A Mechanism of the influence of Gd(III) and other Ln(III) ions on sensitized luminescence of Eu(III) and Tb(III) ions in aqueous and ethanol solutions: The role of hydroxyl bridges

We studied sensitization of Eu(III) and Tb(III) ions by molecules of 1,10-phenanthroline and 2,2-bipyridil in D₂O and d ₆-ethanol and the influence of Nd(III), Pr(III), Sm(III), Gd(III), and Ho(III) ions on the luminescence intensity I _lum and lifetime τ_lum of Eu(III) and Tb(III) in solutions. The stability constants of complexes of Eu(III) and Gd(III) with 2,2′-bipyridil are measured by spectrophotometric and luminescence methods. It is shown that luminescence of Eu(III) is quenched by Gd(III) ions at the ion concentration equal to 10^?2–10^?1 M, which is caused by competing between these ions for a sensitizer. At the concentration of Ln(III) ions equal to 10^?6?10^?3 M, the sensitized luminescence of Eu(III) and Tb(III) was quenched and τ_lum decreased in the presence of Nd(III) ions, whereas in the presence of Gd(III) the luminescence intensity increased. It is proved that a bridge that connects the two ions upon energy transfer is formed by hydroxyl groups. The intensity of luminescence of Eu(III) and Tb(III) in aqueous solutions and its lifetime decreased in the presence of hydroxyl groups, while upon addition of Gd(III) to these solutions these quantities were restored. We also found that the addition of Gd(III) to deoxygenated ethanol solutions of 2,2′-bipyridil and Eu(III) slows down photochemical and thermal reactions between bipyridil and Eu(III), resulting in the increase in the luminescence intensity of Eu(III).     

Luminescent properties of (Y,Gd)BO3:Bi,RE (RE=Eu, Tb) phosphor under VUV/UV excitation

Bi³⁺- and RE³⁺-co-doped (Y,Gd)BO₃ phosphors were prepared and their luminescent properties under vacuum ultraviolet (VUV)/UV excitation were investigated. Strong red emission for (Y,Gd)BO₃:Bi³⁺,Eu³⁺ and strong green emission for (Y,Gd)BO₃:Bi³⁺,Tb³⁺ are observed under VUV excitation from 147 to 200 nm with a much broader excitation region than that of single Eu³⁺-doped or Tb³⁺-doped (Y,Gd)BO₃ phosphor. Strong emissions are also observed under UV excitation around 265 nm where as nearly no luminescence is observed for single Eu³⁺-doped or Tb³⁺-doped (Y,Gd)BO₃. The luminescence enhancement of Bi³⁺- and RE³⁺-co-doped (Y,Gd)BO₃ phosphors is due to energy transfer from Bi³⁺ ion to Eu³⁺ or Tb³⁺ ion not only in the VUV region but also in the UV region. Besides, host sensitization competition between Bi³⁺ and Eu³⁺ or Tb³⁺ is also observed. The investigated phosphors may be preferable for devices with a VUV light 147-200 nm as an excitation source such as PDP or mercury-free fluorescent lamp.     

Use of Terbium(III) as a Probe for the Ion-Binding Properties of Tactic Polyacids and Triacidic Model Compounds

The binding properties of Tb(III) ions in configurationally different environments were investigated using luminescence intensity and lifetime measurements. The emission intensity of Tb(III) (⁵D₄–⁷F₅ transition) is directly dependent upon the number of coordinated water molecules (quenchers) bound in the inner coordination sphere. The more efficiently a ligand coordinates to Tb(III) ion, the more water molecules are expelled from the coordination sphere, thereby enhancing the luminescence intensity and lifetime of the ion. Isotactic and syndiotactic poly(methacrylic acids) (PMAs) were neutralized and complexed with Tb(III) ions in aqueous solutions. The luminescence intensities and lifetimes were monitored with _exc = 265, the hypersensitive excitation band at 286 and 370 nm. The isotactic PMA/Tb(III) complex exhibited a six times greater luminescence intensity than the syndiotactic PMA complex. Lifetime measurements showed 2.4 water molecules coordinated to Tb(III) ion in the isotactic PMA complex, while 3.4 water molecules were found to remain in the syndiotactic complex. Similar studies were also conducted on small organic model compounds such as Kemp's triacid and its configurational isomer. These data supported the polymeric results where the isotactic model, Kemp's triacid, exhibited a higher luminescence intensity and a longer lifetime than the Kemp's isomer. Lifetime results showed the Kemp's molecule retained approximately 2.7 water molecules, compared to four water molecules for the isomer. The validity of using the Kemp's molecules as polymeric models is also discussed.     

