Molecule-like Eu3+-dimers embedded in an extended system exhibit unique photoluminescence properties

Near-Infrared Ratiometric Luminescent Thermometer Based on a New Lanthanide Silicate

A new lanthanide silicate system, Na₂ K[Ln₃ Si₆ O₁₈ ] (Ln=Lu, Yb/ Er, Lu/Eu, or Lu/Yb/Er), comprising microcrystals embedded in an amorphous siliceous matrix, obtained by sintering at 1373 K a Na₃ K[Ln₂ Si₆ O₁₇ ]⋅3 H₂ O nano-crystalline precursor, is reported. The crystal structure of these lanthanide silicates was solved from high-resolution synchrotron power X-ray diffraction data collected at 110 K, and further supported by ²⁹ Si MAS NMR and Eu³⁺ luminescence. The materials crystallize in the Pī triclinic centrosymmetric space group, exhibiting a dense framework consisting of hexameric [Si₆ O₁₈ ]^12- cyclosilicate units, and chains of two distinct {LnO₆ } octahedra. Na₂ K[(Lu_0.75 Yb_0.20 Er_0.05 )₃ Si₆ O₁₈ ] is the first example of a lanthanide silicate operative as a near-infrared ratiometric luminescent thermometer, with good sensitivity at cryogenic temperatures (<100 K). Upon excitation at 903 nm, the ratio between the ² F_7/2 →² F_5/2 (Yb³⁺ ) and ⁴ I_13/2 →⁴ I_15/2 (Er³⁺ ) emissions was used for sensing temperature in the 12-450 K range, reaching a maximum thermal sensitivity of 2.6 % K^-1 at 26.8 K.

Tunable Luminescent Heterometallic Zn2Ln2 Edge-Defective Molecular Cubane with Stimuli-Responsive Properties

Heterometallic Zn₂Ln₂ [Ln = Gd (1), Eu (2), Tb (3), Dy (4)] discrete molecules with edge-defective cubane structure are assembled from a multifunctional fluorescent conjugate ligand and Ln^III/Zn^II mixed-metal ions; they exhibit the tunable luminescence, including ligand-based yellow-green light emission for 1 and 4 and lanthanide-center emission for 2 and 3. The multiple stimuli-responsive photoluminescences were investigated to show a two-step thermal-responsive luminescence increase in the intensity upon cooling and piezochromic luminescence.

Single-crystal X-ray diffraction study of Cs2Er[Si6O14]F and Cs2Er[Si4O10]F

Single-crystal growth experiments in the system CsF-Er2O3-SiO2 resulted in the simultaneous crystallization of two chemically related compounds within the same run: Cs2Er[Si6O14]F (phase I) and Cs2Er[Si4O10]F (phase II). They represent the first examples for cesium erbium silicates containing fluorine. Basic crystallographic data are – phase I: space group Cmca, a=17.2556(6) Å, b=24.6565(7) Å, c=14.4735(5) Å, V=6157.9(3) Å3, Z=16; phase II: space group Pnma, a=22.3748(7) Å, b=8.8390(2) Å, c=11.9710(4) Å, V=2367.5(1) Å3, Z=8. The structures were determined by direct methods and refined to residuals of R(|F|)=0.0229 for 2920 (phase I) and 0.0231 for 2314 (phase II) independent observed reflections with I>2σ(I). The structure of phase I represents a previously unknown structure type with a three dimensional tetrahedral framework consisting of Q3 and Q4 groups in the ratio 2:1. Basic building units of the network are unbranched sechser single-chains running parallel to [001]. The network can be conveniently built up from the condensation of tetrahedral layers parallel to (010) or (100), respectively. The crystal structure of phase II can be classified as a tubular or columnar chain silicate indicating that the backbones of the structure are multiple chains of silicate tetrahedra. This structure is isotypic to a Cs2Y[Si4O10]F, a compound that has been characterized previously. Alternatively, both compounds can be described as mixed octahedral-tetrahedral frameworks, which can be classified according to their polyhedral microensembles. A topological analysis of both nets is presented.

