Potential and limitations of rare-earth luminescence in inverse opals

Inverse opals exhibiting strong photonic effects can cooperate with luminescent materials imbedded in their voids. While this has been demonstrated for dye molecules in the past, inspection of the literature reveals only few experiments on the potential of rare earths in this context. The efforts described focus on the spectral and spatial modification of emissive properties, whereas we here pursue the study of corresponding absorption properties. However, arbitrary incorporation of the luminescent species disturbs the photonic effects, therefore, principal preparative efforts need to be conducted to preserve both, the photonic properties of the opaline hosts and the luminescence efficiency of the guests. In this paper, we describe issues regarding the morphology and efficiency of inverse opal-incorporated rare-earth fluorides and oxifluorides and present an interior coating method for efficiency improvement. In addition, we were in this context, able to demonstrate the feasibility of energy transfer from Tb³⁺ modified host walls to Eu³⁺ guest species.     

Spectroscopic properties of lanthanoid benzene carboxylates in the solid state: Part 2. Polar substituted benzoates

Europium and terbium complexes of ortho, meta and para substituted benzoate ligands including nitrobenzoate (NBA), aminobenzoate (ABA), hydroxybenzoate (OHBA) and methoxybenzoate (MeOBA) have been synthesised by metathesis reactions, carried out in aqueous media. The complexes were characterised by elemental, compositional and structural investigations, including microanalysis, EDTA titrations, differential thermal analysis, infra red spectroscopy, X-ray powder diffraction and single crystal structural analyses. Besides this, strong emphasis was on the determination of the optoelectronic properties of the compounds in the solid state. In this regard, reflectance, excitation and emission spectra were recorded. From these, the emission and excitation efficiencies were determined. The relative intensities as well as the splitting patterns of the ⁵D₀ → ⁷F_J transitions in the europium emission spectra are discussed.     

Rare-earth ions in porous matrices

Initially motivated by the commercial need for cheaper and environmentally friendly luminescent materials for application in fluorescent lamps and cathode ray tubes, the search for new matrices for optically active species has penetrated a scope far beyond “classical” solid-state materials. Porous matrices with voids ranging from the nano-to the microscale have become the subject of recent investigations. Crystalline, amorphous, organomorphous, nanosized matrices and matrices, which are amorphous on the atomic level but have a translational superstructure on the microscale (zeolites, sol-gel materials, polymers, nanoparticles and photonic crystals), are addressed. The optical technologies covered in this research range from mercury free discharge lamps, plasma displays, organic and polymeric light emitting diodes, and novel laser materials to biophotonics and the new generation of white emitting AlGaN solid-state light emitting diodes (LEDs). Due to their specific properties (e.g., high quantum yields, narrow line emission), rare-earth ions are indispensable components of these approaches, be it in the nanoscaling zeolites, sol-gel matrices, or as the active component in optically functional polymers. Optical properties of hybrid materials composed of either rare-earth ions as such, their complexes, or nanoparticles in these matrices, with potential application in the fields mentioned, will form the scope of the present report.     

Synthesis and Biological Activity of 2-Aryl-4-hydroxy-4-methyl-6-oxocyclohexane-1,3-dicarboxamides

Russian Journal of General Chemistry - The reaction of unsubstituted acetoacetamide with aromatic aldehydes in ethanol in the presence of piperidine gave...     

Fluoridhaltige Gäste in Alumosilicaten: Tetrafluoroborate in dem Sodalithen Na8Al6Si6O24(BF4)2

In the course of investigations on optical properties resulting from the interaction of fluorides with alumosilicate host materials and rare earth guests, a well defined BF₄^– ion wasfound to be incorporated within the sodalite of composition Na₈Al₆Si₆O₂₄(BF₄)₂. The resulting cubic molecular structure, which was determined by Rietveld methods (space group P4 n, a = 906.91 pm, wRp = 0.045, Rp = 0.027), contains one anion in each sodalite cage and is, contrarily to expectations, thermally stable. NMR spectroscopic investigations indicated a fast rotatory motion of the BF₄^– tetrahedra at room temperature and agreed with the tetrahedral BF₄^– ions found in IR and Raman spectra. Preliminary attempts to obtain a luminescent material by incorporation of Eu³⁺ through aqueous ion exchange only yielded low rare earth concentrations, giving rise to characteristic red emission lines at 581 nm (⁵D₀ → ⁷F₁) and 615 nm (⁵D₀ → ⁷F₂) in a 1:2 intensity ratio. The material unexpectedly exhibited a strong broad band emission at 520 nm after calcination under Ar, which is attributed to the formation of an Eu²⁺ species. Further calcination under air partially reestablished the Eu³⁺ emission.     

NIR-and upconverted luminescence from rare-earth sodalites

In the recent past, numerous attempts have been made to utilize nano-, meso-, and microporous materials as hosts for luminescent guest species. The accessible spectral range now spreads from the vacuum ultraviolet to the near infrared (NIR), if sodalites are included in this scope. Although borderline materials in this context with respect to pore sizes, examples of the versatility of sodalites in accommodating small but efficient luminescent entities are discussed. In particular, optical materials whose spectral range of operation is allocated in the NIR have recently attracted our attention and will form the focus of this report.     

Multifold Fluorescence Enhancement in Nanoscopic Fluorophore–Clay Hybrids in Transparent Aqueous Media

Valuable emissive properties of organic fluorophores have become indispensable analytical tools in biophotonics, but frequently suffer from low solubilities and radiationless deactivation in aqueous media, that is, in biological ambience as well. In this report, nanoscaled dye–clay hybrids based on laponite, Na_0.7{(Li_0.3Mg_5.5)[Si₈O₂₀(OH)₄]}, are taken advantage of to solubilize neutral dyes, which are natively not encountered in water. Previously reported efficiency and solubility bottlenecks of such hybrids can to a large extent be overcome by comparably simple chemical measures, as demonstrated here for two prominent examples, the fluorescent dyes Nile Red and Coumarin 153. On controlled co‐adsorption of small bifunctional quaternary ammonium ions (Me₃N⁺C₂H₅OH and Me₃N⁺C₂H₅NH₂) we observed an outright efficiency boost by an order of magnitude, and a 30‐fold brightness gain. Even at higher concentrations, transparency and stability of the hybrid dispersions are retained, rendering them useful for employment as optically functional nanoparticles in bioassays and beyond.