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.     

The nature of the effect of Gd(III) on fluorescence of Ln(III) chelates in water solutions

The intensity of fluorescence of Eu(III) and Sm(III) ions sensitized by molecules of n-benzoyltrifluoroacetone and 1,10-phenanthroline introduced in a water solution in a ratio of 3: 1 is studied as a function of the ion concentration in the solution. The comparison of the fluorescence decay curves of Eu(III) and Sm(III) in D₂O and H₂O (pH≥7) solutions containing 10^?4 M of n-Cl-BTFA and 3×10^?5 M of 1,10-phen and the values of τ_fl of Sm(III) in themselves (51–90 μs) are indicative of an insignificant content of water molecules in the first coordination sphere of ions. The effect of other ions on I _fl and τ_fl of Eu(III) ions is studied under these conditions. The intensity of fluorescence of Eu(III) in solutions of 10^?4 M Cl-BTFA and 3×10^?5 H 1,10-phen is found to increase by 1–2 orders of magnitude in the presence of Y(III) and Gd(III) ions, and the magnitude of this effect is unaffected by deoxygenation of the solution. The introduction of a third ion Nd(III) in the solution is shown to attenuate the influence of Gd(III) on I _fl of Eu(III) for Nd(III) concentrations commensurable with the Eu(III) concentration in the solution. The strength of the influence of Gd(III) ions on I _fl of Eu(III) is found to depend on the method of preparation of the solution. The analysis of the results obtained testifies that inhomogeneities consisting of chelates of lanthanide ions displaced from the water structure appear in water. The presence of these inhomogeneities results in efficient energy transfer from ligands of Gd(III) chelates to Eu(III) chelates, which is the reason for the increasing I _fl of Eu(III). The possibility of using data on the enhancement of I _fl of Eu(III) in the presence of Gd(III) and on the reduction of τ_fl of Eu(III) in the presence of Nd(III) for estimating dimensions and structures of displaced systems is discussed.     

Correlation of photoluminescence of (La,Ln) PO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> (Ln = Gd and Y) phosphors with their crystal structures

Eu³⁺-doped (La, Ln) PO₄ (Ln = Gd and Y) phosphors were prepared by a facile co-precipitation method. Their structures and luminescent properties under UV excitation were investigated. Structural characterization of the nanostructured luminescence material was carried out with X-ray powder diffraction analysis. Scanning electron microscopy was carried out to understand the surface morphological features and grain sizes with 50–100 nm. It is found that (La, Gd) PO₄:Eu³⁺ phosphors have the same crystal structure as LaPO₄:Eu³⁺, which is monoclinic with a little different lattice parameters. In the case of (La, Y) PO₄:Eu³⁺ phosphors, however, the gradual change from monoclinic to tetragonal structure of host lattice was observed, as the amount of Y ion increased. From the photoluminescence spectra for (La, Ln) PO₄:Eu³⁺ (Ln = Gd and Y), the emission transition ⁵D₀ → ⁷F₁ has been found to be more prominent over the normal red emission transition ⁵D₀ → ⁷F₂. Furthermore, the size influence on the products was discussed. It was observed that the spectral features possess sharp and bright emission for potential applications on the monitors of the television and some other related electronic systems, in observing the images in orange–red color.     

