Generating a Warm Glow: Lanthanide Complexes Which Luminesce in the Near-IR

This article reviews and expands upon our observations of neodymium and ytterbium-centered luminescence in the near-IR. A variety of neodymium (III) and ytterbium (III) complexes with aminocarboxylate ligands was synthesized and their photophysical properties were investigated in aqueous solutions. Metal-centered emission was observed in the near-IR for complexes of both ions and time-resolved studies were used to show how quenching of the excited states is dependent on both inner and outer sphere coordinated water molecules.     

Luminescent Properties of Europium(III) Compounds with Quinaldic Acid and Neutral Phosphorus-Containing Ligands with a Dimeric Structure

New luminescent mixed-ligand complexes of europium(III) with quinaldic acid and neutral phosphorus-containing ligands with a dimeric structure are synthesized. The structure and the thermal, spectral, and luminescent properties of mixed-ligand europium(III) complexes are studied. It is shown that the quinaldinate ion is coordinated to a europium(III) ion in a bidentate fashion. It is found that the excitation energy transfer to europium (III) ion occurs from levels of quinaldic acid and neutral phosphorus-containing ligands.     

Co-fluorescence effect of rare earth complexes with 4-aminobenzoic acid in a silica matrix

Terbium(III), yttrium(III), and neodymium(III) complexes with 4-aminobenzoic acid have been co-doped into silica matrix. For the samples, the characteristic emissions of terbium(III) increase obviously with the addition of yttrium(III) complex, while the reverse is true with the addition of neodymium(III) complex. Compared with terbium(III) complex doped silica sample, the photoacoustic signal of the ligand decreases for terbium(III)–yttrium(III) complexes co-doped sample, and increases for terbium(III)-neodymium(III) complexes co-doped sample. The fluorescence quantum yields and lifetimes of the samples have been determined. The co-fluorescence mechanism has been discussed from radiative and nonradiative relaxations. The nephelauxetic parameters and photoacoustic branching vectors of neodymium(III) in the silica samples have also been calculated. The spectral result indicates that heteronuclear complexes may form in the silica matrix upon a suitable heat treatment. The co-fluorescence effect found in the inorganic matrix can contribute to the better design and application of rare earths containing fluorescent materials.     

Spectral-Luminescent Properties of Mixed-Ligand Europium(III) Complexes with p-Methylbenzoic Acid

Optics and Spectroscopy - The spectral-luminescent properties of europium(III) complexes with p-methylbenzoic acid and nitrogen- and phosphorus-containing neutral ligands of compositions...     

Spectral-Luminescent Properties of Mixed-Ligand Europium(III) Complexes with O-Methoxybenzoic Acid and Phosphorus-Containing Neutral Ligands

Optics and Spectroscopy - The spectral-luminescent properties of europium(III) complexes with o-methoxybenzoic acid and phosphorus-containing neutral ligands with an island structure and the...     

Luminescent Properties of Europium(III) Compounds with Quinolinic Acid and Phosphorus-Containing Neutral Ligands

Optics and Spectroscopy - Luminescent mixed-ligand europium(III) complexes with quinolinic acid and phosphorus-containing neutral ligands with a dimeric structure of the composition Eu2(QA)3 ·...     

Luminescence properties of compounds of europium(III) with quinaldic acid and phosphor-containing neutral ligands

Luminescent complex mixed-ligand compounds of europium(III) with quinaldic acid and phosphor- containing neutral ligands have been obtained. Their composition and structure have been determined. The thermal and spectral-luminescent properties of the obtained complex mixed-ligand compounds of europium( III) have been studied. It is shown that, during thermolysis, a water molecule and neutral ligand are detached in two stages with endothermic effects. It is established that quinaldinate ion is coordinated to europium(III) ion in a bidentate fashion. The Stark structure of the ⁵D₀–⁷F_j (j = 0, 1, 2) transitions in low-temperature luminescence spectra of complex compounds of europium(III) has been analyzed.     

