Lanthanide-calixarene hybrid materials are of particular interest due to the combination of the interesting properties of the ligand cavity-like structure and the luminescent features of lanthanides. The aim of this study was to synthesize and investigate the photophysical properties of Eu3+, Tb3+ and Gd3+ hybrids based on calix[4] arene-tetracarboxylate. The preparation of two structurally different Tb3+ compounds (calix-TA-SC-Tb and calix-TA-Tb) was dictated by the ligand to metal molar ratio and the synthesis time. Analysis of calix-TA-SC-Tb monocrystals revealed the formation of a mononuclear complex of C-2 symmetry containing Tb3+ coordinated by four calixarene ionized groups and formate anion encapsulated within the upper cavity. Syntheses of other hybrids failed in producing high-quality crystals and the structures could not be solved. The solid-state luminescent properties of hybrids were evaluated, and the structure/property relationship was investigated. Based on the emission and excitation spectra, the energy diagrams for calix-TA-Eu, calix-TA-Tb and calix-TA-Gd were proposed.

Nanostructured phosphors LaPO4:Eu3+/Tb3+ were prepared via a combined approach using microwave heating and a bifunctional solvent (ethylene glycol) acting as both microwave absorber and capping agent. The synthesized samples were characterized by X-ray diffraction (XRD), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM) and photoluminescence (PL) measurements. All samples crystallized in a monoclinic monazite-type structure. Electron microscopy analysis revealed a hierarchical organization of self-assembled seed crystals of lanthanum phosphate into nanoparticles that, in turn, gave rise to sponge-like aggregates. The co-doped samples exhibited self-activated blue luminescence from the host matrix, as well as red and green emissions due to the presence of Eu3+ and Tb3+ ions, respectively. Furthermore, the spectroscopic analysis indicated energy transfer from terbium to europium ions.The synthetic route described here is efficient to prepare nanomaterials with advanced optical properties, which exhibit a potential for applications in photonics, sensing and biolabelling.

Polyaniline (PAni) and magnetite (Fe3O4) are well-known semiconducting materials with quite different conduction mechanisms: localized conductivity for magnetite and long-range conductivity for PAni. Fe3O4 nanoparticles were used to polymerize aniline, forming a PAni/Fe3O4 hybrid nanocomposite. The microstructural evolution and the electrical behavior of this nanocomposite were studied by dielectric relaxation spectroscopy (DRS). Albeit being a powerful technique to probe the electrical properties of materials, DRS has not yet been used to characterize such system in reasonable detail. The dc conductivity for pure magnetite was approximately 10−6 S cm−1, while the values for the PAni/Fe3O4 nanocomposites were 1 order of magnitude higher. The Fe3O4 nanoparticles behave like a material composed of packed grains, with substantial grain volume and grain boundary effects, leading to different dielectric responses at high and low frequencies. The partial consumption of Fe3O4 during polymerization results in smaller magnetic crystals embedded within the PAni matrix, and the decreased number of crystallite interfaces leads to lower interfacial resistance. Hence, the formation of PAni causes a decrease in the material’s volume resistance and imparts long-range conduction pathways on the material. This work shows the feasibility of using DRS to follow the microstructural evolution of a nanocomposite and changes in its conduction mechanisms, which are essential for the proper development of novel materials and devices.

The reaction between cucurbit[6]uril (CB[6]) and lanthanide chlorides (Eu, Sm, Tb and Tm) in acidic aqueous media led to four new structures. The compounds obtained are isostructural with general formula [Ln2(H2O)12(H2O@CB[6])]Cl6(H2O)4 (Ln = Eu(3+) (1), Sm(3+) (2), Tb(3+) (3) and Tm(3+) (4)) and crystallize in the P21/c space group. For the complexes with Eu(3+), Sm(3+) and Tb(3+), the luminescent properties in the solid state and aqueous media were explored and all spectroscopic observations are in excellent agreement with the single crystal structure data. The excitation and emission spectra show the typical f-f transitions characteristic of the trivalent lanthanide ions. The transitions (7)FJ ← (5)D1 (J = 0,1,2) in the europium compound and (7)FJ ← (5)D4 (J = 0,1,2) in the terbium compound, not yet reported in lanthanide-CB[n] compounds, were also observed.

