Tunable 4f/5f Bimodal Emission in Europium-Incorporated Uranyl Coordination Polymers

Ratiometric fluoroprobe based on Eu-MOF@Tb3+ for detecting tetracycline hydrochloride in freshwater fish and its application in rapid visual detection

Tetracycline hydrochloride (TCH), a prevalent antibiotic in aquaculture for treating bacterial infections, poses challenges for on-site detection. This study employed the reversed-phase microemulsion method to synthesize a uniform nano metal-organic framework (MOF) material, europium-benzene-p-dicarboxylic acid (Eu-BDC), doped with Tb3+ to form a dual-emission fluorescence probe. By leveraging the combined a-photoinduced electron-transfer (a-PET) and inner filter effect (IFE) mechanisms, high-sensitivity TCH detection in Carassius auratus and Ruditapes philippinarum was achieved. The detection range for TCH is 0.380-75 μM, with a low limit of detection (LOD) at 0.115 μM. Upon TCH binding, Eu-BDC fluorescence rapidly decreased, while Tb3+ fluorescence remained constant, establishing a ratiometric fluorescence change. Investigation into the TCH quenching mechanism on Eu-BDC was conducted using time-dependent density functional theory (TD-DFT) calculations and fluorescence quenching kinetic equations, suggesting a mixed quenching mechanism. Furthermore, a novel photoelectric conversion fluorescence detection device (FL-2) was developed and evaluated in conjunction with high-performance liquid chromatography-diode-array detection (HPLC-DAD). This is the first dedicated fluorescence device for TCH detection, showcasing superior photoelectric conversion performance and stability that reduces experimental errors associated with smartphone photography methods, presenting a promising avenue for on-site rapid TCH detection.

Ultrastrong Electron-Phonon Coupling in Uranium-Organic Frameworks Leading to Inverse Luminescence Temperature Dependence

Electron-phonon interactions, crucial in condensed matter, are rarely seen in Metal-Organic Frameworks (MOFs). Detecting these interactions typically involves analyzing luminescence in lanthanide- or actinide-based compounds. Prior studies on Ln- and Ac-based MOFs at high temperatures revealed additional peaks, but these were too faint for thorough analysis. In our research, we fabricated a high-quality, crystalline uranium-based MOF (KIT-U-1) thin film using a layer-by-layer method. Under UV light, this film showed two distinct "hot bands," indicating a strong electron-phonon interaction. At 77 K, these bands were absent, but at 300 K, a new emission band appeared with half the intensity of the main luminescence. Surprisingly, a second hot band emerged above 320 K, deviating from previous findings in rare-earth compounds. We conducted a detailed ab-initio analysis employing time-dependent density functional theory to understand this unusual behaviour and to identify the lattice vibration responsible for the strong electron-phonon coupling. The KIT-U-1 film's hot-band emission was then utilized to create a highly sensitive, single-compound optical thermometer. This underscores the potential of high-quality MOF thin films in exploiting the unique luminescence of lanthanides and actinides for advanced applications.

Local Structure and Speciation-Driven UO22+ → Sm3+ Energy Transfer for Enhanced Luminescence in Li2B4O7

Herein, we report the uranyl sensitization of Sm3+ emissions in uranium-codoped Li2B4O7:Sm3+ phosphor. The uranyl speciation in codoped [Sm, U] LTB samples was determined by synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy that revealed two coordination shells for U(VI) ions with bond distances of U-Oax (∼1.81 Å) and U-Oeq (∼2.30 Å). EXAFS fitting suggested that the uranyl moiety is present as pentagonal bipyramids (UO7) and hexagonal bipyramids (UO8) with five and six equatorial oxygen ligands, respectively. The alteration of the local structure of Sm3+ from [SmO4] to [SmO7] polyhedra and the changes in the coordination number of equatorial oxygen for uranyl were observed with different codoping concentrations of Sm3+ and uranium. Density functional theory (DFT) calculations suggested the lowering of defect formation energy for Li vacancies on codoping of Sm and U. Hence, we proposed the increase of the equatorial coordination number of UO22+ on the increase in the lithium vacancies in LTB. In addition, DFT supported the feasibility of efficient energy transfer (ET) due to the overlap of uranium and Sm3+ excited state levels. The influence of the same on the spectral features and UO22+ → Sm3+ energy transfer was investigated by time-resolved photoluminescence (PL) studies. The ET efficiency from the UO22+ to Sm3+ was 70.5% in 0.5 mol % codoped [Sm, U] LTB samples. The correlation of EXAFS and luminescence properties indicated a red shift in vibronic features of uranyl emission with increase in the equatorial coordination of the uranyl moiety from five to six. Additionally, a higher probability of ET was observed for uranyl speciation as UO8 hexagonal bipyramids. Temperature-dependent emissions and decay profiles were collected under uranyl excitation to investigate the thermal dependence of ET. A high energy barrier (Ea ∼ 4027 cm-1) was evaluated for the thermal quenching of Sm3+ emissions. This work provides insights into the modulation of luminescence and ET efficiency via structural changes in uranyl and Sm local environment in LTB phosphor.

