Synthesis and Characterization of Polymers Containing Rare Earth Metals

Europium and terbium salts of methacrylic acid (MA) and octanoic acid (OCA) were prepared by a method similar to that described in the literature. Either Eu(MA)₃ or Tb(MA)₃ with three double bonds (C?C) was used as a crosslinker containing rare earth metal ions, but the octanoic acid salts were used as additives. The salts were dissolved in methacrylic acid (<20%) and then copolymerized with methyl methacrylate (>80%) using AIBN (0.2 wt%) as initiator. The two types of polymers, one containing Eu(MA)₃ or Tb(MA)₃ and the other with Eu(OCA)₃ or Tb(OCA)₃, were synthesized by bulk copolymerization in molds made of two glass plates and characterized. The fluorescence spectroscopy of these polymers under ultraviolet/visible excitation light was investigated. The fluorescence excitation and emission spectra of the polymers showed the characteristic spectra of the free Eu³⁺ or Tb³⁺. The fluorescence intensity of the rare earth metal ions increased with increasing rare earth metal content. Fluorescence measurements for Eu(MA)₃, Tb(MA)₃, and Eu(OCA)₃ polymers do not display fluorescence quenching behavior within the range of the rare earth metal content used in our experiments. But for Tb(OCA)₃ polymers, this phenomenon was observed, illustrating that ionic aggregates exist in Tb(OCA)₃ polymeric systems.     

Cofluorescence of dyes in nanoparticles from metal ion complexes with diketones

Nanoparticles (NPs) from diketonates of Al³⁺, Sc³⁺, In³⁺ and Ln³⁺ doped with dye molecules are synthesized. The appearance of sensitized fluorescence (cofluorescence) of dye molecules due to energy transfer from the ensemble of complexes forming NPs is revealed in aqueous solutions of these NPs. It is shown that the dye cofluorescence in NPs from Eu complexes occurs as a result of two distinct processes of energy transfer (ET) to dye molecules: from singlet levels of ligands and from Eu³⁺ ions. It is found that the efficiency of ET from Eu³⁺ ions to dyes in NPs from Eu(DBM)₃phen is one order of magnitude higher than the efficiency of ET from S₁-levels of ligands to dyes in NPs from Al complexes with the same ligands. It is shown that the excitation of dye molecules through ligands of NPs results in the enhancement of the intensity of their fluorescence by a factor of 1.5–2 orders of magnitude compared to the excitation of their own first band of absorption.     

苯并咪唑衍生配体锌-铕(或铽)异金属双核配合物的合成、结构与光学性质

合成了四个锌-铕(或铽)异金属双核配合物[ZnLnL¹(NO₃)₃Py] (Ln=Eu (1), Tb (2); HL¹=1-H-2-(2-羟基-3-甲氧基苯基)苯并咪唑; Py=吡啶)和[ZnLnL²(NO₃)₃Py] (Ln=Eu (3), Tb (4); HL²=1-H-2-(2-羟基-3-甲氧基-5-溴苯基)苯并咪唑; Py=吡啶), 其中1、2、3是单晶态, 化合物4则为多晶样品; 通过单晶X射线衍射、元素分析、傅里叶变换红外光谱和电喷雾质谱对化合物进行了表征. 化合物的紫外-可见吸收光谱、荧光激发和发射光谱表明配体的激发态能量有效传递到配合物中的镧系金属离子中, 含有铽(III)离子的配合物发射出其特征发射光谱, 而含有铕(III)离子的配合物由于其它去活方式, 没有辐射出铕(III)离子的特征发射光谱.     