Luminescence properties of europium(III) compounds with quinaldic acid and nitrogen-containing ligands

Luminescent mixed-ligand Eu(III) complexes with quinaldic acid and nitrogen-containing dimeric ligands are synthesized. The thermal and spectral-luminescent properties of the obtained mixedligand Eu(III) complexes are studied. It is shown that a water molecule and a neutral ligand are detached during thermolysis in two stages with endothermic effects. It is found that the quinaldinate ion is coordinated to a europium(III) ion in a bidentate fashion. The Stark structure of the 5D₀–7F _j (j = 0, 1, 2) transitions in the low-temperature luminescence spectra of europium(III) complexes is analyzed.     

Near-infrared luminescence emitted by an electrically switched liquid crystal cell

Switching of near-infrared emission was observed for liquid crystal (LC) cells filled with a chiral nematic liquid-crystal mixture (mixture of E7 and cholesteryl nonanoate) doped with luminescent neodymium(III) or ytterbium(III) β-diketonate complexes. The operating principle of the LC cell is based on an electrically induced phase transition from a chiral nematic to a nematic phase. The chiral nematic phase scatters the excitation light more strongly, resulting in more efficient light absorption and intenser photoluminescence.     

Judd-Ofelt Analysis of Photoacoustic Spectra of Powdered Neodymium Compounds

Photoacoustic (PA) spectra of powdered neodymium oxide: Nd₂O₃ (A type), neodymium hydrated chloride: NdCl₃-6H₂O and neodymium fluoride: NdF₃ are reported. PA band shifts as compared to their positions in aqueous Nd(III) ion have been used to calculate the nephelauxetic parameters of their compounds. The variation of these parameters and correlation with the nature of metal-ligand bonding have been discussed. A novel method is introduced to determine relative values of Judd-Ofelt parameters and oscillator strengths of powdered samples using PA spectroscopy. It is found that a linear correlation exists between relative values of τ₂ and relative oscillator strengths of hypersensitive transitions of the title compounds. It can be hoped that the new method of PA technique may serve for the Judd-Ofelt quantitative analysis of powdered rare earth compounds.     

Exchange interactions and spin dynamics in a [CuNd2(C4O4)4(H2O)16]·2H2O crystal

Crystalline [CuNd₂(C₄O₄)₄(H₂O)₁₆]·2H₂O constructed of complexes of trivalent neodymium and divalent copper, has been synthesized and studied by EPR. The square anion groups (C₄O₄) enter as bridge ligands, forming chains of neodymium ions interconnected by (C₄O₄)Cu(C₄O₄) fragments. It is found that the relaxation rate of the neodymium subsystem at room temperature significantly exceeds the exchange interaction rate between copper and neodymium ions. Under these conditions the magnetic properties of the crystal are determined by two magnetically nonequivalent chains of copper ions, which do not interact. The intrachain exchange interaction via hydrogen bonds is estimated to be ∼0.1 cm⁻¹. As one proceeds from the high-temperature (250<T<300 K) to the low-temperature region (T<40 K), a substantial change in the nature of the interaction is revealed. An unusual magnetic structure given in a crystal is observed at low temperatures, which is determined by the presence of two magnetically nonequivalent “ribbons,” formed by the interacting copper and neodymium ions: chains of copper ions are framed on two sides by chains of neodymium ions. The magnitude of the parameter of the exchange interaction between the copper and neodymium ions is estimated as J ^Cu-Nd⩾0.2 cm⁻¹. An exchange interaction between magnetically nonequivalent neodymium ions is not revealed in the EPR spectra. Fiz. Tverd. Tela (St. Petersburg) 39, 2057–2061 (November 1997)     

Towards the origin of effective An(III)/Ln(III) separation by tridentate N-donor ligands: a theoretical study on atomic charges and polarisabilities for Cm(III)/Gd(III) separation

Soft N-donor ligand have shown to separate An(III) from Ln(III). The origin of the selectivity has not been entirely identified, and similar ligands show very different separation qualities. In this study we present a theoretical investigation of several relevant N-donor ligands in terms of atomic charges and polarisabilities obtained from an atoms in molecules approach. These allow new insights into the bonds between the ligands’ nitrogen atoms and the metal cation and explain a major part of the selectivity towards actinide ions. We deduct the superiority of 2,6-bis(1,2,4-triazine-3-yl)pyridines in separation quality compared to similar ligands for the Cm(III)/Gd(III) separation. Furthermore, improvements of existing ligands are developed that allow not only a direct experimental confirmation but also a systematic experimental study of the interactions and their influence on the selectivity.     

