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AlB4O6N, Al0.97Cr0.03B4O6N, and Al0.83Cr0.17B4O6N are the first representatives of the recently established structure‐family of oxonitridoborates containing Al3+. These compounds are isotypic to CrB4O6N and are synthesized in a multi‐anvil press under high‐pressure/high‐temperature conditions of 7.0 GPa/1350 °C. Structural refinement by single‐crystal X‐ray diffraction shows that they crystallize in the space group P63mc (no. 186) with two formula units per cell. Detailed characterization including high‐temperature X‐ray powder diffraction (HT‐XRD), electron probe microanalysis (EPMA), measurements of second harmonic generation (SHG), hardness, photoluminescence properties, vibrational spectroscopy, and band structure calculations reveal intriguing physicochemical properties that strongly resemble the famous material ruby. [ABSTRACT FROM AUTHOR]

Two new isostructural semiconducting metal‐phosphonate frameworks are reported. Co2[1,4‐NDPA] and Zn2[1,4‐NDPA] (1,4‐NDPA4− is 1,4‐naphthalenediphosphonate) have optical bandgaps of 1.7 eV and 2.5 eV, respectively. The electrocatalyst derived from Co2[1,4‐NPDA] as a precatalyst generated a low overpotential of 374 mV in the oxygen evolution reaction (OER) with a Tafel slope of 43 mV dec−1 at a current density of 10 mA cm−2 in alkaline electrolyte (1 mol L−1 KOH), which is indicative of remarkably superior reaction kinetics. Benchmarking of the OER of Co2[1,4‐NPDA] material as a precatalyst coupled with nickel foam (NF) showed exceptional long‐term stability at a current density of 50 mA cm−2 for water splitting compared to the state‐of‐the‐art Pt/C/RuO2@NF after 30 h in 1 mol L−1 KOH. In order to further understand the OER mechanism, the transformation of Co2[1,4‐NPDA] into its electrocatalytically active species was investigated. [ABSTRACT FROM AUTHOR]

The impact of the surrounding ligand field is successfully exploited in the case of Eu2+ to tune the emission characteristics of inorganic photoactive materials with potential application in, e.g. phosphor‐converted white light‐emitting diodes (pc‐wLEDs). However, the photoluminescence of Mn2+ related to intraconfigurational 3d5–3d5 transitions is also strongly dependent on local ligand field effects and has been underestimated in this regard so far. In this work, we want to revive the idea how to electronically tune the emission color of a transition metal ion in inorganic hosts by unusual electronic effects in the metal‐ligand bond. The concept is explicitly demonstrated for the weakly coordinating layer‐like borosulfate ligand in the Mn2+‐containing solid solutions Zn1‐xMnx[B2(SO4)4] (x = 0, 0.03, 0.04, 0.05, 0.10). Zn[B2(SO4)4]:Mn2+ shows orange narrow‐band luminescence at 590 nm, which is an unusually short wavelength for octahedrally coordinated Mn2+ and indicates an uncommonly weak ligand field. On the other hand, the analysis of the interelectronic Racah repulsion parameters reveals ionic Mn−O bonds with values close to the Racah parameters of the free Mn2+ ion. Overall, this strategy demonstrates that electronic control of the metal‐ligand bond can be a tool to make Mn2+ a potent alternative emitter to Eu2+ for inorganic phosphors. [ABSTRACT FROM AUTHOR]

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The anionic diamido N‐heterocyclic carbene 1 is used to prepare a series of linear as well as trigonal, heteroleptic CuI complexes with small molecular ligands such as pyridine derivatives or triphenylphosphine. A key role lies in the versatile precursor for these complexes, a moisture‐ and air‐stable 1D coordination polymer [1 ⋅ Cu]n composed of only the NHC ligand and CuI, such that the copper is linearly coordinated by the carbene carbon atom and one oxygen atom of the backbone of the carbene. This polymer can easily be cleaved into monomeric complexes by addition of the desired ligand to dispersions of the polymer in dichloromethane. In solution, the complexes are in equilibrium with this highly insoluble polymer and free ligand. Thus, analytical and spectroscopical experiments with the compounds are limited to their crystalline state, characterized by single crystal X‐ray diffraction experiments. Some of the complexes exhibit visible luminescence in the solid state upon irradiation with ultraviolet light. The spectral features (emission wavelength, Stokes shift, width of the emission band, vibrational fine structure) significantly differ among the complexes. Quantum mechanical computations reveal a subtle interplay of several factors such as coordination number and charge transfer character of the emissive state. [ABSTRACT FROM AUTHOR]