The influence of excitation of the 4f-orbital of Eu(fod)3 on complex formation with adamantanone and anomalous enhancement of Eu3+ luminescence under the action of H2O and D2O molecules in toluene

The influence of excitation of the 4f-orbital of, β-diketonate Eu(fod)₃ (fod is heptafluorodimethyloctanedione) on the formation of the coordination bond with adamantanone (1) was studied by the nonradiative energy transfer technique. The kinetic parameters of fluorescence (FL) and the lifetime (τ) of the Eu³⁺ ion in toluene solutions were studied. The increase in the stability of the Eu(fod)₃·1 complex when f—f-transitions of the Eu³⁺ ion are excited is related to an increase in the acceptor capability of Eu(fod)₃ due to the increasing fraction of the covalent component determined by the participation of 4f-orbitals. An unexpected effect of enhancement of the Eu(fod)₃ fluorescence under the action of H₂O (D₂O) molecules in toluene solutions was observed. The effect is assumed to be caused by an increase in the negative inductive effect when outer-sphere associates with the fluorinated radical of β-diketonate are formed. The mechanisms of the influence of electron-donating inner-sphere ligands and outer-sphere associates on the quantum yield of fluorescence of Eu(fod)₃ are discussed.     

Fluorescence characteristics of europium ions stabilized in solid polymer electrolytes containing polyether structure

Polyethylene oxide (PEO) oligomers can dissolve lanthanide salts. The terminal hydroxyl groups of PEO affect the solubility of the lanthanide salts in the PEO considerably. However, no intensive fluorescence was observed from Eu³⁺ dispersed in PEO or other ion-conductive polymers containing terminal hydroxyl groups, because of the quenching effect of the terminal hydroxyl groups. Copolymer of ω-methoxy oligo(oxyethylene) methacrylate and methyl methacrylate (P(MEOM-co-MMA)) could dissolve small amount of Eu(NO₃)₃, but the copolymer film containing Eu³⁺ shows intensive fluorescence (Ex = 269.0 nm, Em = 570.0 nm). This was prepared as a soft film, and there was a clear dependence of the Eu³⁺ concentration on the fluorescence intensity. A linear relation between the film thickness and the fluorescence intensity was also observed. Little fluorescence was found for Eu³⁺ in the blend of the corresponding two homopolymers, i.e. poly-(ω-methoxy oligo (oxyethylene) methacrylate) (PMEOM) and poly(α-methyl methacrylate) (PMMA). This strongly suggests that intensive fluorescence requires a mixed state of MEOM and MMA units at molecular level.     

Excitation Energy-Transfer Processes in the Sensitization Luminescence of Europium in a Highly Luminescent Complex

The excitation energy transfer (EET) pathways in the sensitization luminescence of Eu^III and the excitation energy migration between the different ligands in [Eu(fod)₃dpbt] [where fod=6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione and dpbt=2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine], exhibiting well-separated fluorescence excitation and phosphorescence bands of the different ligands, were investigated by using time-resolved luminescence spectroscopy for the first time. The data clearly revealed that upon the excitation of dpbt, the sensitization luminescence of Eu^III in [Eu(fod)₃dpbt] was dominated by the singlet EET pathway, whereas the triplet EET pathway involving T₁(dpbt) was inefficient. The energy migration from T₁(dpbt) to T₁(fod) in [Eu(fod)₃dpbt] was not observed. Moreover, upon the excitation of fod, a singlet EET pathway for the sensitization of Eu^III luminescence, including the energy migration from S₁(fod) to S₁(dpbt) was revealed, in addition to the triplet EET pathway involving T₁(fod). Under the excitation of dpbt at 410 nm, [Eu(fod)₃dpbt] exhibited an absolute quantum yield for Eu^III luminescence of 0.59 at 298 K. This work provides a solid and elegant example for the concept that singlet EET pathway could dominate the sensitization luminescence of Eu^III in some complexes.     

Triboluminescence of Lanthanide Coordination Polymers with Face-to-Face Arranged Substituents

Luminescence upon the grinding of solid materials (triboluminescence, TL) has long been a puzzling phenomenon in natural science and has also attracted attention because of its broad application in optics. It has been generally considered that the TL spectra exhibit similar profiles as those of photoluminescence (PL), although they occur from distinct stimuli. Herein, we describe for the first time a large spectral difference between these two physical phenomena using lanthanide^III coordination polymers with efficient TL and PL properties. They are composed of emission centers (Tb^III and Eu^III ions), antenna (hexafluoroacetylacetonate=hfa), and bridging ligands (2,5-bis(diphenylphosphoryl)furan=dpf). The emission color upon grinding (yellow TL) is clearly different from that upon UV irradiation (reddish-orange PL) in Tb^III/Eu^III-mixed coordination polymers [Tb,Eu(hfa)₃(dpf)]_n (Tb/Eu=1). The results directly indicate the discrete excitation processes of PL and TL.     