Photoacoustic Spectra Studies on Neodymium Complexes

A series of neodymium complexes crystals were synthesized and their photoacoustic spectra were determined. The excited state energy levels of Nd(III) in different complexes were discussed and their relaxation processes were studied. The different coordination environments were shown by comparing the band due to Nd(III) ⁴19/2 – ⁴G5/2, C7/2 transitions in different complexes. The fine structure of this absorption shows that the Nd-0 bond forms a stronger coordinated bond than that of Nd-N system.     

Curcuminoid Ligands for Sensitization of Near-Infrared Lanthanide Emission

Fluorescent lanthanide complexes were synthesized using a non-phenolic analog of curcumin as the principal chromophoric chelating ligand. Sensitized, near-infrared fluorescence is observed in these complexes as a result of photo-excitation of the chromophoric ligands, population of the molecular triplet state, and transfer of energy to the emitting lanthanide ion. For the purpose of intra-molecular energy transfer, the triplet states of curcuminoid ligands are more favorably matched with the excited electronic states of neodymium and ytterbium ions than those associated with less conjugated β-diketonate ligands. Sensitization of fluorescence through an internal redox reaction, thought to occur in other ytterbium complexes, is predicted to be less probable under the present circumstances.     

Aromatic Chromophore-Tethered Schiff Base Ligands and Their Iron(III)/Chromium(III) Salen and Saloph Capped Complexes

Aromatic chromophores; pyrene, phenanthrene, anthracene, naphtalene and benzene-tethered Schiff base ligands and their iron(III)/chromium(III) Salen and Saloph capped complexes have been synthesized. Compounds have been characterized by means of FT-IR Spectroscopy, (1)H-NMR Spectroscopy, Magnetic Susceptibility, Elementel Analsis, TG/DTA measurements. Their fluorescence and absorbance properties have been investigated by Luminescence Spectroscopy and UV-vis Spectroscopy. Generally, ligands show an intense excimer fluorescence emissions in acetonitrile-methanol medium while iron(III) and chromium(III) complexes exhibit low fluorescence's. Intensity compared to ligands iron and chromium centers act as an extra chromophore that quench the pyrene, phenanthrene, anthracene, naphtalene and benzene molecules' singlet state. The mechanism of quenching is attributed to a iron (or chromium)-to-pyrene (or phenanthrene, anthracene, naphtalene and benzene) electronic energy transfer process.     

Effect of the medium and the formation of nanostructures on deexcitation of electronic excitation of Eu(III) and Tb(III) chelates

The intensity I _lum and lifetime τ_lum of the luminescence of complexes of Eu(III) and Tb(III) ions with β-diketones and o-phenanthroline in water-ethanol solutions of these ligands have been analyzed as functions of the concentrations of ligand, luminescing lanthanide ions, and added ions causing columinescence and of the solvent deuteration. It is shown that the formation of nanostructures from Ln complexes and their coarsening leads to an increase in τ_lum of Eu(III) and Tb(III) and that this increase is due to the suppression of both photochemical deexcitation of these ions and transfer of their electronic excitation energy to OH vibrations of water molecules. The disappearance of the dependence of I _lum of Eu(III) on deuteration of water-ethanol solutions of n-methoxybenzoyltrifluoracetone + o-phenanthroline caused by adding Gd(III) ions is explained by the shift of the equilibrium of formation of complexes of Ln chelates to neutral hydrophoblic forms corresponding to the formation of nanostructures of these chelates in the solution. The differences in effect of La(III) and Gd(III) ions on I _lum and τ_lum of Eu(III) and Tb(III) complexes are explained. It is shown that the widely discussed effect of columinescence not only results from the energy migration in mixed structures of Eu or Tb complexes and Gd complexes but is also due to a large extent to the decrease in τ_lum of Eu(III) or Tb(III) caused by their incorporation into nanostructures.     

