Magnetism and Afterglow United: Synthesis of Novel Double Core‐Shell Eu2+^{2+}‐doped Bifunctional Nanoparticles

Afterglow–magnetic nanoparticles (NPs) offer enormous potential for bioimaging applications, as they can be manipulated by a magnetic field, as well as emitting light after irradiation with an excitation source, thus distinguishing themselves from fluorescent living cells. In this work, a novel double core–shell strategy is presented, uniting co‐precipitation with combustion synthesis routes to combine an Fe$_{3}$O$_{4}$ magnetic core (≈15 nm) with an afterglow SrAl$_{2}$O$_{4}$:Eu$^{2+}$,Dy$^{3+}$ outer coat (≈10 nm), and applying a SiO$_{2}$ protective middle layer (≈16 nm) to reduce the luminescence quenching caused by the Fe core ions. The resulting Fe$_{3}$O$_{4}$@SiO$_{2}$@SrAl$_{2}$O$_{4}$:Eu$^{2+}$,Dy$^{3+}$ NPs emit green light attributed to the 4f$^{6}$5d$^{1}$→4f$^{7}$ ($^{8}$S$_{7/2}$) transition of Eu$^{2+}$ under UV radiation and for a few seconds afterwards. This bifunctional nanocomposite can potentially be applied for the detection and separation of cells or diagnostically relevant molecules

Photoluminescence properties of Yb²⁺ ions doped in the perovskites CsCaX₃ and CsSrX₃ (X = Cl, Br, and I) – a comparative study

The Yb²⁺-doped perovskite derivatives CsMX₃ (M = Ca and Sr; X = Cl, Br, and I) are ideal systems for obtaining a detailed insight into the structure–luminescence relationship of divalent lanthanides. The investigation of the respective photoluminescence properties yielded two emission bands in the violet and blue spectral range for all compounds, which are assigned to the spin-allowed and spin- forbidden 5d–4f transitions, respectively. The impact on their energetic positions is dependent on both the covalency of the Yb²⁺-halide bond and the corresponding bond length in agreement with expectations. The excitation spectra provide a detailed fine structure at low temperatures and can be partly interpreted separating the 4f¹³ core from the 5d electron in the excited state. The local crystal field in CsSrI₃:Yb²⁺ provides a special case due to the trigonal distortion induced by the crystal structure that is clearly evident in the luminescence features of Yb²⁺. The structure–property relationship of several spectroscopic key quantities of Yb²⁺ in this series of halides is analyzed in detail and parallels the properties of Eu²⁺ ions doped in the given perovskites

Syntheses, Crystal Structure and Physico-Chemical Studies of Sodium and Potassium Alcoholates Bearing Thienyl Substituents and their Derived Luminescent Sm(III) Alkoxides

International audienceThe synthesis, structural characterization, electrochemistry and luminescence properties of a series of alkali metal alcoholates and Sm(III) alkoxides with thiophene−based−OR substituents are presented. The alkali metal alcoholates 7-15 have been obtained by deprotonation of the carbinol with NaH or KH. Their molecular structures consist of tetranuclear alkali metal alcoholates with a distorted cubane−like M4O4 core (X-ray structure analyses). Each alkali metal is surrounded by three carbinolate ligands and (depending on the derivative) by additional tetrahydrofuran molecules. The mononuclear samarium alkoxides {Sm[OC(C4H3S)3]3(thf)3} * thf (16) and {Sm[OC(C16H13S)]3(thf)3} * thf (17) were synthesized by the salt metathesis reactions between {[KOC(C4H3S)3]4(thf)2} * thf (7), [NaOC(C4H3S)3]4(thf)2 (8) or {[KOC(C16H13S)]4(thf)3} * ½ thf (11), respectively, and SmCl3 in thf solution. The molecular structures of these air−sensitive base adducts have been determined by single−crystal X−ray crystallography and reveal an approximately octahedral coordination sphere around the samarium metal centres with three methoxido ligands and three facially arranged thf molecules. The electrochemical properties are essentially dominated by the oxidation of the thienyl units. The emission spectra of the carbinols and their derived potassium and sodium compounds display broad bands attributed to the π*→π transitions of the aromatic ligands. Luminescence studies performed on complexes 16 and 17 reveal the typical f−f transitions of the Sm(III) ion. The photophysical data suggest that an energy transfer from the ligand to the metal centre operates