Triboluminescence of Lanthanide Coordination Polymers with Face‐to‐Face Arranged Substituents

Luminescence upon the grinding of solid materials (triboluminescence, TL) has long been a puzzling phenomenon in natural science and has also attracted attention because of its broad application in optics. It has been generally considered that the TL spectra exhibit similar profiles as those of photoluminescence (PL), although they occur from distinct stimuli. Herein, we describe for the first time a large spectral difference between these two physical phenomena using lanthanide^III coordination polymers with efficient TL and PL properties. They are composed of emission centers (Tb^III and Eu^III ions), antenna (hexafluoroacetylacetonate=hfa), and bridging ligands (2,5‐bis(diphenylphosphoryl)furan=dpf). The emission color upon grinding (yellow TL) is clearly different from that upon UV irradiation (reddish‐orange PL) in Tb^III/Eu^III‐mixed coordination polymers [Tb,Eu(hfa)₃(dpf)]_n (Tb/Eu=1). The results directly indicate the discrete excitation processes of PL and TL.     

Luminescence Tuning and White‐Light Emission of Co‐doped Ln–Cd–Organic Frameworks

Four new three‐dimensional isostructural lanthanide–cadmium metal–organic frameworks (Ln–Cd MOFs), [LnCd₂(imdc)₂(Ac)(H₂O)₂]?H₂O (Ln=Pr ( 1 ), Eu ( 2 ), Gd ( 3 ), and Tb ( 4 ); H₃imdc=4,5‐imidazoledicarboxylic acid; Ac=acetate), have been synthesized under hydrothermal conditions and characterized by IR, elemental analyses, inductively coupled plasma (ICP) analysis, and X‐ray diffraction. Single‐crystal X‐ray diffraction shows that two Ln^III ions are surrounded by four Cd^II ions to form a heteronuclear building block. The blocks are further linked to form 3D Ln–Cd MOFs by the bridging imdc^3? ligand. Furthermore, the left‐ and right‐handed helices array alternatively in the lattice. Eu–Cd and Tb–Cd MOFs can emit characteristic red light with the Eu^III ion and green light with the Tb^III ion, respectively, while both Gd–Cd and Pr–Cd MOFs generate blue emission when they are excited. Different concentrations of Eu³⁺ and Tb³⁺ ions were co‐doped into Gd–Cd/Pr–Cd MOFs, and tunable luminescence from yellow to white was achieved. White‐light emission was obtained successfully by adjusting the excitation wavelength or the co‐doping ratio of the co‐doped Gd–Cd and Pr–Cd MOFs. These results show that the relative emission intensity of white light for Gd–Cd:Eu³⁺,Tb³⁺ MOFs is stronger than that of Pr–Cd:Eu³⁺,Tb³⁺ MOFs, which implies that the Gd complex is a better matrix than the Pr complex to obtain white‐light emission materials.     

Luminescence Properties of Terbium-, Cerium-, or Europium-Doped α-Sialon Materials

