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The influence of activation as key parameter for oxygen sensing by luminescent metal–organic frameworks has been investigated and quantified for the archetype MOF‐76(Eu). Activation at different conditions (regarding temperature and solvent‐exchange for distinct vacuum pressure and heating time), shows an influence on the overall quenching, response time and cyclability due to different pore accessibility and surface area and therefore on the overall performance of the sensor. The optical sensing process is based on luminescence quenching, analyzed from high vacuum (10−7 bar) to ambient pressure by dosing oxygen from 0.01 bar to 1 bar. Strong influence of the different activation parameters is observed, as MOF‐76(Eu) activated at 50 °C shows limited quenching of the luminescence intensity within 30 min, while methanol‐exchange and subsequent activation at 250 °C leads to a quenching rate of 98.6 %. In addition, the sensor response occurs more than 1000 times faster within 0.2 s. These results correlate well with physisorption data, which reveal a significant change in porosity and surface area according to the degree of activation. For a better understanding of the involved processes, adsorption isotherms were recorded, surface areas determined and correlated to the photophysical parameters, including Stern‐Volmer kinetics and cycling experiments for the differently activated MOF sensors. [ABSTRACT FROM AUTHOR]

This study is focused on determining the refractive index as a crucial parameter for evaluating the intrinsic quantum yield and the ligand sensitisation efficiency in solid‐state trivalent lanthanide coordination compounds. For this, eight trivalent europium complexes with phenyl‐terpyridine ([EuX3(ptpy)(L)], X=Cl− or NO3−, ptpy=4′‐phenyl‐2,2′ : 6′,2′′‐terpyridine, L=H2O or other molecules) were examined. Their refractive indices were determined using the Becke lines test by immersing transparent material in a series of media with known refractive indices. Using the set of media presented here, determining crystalline materials′ refractive indices from 1.41 to 1.73 with a step of 0.01 is possible. Assessment of the refractive indices of the complexes mentioned above allowed a comprehensive analysis of their photophysical properties in the solid state. Moreover, this method can be extrapolated for other solid‐state materials, offering valuable insights in the broader field of photophysics. In addition to photoluminescence investigations, the compounds presented were characterised by single‐crystal X‐ray diffraction (SCXRD), powder X‐ray diffraction (PXRD), Hirschfeld surface area analysis, UV‐Vis reflectance spectroscopy, hydrolysis sensitivity analysis, and simultaneous thermogravimetry and differential thermal analysis coupled with mass‐spectrometry (STA‐MS). [ABSTRACT FROM AUTHOR]

Pressure dependent optical dioxygen sensing was studied by a comparison of six archetype metal–organic frameworks (MOFs: UiO-66(Zr), UiO-67(Zr), UiO-67(Zr)-bipy, MIL-68(In), MIL-100(In) and DUT-5(Al)) based on the quenching of the photoluminescence emission of the MOFs post-synthetically modified with Eu3+ in the pore systems. MOF-76(Eu) as an example of a luminescent LnMOF with Eu3+ ions as coordinative centers of the framework was included in the comparison. Pressure dependence was investigated starting with high vacuum (10−7 bar) to ambient pressure by quantitatively analyzing the response of the Eu3+ photoluminescence emission towards oxygen. The MOFs show fast response, leading to reversible "turn-off" and "turn-on" effects most prominent for Eu3+@MIL-68 directly observable by a luminescence emission quenching efficiency of 93.8% within 2 s. Intensity changes were already measured at oxygen pressures of 10−5 bar, indicating high sensitivity. Furthermore, the sensing process follows the Stern–Volmer relationship, although a certain pressure dependence also affects the kinetics especially in the low-pressure region, so that applying only Stern–Volmer is not valid over the whole pressure range, as the quenching rate increases with decreasing pressure. In addition, the process is reversible and robust, which was elaborated by multiple sorption/desorption studies including cycling over ten sensing cycles. Selectivity of the processes were evaluated for other atmospheric gases N2, CO2 indicating only minor quenching that still allows oxygen detection for a pO2 of 10−5 bar. Altogether, this work presents analysis-based proof on the validity of broad and rapid sensitive on-the-fly optical oxygen sensing with lanthanide-loaded MOFs. [ABSTRACT FROM AUTHOR]

