VIV-UV excited luminescent properties of LnCa4O(BO3)3 : RE3+(Ln = Y, La, Gd; Re=Eu, Tb, Dy, Ce)

Calcium lanthanide oxyborate doped with rare-earth ions LnCa(4)O(BO3)(3):RE3+ (LnCOB:RE, Ln = Y, La, Gd, RE = Eu, Tb, Dy, Cc) was synthesized by the method of solid-state reaction at high temperature. Their fluorescent spectra were measured from vacuum ultraviolet (VUV) to visible region at room temperature. Their excitation spectra all have a broadband center at about 188 nm, which is ascribed to host absorption. Using Dorenbos' and J phi rgensen's work [P. Dorenbos, J. Lumin. 91 (2000) 91, R. Resfeld, C.K. J phi rgensen. Lasers and Excite States of Rare Earth [M], Springer, Berlin, 1977, p. 45], the position of the lowest 5d levels E(Ln,A) and charge transfer band E-ct were calculated and compared with their excitation spectra.Eu3+ and Tb3+ ions doped into LnCOB show efficient luminescence under VUV and UV irradiation. In this system, Ce3+ ions do not show efficient luminescence and quench the luminescence of Tb3+ ions when Tb3+ and Ce3+ ions are co-doped into LnCOB. GdCOB doped with Dy3+ shows yellowish white light under irradiation of 254 nm light for the reason that Gd ions transfer the energy from itself to Dy.

A new hydrometallurgical process for extracting rare earths from apatite using solvent extraction with P-350

In this paper, a new process is proposed to recover rare earths from nitric acid leaching of apatite without interfering with the normal route for fertilizer production using solvent extraction with dimethyl heptyl methyl phosphonate CH3P(O)(OC8H17)(2) (P-350, B). In the present work, the leaching conditions are studied. In selected condition, apatite was dissolved in 20% (v/v) nitric acid solution at 60-70 degrees C while agitating. The most suitable acidity for extraction is 0.4 M HNO3. More than 98% of rare earths in apatite can be recovered using countercurrent extraction process with six stages when phase ratio = 0.5, and defluorination is unnecessary. The influences of phase ratio, stage number, acidity and salting-out agent on extractabilities Of P-350 are studied. The results show that rare earths can be separated with P-350 from Ca, P, Fe and other impurities. Mixed rare earth oxides (REO) of which purity is more than 95% with yield over 98% can be obtained.

Synergistic extraction of rare earths(III) from chloride medium with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 and di-(2-ethylhexyl)-2-ethylhexylphosphonate

The synergistic effect of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 (HPMBP, HA) and di-(2ethylhexyl)-2-ethylhexylphosphonate (DEHEHP, B) in the extraction of rare earths (RE) from chloride solutions has been investigated. Under the experimental conditions used, there was no detectable extraction when DEHEHP was used as a single extractant while the amount of RE(III) extracted by HPMBP alone was also low. But mixtures of the two extractants at a certain ratio had very high extractability for all the RE (III). For example, the synergistic enhancement coefficient was calculated to be 9.35 for Y3+, and taking Yb3+ and Y3+ as examples, RE3+ is extracted as RE(OH)A(2).B. The stoichiometry, extraction constants and thermodynamic functions such as Gibbs free energy change Delta G (-17.06kJmol(-1)), enthalpy change Delta H (-35.08kjmol(-1)) and entropy change Delta S (-60.47JK(-1)mol(-1)) for Y3+ at 298 K were determined. The separation factors (SF) for adjacent pairs of rare earths were calculated. Studies show that the binary extraction system not only enhances the extraction efficiency of RE(III) but also improves the selectivity, especially between La(III) and the other rare earth elements.

Lanthanide complex/polymer composite optical resin with intense narrow band emission, high transparency and good mechanical performance

Novel composite resins possessing good luminescent properties have been synthesized through a free radical copolymerization of styrene, alpha-methylacrylic acid and the binary or ternary complexes of lanthanide ions (Eu3+ and Tb3+). These polymer-based composite resins not only possess good transparency and mechanical performance but also exhibit an intense narrow band emission of lanthanide complexes under UV excitation. We characterized the molecular structure, physical and mechanical performance, and luminescent properties of the composite resins. Spectra investigations indicate that alpha-methyl-acrylic acid act as both solubilizer and ligand. Photoluminescence measurements indicate that the lanthanide complexes show superior emission lines and higher intensities in the resin matrix than in the corresponding pure complex powders, which can be attributed to the restriction of molecular motion of complexes by the polymer chain networks and the exclusion of water molecules from the complex. We also found that the luminescence intensity decreased with increasing content of alpha-methylacrylic acid in the copolymer system. The lifetime of the lanthanide complexes also lengthened when they were incorporated in the polymer matrix. In addition, we found that the relationships between emission intensity and Tb (Eu) content exhibit some extent of concentration quenching.