New interesting luminescent α-sialon (M_(m/val+)^val+ Si_12-(m+n) Al_(m+n)OnN_(16−n)) (M=Ca, Y) materials doped with Ce, Tb, or Eu have been prepared and their luminescence properties studied. These show that Tb and Ce are in the 3+ and Eu in the 2+ state. Low-energy 4f↔5d transitions are observed as compared to the luminescence of these ions doped in oxidic host-lattices. This is partially explained by the nitrogen-rich coordination of the rare-earth ion and partially by the narrow size of the lattice site. The latter gives rise to a strong crystal-field splitting of the 5d band and a rather large Stokes shift for Ce³⁺ and Eu²⁺ (6500-7500 and 7000-8000 cm⁻¹, respectively). For (Y,Tb)-α-sialon the Tb³⁺ 4f→5d excitation band (∼260 nm) is in the low-energy host-lattice absorption band (?290 nm), giving rise to a strong absorption for 254-nm excitation, but a low quantum efficiency. The latter is due to photoionization processes or selective excitation of Tb³⁺ at the defect-rich surface, resulting in radiationless transitions. Ce- and Eu-doped Ca-α-sialon show bright long-wavelength luminescence (maxima at 515-540 and 560-580 nm for Ce and Eu, respectively) with a high quantum efficiency and high absorption for 365- and 254-nm excitation. The Eu²⁺ emission intensity and absorption increases for increasing m, which is explained by the Eu²⁺ richer α-sialon composition. The position of the Eu^2α emission does not shift with changing composition of the host-lattice (m, n values), indicating that the local coordination of the Eu²⁺ ion is hardly dependent on the matrix composition.     

Lanthanide metal polymer complexes. Synthesis,characterization and application

Our recent results on the investigation of lanthanide metal polymer complexes were presented. Luminescence properties of Tb³⁺ or Eu³⁺ -polycarboxylate complexes in aqueous solution were investigated. The excitation band near 300 nm for Tb or Eu(polyacrylate) solutions were drastically enhanced by the addition of hydroxy radical generating reagents as well as ultrasonic irradiation. These spectral changes were attributed to the energy transfer from chromophore molecules formed by generated hydroxy radicals in both systems. Since the increase in the luminescence intensity was proportional to the hydroxy radical concentration, the Eu³⁺ or Tb³⁺ (PAA) system can provide a convenient method for the determination of hydroxy radical concentration in aqueous solution. We have also utilized lanthanide metal ion complexes as a luminescent emitter in electroluminescence (EL) devices. The configuration of the EL cell and experimental results were discussed.     

Visual Detection of Triethylamine and a Dual Input/Output Logic Gate Based on a Eu3+-Complex

A series of Ln³⁺-metal centered complexes, Ln(TTA)₃(DPPI) (Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3; or Ln = Gd, 4) [(DPPI = N-(4-(1H-imidazo [4,5-f][1,10]phenanthrolin-2-yl)phenyl)-N-phenylbenzenamine) and (TTA = 2-Thenoyltrifluoroacetone)] have been synthesized and characterized. Among which, the Eu³⁺-complex shows efficient purity red luminescence in dimethylsulfoxide (DMSO) solution, with a Commission International De L’ Eclairage (CIE) coordinate at x = 0.638, y = 0.323 and Φ_Eu^L = 38.9%. Interestingly, increasing the amounts of triethylamine (TEA) in the solution regulates the energy transfer between the ligand and the Eu³⁺-metal center, which further leads to the luminescence color changing from red to white, and then bluish-green depending on the different excitation wavelengths. Based on this, we have designed the IMPLICATION logic gate for TEA recognition by applying the amounts of TEA and the excitation wavelengths as the dual input signal, which makes this Eu³⁺-complex a promising candidate for TEA-sensing optical sensors.     

Electrochemical and Spectroscopic Study of EuIII and EuII Coordination in the 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid

Separation processes based on room temperature ionic liquids (RTIL) and electrochemical refining are promising strategies for the recovery of lanthanides from primary ores and electronic waste. However, they require the speciation of dissolved elements to be known with accuracy. In the present study, Eu coordination and Eu^III/Eu^II electrochemical behavior as a function of water content in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][NTf₂]) was investigated using UV–visible spectrophotometry, time-resolved laser fluorescence spectroscopy, electrochemistry, and X-ray absorption spectroscopy. In situ measurements were performed in spectroelectrochemical cells. Under anhydrous conditions, Eu^III and Eu^II were complexed by NTf₂, forming Eu−O and Eu−(N,O) bonds with the anion sulfoxide function and N atoms, respectively. This complexation resulted in a greater stability of Eu^II, and in quasi-reversible oxidation–reduction with an E₀’ potential of 0.18 V versus the ferrocenium/ferrocene (Fc⁺/Fc) couple. Upon increasing water content, progressive incorporation of water in the Eu^III coordination sphere occurred. This led to reversible oxidation–reduction reactions, but also to a decrease in stability of the +II oxidation state (E₀’=−0.45 V vs. Fc⁺/Fc in RTIL containing 1300 mm water).     

