Search

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]

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]

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]

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]

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]

Divalent europium doped barium orthosilicate is a very important phosphor for the production of light emitting diodes (LEDs), generally associated to the green emission color of micron-sized crystals synthesized by means of solid-state reactions. This work presents the combustion synthesis as an energy and time-saving preparation method for very small nano-sized Ba2SiO4 particles, flexibly doped to acquire different emission energies. The size of the resulting spherical nanoparticles (NPs) of the green emitting Ba2SiO4:Eu2+ was estimated to about 35 nm applying the Scherrer equation and further characterized with aid of atomic force microscopy (AFM) as well as scanning electron microscopy (SEM). This phosphor is able to build homogeneous luminescent suspensions and was successfully down-sized without changing the optical properties in comparison to the bulk phosphors. Besides the X-ray diffraction (XRD) analysis and the different types of microscopy, the samples were characterized by luminescence spectroscopy. Undoped Ba2SiO4 NPs are not luminescent, but show characteristic red emission of the 5D0 → 7FJ (J = 0-4) electronic transitions when doped with Eu3+ ions. Moreover, these orthosilicate nanoparticles generate blue light at low temperatures due to impurity-trapped excitons, introduced by the partial substitution of the Ba2+ with Sr2+ ions in the Ba2SiO4 lattice causing a substantial distortion. A model for the temperature behavior of the defect luminescence as well as for their nature is provided, based on temperature-dependent luminescence spectra and lifetime measurements. [ABSTRACT FROM AUTHOR]

• Transition metal, lanthanide, and actinide ions embedded in solids are prone to the surrounding ligand field. • Optical and magnetic properties of these elements are described by ligand field theory. • The angular overlap model (AOM) is chemically very intuitive and works with just a few parameters. • Several application areas of the AOM for f elements are discussed. Lanthanoid ions are well-known for their characteristic optical and magnetic properties interesting for a wide range of applications. Most of these properties show a subtle dependence on the surrounding ligands. Unlike the transition metal ions with their often encountered octahedral or tetrahedral coordination in compounds, rare earth ions are typically found in coordination geometries with low symmetries and high coordination numbers. The quantitative treatment of the ligand field in the so-called Wybourne scheme then becomes overparametrized and not readily insightful but merely a technical tool. In this review, we want to present the alternative approach by the chemically intuitive angular overlap model (AOM) of ligand field theory that is independent from symmetry and allows to decompose any coordination geometry into its separate metal–ligand bonds with well-known bonding character. It is the goal of this review to demonstrate its strength in the semi-quantitative description of opto-magnetic properties of the rare earth ions on carefully selected examples from practice. Finally, we compare the AOM to conventional Wybourne-parametrized ligand field theory and show how the two schemes of ligand field theory are related to one another. Overall, this review offers a perspective on future approaches to ligand field calculations with f elements with the benefit of full transparency and intuitive understanding rather than technical fitting. [ABSTRACT FROM AUTHOR]

Ratiometric luminescence thermometry employing luminescence within the biological transparency windows provides high potential for biothermal imaging. Nd3+ is a promising candidate for that purpose due to its intense radiative transitions within biological windows (BWs) I and II and the simultaneous efficient excitability within BW I. This makes Nd3+ almost unique among all lanthanides. Typically, emission from the two 4F3/2 crystal field levels is used for thermometry but the small ~100 cm−1 energy separation limits the sensitivity. A higher sensitivity for physiological temperatures is possible using the luminescence intensity ratio (LIR) of the emissive transitions from the 4F5/2 and 4F3/2 excited spin-orbit levels. Herein, we demonstrate and discuss various pitfalls that can occur in Boltzmann thermometry if this particular LIR is used for physiological temperature sensing. Both microcrystalline, dilute (0.1%) Nd3+-doped LaPO4 and LaPO4: x% Nd3+ (x = 2, 5, 10, 25, 100) nanocrystals serve as an illustrative example. Besides structural and optical characterization of those luminescent thermometers, the impact and consequences of the Nd3+ concentration on their luminescence and performance as Boltzmann-based thermometers are analyzed. For low Nd3+ concentrations, Boltzmann equilibrium starts just around 300 K. At higher Nd3+ concentrations, cross-relaxation processes enhance the decay rates of the 4F3/2 and 4F5/2 levels making the decay faster than the equilibration rates between the levels. It is shown that the onset of the useful temperature sensing range shifts to higher temperatures, even above ~ 450 K for Nd concentrations over 5%. A microscopic explanation for pitfalls in Boltzmann thermometry with Nd3+ is finally given and guidelines for the usability of this lanthanide ion in the field of physiological temperature sensing are elaborated. Insight in competition between thermal coupling through non-radiative transitions and population decay through cross-relaxation of the 4F5/2 and 4F3/2 spin-orbit levels of Nd3+ makes it possible to tailor the thermometric performance of Nd3+ to enable physiological temperature sensing. [ABSTRACT FROM AUTHOR]