Design, synthesis and characterization of a highly luminescent Eu-complex monomer featuring thenoyltrifluoroacetone and 5-acryloxyethoxymethyl-8-hydroxyquinoline

A multi-functional ligand, 5-acryloxyethoxymethyl-8-hydroxyquinoline (Hamq), was synthesized, which contained a polymerizable C=C double bond for the copolymerization with other vinyl monomers and acted as photon antenna able to transfer energy to Eu³⁺ ions effectively. The triplet state energy of Hamq was determined to be 22,370 cm⁻¹ via the phosphorescence spectra of Hamq and its gadolinium complex. The title complex monomer Eu(tta)₂(amq) was prepared by coordination reaction of Hamq with europium isopropoxide and 2-thenoyltrifluoroacetone (Htta) in dry organic solvents under argon atmosphere and characterized by elemental analysis and IR spectrum. The photophysical properties of the complex were studied in detail with UV-vis, luminescence spectra, luminescence lifetime and quantum yield. The complex exhibited nearly monochromatic red emission at 612 nm, a remarkable luminescence quantum yield at room temperature (30.6%) upon ligand excitation and a long ⁵D₀ lifetime (389 μs), which indicated that the ligand Hamq could sensitize the luminescence of Eu(III) ion efficiently in Eu(tta)₂(amq), resulting in a strong luminescence of its copolymer poly[MMA-co-Eu(TTA)₂(amq)] under UV excitation. The excellent luminescence properties of the complex made it not only a promising light-conversion molecular device but also an excellent luminescent monomer.     

Synthesis and Fluorescence Properties of Lanthanide (III) Perchlorate Complexes with Naphthyl-Naphthalinesulphonylpropyl Sulfoxide

A ligand with double sulfinyl groups, naphthyl-naphthalinesulphonylpropyl sulfoxide(dinaphthyl disulfoxide, L), was synthesized by a new method and its several lanthanide (III) complexes were synthesized and characterized by element analysis, molar conductivity, coordination titration analysis, IR, TG-DTA, ¹HNMR and UV spectra. The composition of these complexes, were RE₂(ClO₄)₆·(L)₅·nH₂O (RE = La, Nd, Eu, Tb, Yb, n = 2 ∼ 6, L = C₁₀H₇SOC₃H₆SOC₁₀H₇). The fluorescent spectra illustrated that the Eu (III) complex had an excellent luminescence. It was supposed that the ligand was benefited for transferring the energy from ligand to the excitation state energy level (⁵D₀) of Eu (III). The Tb (III) complex displayed weak luminescence, which attributed to low energy transferring efficiency between the average triplet state energy level of ligand and the excited state (⁵D₄) of Tb (III). So the Eu (III) complex displayed a good antenna effect for luminescence. The phosphorescence spectra and the relationship between fluorescence lifetime and fluorescence intensity were also discussed.     

Effect of C-H bonds on the quenching of luminescent lanthanide chelates

The quenching of europium(III) and terbium(III) chelate luminescence by high-energy C-H vibrational manifolds was studied with two types of stable chelates, i.e., a seven-dentate phenylethynylpyridine derivative and a nine-dentate terpyridine derivative. The replacement of C-H bonds by C-D bonds in the chelating parts of the ligands had a clear positive effect on Eu³⁺ luminescence but a negligible effect on Tb²⁺ luminescence. In aqueous solution, however, the positive effect was undetectable, if the chelating ligand did not create complete shielding of the ion against aqueous quenching. In chelates, where the coordination of water molecules to the inner sphere is prevented, the residual quenching through C-H vibrational quanta can be avoided by replacement of all C-H bonds in the vicinity of the emitting ion by C-D bonds.     

Thermally stimulated recombination processes and luminescence in Li<Subscript>6</Subscript>(Y,Gd,Eu)(BO<Subscript>3</Subscript>)<Subscript>3</Subscript> crystals

The thermally stimulated recombination processes and luminescence in crystals of the lithium borate family Li₆(Y,Gd,Eu)(BO₃)₃ have been investigated. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence spectra), the temperature dependences of the X-ray luminescence intensity, and the glow curves for the Li₆Gd(BO₃)₃, Li₆Eu(BO₃)₃, Li₆Y_0.5Gd_0.5(BO₃)₃: Eu, and Li₆Gd(BO₃)₃: Eu compounds have been measured in the temperature range 90–500 K. In the X-ray luminescence spectra, the band at 312 nm corresponding to the ⁶ P _J → ⁸ S _7/2 transitions in the Gd³⁺ ion and the group of lines at 580–700 nm due to the ⁵ D ₀ → ⁷ F _J transitions (J = 0–4) in the Eu³⁺ ion are dominant. For undoped crystals, the X-ray luminescence intensity of these bands increases by a factor of 15 with a change in the temperature from 100 to 400 K. The possible mechanisms providing the observed temperature dependence of the intensity and their relation to the specific features of energy transfer of electronic excitations in these crystals have been discussed. It has been revealed that the glow curves for all the crystals under investigation exhibit the main complex peak with the maximum at a temperature of 110–160 K and a number of weaker peaks with the composition and structure dependent on the crystal type. The nature of shallow trapping centers responsible for the thermally stimulated luminescence in the range below room temperature and their relation to defects in the lithium cation sublattice have been analyzed.     