The bromine‐lithium exchange‐borylation‐Suzuki sequence efficiently furnishes phenothiazine‐terephthalonitrile donor‐acceptor dyads and triads in high yields. In contrast to most phenothiazine‐acceptor conjugates the title compounds are ligated in p‐position to the phenothiazine nitrogen atom. Moreover, the acceptors are either directly linked or ligated by an arylene bridge and p‐anisyl N‐substituents on the phenothiazine are chosen to lock the tricycle into an intra‐configuration. Cyclic voltammetry reveals effects of bridging and ligation of the N‐substituent. Optical spectroscopy likewise displays similar band gaps, large Stokes shifts and substantial to high quantum yields in solution, in the solid state and in PMMA matrix. Time‐resolved fluorescence spectroscopy indicates quite long fluorescence decay times in solution and emission components in the microsecond time range. TADF properties are further assessed by fluorescence increase in deoxygenated solution, gated emission spectroscopy and temperature‐dependent determination of phosphorescence. The nature of the electronically excited states is investigated by DFT/MRCI. While for the directly ligated dyad a singlet‐triplet energy gap ΔE(S1-T1) ${{E}_{{({\rm S}}_{1}-{{\rm T}}_{1})}{\rm \ }}$ of 0.24 eV can be estimated and is consistently confirmed by quantum chemical calculations on the lowest energy conformer, even lower ΔE(S1-T1) ${{\rm \Delta }{E}_{{(S}_{1}-{T}_{1})}{\rm \ }}$ of 0.029 and 0.008 eV are estimated for the investigated dyads and the triad in the solid state and in PMMA matrix. [ABSTRACT FROM AUTHOR]

The development of dual‐state emissive (DSE) fluorophores, i. e. organic molecules showing balanced emission in both solution and as molecular solids, has recently become an emerging approach in material science, biology, sensing, and optoelectronics. However, the majority of existing DSE fluorophores represents structural modifications of the scaffolds known for their aggregation‐induced emission (AIE) properties, e. g. tetraphenylethylenes (TFE), triphenylamines (TFA), and others. In this study, we introduce aurones as an easily accessible scaffold for the construction of DSE fluorophores and describe the main design principles allowing to achieve the balanced emission in both solution and solid state. Herein, we present the solid‐state fluorescence in a systematic series of aurone derivatives for the first time. We propose that the newly found DSE properties of aurones in combination with their established biological activity can be applied efficiently in biomedical studies and diagnostic tools. [ABSTRACT FROM AUTHOR]

Red‐emitting narrow‐band phosphors are of utmost importance for next‐generation white‐light phosphor‐converted light‐emitting diodes (pc‐wLEDs) for improved efficacy and optimized correlated color temperatures. A promising representative crystallizing in an ordered variant of the UCr4C4 structure type is Sr[Li2Al2O2N2]:Eu2+ (SALON:Eu2+) emitting at a desirable wavelength of 614 nm. Despite an expected eightfold coordination of the Eu2+ ions by four N3− and O2− ions, respectively, the exact local coordination symmetry and a 1:1 ratio between the two types of ligands is not straightforwardly proven by X‐ray diffraction. Low‐temperature luminescence spectroscopy in conjunction with ligand field theory are powerful alternatives to resolve local features of Eu2+ as its excited 4f65d1 configuration reacts sensitively to the polarity of the ligands. The dominant emission at 614 nm shows pronounced vibronic fine structure at 10 K. In addition, weak emission bands can be resolved at 570 and 650 nm even at a low doping concentration of 0.5 mol% and are assigned to Eu2+ ions being eightfold coordinated by N3− and O2− ions in a ratio different from 1:1. Due to the feature of vierer ring‐type channels in SALON:Eu2+, those Eu2+ centers are sufficiently close for mutual energy transfer, which is characterized by time‐resolved luminescence at 10 K. [ABSTRACT FROM AUTHOR]