Synthesis of Sr2CeO4: Eu-3 by citrate-gel method and its luminescence properties

A novel phosphor Sr2CeO4 was synthesized by the citrate-gel method. The results of XRD show that the temperature at which the crystallization starting is lowered and the soak time for complete crystallization is decreased. The values of pH of the precursor and the ratio( R) between the citrate and cation ions have an effect on the crystallization process. The host can transfer its exciting energy to rare earth ion Eu3+. The doped compound emits strong white light when the concentration of the doped Eu3+ is low. When that of Eu3+ is increased, it emits strong red light. The fluorescence from the higher excited states can be observed because the multiphonon relaxation probability between Eu3+ ions is low.

Langmuir-Blodgett films based on europium-substituted heteropolytungstate and their luminescence properties

Several new hybrid organic-inorganic Langmuir-Blodgett (LB) films containing europium-substituted hetero-polytungstate Eu (XW11O39)(2)''(-) (X=Ge, Si, B) were successfully obtained using LB technique. When the heteropolytungstate anions are dissolved in the subphase, dimethyldioctadecylammonium bromide compression isotherms have been modified, which shows that the polyanions interact with the monolayer. Y-type LB films were obtained from the systems. Low-angle X-ray has shown that these LB films have well-defined lamella. The LB films were characterized by luminescence spectra and the characteristic luminescence behavior for europium-substituted heteropolytungstate complexes and their LB films were discussed. The results of excitation spectra indicate that the energy could be effectively transferred from ligands to the Eu3+ ions in the LB films and the luminescence efficiency could be greatly increased. The results of luminescence spectra indicate that the formations of hybrid organic-inorganic LB films have a great effect on the luminescence of europium-substituted heteropolytungstate. The lifetime shortening was observed in LB films.

Luminescence properties of Eu(phen)(2)Cl-3 doped in sol-gel-derived SiO2-PEG matrix

Rare earth complex Eu(phen)(2)Cl-3 was introduced into a SiO2-PEG-400 hybrid material by a sol-ger method. The result indicated that Poly(ethylene glycol) (PEG) could associate with Eu3+ and change the surroundings of Eu3+ in the hybrid material, greatly improving the decay time. Transparent SiO2-PEG400 hybrid doped with a very small amount of Eu(phen)(2)Cl-3 has better mechanical properties and can retain excellent luminescence properties of the rare earth complex. (C) 2000 Elsevier Science B.V. All rights reserved.

Laser-time-resolved fluorescence spectroscopy in immunoassays

This paper described a laser-excited time-resolved fluoroimmunoassay set. It made lanthanide ion to couple the anhydrde of diethylenetriaminepentaacetic acid (DTPAA) for labeling antibodies. The experiment used polystyrene tap coated with HCV antigen as the solid phase and a chelate of the rare earth metal europium as fluorescent label. A nitrogen laser beam was used to excite the Eu3+ chelates and after 60 ys delay time,the emission fluorescence was measured. Background fluorescence of short lifetimes caused by serum components and Raman scattering can be eliminated by set the delay rime. In the system condition, fluorescent spectra and fluorescent lifetimes of Eu3+ beta-naphthoyltrifluroacetone (NTA) chelates were measured. The fluorescent lifetime value is 650 mu s. The maximum emssion wavelength is 613 nm. The linear range of europium ion concentration is 1 x 10(-7)- 1 x 10(-11) g.mL(-1) and the detection limit is 1 x 10(-13) g.mL(-1). The relative standard deviation of determination ( n = 12) for samples at 0.01 ng.mL(-1) magnitude is 6.4%. Laser-TRFIA was also found to be suitable for diagnosis of HCV. The sensitvity and specificity were comparable to enzyme immunoassay. The result was obtained with laser-TRFIA for 29 human correlated well with enzyme immunoassay.

Preparation and characterization of ternary europium complex-doped thin sol-gel hybrid film by fluorescence spectroscopy

Ternary europium complex with dibenzoylmethane (DBM) and 1,10-phenanthroline (phen) was in-situ synthesized in thin SiO2/polyvinyl butyral (PVB) hybrid films by a two-step sol-gel process and characterized by;means of fluorescence spectroscopy. The luminescence spectra, fluorescence lifetimes and photostability were all investigated. The results showed that the hybrid films exhibited the characteristic emission bands of the Central rare earth Eu3+. In addition, Eu3+ presented longer fluorescence lifetime than in an ethanol solution and the complex had a higher photostability in the hybrid film than in the PVB film containing the corresponding pure complex.