Low-vibrational luminescent polymers including tris(bis-perfluoromethane and ethanesulfonylaminate)neodymium(III) with 8 coordinated DMSO-d6

Novel Nd(III) complexes, tris(bis-perfluoromethane and ethanesulfonylaminato)neodymium(III)octa(deuterated dimethylsulfoxide) were designed and synthesized to apply to luminescent materials in plastic optical fiber. The IR and the near-IR spectra analyses has been done to estimate the radiationless transition via vibrational excitation of the Nd(III) complexes. [Nd(pms)₃(DMSO-d₆)₈] and [Nd(pes)₃(DMSO-d₆)₈] in polyhexafluoroisopropylmethacrylate gave a emission quantum yield of 1.3% and 1.6%, which was the largest in luminescent Nd(III) polymers. A research field for telecommunication network using 1.3 μm light would be achieved by luminescent Nd(III) materials encapsulated low-vibrational coordination sites.     

Synthesis and Luminescent Properties of Lanthanide Complexes with Structurally Related Novel Multipodal Ligands

To explore the relationship between the structure of the ligands and the luminescent properties of the lanthanide complexes, a series of lanthanide nitrate complexes with two novel structurally related multipodal ligands, 1,3-bis{[(2’-(2-picolylaminoformyl))phenoxyl]methyl}benzene (L ^I ) and 1,2-bis{[(2’-(2-picolylaminoformyl))phenoxyl]methyl}benzene (L ^II ), have been synthesized and characterized by elemental analysis, infrared spectra and molar conductivity measurements. At the same time, the luminescent properties of the Eu(III) and Tb(III) nitrate complexes in solid state and the Tb(III) nitrate complexes in solvents were investigated at room temperature. Under the excitation of UV light, these complexes exhibited characteristic emissions of central metal ions. The lowest triplet state energy levels T₁ of these ligands both match better to the lowest resonance energy level of Tb(III) than to Eu(III) ion. The influence of the structure of the ligands on the luminescent intensity of the complexes was also discussed.     

基于液体荧光法的钕元素测定

探讨了钕与丙氨酸、咪唑形成荧光配合物的各个因素,确定了用液体荧光法测定钕元素的最佳条件。实验表明,钕与丙氨酸和咪唑形成荧光配位化合物的最佳条件为:丙氨酸和咪唑的量的比为5∶1,pH=5.0;钕配位化合物荧光强度的最佳测量条件为:激发波长220 nm,发射波长350 nm,激发狭缝带宽5 nm,发射狭缝带宽10 nm;溶液钕含量的最低测量下限为0.5μg/mL。应用该方法测定了氧化钕和陶瓷产品中的钕含量。     

Inert and stable erbium(III)-cored complexes based on metalloporphyrins bearing aryl-ether dendron for optical amplification: synthesis and emission enhancement

We have developed novel inert and stable erbium (Er)(III)-cored complexes based on metalloporphyrins for optical amplification. The functionalized metalloporphyrin ligands have been designed and synthesized to provide enough coordination sites for the formation of inert and stable 9-coordinated Er(III)-cored complexes. Er³⁺ ions were encapsulated by the metalloporphyrin ligands, such as Zn(II)- and Pt(II)-porphyrins. The near-infrared (IR) emission intensity of Er³⁺ ion is much stronger in the Er(III)-cored complex based on Pt(II)-porphyrin than Er(III)-cored complex based on Zn(II)-porphyrin. Furthermore, we have incorporated a G2-aryl-ether functionalized dendron into the Er(III)-cored complex, yielding an Er(III)-cored dendrimer complex bearing the Pt(II)-porphyrin. The Er(III)-cored dendrimer complex shows the stronger near-IR emission intensity than the corresponding complex based on Pt(II)-porphyrin by seven times in solid state. The lifetimes of the emission band of Pt(II)-porphyrin ligands in the visible region were found to be 30 and 40 μs for the Er(III)-cored complex and the Er(III)-cored dendrimer complex based on Pt(II)-porphyrin in deoxygenated THF solution samples, respectively. Also, in both cases, the sensitized luminescence intensity is increased in deoxygenated solution. Therefore, it indicates that the energy transfer from the metalloporphyrins to Er³⁺ ions takes places through the triplet state. In this paper, the synthesis and photophysical properties of novel Er(III)-cored complexes based on metalloporphyrins and Er(III)-cored dendrimer complex based on metalloporphyrin will be discussed.