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In an article published in Advanced Functional Materials, Markus Suta, Hubert Huppertz, and their colleagues introduce a new oxonitridoborate compound called AlB4O6N:Cr3+. This compound exhibits a highly efficient red line emission and has the potential to serve as an alternative luminescent pressure sensor. The researchers suggest that AlB4O6N:Cr3+ could offer more precise pressure calibration in diamond anvil cells compared to the current standard, ruby. The authors express gratitude to Abraham Siedler and Marie-Theres Wildauer for their contributions to the design of the inside back cover. [Extracted from the article]

Apart from the energy gap law, control parameters over nonradiative transitions are so far only scarcely regarded. In this work, the impact of both covalence of the lanthanoid–ligand bond and varying bond distance on the magnitude of the intrinsic nonradiative decay rate between the excited 6P5/2 and 6P7/2 spin–orbit levels of Gd3+ is investigated in the chemically related compounds Y2[B2(SO4)6] and LaBO3. Analysis of the temperature‐dependent luminescence spectra reveals that the intrinsic nonradiative transition rates between the excited 6PJ (J = 5/2, 7/2) levels are of the order of only 10 ms−1 (Y2[B2(SO4)6]:Gd3+: 8.9 ms−1; LaBO3:Gd3+: 10.5 ms−1) and differ due to the different degree of covalence of the GdO bonds in the two compounds. Comparison to the established luminescent Boltzmann thermometer Er3+ reveals, however, that the nonradiative transition rates between the excited levels of Gd3+ are over three orders of magnitude slower despite a similar energy gap and the presence of a single resonant phonon mode. This hints to a fundamental magnetic dipolar character of the nonradiative coupling in Gd3+. These findings can pave a way to control nonradiative transition rates and how to tune the dynamic range of luminescent Boltzmann thermometers. [ABSTRACT FROM AUTHOR]

Eu2+‐activated phosphors of the UCr4C4 structure type have emerged as promising new (ultra‐)narrow band phosphors. Especially the UCr4C4‐type alkali lithosilicates have caused a sensation in the field of phosphor research in the recent years due to their consistent (ultra)narrow‐band luminescence in the cyan and green range that can pave the way to novel backlighting LEDs with high color gamut. The compound "K2Na2[Li3SiO4]4:Eu2+" stands out with a strikingly narrow emission in the cyan range (<0.2 eV or <30 nm full width at half maximum in the energy or wavelength scale, respectively) but the position of the Eu2+ ions within this structure has been so far controversial. High‐resolution photoluminescence spectroscopy at 10 K reveals a complex emission spectrum with seven emission bands in the violet to green range. Combination with single‐crystal X‐ray diffraction (SCXRD) demonstrates that the cation channels in the structure also contain Li+ ions. The presence of emission bands in the violet and blue spectral range reveals that the Eu2+ ions also occupy the available K sites in the structure independently confirmed by advanced ligand field calculations. This study demonstrates that a combination of SCXRD, photoluminescence spectroscopy, and theory can help elucidate advanced structural problems. [ABSTRACT FROM AUTHOR]

Luminescence thermometry is used in a variety of research fields for noninvasive temperature sensing. Lanthanide‐doped micro‐/nanocrystals are exceptionally suitable for this. The popular concept of luminescence‐intensity‐ratio thermometry is based on emission from thermally coupled levels in a single lanthanide ion, following Boltzmann's law. These thermometers can measure temperature with low uncertainty, but only in a limited temperature range. In this work, a Ho3+‐based thermometer is presented and quantitatively modeled with sustained low temperature uncertainty from room temperature up to 873 K. The thermometer shows bright green and red luminescence with a strong and opposite dependence on temperature and Ho3+ concentration. This is the result of temperature‐dependent competition between multi‐phonon relaxation and energy transfer, feeding the green‐ and red‐emitting levels, respectively, following excitation with blue light. This simple and quantitative model of this competition predicts the output spectrum over a wide range of temperatures (300–873 K) and Ho3+ concentrations (0.1–30%). The optimum Ho3+ concentration can thus be determined for reliable measurements over any temperature range of interest. Quantitative modeling as presented here is crucial to optimally benefit from the potential of energy‐transfer thermometers to achieve low measurement uncertainties over a wide temperature range. [ABSTRACT FROM AUTHOR]

