Eu3+ doped ZnAl layered double hydroxides as calibrationless, fluorescent sensors for carbonate.

The photoluminescence properties (PL) of Eu3+ hosted in the hydroxide layers of layered double hydroxides (LDHs) enables calibrationless quantification of anions in the interlayers. The concept is demonstrated during the nitrate-to-carbonate ion exchange in Zn2+/Al3+/Eu3+ LDHs and can be implemented as a remote optical sensor to detect intrusion of anions such as Cl- or CO32-.

Mesostructuring layered materials: self-supported mesoporous layered double hydroxide nanotubes.

Synthesis of layered materials exhibiting hierarchical porosity remains challenging, but nevertheless worthwhile because it turns such solids into functional materials with high specific surface area. Using a soft-templating strategy in combination with the incorporation of 8-fold coordinated Eu3+, self-assembly of self-supported layered double hydroxide (LDH) nanotubes has been achieved. Heteromorphic equimolar substitution of Al3+ by Eu3+ in Zn2+/Al3+ LDH solids intercalated with 1,3,5-benzenetricarboxylate anions (BTC) assists precipitation of the double hydroxide layers onto the convex surface of Pluronic® P-123 worm-like micelles, yielding multilayer cylinders of BTC-intercalated LDHs. Removal of the micellar template is easily achieved by liquid extraction with methanol, yielding a network of interconnected, well-defined, self-supported, multi-walled, hollow cylindrical nanotubes. Removal of Eu3+ from the synthesis disables formation of the nanotubular morphology, but still yields LDHs containing a network of embedded mesopores, resulting in a specific surface area that is 5-fold higher as compared to standard LDHs.

A class of novel luminescent layered double hydroxide nanotubes.

Herein, we report a class of novel lanthanide-doped self-supported layered double hydroxide (LDH) nanotubes featuring a combination of micro- and mesoporosity. The synthesis of the nanotubes has been achieved by a soft-templating strategy. Incorporation of La3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+ or Tb3+ in the LDHs assisted the self-assembly of the double hydroxide layers onto the surface of Pluronic P-123 worm-like micelles, enabling the formation of the nanotubes. Removal of the micellar template provides accessibility to the mesopores, yielding a network of hollow cylindrical nanotubes with internal diameter of about 10 nm. An antenna molecule (benzene-1,3,5-tricarboxylate, BTC) is hosted in their 1-nanometre-wide micropores. Upon UV excitation, the nanotubes emit light in a set of wavelengths ranging from the ultraviolet to the infrared.

Coordination of Eu3+ Activators in ZnAlEu Layered Double Hydroxides Intercalated by Isophthalate and Nitrilotriacetate.

Luminescent layered double hydroxides (LDH) intercalated by isophthalate (ISO) and nitrilotriacetate (NTA) have been synthesized and characterized by powder X-ray diffraction (PXRD), extended X-ray absorption fine structure (EXAFS), elemental analysis (ICP-OES and CHN), and photoluminescence spectroscopy. While PXRD shows the successful formation of ZnAlEu LDHs, EXAFS reveals that the Eu activators are hosted in the hydroxide layers with an eightfold, oxygen-rich coordination, distinct from the sixfold coordination expected for the octahedral sites of metal cations in LDHs. This kind of coordination should locally distort the brucite-like layers. Additionally, the intercalation of ISO and NTA in the LDHs is shown to change the coordination environment around Eu compared to nitrate-intercalated ZnAlEu LDHs, which suggests that these anions directly interact with the Eu centers and/or strongly affect their coordination geometry. Finally, from the photoluminescence results, analyzed based on the Judd-Ofelt theory, it is determined that Eu is most likely in an environment with no inversion symmetry.

Odd-Even Effect on Luminescence Properties of Europium Aliphatic Dicarboxylate Complexes.

The odd-even effect in luminescent [Eu2 (L)3 (H2 O)x ]⋅y(H2 O) complexes with aliphatic dicarboxylate ligands (L: OXA, MAL, SUC, GLU, ADP, PIM, SUB, AZL, SEB, UND, and DOD, where x=2-6 and y=0-4), prepared by the precipitation method, was observed for the first time in lanthanide compounds. The final dehydration temperatures of the Eu3+ complexes show a zigzag pattern as a function of the carbon chain length of the dicarboxylate ligands, leading to the so-called odd-even effect. The FTIR data confirm the ligand-metal coordination via the mixed mode of bridge-chelate coordination, except for the Eu3+ -oxalate complex. XRD results indicate that the highly crystalline materials belong to the monoclinic system. The odd-even effect on the 4 f-4 f luminescence intensity parameters (Ω2 and Ω4 ) is explained by using an extension of the dynamic coupling mechanism, herein named the ghost-atom model. In this method, the long-range polarizabilities ( α* ) were simulated by a ghost atom located at the middle of each ligand chain. The values of α* were estimated using the localized molecular orbital approach. The emission intrinsic quantum yield ( QLnLn ) of the Eu3+ complexes also presented an the odd-even effect, successfully explained in terms of the zigzag behavior shown by the Ω2 and Ω4 intensity parameters. Luminescence quenching due to water molecules in the first coordination sphere is also discussed and rationalized.

Hierarchical self-supported ZnAlEu LDH nanotubes hosting luminescent CdTe quantum dots.

Self-supported oligo-layered ZnAlEu LDH nanotubes (∅ 20 nm) self-assemble upon controlled hydrolysis of the metal ions (Zn2+, Al3+, Eu3+) in the presence of 1,3,5-benzenetricarboxylate anions and non-ionic worm-like micelles. Their high surface area and easily accessible cylindrical mesopores (175 m2 g-1; 0.75 cm3 g-1) facilitate interaction with 5 nm CdTe quantum dots, enhancing the overall luminescence behavior.

Highly-sensitive Eu(3+) ratiometric thermometers based on excited state absorption with predictable calibration.

Temperature measurements ranging from a few degrees to a few hundreds of Kelvin are of great interest in the fields of nanomedicine and nanotechnology. Here, we report a new ratiometric luminescent thermometer using thermally excited state absorption of the Eu(3+) ion. The thermometer is based on the simple Eu(3+) energy level structure and can operate between 180 and 323 K with a relative sensitivity ranging from 0.7 to 1.7% K(-1). The thermometric parameter is defined as the ratio between the emission intensities of the (5)D0 → (7)F4 transition when the (5)D0 emitting level is excited through the (7)F2 (physiological range) or (7)F1 (down to 180 K) level. Nano and microcrystals of Y2O3:Eu(3+) were chosen as a proof of concept of the operational principles in which both excitation and detection are within the first biological transparent window. A novel and of paramount importance aspect is that the calibration factor can be calculated from the Eu(3+) emission spectrum avoiding the need for new calibration procedures whenever the thermometer operates in different media.