Photophysical Properties of Lanthanide Hybrids Covalently Bonded To Functionalized MCM-41 by Modified Aromatic Carboxylic Acids

MCM-41 mesoporous silica has been functionalized with aromatic carboxylic acids salicylic acid (Sal) and 2-hydroxyl-3-methylbenzoic acid (HMBA) through co-condensation approach of tetraethoxysilane (TEOS) in the presence of the cetyltrimethylammonium bromide (CTAB) surfactant as a template. Organic ligands salicylic acid or 2-hydroxyl-3-methylbenzoic acid grafted to the coupling agent 3-(triethoxysilyl)-propyl isocyanate (TEPIC) was used as the precursor for the preparation of an organic–inorganic hybrid materials. Novel organic–inorganic mesoporous luminescent hybrid containing Ln³⁺ (Tb³⁺, Eu³⁺) complexes covalently attached to the functionalized ordered mesoporous MCM-41, which were designated as Ln-Sal-MCM-41 and Ln-HMBA-MCM-41, respectively, were obtained by sol–gel process. The luminescence properties of these resulting materials were characterized in detail, and the results reveal that luminescent mesoporous materials have high surface area, uniformity in the mesopore structure and good crystallinity. Moreover, the mesoporous material covalently bonded Tb³⁺ complex (Tb-Sal-MCM-41 and Tb-HMBA-MCM-41) exhibit the stronger characteristic emission of Tb³⁺ and longer lifetime than the corresponding Eu-containg materials Eu-Sal-MCM-41 and Eu-HMBA-MCM-41 due to the triplet state energy of modified organic ligands Sal-TEPIC and HMBA-TEPIC match with the emissive energy level of Tb³⁺ very well. In addition, the luminescence lifetime and emission quantum efficiency of ⁵D₀ Eu³⁺ excited state also indicates the efficient intramolecular energy transfer process in Tb-SAL-MCM-41 and Tb-HMBA-MCM-41.     

Photophysical Properties of Novel Ternary Lanthanide Complexes with Long Chain Mono-L Cis-Butene Dicarboxylate (L = Hexadecyl,Octadecyl and Eicosyl) and 2,2’-Bipyridyl (or 1,10-Phenanthroline)

Maleic anhydride was modified by long chain alcohol (1-hexadecanol, 1-octadecanol and 1-eicosanol) to a novel sort of corresponding long monoester mono-L cis-butene dicarboxylate (L = hexadecyl, octadecyl and eicosyl), i.e. monohexadecyl cis-butene dicarboxylate (MAH), monooctadecyl cis-butene dicarboxylate (MAO), and monoeicosyl cis-butene dicarboxylate (MAE), respectively. Then the some novel ternary lanthanide (Eu³⁺, Tb³⁺) complexes with the as-derived long chain monoester and assistant nitrogen-heterocyclic ligands (2,2’-bipyridyl (bipy) and 1,10-phenanthroline (phen)) were synthesized and characterized by elemental analysis and IR spectra. The photophysical properties of these complexes were studied in detail with ultraviolet absorption spectra, luminescent excitation and emission spectra and luminescent lifetimes, indicating that the intramolecular energy transfer mechanism runs smoothly within these ternary complexes in terms of sensitized functions of bipy and phen and strong characteristic red or green emissions of Eu³⁺ or Tb³⁺ have been achieved.     

Design and Synthesis of a Terbium(III) Complex-Based Luminescence Probe for Time-Gated Luminescence Detection of Mercury(II) Ions