A ligand field theory-based methodology for the characterization of the Eu²⁺ [Xe]4f⁶5d¹ excited states in solid state compounds

The theoretical rationalization of the open-shell 4f and 5d configuration of Eu²⁺ is by far not trivial because it involves a non-standard version of ligand field theory, based on a two-shell Hamiltonian. Here we present our methodology based on ligand field theory, taking the system CsCaBr₃:Eu²⁺ as a case study with an octahedral coordination sphere of Eu²⁺. The ligand field, interelectronic and spin-orbit coupling parameters are deduced from experimental data. The assignment of the transitions to the corresponding irreducible representations of the double group was performed together with the intensity modelling resulting in an excellent match to the experimental spectra

Prospecting lighting applications with ligand field tools and density functional theory: a first-principles account of the 4f⁷–4f⁶5d¹ Luminescence of CsMgBr₃:Eu²⁺

The most efficient way to provide domestic lighting nowadays is by light-emitting diodes (LEDs) technology combined with phosphors shifting the blue and UV emission toward a desirable sunlight spectrum. A route in the quest for warm-white light goes toward the discovery and tuning of the lanthanide-based phosphors, a difficult task, in experimental and technical respects. A proper theoretical approach, which is also complicated at the conceptual level and in computing efforts, is however a profitable complement, offering valuable structure–property rationale as a guideline in the search of the best materials. The Eu²⁺-based systems are the prototypes for ideal phosphors, exhibiting a wide range of visible light emission. Using the ligand field concepts in conjunction with density functional theory (DFT), conducted in nonroutine manner, we develop a nonempirical procedure to investigate the 4f⁷–4f⁶5d¹ luminescence of Eu²⁺ in the environment of arbitrary ligands, applied here on the CsMgBr₃:Eu²⁺-doped material. Providing a salient methodology for the extraction of the relevant ligand field and related parameters from DFT calculations and encompassing the bottleneck of handling large matrices in a model Hamiltonian based on the whole set of 33 462 states, we obtained an excellent match with the experimental spectrum, from first-principles, without any fit or adjustment. This proves that the ligand field density functional theory methodology can be used in the assessment of new materials and rational property design

Green Synthesis of A2SiF6 (A=Li-Cs) Nanoparticles using Ionic Liquids as Solvents and as Fluorine Sources: A Simple Approach without HF

International audienceIn 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+

Raman-Microspectroscopy for the Detection of Spoilage Bacteria

Raman-microspectroscopy was used for the non-destructive characterization and differentiation of six different meat spoilage associated microorganisms, namely Brochothrix thermosphacta DSM 20171, Micrococcus luteus, Pseudomonas fluorescens DSM 4358, Escherichia coli Top10 and K12 and Pseudomonas fluorescens DSM 50090. To evaluate and classify the Raman-spectroscopic data at species and strain level an adequate preprocessing and subsequent principal component analysis was used. The same procedure was extended to an independent test data set, which could be successfully assigned to the correct bacterial species and even to the right strain. The evaluation was not only successful in differentiation of gram-positive and gram-negative bacteria but also the discrimination between the different bacterial species and strains was possible. This means that the training data set, the preprocessing method and the evaluation of the data lead to a robust principal component analysis. Even the correct assignment of unknown samples is possible. The results show that Raman-microspectroscopy in combination with an appropriate chemometric treatment can be a good tool for a rapid examination and classification of microbial cultures

Impact of 1,10-Phenanthroline-Induced Intermediate Valence on the Luminesence of Divalent Europium Halides

Starting from EuX2 (X = Cl, Br, I), we systematically investigated a variety of divalent europium complexes containing bidentate 1,10-phenanthroline (Phen) ligands. Depending on the Eu/Phen ratio, mono-, di-, and polynuclear complexes are formed, with the latter yielding one-dimensional infinity 1[EuBr2(phen)] chains. Seven new divalent europium complexes, [Eu(phen)4(H2O)]Br2 center dot 2MeCN, [Eu(phen)4]I2 center dot 1.7Tol, [EuBr(phen)3]2Br2 center dot 4MeCN, [EuCl2(phen)2]2 center dot 2MeCN, [EuBr2(phen)2]2, [EuI2(phen)2]2, and [EuBr2(phen)]x, are presented in this work. All species show remarkable optical properties based on a partial electron transfer from the EuII center to the Phen ligand. The photophysical characterization is further supported by electrochemistry studies in order to describe the intermediate valence of the Eu center