Spectroscopic studies of lanthanide(III) ion complexes with diethyl(phthalimidomethyl) phosphonate

Complexation and photophysical properties of complexes of lanthanide ions, Ln(III), with diethyl(phthalimidomethyl)phosphonate ligand, DPIP, were studied. Interactions between Ln(III) and DPIP were investigated using Nd(III) absorption and Eu(III) and Tb(III) luminescence (emission and excitation) spectra, recorded in acetonitrile solution containing different counter ions (NO₃^-, Cl^- and ClO₄^-). Results of the absorption spectroscopy have shown that counter ions play a significant role in the complexation of Ln(III)/DPIP complexes. Studies of luminescence spectra of Eu(III) and Tb(III) ions proved that the formation of Ln(III)/DPIP complexes of stoichiometry Ln:L=1:3 is preferred in solution. Based on the results of elemental analysis, Nd(III) absorption spectra and IR and NMR data, it was shown that the DPIP ligand binds Ln(III) ions via oxygen from phosphoryl group, forming complexes of a general formula Ln(DPIP)₃(NO₃)₃·H₂O, in which the NO₃^- ions are coordinated with the metal ion as bidentate ligands. Luminescent properties and energy transfer, from the ligand to Ln(III) ions in the complexes formed, were studied based on the emission and excitation spectra of Eu(III) and Tb(III). Their luminescent lifetimes and emission quantum yields were also measured.     

Luminescence properties of lanthanide(III) ions in concentrated carbonate solution

Luminescence properties of lanthanide(III) ions (Ln = Nd, Sm, Eu, Gd, Tb, Dy and Tm) were investigated by measuring the excitation and emission spectra, and emission lifetimes in H₂O and D₂O solutions of 3 moll^?1 K₂CO₃, where anionic tetra-carbonate complexes, [Ln(CO₃)₄]^5- were the predominant species.

Electronic transitions of the carbonato complex corresponding to both the excitation and emission spectra were assigned from the energy level diagrams of Ln(III) and compared with those of the aqua ion. Enhancement of emission intensity of the complex was observed at particular excitation transitions of Eu(III), Gd(III) and Tb(III), and at particular emission transitions of Sm(III), Eu(III), Dy(III) and Tm(III). The enhancement at the emission transition was estimated quantitatively as a branching ratio from the lowest emitting state of Ln(III), and discussed in terms of hypersensitivity.

Emission lifetimes of the carbonato complexes were all longer than those of aqua ions in H₂O solution, while the lifetimes of the complexes for Eu(III) and Tb(III) shorter than those in D₂O solution. The difference in non-radiative decay constants for the excited complex in H₂O and D₂O solutions was found to be proportional to an exponential of the energy gap of Ln(III). The lifetime ratio between the H₂O and D₂O solutions showed the order of Sm > Dy > Eu > Tb, corresponding to the opposite order of the energy gap. These were discussed in terms of an energy gap law, i.e. a relationship between the energy gap of Ln(III) and vibration energies of the ligand or water molecules.     

The influence of the solution preparation method on the co-luminescence intensity of chelates of Eu(III) ions and estimation of the size of arising nanostructures

The luminescence intensity of Eu(III) ions (I ^Eu) in 3: 1 aqueous solutions of thenoyltrifluoroacetone, n-methoxybenzoylacetone, and dibenzoylmethane with 1,10-phenanthroline is studied in the presence and the absence of La(III), Gd(III), and Nd(III) ions. It is found that, in binary solutions of Eu(III) with La and Gd, the intensity I ^Eu, as well as the influence of chelates of La and Gd on I ^Eu, is considerably greater if these ions are introduced into the solutions of β-diketones and 1,10-phenanthroline simultaneously and homogeneously than when they are introduced into these solutions successively. This result is explained by the difference in the distribution of different Ln chelates over nanostructures. The average size of the structures arising is estimated.     