A surfactant-assisted bottom-up synthesis route provides access to nanoscale metal–organic frameworks (nMOFs) that exploit size-dependent property advantages. This includes an increased surface-to-volume ratio, improved dispersibility and superior morphological properties by a narrow size distribution compared to the bulk analogues. Photophysical properties such as photoluminescence are also influenced by particle size, surfactant components and post-synthetic modification. The series of the related organic linkers (H2bdc, H2bpdc and H2bpydc) together with trivalent lanthanides (Ln3+ = Eu3+, Tb3+) in synthesis and post-synthetic modification together with surface-active agents (CTAB, PVP) were used to assemble luminescent nMOFs for three archetype MOFs: nLn3+-bdc, nDUT-5:Ln3+ and nMOF-253:Ln3+. Both, dispersibility and morphology benefit from the CTAB- and PVP-controlled bottom-up particle downsizing down to 35 nm. DLS confirms homogeneous, narrow particle size distributions down to ±5 nm, which is 21-times smaller than the bulk analogues. Moreover, excellent luminescence QYs of up to 78.1(3)% were determined for the Ln3+-containing nMOFs. Successful post-synthetic modification with trivalent lanthanide ions of nMOFs was accomplished showing an improved photoluminescence sensitization effect compared to the bulk MOFs and exhibiting increased Ln3+-to-linker emission intensity ratios. The amount and photophysical properties of surfactants encapsulating the nMOFs were further quantified by DTA/TG-MS and UV-Vis-DRS. Finally, this work aims to elaborate thoroughly on the previously mentioned properties of nMOFs by comparison with their bulk analogues. Since surfactants play a key role in this synthesis route, the pros and cons of this approach were also assessed concerning several nMOF features. [ABSTRACT FROM AUTHOR]

A new polymorphic modification of lanthanum sulfate was obtained by thermal dehydration of the respective nonahydrate. According to powder X-ray diffraction, it was established that β-La2(SO4)3 crystallized in the C2/c space group of the monoclinic system with the KTh2(PO4)3 structure type (a = 17.6923(9), b = 6.9102(4), c = 8.3990(5) Å, β = 100.321(3)°, and V = 1010.22(9) Å3). Temperature dependency studies of the unit cell parameters indicated almost zero expansion along the a direction in the temperature range of 300–450 K. Presumably, this occurred due to stretching of the [LaO9]n chains along the c direction, which occurred without a significant alteration in the layer thickness over the a direction. A systematic study of the formation and destruction processes of the lanthanum sulfates under heating was carried out. In particular, the decisive impact of the chemical composition and formation energy of compounds on the thermodynamic and kinetic parameters of the processes was established. DFT calculations showed β-La2(SO4)3 to be a dielectric material with a bandgap of more than 6.4 eV. The processing of β-La2(SO4)3 with the Kubelka–Munk function exhibited low values below 6.4 eV, which indicated a fundamental absorption edge above this energy that was consistent with LDA calculations. The Raman and infrared measurements of β-La2(SO4)3 were in accordance with the calculated spectra, indicating that the obtained crystal parameters represented a reliable structure. [ABSTRACT FROM AUTHOR]

We report the multi-step synthesis of the tetradentate 2-(naphthalen-2-yl)-5-[N,N-bis(2-pyridylmethyl)aminomethyl]-1,3,4-oxadiazole ligand (LTetra-ODA) along with its corresponding [FeII(LTetra-ODA)(NCBH3)2]·1.5CH3OH (C1) complex, which is the first mononuclear 1,3,4-oxadiazole based Fe(II) spin crossover (SCO) complex, and its zinc analogue [ZnII(LTetra-ODA)(NCBH3)2]·0.5H2O (C2). The spin transition is followed by variable temperature (VT-) X-ray crystallography of [Fe(LTetra-ODA)(NCBH3)2]·1.5CH3OH (C1) at 120 and 220 K. The magnetic susceptibility measurements on the bulk sample recorded from 2 to 300 K show that the complex exhibits a complete abrupt reversible spin transition with a T1/2 of 207 K. The loss of the lattice solvent methanol shifts the T1/2 slightly to around 210 K. The spin transition in solution for [Fe(LTetra-ODA)(NCBH3)2]·1.5CH3OH (C1) was followed using the VT-1H-NMR Evans method in CD3CN, with a T1/2 of 357 K. Solid state VT luminescence studies provide some preliminary evidence of interplay of luminescence and spin transition in the [Fe(LTetra-ODA)(NCBH3)2]·1.5CH3OH (C1) complex. [ABSTRACT FROM AUTHOR]