Integration of quantum dots with Zn2GeO4 nanoellipsoids to expand the dynamic detection range of uranyl ions in fluorescent test strips

Fluorescent colorimetric test strips normally have a narrow dynamic detection-range due to the limited responsive range from single responsive materials, which cannot meet the wide detection requirement in practical applications. Herein, we developed an approach to detect uranyl ions (UO₂²⁺) with a broad detection range using the synthesized ZnS:Mn quantum dots (QDs) modified Zn₂GeO₄ nanoellipsoids (Zn₂GeO₄ @ZnS:Mn NEs), containing two responsive materials with the opposite signal responses at different UO₂²⁺ concentrations. Specifically, a red to chocolate color change was observed at low analyte concentrations (0.01-100 μM) resulting from the photoinduced electron transfer effect from ZnS:Mn QDs to UO₂²⁺. A sequentially olive drab to green color change has been observed when further increasing the UO₂²⁺ concentration (100-1000 μM) as a result of the antenna effect between Zn₂GeO₄ nanoellipsoids and UO₂²⁺. In addition, a low-cost and portable fluorescent test strip has been further fabricated through embedding Zn₂GeO₄ @ZnS:Mn NEs on a microporous structure membrane, demonstrating a facile yet effective colorimetric response to UO₂²⁺ in lab water, lake water, and seawater with a wide dynamic range. Therefore, it is potentially attractive for real-time and on-site detection of UO₂²⁺ in sudden-onset situations.

Efficient Ce3+ → Tb3+ energy transfer pairs with thermal stability and internal quantum efficiency close to unity

The incorporation of Ce3+–Tb3+ pairs has been reported in the Ca3Lu2Si6O18 (CLSO) host for identifying a novel green-emitting material with extremely high internal quantum efficiency (close to unity) and excellent thermal stability.

Hydrothermal Syntheses of Uranium Oxide Hydrate Materials with Sm(III) Ions: pH-Driven Diversities in Structures and Morphologies and Sm-Doped Porous Uranium Oxides Derived from Their Thermal Decompositions

We report the hydrothermal syntheses of three uranyl oxide hydroxy-hydrate (UOH) materials containing Sm(III) ions (UOH-Sm) by controlling the solution pH and a new way to make Sm-doped porous uranium oxides with different U-to-Sm atomic ratios via their thermal decompositions. While layer-structured UOH-Sm phases with U-to-Sm atomic ratios of 1 (UOH-Sm1) and 4 (UOH-Sm2) were obtained from the reaction of schoepite and samarium nitrate with final solution pH values of over 4, similar reactions without pH adjustment with final solution pH values of less than 4 led to the formation of a uranyl oxide framework (UOF-Sm) with a U-to-Sm atomic ratio of 5.5. The crystal structure of compound UOF-Sm was revealed with synchrotron single-crystal X-ray diffraction and confirmed with transmission electron microscopy. The two-dimensional uranyl oxide hydroxide layers, similar to that for β-U₃O₈, are linked by double pentagonal uranyl polyhedra to form a three-dimensional framework with Sm(III) ions in the channels. Scanning electron microscopy characterization revealed nanoplate crystal morphologies for the two UOH-Sm phases, in contrast to the needle morphology for UOF-Sm. Subsequent thermal treatments led to the formation of Sm-doped uranium oxides, maintaining the original crystal shapes and U-to-Sm ratios but with nanopores. This work demonstrated that the hydrothermal synthesis conditions, especially fine-tuning of the solution pH, have a significant impact on the uranium hydrolysis, thus leading to well-defined products. This will facilitate the targeted syntheses of UOH phases with lanthanide (Ln) ions and explore the subsequent applications of these materials and Ln-doped porous uranium oxides as potential nuclear or functional materials.