Synthesis, luminescence, energy transfer and Langmuir-Blodgett films of amphiphilic complexes of rare earths with monooctadecyl phthalate

Three new amphiphilic rare earth complexes with only two organic long chains Ln (MOP)(2)Cl (MOP=monooctadecyl phthalate, Ln=Eu, Tb, Gd) were synthesized and characterized by elemental analysis. The complexes (Eu, Tb) showed good luminescence property with long fluorescence lifetime, whereas the intensity and lifetime of Tb complex are greater than those of Eu complex, By measuring the triplet energy levels of ligand based on energy transfer mechanism, above phenomena have been well explained. The Langmuir films of the complexes on the air/water interface were also studied and the results show that all of them have good film-forming property.

pH-potentiometric study on rare earths and calcium binary and ternary complexes with DL-malic acid and L-hydroxyproline

The stability constants of M-L binary system and M-L-L' (M = La3+ similar to Yb3+, Y3+ and Ca2+; L= DL-malic aicd, L' = L-hydroxyproline) ternary system were determined by pH-(0)-tentiometric method under the simulating physiological condition(37 degrees C, I=0.15 mol/L NaCl). The complex species MpLqLr'H-s(abbr as pqrs) in the sytems were ascertained by program COMPLEX. The results show that there are three species(1101, 1100 and 1200) in M-L binary system and one species(1010) in M-L' binary system. In addition to the above four species, a new species, 1112 was found in the M-L-L' ternary system, which is the only species of mixed ligands. Rare earth ions form more stable complexes than calcium ion does and the stability differences between their complexes in the ternary system are less than that in the binary system. The distributions of all the species in La-L-L' ternary system vs pH are discussed.

Luminescence properties of sol-gel derived silica gels doped and undoped with RE-complexes (RE=Eu, Tb)

The luminescence properties of silica gels and silica gels doped with two rare earth complexes, Eu(TTA)(3) and Tb(o-CBA)(3) (TTA=thenoyltriffuocetate, o-CBA=o-chlorobenzoic acid) are reported and discussed. Pure silica gels show a blue luminescence, and the maximum excitation and emission wavelengths depend strongly on the solvents used. Both of the studied rare earth complexes exhibit the characteristic emissions of the rare earth ions in silica gels, i.e., Eu3+5D0-->F-7(J)(J=0,1,2,3,4), Tb3+5D4-->F-7(J)(J=3,4,5,6) transitions. Compared with the pure RE-complexes powder, the silica gels doped with RE-complexes show fewer emission lines of the rare earth ions. Furthermore the rare earth ion (Tb3+) presents a longer lifetime (1346 mu s) in silica gel doped with Tb(o-CBA)3 than in pure Tb((o-CBA)(3) powder (744 mu s). The reasons responsible for these results are discussed in the context.

Luminescence of RE3+ and energy transfer from Gd3+ to RE3+ (RE=Dy, Eu) in SrGdAlO4:RE3+

Spectral properties of Gd3+, Dy3+ and Eu3+ ions in SrGdAlO4 are reported in detail A cooperative vibronic transition of Gd3+ and the emission from the higher D-5(J) (J=1, 2, 3) levels of Eu3+ were observed. Energy transfer occurs from Gd3+ to Dy3+ and to Eu3+. The influence of Gd3+ and Dy3+ concentrations on the luminescence intensity is discussed.

The spectral properties of BaB8O13:Eu,Tb phosphors

The luminescence properties of BaB8O13:xEu,yTb phosphors which were synthesized in air atmosphere have been studied. The emissions of europium(III), terbium(III) and europium(II) have been observed in BaB8O13:xEu, yTb phosphors. Electron paramagnetic resonance (EPR) studies were carried out. The intensities of EPR peaks of europium(II) are increased if terbium(III) is increased in BaB8O13:Eu3+,yTb(3+) phosphors. So the valence state of europium is influenced by terbium(III). These phenomena can be explained by an electron transfer mechanism. We found a new kind of method to prepare trichromatic phosphor that two rare earth ions activated in a BaB8O13 matrix.

Electron Transfer and its Equilibrium between Eu and Tb in SrMgF4 System

Emission of europium(II) and europium(III) have been observed in SrMgF4 xEu, yTb phosphors winch are synthesized in Ar flow. The valence state of En is influenced by terbium, It is noted that the intensities of the ESR peaks corresponding to Eu2+ are increased when terbium ion is codopech this can be explained by electron transfer mechanism which is Eu3++Tb3+-->Eu2++Tb4+. And its equilibrium constant is calculated.