Synthesis,characterization, luminescence properties and antioxidant activity of Ln(III) complexes with a new aryl amide bridging ligand

A novel Aryl amide ligand H₂L and its eight complexes, [LnH₂L(NO₃)₂·H₂O]NO₃ [Ln=Sm(III), Er(III), Tb(III), Dy(III), La(III), Gd(III), Nd(III), and Pr(III)], are presented. The ligand and complexes were synthesized and characterized based on elemental analyses, molar conductance, IR, ¹H and ¹³C-NMR, UV–VIS., and TGA studies. The conductivity data show a 1:1 electrolytic nature with a general formula [LnH₂L(NO₃)₂·2H₂O]NO₃ The IR spectra reveal coordination of the ligand through the azomethine nitrogen and the phenolic hydroxyl of the ligand to the lanthanide ion. The coordinated nitrate ions behave in a bidentate fashion. The thermal decomposition studies indicate the presence of two water molecules in the inner coordination sphere. Under the excitation at 319 nm, the luminescence emission properties for Sm, Tb, and Dy complexes are observed. These observations show that the ligand favors energy transfers to the emitting energy level of these lanthanide ions. Furthermore, the antioxidant activity of the ligand and its Ln(III) complexes was determined by DPPH radical scavenging method, which indicates that the Ln(III) complexes exhibit more effective antioxidant activity than the ligand alone.     

Luminescence efficiency and nonradiative transitions in lanthanide formates

Absolute quantum yields and luminescence lifetimes were measured for Eu, Tb, Gd, formates and Y formate activated by Eu³⁺ as functions of temperature, deuterium substitution in ligands, and Eu³⁺ concentration in Y formates. Radiative and nonradiative transition probabilities in the lanthanide formates were determined using the quantum yield φ and luminescence lifetime τ. The probabilities of radiative transitions in Eu³⁺ were also found by employing corrected luminescence spectra. Relaxation mechanisms of electronic excitation energy in the studied crystals were discussed.     

Luminescent Properties of the Hexakis(Nitrito)Europate(Iii) Ion [Eu(No2)6]3−

Abstract

The 12-coordinated hexakis(nitrato)europate(III) ion displays a luminescence spectrum compatible with T_h, symmetry, with essentially a single emission line at 16 873 cm^?1 arising from the ⁵D₀→⁷F₁ transition. At low temperature (4.2 - 170 K), the lifetime of the ⁵D₀ level amounts to 10.9 ms and then sharply decreases because of vibrational de-excitation processes (E_a = 2 250 ± 1 490 cm^?1). The forbidden ⁵D₀→⁷F₀ transition displays an extensive pattern of Stokes and anti Stokes vibrational components and its energy reflects a nephelauxetic parameter for the nitrite ions δO(NO₂) equal to -14.4, slightly larger than the one associated to the nitrate ion in [Eu(NO₃)₆]^3-. The ligand excitation spectrum contains several bands displaying extensive vibrational structure mostly due to the δ(NO₂) vibrational mode.     

Synthesis and photophysical properties of novel polymeric Eu(III) complex with bicoordination ligand

A novel complex of Eu(III) with bicoordination ligand: 4,4′-bis[2-(2′-pyridyl) benzimidazol-yl]-biphenyl (Bmbp) has been synthesized. The structure of the ligand was characterized by ¹H NMR, FT-IR and UV-vis; Eu(III) complex was characterized by FT-IR, UV-vis, elemental analysis, conductivity measurements and gel-permeation chromatography (GPC). The luminescence properties were investigated by UV-vis and fluorescence spectra. The experimental results show that the complex contain more than one Eu(III) ion, the emission at 614 nm from the ⁵D₀→⁷F₂ electronic dipole transition is large enhanced, and the complex is excellent energy transfer from ligand to Eu³⁺in the solid state. Thermal property measurement and analysis show that it has a good thermal stability.     