Time-gated luminescence detection technique using lanthanide complexes as luminescent probes is a useful and highly sensitive method. However, the effective application of this technique is limited by the lack of the target-responsive luminescent lanthanide complexes that can specifically recognize various analytes in aqueous solutions. In this work, a dual-functional ligand that can form a stable complex with Tb³⁺ and specifically recognize Hg²⁺ ions in aqueous solutions, N,N,N ¹ ,N ¹ -{[2,6-bis(3′-aminomethyl-1′-pyrazolyl)-4-[N,N-bis(3″,6″-dithiaoctyl)-aminomethyl]- pyridine]} tetrakis(acetic acid) (BBAPTA), has been designed and synthesized. The luminescence of its Tb³⁺ complex is weak, but can be effectively enhanced upon reaction with Hg²⁺ ions in aqueous solutions. The luminescence response investigations of BBAPTA-Tb³⁺ to various metal ions indicate that the complex has a good luminescence sensing selectivity for Hg²⁺ ions, but not for other metal ions. Thus a highly sensitive time-gated luminescence detection method for Hg²⁺ ions was developed by using BBAPTA-Tb³⁺ as a luminescent probe. The dose-dependent luminescence enhancement of the probe shows a good linearity with a detection limit of 17 nM for Hg²⁺ ions. These results demonstrated the efficacy and advantages of the new Tb³⁺ complex-based luminescence probe for the sensitive and selective detection of Hg²⁺ ions.     

Luminescent Properties of a Polymer Photoluminescent Composite Containing the Binuclear (EU,TB) Complex as an Emitter

Uninuclear europium (Eu), as well as binuclear Eu and terbium (Tb), complexes were synthesized using acrylic acid (AA) as the first ligand and 1,10-phenanthroline (Phen) as the second ligand. The relative weight ratio of the europium (III) (Eu³⁺) to terbium (III) (Tb³⁺) ions of the binuclear complex was 1:1 as determined via energy dispersive X-ray analysis. The structures of the Eu(AA)₃Phen and Eu_0.5Tb_0.5(AA)₃Phen complexes were characterized by Fourier transform infrared spectroscopy. A series of tri-cellulose acetate (TCA)/ the Eu(AA)₃Phen and TCA/Eu_0.5Tb_0.5(AA)₃Phen composites were prepared by solution blending, and their luminescent properties were investigated by fluorescence spectrophotometry. The excitation spectra of all composites indicated that the TCA matrix probably affected the energy absorption and transfer of organic ligands. In TCA/Eu_0.5Tb_0.5(AA)₃Phen composites the introduced Tb³⁺ ions had some influence on energy absorption and transfer of organic ligands; the energy transfer process of the complex is suggested to be as follows: Phen→AA→Tb³⁺ion→Eu³⁺ion. The emission spectra indicated that the luminescent intensity of the TCA/Eu_0.5Tb_0.5(AA)₃Phen composites was noticeably stronger than that of the TCA/Eu(AA)₃Phen composites, suggesting that the comparatively stable and high-efficiency energy transfer process was only slightly influenced by the TCA matrix. In summary, the TCA/Eu_0.5Tb_0.5(AA)₃Phen (90/10) composite possesses fine luminescent properties for potential usage as red fluorescent materials.     

Preparation and characterization of a layered transparent luminescent thin film of silica-CTAB-Tb(acac)3 composite with mesostructure

A layered luminescent mesostructured thin film of silica-CTAB-Tb(acac)₃ composite has been synthesized by a dip-coating process through an in situ sol-gel method. The terbium (Tb³⁺) ion and β-diketone organic ligand acetylacetone (acac) were introduced into the precursor solution, respectively. The as-synthesized composite film was transparent, colorless and possessed a layered structure. After the composite film was dried at 50 °C for a few minutes Tb(acac)₃ complex was synthesized in the mesostructured thin film, which can be indicated by the luminescence of the composite film under the UV lamp. The properties of the samples were characterized by XRD, absorption, Fourier transform infrared spectroscopy, and luminescent spectra.     

Efficiency of the energy transfer in lanthanide-organic chelates; spectral overlap integral

The present work is devoted to the evaluation of the efficiency of the sensitized luminescence of the lanthanide complexes. In particular the dependence of the quantum yield of the luminescence on the physical factors that determine the spectral overlap integral is analyzed in detail. The calculations are based on the model of the evaluation of the spectral overlap integral proposed by Malta. It is shown that the theoretical trend in the change of the quantum yield reproduces the general properties of the experimental behavior observed in particular for Tb³⁺ complexes.     