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Luminescence (nano)thermometry is an increasingly important field for remote temperature sensing with high spatial resolution. Most typically, ratiometric sensing of the luminescence emission intensities of two thermally coupled emissive states based on a Boltzmann equilibrium is used to detect the local temperature. Dependent on the temperature range and preferred spectral window, various choices for potential candidates appear possible. Despite extensive experimental research in the field, a universal theory covering the basics of luminescence thermometry is virtually nonexistent. In this manuscript, a general theoretical framework of single ion luminescent thermometers is presented that offers simple, user‐friendly guidelines for both the choice of an appropriate emitter and respective embedding host material for optimum temperature sensing. The results show that the optimum performance (thermal response and sensitivity) around T0 is realized for an energy gap ∆E21 between thermally coupled levels between 2kBT0 and 3.41kBT0. Analysis of the temperature‐dependent excited state kinetics shows that host lattices in which ∆E21 can be bridged by one or two phonons are preferred over hosts in which higher order phonon processes are required. Such a framework is relevant for both a fundamental understanding of luminescent thermometers but also the targeted design of novel and superior luminescent (nano)thermometers. [ABSTRACT FROM AUTHOR]

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The unprecedented borate hydride Sr5(BO3)3H and deuteride Sr5(11BO3)3D 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 4f65d–4f7 transition of Eu2+. The observed 1H NMR chemical shift is in good agreement with previously reported 1H chemical shifts of ionic metal hydrides as well as with quantum chemical calculations and very different from 1H chemical shifts usually found for hydroxide ions in similar materials. FTIR and Raman spectroscopy of different samples containing 1H, 2H, natB, and 11B 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. [ABSTRACT FROM AUTHOR]

Lanthanide‐doped luminescent nanoparticles are an appealing system for nanothermometry with biomedical applications due to their sensitivity, reliability, and minimal invasive thermal sensing properties. Here, four unique hybrid organic–inorganic materials prepared by combining β‐NaGdF4 and PMOs (periodic mesoporous organosilica) or mSiO2 (mesoporous silica) are proposed. PMO/mSiO2 materials are excellent candidates for biological/biomedical applications as they show high biocompatibility with the human body. On the other hand, the β‐NaGdF4 matrix is an excellent host for doping lanthanide ions, even at very low concentrations with yet very efficient luminescence properties. A new type of Er3+–Yb3+ upconversion luminescence nanothermometers operating both in the visible and near infrared regime is proposed. Both spectral ranges permit promising thermometry performance even in aqueous environment. It is additionally confirmed that these hybrid materials are non‐toxic to cells, which makes them very promising candidates for real biomedical thermometry applications. In several of these materials, the presence of additional voids leaves space for future theranostic or combined thermometry and drug delivery applications in the hybrid nanostructures. [ABSTRACT FROM AUTHOR]

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Two new scandium‐containing coordination polymers, with the formulae {(CH3)2NH2}[Sc(BPDC)2] (1) and [Sc(OH) (BPyDC)] (2) were solvothermally synthesized by using the linear linker molecules biphenyl‐4,4'‐dicarboxylic acid (H2BPDC) and 2,2'‐bipyridine‐5,5'‐dicarboxylic acid (H2BPyDC). Crystal structures were determined from single‐crystal and powder X‐ray diffraction data, respectively. The crystal structures of 1 and 2 contain isolated ScO6 or chains of trans corner‐sharing ScO6 octahedra as the inorganic building unit (IBU), which are connected by the linker molecules to a 3D framework or a layered structure, respectively. The compounds were characterized by IR‐spectroscopy, elemental analysis, thermogravimetric analysis and photoluminescence spectroscopy. 1 shows blue emission at 400 nm, while 2 exhibits intense green emission at 550 nm with a high quantum yield (QY) of 69 %. [ABSTRACT FROM AUTHOR]