Photoluminescence properties of a novel phosphor, Na3La9O3(BO3)8:RE(RE=Eu,Tb)

The new oxyborate phosphors, Na₃La₉O₃(BO₃)₈:Eu³⁺ (NLBO:Eu) and Na₃La₉O₃(BO₃)₈:Tb³⁺ (NLBO:Tb) were prepared by solid-state reactions. The photoluminescence characteristics under UV excitation were investigated. The dominated emission of Eu³⁺ corresponding to the electric dipole transition ⁵D₀→⁷F₂ is located at 613 nm and bright green luminescence of NLBO:Tb attributed to the transition ⁵D₄→⁷F₅ is centered at 544 nm. The concentration dependence of the emission intensity showed that the optimum doping concentration of Eu and Tb is 30% and 10%, respectively.     

Tunable photoluminescence of NaYF4:Eu nanocrystals by Sr codoping

NaYF₄:Eu/Sr nanocrystals were synthesized by a hydrothermal method. Tunable photoluminescence of the NaYF₄:Eu nanocrystals was successfully achieved by codoping with Sr²⁺ ions. With increasing Sr²⁺ concentration, not only the X-ray diffraction peaks of the nanocrystals become broader, but also the positions of them shift toward larger lattice parameters. Eu³⁺ and Eu²⁺ have been found to coexist in an NaYF₄:Eu/Sr. The Eu³⁺/Eu²⁺ emission intensity ratio changed with the Sr²⁺ concentration and excitation wavelength. More interestingly, the spectral configurations of Eu²⁺ and Eu³⁺ also varied with the excitation wavelength, indicating that the nanocrystals have multiple luminescence centers or emitting states.     

VUV-UV Photoluminescence Spectra of Strontium Orthophosphate Doped with Rare Earth Ions

The measurements of VUV-UV photoluminescence emission (PL) and photoluminescence excitation (PLE) spectra of rare earth ions activated strontium orthophosphate [Sr₃(PO₄)₂:RE, RE = Ce, Sm, Eu, Tb] are performed. Whenever the samples are excited by VUV or UV light, the typical emission of Ce³⁺, Sm³⁺, Eu³⁺, Eu²⁺ and Tb³⁺ ions can be observed in PL spectra, respectively. The charge transfer bands (CTBs) of Sm³⁺ and Eu³⁺ are found, respectively, peaking at 206 and 230 nm. The absorption bands peaking in the region of 150-160 nm are assigned to the host lattice sensitization bands, i.e., the band-to-band transitions of PO₄³⁻ grouping in Sr₃(PO₄)₂. It is speculated that the first f-d transitions of Sm³⁺ (Eu³⁺), and the CTB of Tb³⁺are, respectively, located around 165 (1 4 3) and 167 nm by means of VUV-UV PLE spectra and relational empirical formula, these f-d transitions or CT bands are included in the bands with the maxima at 150-160 nm, respectively. The valence change of europium from trivalent to divalent in strontium orthophosphate prepared in air is observed by VUV-UV PL and PLE spectra.     

Fluorimetry and differential scanning calorimetry analysis of ionomers with low Eu3+ contents

Fluorimetry and differential scanning calorimetry have been used to characterize ionomers that were synthesized by copolymerization of methyl methacrylate, methacrylic acid, and europium methacrylate (EMA). Under excitation of UV light at 375 nm no self-quenching was found in fluorescence of EMA-containing ionomers at 615 nm within the Eu³⁺ concentration range of 1.6 × 10⁻² to 11.49 × 10⁻² mol %, which means that the distance between two Eu³⁺ ions is larger than 50 Å. In the same concentration range self-quenching took place in europium octanoate (EOA)-containing ionomers in which EOA was doped as an additive. Only one T_g was found for both kinds of polymers within the concentration range of Eu³⁺ ions. For all ion contents studied, T_g values were essentially independent of ion content and values were slightly higher for the EMA containing ionomers. © 1997 John Wiley & Sons, Inc.     