Chemical evaluation of gunshot residues (GSR) produced by non-toxic lead-free ammunition (NTA) has been a challenge to forensic analyses. Our group developed some luminescent markers specific to the detection of GSR. Here, we evaluated the performance of selected markers in experiments that mimic forensic context and/or routines in which luminescent characteristics would be very useful. We evaluated the influence of markers' addition on the bullet's speed, the rate of shot failure (i.e., when the cartridge case is not fully ejected and/or a new ammunition is not automatically replaced in the gun chamber) as a function of marker percentage, the possibility of collecting luminescent gunshot residue (LGSR) in unconventional locations (e.g. the shooters' nostrils), the LGSR lifetime after hand washing, the transfer of LGSR to objects handled by the shooter, and the dispersion of LGSR at the crime scene and on simulated victims. It was observed that high amounts of marker (10 wt%) cause high rates of failure on pistols, as well as a substantial decrease in bullet speed. However, the use of 2 wt% of marker minimizes these effects and allows LGSR detection, collection and analysis. Moreover, in all conditions tested, markers showed high performance and provided important information for forensic analyses. For instance, the LGSR particles were found on the floor, ranging from 0 to 9.4 m away from the shooter, on the door panel and seats after a car shooting experiment, and were found easily on a pig leg used to simulate a victim. When a selective tagging was done, it was possible to obtain positive or negative correlation between the victim and shooter. Additionally LGSR possesses a fairly long lifetime (9 h) and good resistance to hand washing (up to 16 washes).

This paper focuses on the synthesis and the photoluminescent properties of Ca3−xAl2O6:xEu3+ (0≤x≤0.1) nanophosphors prepared by microwave-assisted combustion method without any further heat treatment. X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy were used to characterize the produced samples. Nanosized particles smaller than 120nm were obtained as confirmed by SEM. When exposed to UV light radiation at 254nm, the europium-doped nanoparticles showed strong reddish-orange luminescence due to the characteristic transitions 5D0→7F1 (orange) and 5D0→7F2, (red). The maximum emission intensity of the visible emission was obtained for x=0.05. It was also found that higher doping concentrations led to the luminescence quenching by a cross-relaxation mechanism between Eu3+ ions in the lattice.

The methaneseleninate and 1,10-phenanthroline were used as ligands in the synthesis of new lanthanide complexes. The photostability, emission quantum yield (q) and quantum efficiency (η) of the 5D0 emitting level of the Eu3+ ion were determined. An energy level diagram was used to establish the most relevant channels involved in the ligand-to-metal intramolecular energy transfer process. The nephelauxetic effect was investigated to assess the covalency of the ligand–metal chemical bond. The values of the experimental 4f–4f intensity parameters, suggest that this ion is in a chemical environment less polarisable than in the case of complexes with β-diketonates as ligands.

The synthesis, characterization and photoluminescent properties of new europium complexes with 2,4,6-trichlorophenyl acetoacetate (TCA) and 3-amino-2-carboxypyridine-N-oxide (picNO) ligands have been investigated. Results of the characterization are in agreement with the molecular formula proposed. The emission spectra at 77K of the [Eu(TCA)2(H2O)5]OH and [Eu(TCA)2(picNO)(H2O)2]OH complexes, excited at 333nm, display the typical transitions of the europium ion, 5D0→7FJ (J=0–4), indicating an efficient luminescence sensitization of this ion by the TCA ligand. The satisfactory agreement between experimental and theoretical absorption spectra of the organic part of the complexes suggests that the geometries optimized by the Sparkle model are correct. These results suggest these complexes as potential candidates as useful markers.