Preparation and Time-Resolved Luminescence Bioassay Application of Multicolor Luminescent Lanthanide Nanoparticles

Because highly luminescent lanthanide compounds are limited to Eu³⁺ and Tb³⁺ compounds with red (Eu, ~615 nm) and green (Tb, ~545 nm) emission colors, the development and application of time-resolved luminescence bioassay technique using lanthanide-based multicolor luminescent biolabels have rarely been investigated. In this work, a series of lanthanide complexes covalently bound silica nanoparticles with an excitation maximum wavelength at 335 nm and red, orange, yellow and green emission colors has been prepared by co-binding different molar ratios of luminescent Eu³⁺–Tb³⁺ complexes with a ligand N,N,N¹,N¹-(4′-phenyl-2,2′:6′,2′′-terpyridine-6,6′′-diyl)bis(methylenenitrilo) tetrakis (acetic acid) inside the silica nanoparticles. The nanoparticles characterized by transmission electron microscopy and luminescence spectroscopy methods were used for streptavidin labeling, and time-resolved fluoroimmunoassay (TR-FIA) of human prostate-specific antigen (PSA) as well as time-resolved luminescence imaging detection of an environmental pathogen, Giardia lamblia. The results demonstrated the utility of the new multicolor luminescent lanthanide nanoparticles for time-resolved luminescence bioassays.     

Luminescent properties of SrAl2B2O7: Ce, Tb

By using metal nitrates as starting materials, SrAl₂B₂O₇: Tb³⁺ and SrAl₂B₂O₇: Ce³⁺, Tb³⁺ powder phosphors were prepared by sol-gel method. X-ray diffraction (XRD), photoluminescence excitation and emission, as well as kinetic decays were employed to characterize the resulting samples. The results show that energy transfers from Ce³⁺ to Tb³⁺ ions. The emission intensity of Tb³⁺ ions in SrAl₂B₂O₇ could be greatly intensified when Ce³⁺ ions are doped into SrAl₂B₂O₇: Tb³⁺. The decay times of SrAl₂B₂O₇: Tb³⁺ were prolonged when Ce³⁺ ions were doped. The doping of Ce³⁺ ions not only improved the luminescent intensity, but also made the materials gets stable luminescent properties.     

Effects of Silver Island Films on the Luminescent Intensity and Decay Times of Lanthanide Chelates

We examined the emission intensity and decay times of chelates Tb³⁺ and Eu³⁺ in micron thick samples between films of sub-wavelength size silver particles. We observed modest increases in emission intensities for the complexes between the silver particles as compared to between unsilvered quartz plates. The intensity decay times were dramatically decreased by the silver particles, which was in part mediated by diffusion toward the silver particles. These results indicated that luminescent lanthanides in close proximity to silver particles display increased rates of radiative decay. The use of luminophore-metallic surface interactions provides new opportunities for creation of luminescent probes with novel spectral properties.     

High brightness and precise adjustment of multicolor-tunable luminescence of Lu2GeO5:Tb3+, Eu3+ phosphors for white LEDs

High brightness and precise adjustment of luminescence colour of phosphors are two main targets in the research of phosphor-converted white LEDs. However, few feasible strategy can be employed to achieve the multicolor-tunable luminescence under the premise of maintaining high quantum efficiency. Here, we demonstrate a high-efficiency energy-transfer process from Tb³⁺ to Eu³⁺ ions with a higher luminescent quantum efficiency (64.5% and 53.4%, respectively), and green-red multicolor emission in Lu₂GeO₅ host via varying the doping content of Tb³⁺ and Eu³⁺ ions. Besides, Lu₂GeO₅:Tb³⁺, Lu₂GeO₅: Eu³⁺ and Lu₂GeO₅: Tb³⁺, Eu³⁺ all exhibit weak thermal quenching which ensures the stable use of white LED device in the high temperature environment. This paper provides a novel multicolor-tunable phosphor with high brightness, efficient energy transfer and weak thermal quenching, which presents a potential application for UV-converted white LEDs.     

