: tetragonal, P4/nmm, a = 406.58(3) pm, c = 693.12(5) pm, c/a = 1.705, Z = 2) resulted from the reaction of elemental europium (Eu), sodium hydride (NaH) and sodium chloride (NaCl), while powder samples were prepared from the binary components europium dihydride (EuH2) and dichloride (EuCl2). Low temperature X-ray powder diffraction proved the absence of phase transitions for 12(2) K ≤ T ≤ 295(2) K. Bright green emission was observed under UV-excitation and assigned to the 4f65d1–4f7 transition of divalent europium. Temperature-dependent luminescence absorption and emission, as well as lifetime measurements were carried out on single crystal and powder samples. Surprisingly, only limited concentration quenching was found. Additionally, two emission bands (485 and 510 nm) are observed, whose intensity ratio depends strongly on temperature. In order to explain this behavior for a single Eu2+ site, we suggest either a dynamical Jahn–Teller effect in the excited 5d1 state or emission from both a 4f65d1 state and a trapped exciton state.

During the investigation of concentration dependent properties of phosphors, such as emission intensities, the knowledge of the activator ion concentration is of great importance. Herein we present a study on recovery rate and homogeneity of the activator ion concentration by chemical analysis in luminescent europium doped metal hydrides. The analysis method was established on the model system EuxSr1−xH2 and applied to brightly emitting hydridic perovskites LiMH3:Eu2+ and LiMD3:Eu2+ (M = Sr, Ba). The nominal activator ion concentrations calculated from initial weights are in good agreement with those determined via ICP-MS for 10−3% ≤ x both for the hydrides (deuterides) and the parent alloys. The synthesis protocol thus allows a reliable method for reproducibly doping europium into metal hydrides. Luminescence spectra of LiEuxSr1−xH3 with x = 0.0037% show a broad band emission at room temperature typical for Eu2+ 4f65d1–4f7 transitions. Below 80 K, a vibronic fine structure is observed with vibrational coupling frequencies of approximately 100, 370 and 970 cm−1.

Chemical bonding in and electronic structure of lithium and magnesium rhodium hydrides are studied theoretically using DFT methods. For Li3RhH4 with planar complex RhH4 structural units, Crystal Orbital Hamilton Populations reveal significant Rh−Rh interactions within infinite one-dimensional ∞ 1 [RhH4] stacks in addition to strong rhodium−hydrogen bonding. These metal−metal interactions are considerably weaker in the hypothetical, heavier homologue Na3RhH4. Both compounds are small-band gap semiconductors. The electronic structures of Li3RhH6 and Na3RhH6 with rhodium surrounded octahedrally by hydrogen, on the other hand, are compatible with a classical complex hydride model according to the limiting ionic formula (M+)3[RhH6]3− without any metal−metal interaction between the 18-electron hydridorhodate complexes. In MgRhH, building blocks of the composition (RhH2)4 are formed with strong rhodium−hydrogen and significant rhodium−rhodium bonding (bond lengths of 298 pm within Rh4 squares). These units are linked together to infinite two-dimensional layers ∞ 2 [(RhH2/2)4] via common hydrogen atoms. Li3RhH4 and MgRhH are accordingly examples for border cases of chemical bonding where the classical picture of hydridometalate complexes in complex hydrides is not sufficient to properly describe the chemical bonding situation.

We identify and analyze dephasing mechanisms that broaden the optical transitions of rare-earth ions in randomly oriented transparent ceramics. The study examines the narrow F_0^7 ↔ D_0^5 transition of Eu^(3+) dopants in a series of Y_2O_3 ceramic samples prepared under varying conditions. We characterize the temperature and magnetic field dependence of the homogeneous linewidth, as well as long-term spectral diffusion on time scales up to 1 s. The results highlight significant differences between samples with differing thermal treatments and Zr^(4+) additive concentrations. In particular, several distinct magnetic interactions from defect centers are observed, which are clearly distinguished from the broadening due to interactions with two-level systems and phonons. By minimizing the broadening due to the different defect centers, linewidths of the order of 4 kHz are achieved for all samples. The linewidths are limited by temperature-dependent interactions and by an interaction that is yet to be identified. Although the homogeneous linewidth can be narrowed further in these ceramic samples, the broadening is now comparable to the linewidths achieved in rare-earth-ion–doped single crystals. Thus, this work emphasizes the usefulness of studying ceramics to gain insights into dephasing mechanisms relevant to single crystals and suggests that ceramics may be an interesting alternative for applications in classical and quantum information processing.