New lanthanide complexes with benzeneseleninic (ABSe) and 4-chloro-benzeneseleninic (ABSeCl) acids have been synthesized and characterized by elemental analysis, infrared and UV–visible spectroscopies. The emission spectra of the trivalent europium complexes presented the typical electronic 5D0→7FJ transitions of the ion (J=0–4). The ground-state geometries of the europium complexes have been calculated by using the Sparkle/AM1 model. From these results, the 4f–4f intensity parameters and energies of the ligand singlet and triplet excited states have been obtained. The lower emission quantum yield for the [Eu(ABSe)3(H2O)2](H2O)2 compound, as compared to the [Eu(ABSeCl)3(H2O)2] one, can be associated to the higher numbers of water molecules, in the first and second coordination spheres, that contribute to the luminescence quenching. The [Eu(ABSe)3(H2O)2](H2O)2 complex presents an intermediate state whose energy difference with respect to the first excited singlet state is resonant with three phonons from the water molecules, favouring a multiphonon relaxation process from the singlet state followed by a fast internal conversion process; this effect is less pronounced in the complex with the ABSeCl ligand. The luminescence decay curves of the gadolinium complexes indicate that the level responsible for the intramolecular energy transfer process has a triplet character for both compounds. The nephelauxetic effect in these compounds was investigated under the light of a recently proposed covalency scale based on the concept of overlap polarizability of the chemical bond.

In this paper, we report the hydrothermal synthesis of three lanthanide-organic framework materials using as primary building blocks the metallic centers Eu(3+), Tb(3+), and Gd(3+) and residues of mellitic acid: [Ln(2)(MELL)(H(2)O)(6)] (where Ln(3+) = Eu(3+), Tb(3+), and Gd(3); hereafter designated as (1), (2) and (3)). Structural characterization encompasses single-crystal X-ray diffraction studies, thermal analysis, and vibrational spectroscopy, plus detailed investigations on the experimental and predicted (using the Sparkle/AM1 model) photophysical luminescent properties. Crystallographic investigations showed that the compounds are all isostructural, crystallizing in the orthorhombic space group Pnnm and structurally identical to the lanthanum 3D material reported by the group of Williams. (2) is highly photoluminescent, as confirmed by the measured quantum yield and lifetime (37% and 0.74 ms, respectively). The intensity parameters (Omega(2), Omega(4), and Omega(6)) of (1) were first calculated using the Sparkle/AM1 structures and then employed in the calculation of the rates of energy transfer (W(ET)) and back-transfer (W(BT)). Intensity parameters were used to predict the radiative decay rate. The calculated quantum yield derived from the Sparkle/AM1 structures was approximately 16%, and the experimental value was 8%. We attribute the registered differences to the fact that the theoretical model does not consider the vibronic coupling with O-H oscillators from coordinated water molecules. These results clearly attest for the efficacy of the theoretical models employed in all calculations and open a new window of interesting possibilities for the design in silico of novel and highly efficient lanthanide-organic frameworks.

Zinc oxide was obtained by combustion reaction synthesis method using microwaves energy to provide ignition to the mixture of zinc nitrate, europium and urea. The influence of the europium concentration on the structure, morphology and luminescence characteristics of the ZnO powders was investigated. The proportion of each reagent and fuel was calculated based on the propellants chemistry concepts. The solutions were mixed in a vitreous silica basin and submitted of external heating in a microwaves oven until self-ignition occurred. The resulting powders were characterized by X-ray diffractometer (XRD), granulometric distribution, scanning electronic microscopy (SEM) and emission spectroscopy. The XRD results showed the formation of ZnO:Eu3+ as main phase and Eu2O3 as secondary phase. The powder presented morphology constituted of fine particles agglomerates (< 100nm) and red luminescence characteristic from Eu3+ ion.

Thin ceramic powders of zinc aluminate ZnAl2O4 co-doped with Er3+ and Yb3+ were prepared by a combustion reaction and characterized from the spectroscopic point of view, with the aim of investigating the effect and mechanisms of upconversion emissions. The characteristic cubic spinel structure was predominantly formed for all doped samples, and intense upconversion emission was observed in the green and red spectral regions, under 980 nm diode laser excitation. The upconversion mechanism of both emissions was confirmed to involve two photon absorptions and it was found that the efficiencies of the emissions are considerably enhanced by increasing the Yb3+ concentration in relation to Er3+. The results indicate the potential of ZnAl2O4:Er3+, Yb3+ phosphor powders for applications in luminescent display panels and other photonic devices.