3D Uranyl Organic Frameworks Supported by Rigid Octadentate Carboxylate Ligand: Synthesis, Structure Diversity, and Luminescence Properties

Seven three dimensional (3D) uranyl organic frameworks (UOFs), formulated as [NH₄ ][(UO₂ )₃ (HTTDS)(H₂ O)] (1), [(UO₂ )₄ (HTTDS)₂ ](HIM)₆ (2, IM=imidazole), [(UO₂ )₄ (TTDS)(H₂ O)₂ (Phen)₂ ] (3, Phen=1,10-phenanthroline), [Zn(H₂ O)₄ ]_0.5 [(UO₂ )₃ (HTTDS)(H₂ O)₄ ] (4), and {(UO₂ )₂ [Zn(H₂ O)₃ ]₂ (TTDS)} (5), {Zn(UO₂ )₂ (H₂ O)(Dib)_0.5 (HDib)(HTTDS)} (6, Dib=1,4-di(1H-imidazol-1-yl)benzene) and [Na]{(UO₂ )₄ [Cu₃ (u₃ -OH)(H₂ O)₇ ](TTDS)₂ } (7) have been hydrothermally prepared using a rigid octadentate carboxylate ligand, tetrakis(3,5-dicarboxyphenyl)silicon(H₈ TTDS). These UOFs have different 3D self-assembled structures as a function of co-ligands, structure-directing agents and transition metals. The structure of 1 has an infinite ribbon formed by the UO₇ pentagonal bipyramid bridged by carboxylate groups. With further introduction of auxiliary N-donor ligands, different structure of 2 and 3 are formed, in 2 the imidazole serves as space filler, while in 3 the Phen are bound to [UO₂ ]²⁺ units as co-ligands. The second metal centers were introduced in the syntheses of 4-7, and in all cases, they are part of the final structures, either as a counterion (4) or as a component of framework (5-7). Interesting, in 7, a rare polyoxometalate [Cu₃ (μ₃ -OH)O₇ (O₂ CR)₄ ] cluster was found in the structure. It acts as an inorganic building unit together with the dimer [(UO₂ )₂ (O₂ CR)₄ ] unit. Those uranyl carboxylates were sufficiently determined by single crystal X-ray diffraction, and their topological structures and luminescence properties were analyzed in detail.

Structural, spectroscopic, and computational evaluations of cation–cation and halogen bonding interactions in heterometallic uranyl hybrid materials

A route for systematically accessing the oxo atoms of the linear uranyl (UO₂²⁺) cation via cation–cation and halogen bonding interactions is detailed, and interaction strengths are probed via structural, vibrational, and computational means.

Introducing Bluish-Green Light-Emitting Diodes (OLEDs) and Tuning Their Color Intensity by Uranium Complexes: Synthesis, Characterization, and Photoluminescence Studies of 8-Hydroxyquinoline Complexes of Uranium

To improve our understanding of the chemistry of actinide complexes and to spur their development in the field of actinide markers, two new uranium complexes were synthesized using 8-hydroxyquinoline and 5,7-dichloro-8-hydroxyquinoline. The prepared complexes were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, ultraviolet-visible spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The impact of the electron-withdrawing group of the ligand on the photoluminescence spectra of the complexes in solution and in the solid state was scrutinized. The bandgap of the complexes was calculated using the density functional theory (DFT) method to investigate the effects of the electron-withdrawing groups on energy levels. The synthesized uranium complexes demonstrated appropriate levels of the lowest unoccupied molecular orbital energy, leading to favorable dye stability. The prepared uranium complexes showed blue fluorescent emission, and the sample with the most intense fluorescence was used to construct bluish-green organic light-emitting diodes using simple solution processing fabrication methods. Absorbance spectra, emission spectra, DFT-calculated energy levels, and comparisons of the fabricated organic light-emitting diodes indicated that the electron-withdrawing group was a key factor in photoluminescence behavior.

Fabrication of blue organic light-emitting diodes from novel uranium complexes: synthesis, characterization, and electroluminescence studies of uranium anthracene-9-carboxylate complexes