Tb ions in presence of ZnS:Mn nanocrystals immobilized on silica: Energy transfer ZnS→Tb and coordination state of Mn ions

Three-component luminescent material consisting of silica xerogel as a support with immobilized ZnS:Mn²⁺ nanocrystals and Tb³⁺ ions was compared with such two-component materials as the silica support with ZnS:Mn²⁺ as well as the support with Tb³⁺. In each case the nanocrystals and the lanthanide ions were immobilized at silica surface by impregnation procedure. Size of the ZnS quantum dots doped with Mn²⁺ were estimated by Scherrer method from the X-ray diffraction (XRD) pattern. The materials have been characterized by EPR and optical spectroscopy techniques. EPR spectra allow to distinguish two different Mn²⁺ sites: the first is assigned to isolated Mn²⁺ substitutionally and incorporated into cubic ZnS lattice and the second is ascribed to the Mn²⁺ situated near the nanocrystal surface. From the optical spectra we have found that in the three-component material, energy transfer from excited ZnS:Mn²⁺ nanocrystals to Tb³⁺ ions takes place. The different mechanisms of such transfer are discussed.     

稀土铽配合物的升频转换荧光

以波长为532nm的激光作为激发光,观测了铽(Tb)三种不同配合物的荧光光谱,讨论和分析了铽配合物的升频转换荧光的特性、发光机制及配体的影响.     

Intramolecular Energy Transfer and Co-luminescence Effect in Rare Earth Ions (La, Y, Gd and Tb) Doped with Eu3+ β-diketone Complexes

In this paper, Eu³⁺ β-diketone Complexes with the two ligands 1-(2-naphthoyl)-3, 3, 3-trifluoroacetonate (TFNB) and 2’2-bipyridine (bpy) have been synthesized. Furthermore, we reported a systematical study of the co-fluorescence effect of Eu(TFNB)₃bpy doped with inert rare earth ions (La³⁺, Gd³⁺ and Y³⁺) and luminescence ion Tb³⁺. The co-luminescence effect can be found by studying the luminescence spectra of the doped complexes, which means that the existence of the other rare earth ions (La³⁺, Y³⁺, Gd³⁺ and Tb³⁺) can enhance the luminescence intensity of the central Eu³⁺, which may be due to the intramolecular energy transfer between rare earth ions and Eu³⁺. The efficient intramolecular energy transfer in all the complexes mainly occurs between the ligand TFNB and the central Eu³⁺. Full characterization and detail studies of luminescence properties of all these synthesized materials were investigated in relation to co-fluorescence effect between the central Eu³⁺ and other inert ions. Further investigation into the luminescence properties of all the complexes show that the characteristic luminescence of the corresponding Eu³⁺ through the intramolecular energy transfers from the ligand to the central Eu³⁺. Meantime, the differences in luminescence intensity of the ⁵D₀→⁷F₂ transition, in the ⁵D₀ lifetimes and in the ⁵D₀ luminescence quantum efficiency among all the synthesized materials confirm that the doped complex Eu_0.5Tb_0.5(TFNB)₃bpy exhibits higher ⁵D₀ luminescence quantum efficiency and longer lifetime than the pure Eu(TFNB)₃bpy complex and other materials.     

Facile synthesis, structural and optical characterization of LnF3:Re nanocrystals by ionic liquid-based hydrothermal process

A novel and easy synthesis of highly luminescent rare-earth ion-doped LnF₃ (LnF₃:Re) nanocrystals by ionic liquid-based hydrothermal process was reported. Ionic liquids [bmim]BF₄ (1-butyl, 2-methylimidazolium tetrafluoroborate) acts as co-solvent, template and reactant. X-ray diffraction and field emission scanning electron microscopy were used to characterize the structural properties of the products. The luminescent properties of LaF₃:Re nanocrystals were evaluated under ultraviolet (397 nm for Eu³⁺, 254 nm for Ce³⁺, Tb³⁺) and (or) near-infrared (980 nm for Er³⁺) excitation. Under 980 nm laser excitation, intense green upconversion emissions were observed for LaF₃:Er(1%) samples in the solid state and dispersion in water and ethanol. The quantum efficiency of LaF₃:Ce(15%),Tb(5%) nanocrystals was about 34%. Our reports provide a facile method for the preparation of LnF₃:Re nanocrystals with excellent photoluminescent properties.     