Olive-green single crystals of EuHCl are prepared by reaction of Eu powder, NaH, and NaCl in a molar ratio of 1:1:1 (Nb capsule, 900 °C, 13 h).

We have measured inhomogeneous linewidths and coherence times (T 2) of nuclear spin transitions in a Eu3+ :Y2O3 transparent ceramic by an all-optical spin echo technique. The nuclear spin echo decay curves showed a strong modulation which was attributed to interaction with Y nuclei in the host. The coherence time of the 29 MHz spin transition in 151Eu3+ was 16 ms in a small applied magnetic field. Temperature dependent measurements showed that the coherence time was constant up to 18 K and was limited by spin-lattice relaxation for higher temperatures. Nuclear spin echoes in 153Eu3+ gave much weaker signals than for the case of 151Eu3+ . The spin coherence time for the 73 MHz spin transition in 153Eu3+ was estimated to 14 ms in a small magnetic field. The study shows that the spin transitions of ceramic Eu3+ :Y2O3 have coherence properties comparable to the best rare-earth-doped materials available.

EuHxF2-x is prepared by solid state reaction of EuF2 and EuH2 under H2 pressure (autoclave, 470 °C, 30 bar).

EuxM1-x (M: Ca, Sr, Ba) alloys are synthesized by melting the elements in Nb ampules and subsequently hydrogenated to EuxM1-xH2 (autoclave, 270 bar H2, 500 K).

Based on results from density-functional calculations we present an interesting and unusual mechanism for a structural change in a certain class of intermetallic compounds that can be induced through hydrogen absorption. Through an atomic rearrangement, palladium-rich intermetallic compounds MPd3 (M = Mg, In, Tl) can change the structure from a tetragonal ZrAl3 or TiAl3 type to a cubic AuCu3 type structure. Within the density-functional calculations we study a possible reaction pathway via a gliding of atomic layers with and without the presence of hydrogen. Subsequently, we argue that H-Pd interactions can be held responsible for the structural change upon hydrogen uptake, and that entropic and packing effects can explain the existence of the lower-symmetric structures in the absence of hydrogen.

Luminescence of divalent europium has been investigated for the first time in metal hydrides. A complete solid-solution series was found for the pseudobinary system Eu(x)Sr(1-x)H(2) [a = 637.6(1) pm -12.1(3)x pm, b = 387.0(1)-6.5(2)x pm, c = 732.2(2)-10.1(4)x pm]. Europium-doped alkaline-earth hydrides Eu(x)M(1-x)H(2) (M = Ca, Sr, Ba) with a small europium concentration (x = 0.005) exhibit luminescence with maximum emission wavelengths of 764 nm (M = Ca), 728 nm (M = Sr), and 750 nm (M = Ba); i.e., the emission energy of divalent europium shows an extremely large red shift compared to the emission energies of fluorides or oxides. Theoretical calculations (LDA+U) confirm decreasing band gaps with increasing europium content of the solid solutions.

Homogeneous linewidths below 10 kHz are reported for the first time in high-quality Eu3+ doped Y 2O3 transparent ceramics. This result is obtained on the 7F0→5D0 transition in Eu3+ doped Y 2O3 ceramics and corresponds to an improvement of nearly one order of magnitude compared to previously reported values in transparent ceramics. Furthermore, we observed spectral hole lifetimes of ∼15 min that are long enough to enable efficient optical pumping of the nuclear hyperfine levels. Additionally, different Eu3+ concentrations (up to 1.0%) were studied, resulting in an increase of up to a factor of three in the peak absorption coefficient. These results suggest that transparent ceramics can be useful in applications where narrow and deep spectral holes can be burned into highly absorbing lines, such as quantum information processing and spectral filtering, This work was supported by the ANR projects RAMACO (No. 12-BS08-0015-01) and DISCRYS (No. 14-CE26-0037-01), Idex No. ANR-10-IDEX-0001-02 PSL⋆, and Nano’K project RECTUS. C.W.T. and R.L.C. acknowledge support from National Science Foundation (NSF) Award Nos. CHE-1416454 and PHY-1415628 and M.O.R. and L.E.B. from Project No. MAT2013- 43301-R of the Spanish Ministry of Economy and Competitiveness (MINECO) and Comunidad Autónoma de Madrid under Grant No. S2013/MIT-2740