Inorganic hosts, such as SrB4O7 or certain nitrides, intrinsically stabilize Eu2+ even when the dopant is an Eu3+‐based precursor and reducing conditions are not employed in the synthesis. Although this concept is well known in the synthesis of phosphorescent materials, the mechanistic details are scarcely understood. Herein, we demonstrate that trapped charge carriers, such as color centers, can also act as redox partners to stabilize certain oxidation states of activators. Eu‐activated CsMgCl3 and CsMgBr3 are used as examples. Upon doping with EuCl3 and in the absence of reducing conditions during the synthesis, dominant cyan or green luminescence from Eu2+ ions was observed. Photoluminescence spectroscopy at 10 K revealed that the reduction is correlated to color centers localized at defects. Although defects are typically undesired in phosphors, we have shown that their role may be underestimated and they could be used on purpose in the preparation of selected inorganic phosphors. [ABSTRACT FROM AUTHOR]

Anorganische Wirtsverbindungen wie SrB4O7 oder ausgewählte Nitride können Eu2+ intrinsisch stabilisieren, selbst wenn Eu3+‐Ausgangsmaterialien und keine reduzierenden Bedingungen in der Synthese genutzt werden. Obwohl dies im Bereich der Leuchtstoffsynthese bekannt ist, sind mechanistische Details nur unzureichend verstanden. Hier zeigen wir, dass lokalisierte Ladungsträger wie Farbzentren auch als Redoxpartner agieren können, um bestimmte Oxidationszustände von Aktivatoren zu stabilisieren. Die Eu‐dotierten Verbindungen CsMgCl3 und CsMgBr3 dienen als Beispiele. Selbst bei gezielter Dotierung mit EuCl3 und Ausschluss reduzierender Bedingungen kann aufgrund von Eu2+ cyane bzw. grüne Lumineszenz beobachtet werden. Photolumineszenzspektroskopie bei 10 K zeigte, dass diese intrinsische Reduktion mit Farbzentren korreliert, die an Verunreinigungen lokalisiert sind. Obgleich Defekte in Leuchtstoffen unerwünscht sind, zeigt diese Studie, dass ihre Rolle oft unterschätzt wird und sie gezielt in der Präparation ausgewählter anorganischer Leuchtstoffe genutzt werden könnten. [ABSTRACT FROM AUTHOR]

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Anhydrous EuII–acetylenedicarboxylate (EuADC; ADC2− = −O2C‐C≡C‐CO2−) was synthesized by reaction of EuBr2 with K2ADC or H2ADC in degassed water under oxygen‐free conditions. EuADC crystallizes in the SrADC type structure (I41/amd, Z=4) forming a 3D coordination polymer with a diamond‐like arrangement of Eu2+ nodes (msw topology including the connecting ADC2− linkers). Deep orange coloured EuADC is stable in air and starts decomposing upon heating in an argon atmosphere only at 440 °C. Measurements of the magnetic susceptibilities (μeff=7.76 μB) and 151Eu Mössbauer spectra (δ=−13.25 mm s−1 at 78 K) confirm the existence of Eu2+ cations. Diffuse reflectance spectra indicate a direct optical band gap of Eg=2.64 eV (470 nm), which is in accordance with the orange colour of the material. Surprisingly, EuADC does not show any photoluminescence under irradiation with UV light of different wavelengths. Similar to SrADC, EuADC exhibits a negative thermal volume expansion below room temperature with a volume expansion coefficient αV=−9.4(12)×10−6 K−1. [ABSTRACT FROM AUTHOR]