Highly enhanced luminescence of Tb-activated gadolinium oxysulfide phosphor by doping with Zn ions

Gd₂O₂S:Tb phosphor were synthesized by co-precipitation method combined with solid-state reactions. The brightness of terbium-activated gadolinium oxysulfide phosphors were enhanced and size distributions were controlled by doping the phosphor with a specific amount of zinc oxide. By the analysis of X-ray diffractions, the excitation spectrum and emission spectrum, it can be confirmed that no new phase was introduced and lattice size was diminished. In this way, it may ease access to energy transfer between Gd³⁺ ions and Tb³⁺ ions as well as Tb³⁺ ions and Tb³⁺ ions. Therefore, self-sensitizations of Tb³⁺ ions can be enhanced, ⁵D₄-⁷F_J transitions were further improved and ⁵D₃-⁷F_J transitions were lowered. The enhancement of luminescent properties including brightness and chroma purity were also confirmed due to incorporations of Zn²⁺ ions.     

New promising phosphors Ba3InB9O18 activated by Eu/Tb

Borate Ba₃InB₉O₁₈ (BIBO) has been adopted as a host material for phosphors for the first time. Lanthanide ions (Eu³⁺/Tb³⁺)-doped BIBO phosphors have been synthesized by solid-state reaction and luminescent properties investigated under ultravoilet (UV) excitation. For red phosphor BIBO:Eu, dominant emission peaking at 590 nm was attributed to ⁵D₀→⁷F₁ transition of Eu³⁺, which confirmed that the local site of Eu³⁺ occupied by In³⁺ ion in BIBO crystal lattice is at inversion symmetry center. Optimum Eu³⁺ concentration of BIBO:Eu under UV excitation with 227 nm wavelength is around 40%. The green phosphor BIBO:Tb showed bright green emission at 550 with 232 nm light excited and optimal of Tb³⁺ concentration measured in BIBO is about 8%. The corresponding luminescence mechanisms of Ln-doped BIBO (Ln=Eu³⁺/Tb³⁺) were analyzed. The luminescent intensity of Tb³⁺ can be significantly improved by co-doping of Bi³⁺ in the BIBO:Tb lattice. The likely reason was proposed in terms of the different interactions of the host lattice with these ions, and of these ions with each other.     

Photoluminescent properties of CeF3:Tb3+ nanodiskettes prepared by hydrothermal microemulsion

In this paper, CeF₃:Tb³⁺ nanodiskettes were prepared by the hydrothermal microemulsion method for the first time and the photoluminescent properties of CeF₃:Tb³⁺ nanodiskettes were investigated. The structural properties of CeF₃:Tb³⁺ nanodiskettes were characterized by X-ray diffractions and transmission electron microscopy. The photoluminescent properties of CeF₃:Tb³⁺ with different Tb³⁺ ions concentration were investigated by excitation spectra, emission spectra and lifetime measurement. The energy transfer processes from Ce³⁺ to Tb³⁺ and from Tb³⁺ to Tb³⁺ were analyzed and discussed. Results show that CeF₃:Tb³⁺ nanodiskettes may be applied as phosphors for high resolution displaying. PACS 78.55; 78.66; 79.60     

Structure and photophysical behavior of 2,2′-bipyrimidine/lanthanide ion complexes in various environments