Novel open-framework europium silicates prepared under high-temperature and high-pressure conditions

Two new europium silicates, Na15Eu3Si12O36 (denoted as 1) and K2EuSi4O10F (denoted as 2), were successfully synthesized under high-temperature and high-pressure conditions, and structurally characterized by single-crystal and powder X-ray diffraction (XRD). The single-crystal XRD analysis of 1 reveals that its structure is based on [Si6O18]n(12n-) cyclosilicate anions that are built from six SiO4 tetrahedra sharing two of their four O corners with each other. Such [Si6O18]n(12n-) cyclosilicate anions are linked via EuO6 octahedra to form a three-dimensional (3D) framework containing 6-membered ring channels delimited by the SiO4 tetrahedra and EuO6 octahedra along the [010] direction. The structure of 2 consists of infinite tubular chains of corner-sharing SiO4 tetrahedra, which are further linked together via corner sharing O atoms by infinite chains of EuO4F2 octahedra forming a 3-D framework that contains 8-ring and 6-ring channels along the [010] direction. The photoluminescence properties of 1 and 2 were also investigated.

Enhancing multiphoton upconversion through energy clustering at sublattice level

The applications of lanthanide-doped upconversion nanocrystals in biological imaging, photonics, photovoltaics and therapeutics have fuelled a growing demand for rational control over the emission profiles of the nanocrystals. A common strategy for tuning upconversion luminescence is to control the doping concentration of lanthanide ions. However, the phenomenon of concentration quenching of the excited state at high doping levels poses a significant constraint. Thus, the lanthanide ions have to be stringently kept at relatively low concentrations to minimize luminescence quenching. Here we describe a new class of upconversion nanocrystals adopting an orthorhombic crystallographic structure in which the lanthanide ions are distributed in arrays of tetrad clusters. Importantly, this unique arrangement enables the preservation of excitation energy within the sublattice domain and effectively minimizes the migration of excitation energy to defects, even in stoichiometric compounds with a high Yb(3+) content (calculated as 98 mol%). This allows us to generate an unusual four-photon-promoted violet upconversion emission from Er(3+) with an intensity that is more than eight times higher than previously reported. Our results highlight that the approach to enhancing upconversion through energy clustering at the sublattice level may provide new opportunities for light-triggered biological reactions and photodynamic therapy.

Unusual photoluminescence properties of the 3D mixed-lanthanide–organic frameworks induced by dimeric structures: a theoretical and experimental approach

Experimental and theoretical investigation of the 3D Ln-MOFs that present singular spectral signature.

Solvothermal synthesis, crystal structure, and properties of lanthanide-organic frameworks based on thiophene-2,5-dicarboxylic acid

A series of lanthanide-organic framework coordination polymers, {[La(2)(TDC)(2)(NO(3))(H(2)O)(4)](OH)·5H(2)O}(n) (1) and [Ln(TDC)(NO(3))(H(2)O)](n) (TDC = thiophene- 2, 5- dicarboxylic acid; Ln = Nd(2), Sm(3), Eu(4), Gd(5), Tb(6), Dy(7), Ho(8), Er(9), Yb(10)) have been synthesized by solvothermal reaction and characterized by elemental analysis, FT-IR, TG analysis, single-crystal X-ray diffraction and power X-ray diffraction. The single-crystal X-ray diffraction analysis results show that 1 displays a 3-D porous framework with (3,7)-connected {4(10).6(11)}{4(3)} topology. The compounds 2-10 crystallized in the same P2(1)/c space group and exhibits a (3,6)-connected {4.6(2)}(2){4(2).6(10).8(3)} topology, Right-handed and left-handed helical chains coexist in the 2-D layer structure. The luminescence properties of 2-10 and the magnetic properties of 5,7,8,9 were investigated.

New RE microporous heteropolyhedral silicates containing 41516182tetrahedral sheets

Four heteropolyhedral microporous silicates,A3RESi6O15·2.25H2O, crystallizing in theCmm2 space group and based on 41516182tetrahedral sheets [A3= Na2.74K0.26, RE = Ce, abbreviated as TR05; TR06:A3= Na2.72K0.28, RE = La; TR07:A3= Na3, RE = La; TR08:A3= Na2.74(H3O)0.26, RE = La0.68Eu0.32] have been hydrothermally synthesized in Teflon-lined autoclaves at 503 K and structurally characterized using X-ray diffraction single-crystal data. Except for TR05, diffraction data have been collected on {001} twins by merohedry. The four structures are isotypic and based on strongly corrugated 41516182silicate sheets interconnected along [010] by seven-coordinated RE polyhedra to form a microporous heteropolyhedral framework. The framework is crossed by three systems of ellipsoidal channels that host H2O molecules and alkaline ions. The channels run either parallel or perpendicular to the silicate sheets; the largest effective channel width is 4.7 × 2 Å. In TR08 some (H3O)+replaces alkalis. Although the H atoms have not been localized, the configuration of the hydrogen bonding has been deduced from bond lengths and angles.