The possibility to precisely control reaction outcomes for pursuing materials with well-defined features is a main endeavor in the development of inorganic materials. Confining reactions within a confined space, such as nanoreactors, is an extremely promising methodology which allows to ensure control over the final properties of the material. An effective room temperature inverse miniemulsion approach for the controlled synthesis of undoped and Eu3+-doped calcium molybdate crystalline nanophosphors was developed. The advantages and the efficiency of confined space in terms of controlling nanoparticle features like size, shape, and functional properties are highlighted by systematically comparing miniemulsion products with calcium molybdate particles obtained without confinement from a typical batch synthesis. A relevant beneficial impact of space confinement by miniemulsion nanodroplets is observed on the control of size and shape of the final nanoparticles, resulting in 12 nm spherical nanoparticles with a narrow size distribution, as compared to the 58 nm irregularly shaped and aggregated particles from the batch approach (assessed by TEM analysis). Further considerable effects of the confined space for the miniemulsion samples are found on the doping effectiveness, leading to a more homogeneous distribution of the Eu3+ ions into the molybdate host matrix, without segregation (assessed by PXRD, XAS, and ICP-MS). These findings are finally related to the photoluminescence properties, which are evidenced to be closely dependent on the Eu3+ content for the miniemulsion samples, as an increase of the relative intensity of the direct f–f excitation and a shortening of the lifetime (from 0.901 ms for 1 at. % to 0.625 ms for 7 at. % samples) with increasing Eu3+ content are observed, whereas no relationship between these parameters and the Eu3+ content is evidenced for the batch samples. All these results are ascribed to the uniform and controlled crystallization occurring inside each miniemulsion nanodroplet, as opposed to the less controlled nucleation and growth for a classic nonconfined approach. [ABSTRACT FROM AUTHOR]

The redox reactions of various lanthanide metals with 3-(4-pyridyl)pyrazole (4-PyPzH) or 3-(3-pyridyl)pyrazole (3-PyPzH) ligands yield the 2D network ∞ 2 [Eu(4-PyPz)2(Py)2] containing divalent europium, the 3D frameworks ∞ 3 [Ln(4-PyPz)3] and ∞ 3 [Ln(3-PyPz)3] for trivalent cerium, praseodymium, neodymium, holmium, erbium, and thulium as well as ∞ 3 [La(4-PyPz)3], and the 2D networks ∞ 2 [Ln(4-PyPz)3(Py)] for trivalent cerium and thulium and ∞ 2 [Ln2(4-PyPz)6]·Py for trivalent ytterbium and lutetium. The 18 lanthanide coordination polymers were synthesized under solvothermal conditions in pyridine (Py), partly acting as a co-ligand for some networks. The compounds exhibit a variety of luminescence properties, including metal-centered 4f–4f/5d–4f emission in the visible and near-infrared spectral range, metal-to-ligand energy transfer, and ligand-centered fluorescence and phosphorescence. The anionic ligands 3-PyPz− and 4-PyPz− serve as suitable antennas for lanthanide-based luminescence in the visible and near-infrared range through effective sensitization followed by emission through intra–4f transitions of the trivalent thulium, holmium, praseodymium, erbium, and neodymium. ∞ 2 [Ce(4-PyPz)3(Py)], ∞ 3 [Ce(4-PyPz)3], and ∞ 3 [Ce(3-PyPz)3] exhibit strong degrees of reduction in the 5d excited states that differ in intensity compared to the ligand-based emission, resulting in a distinct emission ranging from pink to orange. The direct current magnetic studies show magnetic isolation of the lanthanide centers in the crystal lattice of ∞ 3 [Ln(3-PyPz)3], Ln = Dy, Ho, and Er. [ABSTRACT FROM AUTHOR]

Correct photoluminescence quantum yield (PLQY) determination in the solid state is vital for numerous application fields, such as photovoltaics, solid lighting or the development of phosphors. In order to increase the limited number of suitable standards for such determinations, two new Ln3+‐based complexes with 4′‐phenyl‐2,2′ : 6′,2"‐terpyridine γ‐[Ln4(OAc)12(ptpy)2] (1‐Eu with europium and 1‐Tb with terbium) are presented. The corresponding complexes show solid‐state QYs of 58(4) % and 46(3) %, respectively, exhibiting broadband absorption in the UV range from 380–200 nm. As Ln3+ ions in general exhibit narrow f‐f transitions, spectral regions with a broadness of 20–35 nm can be checked. Both complexes have suitable thermal stability, up to 270 °C, and are stable with respect to air and humidity, for 1‐Eu up to 75 % and for 1‐Tb up to 53 % relative humidity. These complexes are altogether suitable as standards to increase the reliability of PLQY determination and proposed to be used for a relative PLQY determination in the solid state. [ABSTRACT FROM AUTHOR]