The synthesis and structural characterization of 1,7-bis(4-triphenylsiloxy-3-methoxy-phenyl)-1,6-heptadiene-3,5-dione (1 = Ph 3 SiCurcH) and 1,7-bis(4-methoxycarbonyloxy-3-methoxy-phenyl)-1,6-heptadiene-3,5-dione (2 = MeOC(O)CurcH) are reported. Compound 1 represents the first metal-organic curcumin derivative. The complexation of 1 and 2 with Cu2+ has been studied. The new copper(II) complexes (Ph 3 SiCurc) 2 Cu (3) and [MeOC(O)Curc] 2 Cu·4MeCN (4) have been prepared and their crystal structures determined by single crystal X-ray diffraction. Moreover, the optical properties of the solid compound 1 have been investigated in detail. The emission spectrum shows a vibronic fine structure that has been analysed in terms of Franck-Condon factors. The excitation spectrum is broad and structureless and may be interpreted in terms of an interband transition as is also confirmed by diffuse reflectance spectra. Due to the weak intermolecular interactions, an isolated-molecule model is used instead for the assignment of the transitions, which are thus characterized as S 1 ↔ S 0 or π * ↔ π fluorescent transitions. Despite the electric-dipole allowed nature of the transition, the quantum yield is Φ = (2.4 ± 0.3)% in agreement with other findings on curcumin derivatives. • The synthesis of the first Si-based metal-organic curcumin derivative is reported. • The solid compound shows yellow luminescence due to a direct interband transition. • The vibronic fine structure is analysed with an effective Huang-Rhys-Pekar model. • An interpretation as molecular S 1 →S 0 transition despite band formation is possible • The triphenylsiloxy functional groups do not affect the optical properties. [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]

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]

Accurate, fast, and non-invasive methods for the determination of the local pressure magnitude are crucial for the investigation of the physical and chemical behavior of materials at the extreme conditions of high pressure. A promising method for remote operando pressure measurements is luminescence manometry. However, a limiting bottleneck for high-pressure readout is the usually occurring quenching of the emission signal of the luminescent sensor material upon compression. In this work, we reported for the first time the pressure-induced intensity enhancement (by 3 orders of magnitude) of the 4f7(6P 7/2)→4f7 (8S 7/2) emission line of Eu2+ in the UV range due to pressure-induced configurational crossover between the excited 4f65d1 and 4f7 energy levels in SrB 4 O 7 host. The peak centroid of the narrow 4f7 → 4f7 transition exhibits a significant red-shift (∼ -12.84 cm−1 GPa−1; 0.17 nm GPa−1) with simultaneous temperature independence of the line position (4.8·10−4 nm K−1). The pressure sensitivity of the proposed system is competitive to the so far well-established luminescent pressure sensors based on Al 2 O 3 :Cr3+ (ruby) and SrB 4 O 7 :Sm2+ with characteristic narrow line emission in the red range, and offers an alternative spectral range in parallel with an intensity enhancement at higher pressures. This novel pressure gauge may significantly improve the accuracy of the remote pressure measurements and open up new horizons for materials science research at even higher pressures. [Display omitted] [ABSTRACT FROM AUTHOR]