Ultraviolet and visible upconversion emission in Tb3+/Yb3+ co-doped fluorophosphate glasses

Ultraviolet and visible upconversion emissions in Tb³⁺/Yb³⁺ co-doped YF₃–BaF₂–Ba(PO₃)₂ glasses were observed under 980-nm laser diode excitation. The dependence of the emission intensities of Tb³⁺ on the pump power reveals that two-photon processes account for blue cooperative emission of Yb³⁺ at 476 nm and green upconversion emission of Tb³⁺ at 543 nm, and three-photon processes for ultraviolet emission of Tb³⁺ in the wavelength range of 379–435 nm. The effects of Tb³⁺ concentration on the emission intensity and the lifetime of Tb³⁺ and Yb³⁺ are investigated in detail. It is found that the cooperative energy transfer from a pair of excited Yb³⁺ ions to a ground Tb³⁺ ion is responsible for the appearance of blue and green upconversion emissions due to the ⁵D₄→⁷F _J (J=6,5,4,3) transitions of Tb³⁺, and the resonance energy transfer from Yb³⁺ to Tb³⁺ accounts for the population on the ⁵D₃,⁵G₆ level and ultraviolet upconversion emission.     

Energy transfer study of the formation, composition, and size of nanostructures of metal ion complexes in aqueous solutions

We studied the luminescence intensity (I _lum) of the ions Eu(III) and Sm(III) in relation to the concentrations of ions Ln(III) and Al(III) in water at pH 7 at an excess of such beta-diketones as p-methoxybenzoyltrifluoroacetone (MBTA), dibenzoylmethane (DBM), and tenoyltrifluoroacetone (TTA) and in the presence of 1,10-phenanthroline (phen) used as a synergistic agent. Both the enhancement of I _lum (Eu(III)) upon addition of Gd(III) (co-luminescence) and the effect of the third ion are found to depend on the order of addition of the ions to the solution and, therefore, on the sequence of formation of nanostructures of complexes of these ions in the solution, in which the transfer of the triplet energy of the organic part of complexes takes place, leading to an enhancement in I _lum (Eu(III)). The intensity I _lum (Eu(III)) is shown to increase equally rapidly upon addition of either Gd(III) or Al(III) to solutions with DBM + phen. In solutions of all the three beta-diketones studied, the Eu(III) ions incorporate better into nanostructures of triply charged ions whose radius is similar to or smaller than the radius of the Eu(III) ions. Our study of the effect that the replacement of H₂O with D₂O exerts of I _lum of 5 × 10^?8 M Eu(III) at different concentrations of ligands shows that, at [Ln(III)] < [OH^?] and at a concentration of beta-diketones smaller than 3 × 10^?5 M, the deuteration affects I _lum(Eu(III)) and, therefore, the first coordination sphere of Eu(III) contains OH groups. It is shown that, in aqueous solutions with 3 × 10^?5 M TTA + 10^?5 M phen, the increase in I _lum(Eu(III)) caused by the introduction of Gd(III) ions results from two processes occurring in the nanostructures of these complexes: the energy transfer from Gd(III) complexes to Eu(III) complexes and the increase of I _lum of Eu(III) itself under the conditions in the solution where the total concentration [Ln] ? [OH^?] and both the photochemical deactivation of Eu(III) and the exchange of its excitation energy for vibrations of the OH groups are suppressed. The reliability of the size estimation of nanostructures of metal complexes is discussed in terms of the effect of these nanostructures on I _lum of chelates of Eu(III).     

Variation in the Luminescence Lifetimes of Eucl3·nH2O(N=0,L,2,3,6)

Eu³⁺ ion emission spectra and luminescence lifetimes were investigated for EuCl₃ -nH₂O (n=0,1,2,3,6). Each compound exhibited a characteristic set of emission bands and a specific luminescence lifetime. The number of water molecules and chloride ions coordinated to the Eu³⁺ ion in these materials was estimated from the observed lifetimes, spectroscopic implications, and expected lanthanide coordination numbers. Approximation of the observed luminescence decay constant for each material was possible through the use of arithmetic terms associated with both the complexed water molecules and the complexed chloride ions which make up the inner-coordination sphere of the Eu³⁺ ion.