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Copyright of Nachrichten aus der Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: The synthesis and photoluminescence properties of the bright‐yellow organocerium complex [{(Cp t Bu 2 )2Ce(μ‐Cl)}2] (Cp t Bu 2 =1,3‐di(tert‐butyl)cyclopentadienyl) are presented. This coordination compound exhibits highly efficient photoluminescence within the yellow‐light wavelength range, with a high internal quantum yield of 61(±2) % at room temperature. The large red shift is attributed to the delocalizing ability of the aromatic ligands, whilst its quantum yield even makes this compound competitive with Ce3+‐activated LED phosphors in terms of its photoluminescence efficiency (disregarding its thermal stability). A bridging connection between two crystallographically independent Ce3+ ions is anticipated to be the reason for the highly efficient photoluminescence, even up to room temperature. The emission spectrum is characterized by two bands in the orange‐light range at both 10 K and room temperature, which are attributed to the parity‐allowed transitions 5d1(2D3/2)→4f1(2F7/2) and 5d1(2D3/2)→4f1(2F5/2) of Ce3+, respectively. The photoluminescence spectra were interpreted in relation to the structure and vibrational modes of the coordination compound. The spectra and optical properties indicate that trivalent cerium ions are the dominant species in the ground state, which also resolves an often‐encountered ambiguity in organocerium compounds. This result shows that photoluminescence spectroscopy is a versatile tool that can help elucidate the oxidation state of Ce in such compounds. [ABSTRACT FROM AUTHOR]

In this Communication, nanoparticles of the fluoridosilicates A2SiF6 (A=Li, Na, K, Rb, Cs), which are extremely promising host lattices for future LEDs, are presented for the first time. The preparation method we introduce here is a very simple and energy and time saving one, moreover the usage of toxic HF or elemental fluorine is avoided. In detail, the ionic liquid [Bmim]PF6 was used both as solvent and fluoride source in an ionothermally assisted microwave synthesis. The small size of the so-obtained nanoparticles is of huge relevance for their applications as thin films or for the coverage of surfaces, for example in next-generation white LEDs upon doping with Mn4+. [ABSTRACT FROM AUTHOR]

In this paper, the temperature dependence of the photoluminescence of Yb2+ doped into the halidoperovskites CsMX3 (M = Ca, Sr; X = Cl, Br, I) is presented. Yb2+ shows spin-forbidden high-spin (HS) and spin-allowed low-spin (LS) emission bands in all compounds. Upon excitation of the higher energetic LS transition, very different behaviors of the interplay of the two emissive transitions are observed. In the chlorides, the HS-based emission becomes already dominant at higher temperatures than 50 K; in the bromides, a temperature-dependent population of the HS state is observed at higher temperatures than 200 K, whereas in the iodides, the LS emission remains dominant even above 300 K. A vibrational relaxation model is attempted for the explanation of this behavior that reveals a very delicate dependence on the mode energies of the [YbX6]4− octahedra. FIR spectra of the pure Yb2+-based compounds CsYbX3 are also presented to experimentally verify the estimated average mode energies from the model. Finally, the relevance for novel Yb2+-based scintillators is discussed. [ABSTRACT FROM AUTHOR]

The new microporous metal organic framework [La2(H2O)5(H2TPPE)]·3H2O (CAU‐54), is obtained in a hydrothermal reaction of the linker 1,1,2,2‐tetrakis(4′‐phosphonophenyl)ethylene (H8TPPE) and La3+ ions. The extensive characterization including temperature‐dependent crystal structures and spectroscopic properties allowed to understand the unique, multi‐responsive material properties. CAU‐54 exhibits rarely observed reversible photochromism as well as turn‐on photoluminescence by various external chemical or physical stimuli including change of pressure, solvent exchange, and temperature variation. These properties can be unequivocally assigned to the presence of tetraphenylethylene (TPE) moieties of the linker molecules within the MOF, i.e., the ordered spatial arrangement of the linker molecules, the presence of accessible pores as well as the coordination flexibility of the phosphonate groups and the rotational freedom of the linker. By temperature‐dependent steady‐state and time‐resolved luminescence studies, it is shown that this compound exhibits a) blue fluorescence that becomes effectively quenched at room temperature, b) green efficient luminescence with thermal stability up to 400 K, and c) red phosphorescence correlated to the observed photochromism. In addition, CAU‐54 shows unusual thermal expansion properties as shown by temperature‐dependent powder X‐ray diffraction measurements with identified transition points that correlate with the observed temperature‐dependent changes in the photoluminescence. [ABSTRACT FROM AUTHOR]

