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

Poly[diethyl­enetriammonium [aquadi-μ2-sulfato-sulfatocerium(III)]]

A new organically templated open-framework cerium sulfate, {(C4H16N3)[Ce(SO4)3(H2O)]}n, was hydro­thermally synthesized. The CeIII cation is nine-coordinated by nine O atoms, including one water mol­ecule. Two of the SO4 groups afford one monodentate and bidentate linkages as the bridge to connect adjacent CeIII cations, while the third SO4 group attaches the CeIII cation in a bidentate mode. The crystal structure consists of layers composed of eight-membered-ring networks formed by four CeO9 polyhedra and four SO4 tetra­hedra. The triply protonated diethyl­enetriamine cations are located between adjacent layers and connect the layers via hydrogen bonds

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

K2LaCl5

The ternary title compound, dipotassium lanthanum penta­chloride, K2LaCl5, is isotypic with Y2HfS5 and various ternary rare-earth metal(III) halides with the general formula A 2 MX 5 (A = NH4, InI, Na–Cs; M = La–Dy; X = Cl–I). The La3+ cations and three of the four symmetry-independent chloride anions are located on a crystallographic mirror plane. The La3+ cations are surrounded by seven chloride anions, each in the shape of a monocapped trigonal prism, whereas the coordination spheres of the K+ cations exhibit one more cap. Three of the four independent chloride anions reside in a fivefold cationic coordination, leading to distorted square pyramids. The fourth chloride anion has only four cationic neighbours, forming no specific polyhedron

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

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

Na3DyCl6

Single crystals of the title compound, tris­odium hexa­chloridodysprosate, Na3DyCl6, were obtained as a by-product of synthesis using dysprosium(III) chloride and sodium chloride among others. The monoclinic structure with its typical β angle close to 90° [90.823 (4)°] is isotypic with the mineral cryolite (Na3AlF6) and the high-temperature structure of the Na3 MCl6 series, with M = Eu–Lu, Y and Sc. The isolated, almost perfect [DyCl6]3− octa­hedra are inter­connected via two crystallographically different Na+ cations: while one Na+ resides on centres of symmetry (as well as Dy3+) and also builds almost perfect, isolated [NaCl6]5− octa­hedra, the other Na+ is surrounded by seven chloride anions forming a distorted [NaCl7]6− trigonal prism with just one cap as close secondary contact

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

Poly[diethyl­enetriammonium [aquadi-μ2-sulfato-sulfatolanthanum(III)]]

In the title compound, {(C4H16N3)[La(SO4)3(H2O)]}n, the La atom adopts an irregular LaO9 coordination geometry, including one bonded water mol­ecule. The three sulfate groups adopt both monodentate and bidentate coordination to the metal ions. Two of the sulfate groups serve as bridges in the (100) and (010) directions, yielding infinite sheets, whereas the third is pendant to one La3+ cation. The protonated organic species inter­acts with the layers by way of N—H⋯O hydrogen bonds, and O–H⋯O hydrogen bonds involving aqua ligands also occur

Unique thermodynamic relationships for ΔfHo and ΔfGo for crystalline inorganic salts. I, Predicting the possible existence and synthesis of Na2SO2 and Na2SeO2

The concept that equates oxidation and pressure has been successfully utilized in explaining the structural changes observed in the M2S subnets of M2SOx (x = 3, 4) compounds (M = Na, K) when compared with the structures (room- and high-pressure phases) of their parent M2S 'alloy' [Martinez-Cruz et al. (1994), J. Solid State Chem. 110, 397-398; Vegas (2000), Crystallogr. Rev. 7, 189-286; Vegas et al. (2002), Solid State Sci. 4, 1077-1081]. These structural changes suggest that if M2SO2 would exist, its cation array might well have an anti-CaF2 structure. On the other hand, in an analysis of the existing thermodynamic data for M2S, M2SO3 and M2SO4 we have identified, and report, a series of unique linear relationships between the known Delta H-f(o) and Delta(f)G(o) values of the alkali metal (M) sulfide (x = 0) and their oxyanion salts M2SOx (x = 3 and 4), and the similarly between M2S2 disulfide (x = 0) and disulfur oxyanion salts M2S2Ox (x = 3, 4, 5, 6 and 7) and the number of O atoms in their anions x. These linear relationships appear to be unique to sulfur compounds and their inherent simplicity permits us to interpolate thermochemical data (Delta H-f(o)) for as yet unprepared compounds, M2SO (x = 1) and M2SO2 (x = 2). The excellent linearity indicates the reliability of the interpolated data. Making use of the volume-based thermodynamics, VBT [Jenkins et al. (1999), Inorg. Chem. 38, 3609-3620], the values of the absolute entropies were estimated and from them, the standard Delta S-f(o) values, and then the Delta(f)G(o) values of the salts. A tentative proposal is made for the synthesis of Na2SO2 which involves bubbling SO2 through a solution of sodium in liquid ammonia. For this attractive thermodynamic route, we estimate Delta G(o) to be approximately -500 kJ mol(-1). However, examination of the stability of Na2SO2 raises doubts and Na2SeO2 emerges as a more attractive target material. Its synthesis is likely to be easier and it is stable to disproportionation into Na2S and Na2SeO4. Like Na2SO2, this compound is predicted to have an anti-CaF2 Na2Se subnet