In this study, three uranium(vi) complexes, [UO2(C15H9O2)2(CH3CH2OH)2]·2CH3CH2OH (1), [U2O4(C15H9O2)2(CH3O)2(CH3OH)2]·2CH3OH (2), and [U2O4(C15H9O2)4(CH3OH)2]·2H2O (3), were prepared by reacting anthracene-9-carboxylic acid with uranyl acetate dihydrate using various ligand to uranyl acetate ratios in different solvents. The infrared and UV-Vis spectra along with elemental and thermal analyses showed the formation of mono- and dinuclear anthracene-9-carboxylate complexes of uranium. A 1 to 3 molar ratio of uranyl acetate to anthracene-9-carboxylic acid in ethanol resulted in the formation of the mononuclear complex 1, whereas a 1 to 2 and 1 to 3 molar ratio of uranyl acetate to anthracene-9-carboxylic acid in methanol produced the dinuclear complexes 2 and 3, respectively. Single-crystal structure determinations of 1, 2 and 3 revealed hexagonal bipyramidal geometries for the mononuclear uranium complex of 1 and a pentagonal geometry for the dinuclear uranium complexes of 2 and 3. The single-crystal structures of complexes 2 and 3 showed π-π interactions in contrast to complex 1. The strong π-π interactions in complex 2 and 3 lead to an enhanced photoluminescence intensity in comparison with 1 without π-π interaction. The optical properties of the prepared complexes are associated with the ligand-induced resonant system. The fluorescent uranium complex 1 that showed a blue emission upon excitation at 270 nm was used for the fabrication of a blue organic light-emitting diode (BOLED), an industrially important OLED, using a simple solution-process fabrication method.

The structural evolution and tunable photoluminescence of f-element bearing coordination polymers of the 2,4,6-tri-α-pyridyl-1,3,5-triazine ligand

An attempt at expanding the family of f-element bearing TPTZ coordination polymers has resulted in fifteen new complexes with topologies that evolved along the periodic table and tunable photoluminescence properties.

Sensing Uranyl(VI) Ions by Coordination and Energy Transfer to a Luminescent Europium(III) Complex

The release of uranyl(VI) is a hazardous environmental issue, with limited ways to monitor accumulation in situ. Here, we present a method for the detection of uranyl(VI) ions through the utilization of a unique fluorescence energy transfer process to europium(III). Our system displays the first example of a "turn-on" europium(III) emission process with a small, water-soluble lanthanide complex triggered by uranyl(VI) ions.

Bimetallic Uranyl Organic Frameworks Supported by Transition-Metal-Ion-Based Metalloligand Motifs: Synthesis, Structure Diversity, and Luminescence Properties

A bifunctional ligand, 2,2'-bipyridine-4,4'-dicarboxylic acid (H₂bpdc), has been used in the investigation of constructing bimetallic uranyl organic frameworks (UOFs). Seven novel uranyl-transition metal bimetallic coordination polymers, [(UO₂)Zn(bpdc)₂] _n (1), [Cd(UO₂)(bpdc)₂(H₂O)₂·2H₂O] _n (2), [Cu(UO₂)(bpdc)(SO₄)(H₂O)₃·2H₂O] _n (3), [CuCl(UO₂)(bpdc)(Hbpdc)(H₂O)₂·H₂O] _n (4), [Cu(UO₂)(bpdc)₂(H₂O)] _n (5), [Co₂(UO₂)₃(bpdc)₆] _n (6), and [Co₃(UO₂)₄(bpdc)₈(Hbpdc)(H₂O)₂] _n (7), have been successfully constructed through the assembly of various transition-metal salts, uranyl ions, and H₂bpdc ligands under hydrothermal conditions. UOFs 1, 5, 6, and 7 adopt three-dimensional (3D) frameworks with different architectures; UOFs 2 and 3 exhibit two-dimensional (2D) wavelike and stairlike layers, respectively, while UOF 4 is a one-dimensional (1D) chain assembly. These UOFs include a wide range of dimensionalities (1D-3D), interpenetrated frameworks, and cation-cation interaction species, suggesting that anion-dependent structure regulation based on the metalloligand [M(bpdc) _m] ^n- motifs, the coordination modes of the metal centers and bpdc^2- ligands, along with the reaction temperature, has a remarkable influence on the formation of bimetallic UOFs, which could be a representative system for the structural modulation of UOFs with various dimensionalities and structures. Furthermore, the thermal stability and luminescent properties of compounds 1, 3, and 6 are also investigated.

Nine isomorphous lanthanide–uranyl f–f bimetallic materials with 2-thiophenecarboxylic acid and terpyridine: structure and concomitant luminescent properties

Concomitant and semi-selective uranyl and lanthanide luminescence observed within a series of f–f bimetallic molecular materials (UO₂²⁺/Ln = Pr–Er).

Anionic uranyl oxyfluorides as a bifunctional platform for highly selective ion-exchange and photocatalytic degradation of organic dyes

Anionic uranium oxyfluorides with tunable open-volumes were synthesized and they exhibit selective ion-exchange and photocatalytic properties toward methylene blue.