The crystal structures of ³∞[RE2(ADC)3(H2O)6]·2H2O (RE = Pr, Nd, Sm, Eu, Tb, Dy) were solved and refined from X-ray single crystal data. They crystallize in a structure type already known for RE = La, Ce and Gd (P1, no. 2, Z = 2), which is characterized by REO9 polyhedra forming dimeric units being the nodes of a 3D framework structure linked by ADC²- anions (-O2C-C≡C-CO2- = acetylenedicarboxylate). From synchrotron powder diffraction data it was shown that isostructural coordination networks are formed for RE = Ho, Er, Y, whereas for RE = Tm, Yb, Lu a new structure type crystallizing in a highly complex crystal structure with a large orthorhombic unit cell is found. All compounds are obtained by slow evaporation of an aqueous solution containing RE(OAc)3·xH2O and acetylenedicarboxylic acid (H2ADC). The coordination networks of composition ³∞[RE2(ADC)3(H2O)6]·2H2O were thoroughly investigated by thermal analysis and for RE = Eu, Tb, a strong red and green photoluminescence was observed and investigated by means of UV/Vis spectroscopy. [ABSTRACT FROM AUTHOR]

Red‐emitting narrow‐band phosphors are of utmost importance for next‐generation white‐light phosphor‐converted light‐emitting diodes (pc‐wLEDs) for improved efficacy and optimized correlated color temperatures. A promising representative crystallizing in an ordered variant of the UCr4C4 structure type is Sr[Li2Al2O2N2]:Eu2+ (SALON:Eu2+) emitting at a desirable wavelength of 614 nm. Despite an expected eightfold coordination of the Eu2+ ions by four N3− and O2− ions, respectively, the exact local coordination symmetry and a 1:1 ratio between the two types of ligands is not straightforwardly proven by X‐ray diffraction. Low‐temperature luminescence spectroscopy in conjunction with ligand field theory are powerful alternatives to resolve local features of Eu2+ as its excited 4f65d1 configuration reacts sensitively to the polarity of the ligands. The dominant emission at 614 nm shows pronounced vibronic fine structure at 10 K. In addition, weak emission bands can be resolved at 570 and 650 nm even at a low doping concentration of 0.5 mol% and are assigned to Eu2+ ions being eightfold coordinated by N3− and O2− ions in a ratio different from 1:1. Due to the feature of vierer ring‐type channels in SALON:Eu2+, those Eu2+ centers are sufficiently close for mutual energy transfer, which is characterized by time‐resolved luminescence at 10 K. [ABSTRACT FROM AUTHOR]

Eu2+‐activated phosphors of the UCr4C4 structure type have emerged as promising new (ultra‐)narrow band phosphors. Especially the UCr4C4‐type alkali lithosilicates have caused a sensation in the field of phosphor research in the recent years due to their consistent (ultra)narrow‐band luminescence in the cyan and green range that can pave the way to novel backlighting LEDs with high color gamut. The compound "K2Na2[Li3SiO4]4:Eu2+" stands out with a strikingly narrow emission in the cyan range (<0.2 eV or <30 nm full width at half maximum in the energy or wavelength scale, respectively) but the position of the Eu2+ ions within this structure has been so far controversial. High‐resolution photoluminescence spectroscopy at 10 K reveals a complex emission spectrum with seven emission bands in the violet to green range. Combination with single‐crystal X‐ray diffraction (SCXRD) demonstrates that the cation channels in the structure also contain Li+ ions. The presence of emission bands in the violet and blue spectral range reveals that the Eu2+ ions also occupy the available K sites in the structure independently confirmed by advanced ligand field calculations. This study demonstrates that a combination of SCXRD, photoluminescence spectroscopy, and theory can help elucidate advanced structural problems. [ABSTRACT FROM AUTHOR]