The photophysical behavior of 2,2′-bipyrimidine has been studied alone and in the presence of several lanthanide or other metal ions. This substance, which is employed as bridging ligand in homo- and hetero-dinuclear complexes, can form stable complexes with luminescent lanthanide ions like Eu³⁺ and Tb³⁺. Complexes precipitated from common solvents are crystalline with a structure that consists of discrete, centrosymmetric dinuclear entities with a planar ligand configuration. These complexes are strongly luminescent. Luminescence is sensitized by ligand-to-metal energy transfer. However, when the ligand and metal ions are mixed in an unconventional solvent, like a poly(ethylene glycol) oligomer, all reagents stay in solution and produce a different type of complex where only an enhanced ligand-centered fluorescence can be observed. It is possible that such fluorescence is emitted by 2,2′-bipyrimidine in a non-planar configuration. This behavior has also been observed with other heterocyclic ligands that can exist in different conformers, like terpyridine, and it may explain why some ligand-lanthanide complexes sometimes fail to sensitize efficient photoluminescence.     

Synthesis and luminescence properties of lanthanide(III) chelates with polyacid derivatives of thienyl-substituted terpyridine analogues

Two new polyacid derivative ligands of thienyl-substituted terpyridine analogues, N,N,N¹,N¹-[4′-(2?-thienyl)-2,2′:6′,2″-terpyridine-6,6″-diyl]bis(methylenenitrilo) tetrakis(acetic acid) (TTTA) and N,N,N¹,N¹-[2,6-bis(3′-aminomethyl-1′-pyrazolyl)-4-(2″-thienyl)pyridine] tetrakis(acetic acid) (BTTA), were synthesized, and the luminescence properties of their Eu³⁺ and Tb³⁺ chelates were investigated. The Eu³⁺chelates of the two ligands are strongly luminescent having luminescence quantum yields of 0.150 (TTTA-Eu³⁺) and 0.114 (BTTA-Eu³⁺), and lifetimes of 1.284 ms (TTTA-Eu³⁺) and 1.352 ms (BTTA-Eu³⁺), whereas their Tb³⁺ chelates are weakly luminescent. The TTTA-Eu³⁺ chelate was used for streptavidin (SA) labeling, and the labeled SA was used for time-resolved fluoroimmunoassay of insulin in human sera. The method gives the detection limits of 33 pg ml⁻¹.     

Optical properties of red, green and blue emitting rare earth benzenetricarboxylate compounds

Red, blue and green emitting rare earth compounds (RE³⁺=Eu³⁺, Gd³⁺ and Tb³⁺) containing the benzenetricarboxylate ligands (BTC) [hemimellitic (EMA), trimellitic (TLA) and trimesic (TMA)] were synthesized and characterized by elemental analysis, complexometric titration, X-ray diffraction patterns, thermogravimetric analysis and infrared spectroscopy. The complexes presented the following formula: [RE(EMA)(H₂O)₂], [RE(TLA)(H₂O)₄] and [RE(TMA)(H₂O)₆], except for Tb-TMA compound, which was obtained only as anhydrous. Phosphorescence data of Gd³⁺-(BTC) complexes showed that the triplet states (T) of the BTC³⁻ anions have energy higher than the main emitting states of the Eu³⁺ (⁵D₀) and Tb³⁺ (⁵D₄), indicating that BTC ligands can act as intramolecular energy donors for these metal ions. The high values of experimental intensity parameters (Ω₂) of Eu³⁺-(BTC) complexes indicate that the europium ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the T state of BTC ligands to the excited ⁵D₀ and ⁵D₄ levels of the Eu³⁺ and Tb³⁺ ions is discussed. The emission quantum efficiencies (η) of the ⁵D₀ emitting level of the Eu³⁺ ion have been also determined. In the case of the Tb³⁺ ion, the photoluminescence data show the high emission intensity of the characteristic transitions ⁵D₄→⁷F_J (J=0-6), indicating that the BTC ligands are good sensitizers. The RE³⁺-(BTC) complexes act as efficient light conversion molecular devices (LCMDs) and can be used as tricolor luminescent materials.