Synthesis and photoluminescence of the solid phases of the binary system of mixed-ligand Eu(III) and Tb(III) dithiophosphinate complexes

Solid phases of the [Eu(Phen)(i-Bu₂PS₂)₂(NO₃)]–[Tb(Phen)(i-Bu₂PS₂)₂(NO₃)] binary system are synthesized. The results of X-ray diffraction phase analysis and photoluminescence measurements allow the synthesized isostructural phases to be classed with substitutional solid solutions. The photoluminescence measurements revealed Tb(III)→Eu(III) energy transfer which induces Eu³⁺ luminescence.     

Synthesis,Structures, and Luminescent Properties of Chloride and Nitrate LnIII Complexes Coordinated by tris(Pyrazolyl)methane

We report the synthesis of Ln³⁺ nitrate [Ln(Tpm)(NO₃)₃] ⋅ MeCN (Ln=Yb ( 1Yb ), Eu ( 1Eu )) and chloride [Yb(Tpm)Cl₃] ⋅ 2MeCN ( 2Yb ), [Eu(Tpm)Cl₂(μ-Cl)]₂ ( 2Eu ) complexes coordinated by neutral tripodal tris(3,5-dimethylpyrazolyl)methane (Tpm). The crystal structures of 1Ln and 2Ln were established by single crystal X-ray diffraction, while for 1Yb high resolution experiment was performed. Nitrate complexes 1Ln are isomorphous and both adopt mononuclear structure. Chloride 2Yb is monomeric, while Eu³⁺ analogue 2Eu adopts a binuclear structure due to two μ²-bridging chloride ligands. The typical lanthanide luminescence was observed for europium complexes ( 1Eu and 2Eu ) as well as for terbium and dysprosium analogues ([Ln(Tpm)(NO₃)₃] ⋅ MeCN, Ln=Tb ( 1Tb ), Dy ( 1Dy ); [Ln(Tpm)Cl₃] ⋅ 2MeCN, Ln=Tb ( 2Tb ), Dy ( 2Dy )).     

Significant enhancement of luminescence intensity of CaTiO3:Eu3+ red phosphor prepared by sol–gel method and co-doped with Bi3+ and Mg2+

In this study, red phosphors Ca_1?n Mg _n TiO₃:Eu³⁺,Bi³⁺ were prepared by the sol?Cgel method and the impact of single dopant, co-dopants and solid solutions on the photoluminescence of the samples has been also investigated. Our results show that the crystal structure of the host does not have distinct changes when doped with Eu³⁺, Bi³⁺ and/or Mg²⁺. The emission intensity at 615?nm of Eu³⁺ increased at the presence of Bi³⁺ ions owing to the energy transfer from Bi³⁺ ion to Eu³⁺ ion. Moreover, with the addition of Mg²⁺, the red emission of the phosphor was further enhanced due to the stronger absorption at 399 and 467?nm, which match well with the emission of near-UV (395?C400?nm) and blue-LED (450?C470?nm), respectively. Under the near-UV (399?nm) or blue light (467?nm) excitation, the fluorescence quantum yield of the optimal composition Ca_0.9Mg_0.1TiO₃:0.18Eu³⁺,0.018Bi³⁺ is 0.36 and 0.41, respectively, which possesses the higher photoluminescence intensity than CaMoO₄:0.2Bi³⁺,0.05Eu³⁺ and the commercially available Y₂O₂S:Eu³⁺ phosphors under near-UV excitation. Based on these results, we are currently considering the potential application of Ca_0.9Mg_0.1TiO₃:Eu³⁺,Bi³⁺ as a near-UV or blue-chip convertible red-emitting phosphor.