A new compound with the formula [Eu4(ETA)9(OH)3(H2O)3)], where ETA is ethyl 4,4,4-trifluoroacetoacetate, has been synthesized and investigated by photoluminescence spectroscopy. The compound was characterized by means of chemical analysis, vibrational (IR), UV-vis absorption, and luminescence spectroscopies, and X-ray crystallography. The crystal structure of the [Eu4(ETA)9(OH)3(H2O)3)] complex in the solid state, determined by X-ray diffraction analysis, revealed that it crystallizes in the triclinic crystal system, space group P, with four crystallographically independent europium centers. From these structural data, the ground-state geometry of the tetramer has been calculated by using the Sparkle/AM1 model. The emission spectrum shows the characteristic transitions of the Eu3+ ion. The features displayed by the5D0-->7F0 transition in the emission spectrum are consistent with the Eu3+ ion occupying four different sites in chemical environments of low symmetries, in agreement with the X-ray data and the optimized geometry obtained from the Sparkle/AM1 model. These structural results have allowed the theoretical calculation of 4f-4f intensity parameters, including the forced electric dipole and dynamic coupling mechanisms as well as ligand singlet and triplet states, in good agreement with experiment.

New europium and gadolinium tris-beta-diketonate complexes have been prepared and incorporated in sol-gel-derived organic-inorganic hybrids, named di-ureasils. The general formula [Ln(btfa)3(4,4'-bpy)(EtOH)] (Ln=Eu, Gd; 4,4'-bpy=4,4'-bipyridine; btfa=4,4,4-trifluoro-1-phenyl-1,3-butanedione) for the complexes was confirmed by X-ray crystallography and elemental analysis. The ground-state geometry of the Eu3+ complex was calculated from the Sparkle/AM1 model. The calculated quantum yield obtained from the Sparkle model and from the crystal structure (both 46%) are in satisfactory agreement with the experimental value (38+/-4%). In the isolated complex the most efficient luminescence channel is S0-->S1-->T-->(5D1, 5D0)-->7F0-6, where the exchange mechanism dominates in the energy-transfer channel T-->(5D1, 5D0). For the Eu3+-based di-ureasils a 50% quantum yield enhancement compared to the Eu3+ complex is observed, which suggests an effective hybrid host-metal ion interaction and an active energy-transfer channel between the hybrid host and the Eu3+ complex. The Eu3+-based di-ureasils are photostable under UVA (360 nm) excitation, whereas under UVB (320 nm) and UVC (290 nm) photodegradation occurs.

Europium- and terbium-doped zinc aluminate oxide nanocrystals with a spinel structure were successfully prepared by a combustion method, using urea as fuel. The samples thus obtained were characterized by X-ray diffraction, scanning electron microscopy and luminescence spectroscopy. X-ray diffraction results confirmed the formation of ZnAl2O4 spinel phase and a minor amount of ZnO. Our SEM results revealed agglomerates in the shape of irregular plates composed of nanoparticles with dispersed points of second phase in the surface. Powders containing Eu3+ and Tb3+ ions displayed red and green photoluminescence, respectively.

Zinc aluminate (ZnAl2O4) is a ceramic material with spinel structure and is used as catalysis for reduction of NOx and SOx, and also as electronic ceramic. Zinc aluminate when doped with rare earth ions, such as Tb ion, the matrix of ZnAl2O4:Tb acquires luminescent properties. This material has been produced in laboratory scale by different methods of chemical synthesis, such as, spray pyrolysis, hydrothermal synthesis, co-precipitation and Pechini method. Among this method, the combustion reaction is an alternative, simple, fast and safe method, used to prepare ceramic powder with high purity, chemical homogeneity and nanosize particles. So, the aim of this work is to evaluate the influence of the Tb ion in the morphologic characteristics and luminescent properties of the zinc aluminate powder. The resulting powders from the combustion were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and excitation and emission spectroscopy. The XRD results showed the formation of ZnAl2O4:Tb as main phase and TbAlO3 as a secondary phase. The powder presented morphology constituted of the agglomerates of fine particles (<100nm) and green luminescence,characteristic of the Tb ion.

Complexes of Eu3+, Tb3+ and Gd3+ with dipicolinic acid, chelidamic acid and chelidonic acid have been synthesized in order to study the effect of the substituent groups on the luminescence of the lanthanide complexes. The luminescence of the Eu3+ and Tb3+ complexes was quantified by quantum yield measurements. The complexes of Gd3+ have been used to determine the energies of the triplet states of the ligands. The Tb3+ complex synthesized with dipicolinic acid presented the highest quantum yield due to the energy difference between the triplet state of the dipicolinic acid and the emitting level of the Tb3+ ion.

The complexes tris(4,4,4-Trifluoro-1(1-naphthyl)-1,3-butanedionate) (2,2'-bipiridyl) Ln(III), Ln(tan)(3)bipy, where Ln(III) = Eu3+ and Gd3+ have been synthesized, characterized and their photophysical properties (absorption, excitation and luminescence spectra and emission quantum yield) investigated down to 4.2 K. The Eu(tan)(3)bipy complex has its molecular structure experimentally determined using X-ray crystallography and theoretically using the SMLC/AM1 method as well as their electronic singlet and triplet states were calculated, using the INDO/S-CI method with a point charge model to represent the Eu3+ ion, where two values were adopted, + 3.0e and + 3.5e, to investigate the imperfect shielding of the 4f shells. The so calculated + 3.5e model electronic absorption spectrum and low lying triplet state energies agreed very well with the experimental ones. The emission quantum yield of the Eu3+ complex is quite low at room temperature, namely 7%, probably due to the too low lying triplet state, 19,050cm(-1), and increases by a factor of three when the temperature is lowered to 4.2 K. This strong thermal effect indicates the presence of a channel deactivating the main emitting state, what can be due to a LMCT state possibly lying in the same spectral region, as usually found in Eu3+ compounds. (c) 2005 Elsevier B.V. All rights reserved.

It has been synthesized the [Ln⊂bpy.bpy.py(CO2Et)2]3+ cryptates, where Ln=Eu, Tb and Gd. These compounds have been characterized through usual methods and their luminescences have been quantified through spectroscopic measurements such as luminescence lifetime, emission spectrum and emission quantum yield, q. The experimental q value obtained for the [Tb⊂bpy.bpy.py(CO2Et)2]3+ cryptate has been compared to one of the [Eu⊂bpy.bpy.py(CO2Et)2]3+ cryptate, giving q=25% for the former and q=14% for the latter, both in aqueous solution at 300K. The theoretical q value calculated for the Eu(III) cryptate was 19%, being in a very good agreement to the experimental one. The results indicate that the theoretical model which has been used to study the luminescence of complexes can also be satisfactorily applied to cryptates and the design of new ligands with high-energy triplet states should give very efficient light converting molecular devices when the central ion is the Tb(III).

The coordination compounds EUCl3.1.5hmta.H2O, TmCl3.-hmta.H2O, Cr(CH3COO)(2).2hmta, FeCl3.hmta.3H(2)O, Co(NO3)(2).3hmta, CuSO4.3hmta, PbCl2.0.5hmta.5H(2)O, HgCl2.hmta and NiCl2.hmta.H2O (hmta=hexamethylenetetraamine) were synthesized and characterized by elemental analysis, infrared spectroscopy and thermogravimetry. The infrared data are in agreement with coordination through nitrogen. For the hydrated compounds, a first mass-loss step, associated with the release of water molecules, followed by release of an hmta molecule was observed. The anhydrous adducts exhibit a first single-mass loss associated with the release of hmta. For Cr(CH3COO)(2).2hmta, the first mass-loss step is due to release of hmta, and the second is due to the acetate, consistent with the proposed structural formula.