Upconversion Luminescence through Cooperative and Energy-Transfer Mechanisms in Yb3+-Metal-Organic Frameworks

Lanthanide-doped metal–organic frameworks (Ln-MOFs) have versatile luminescence properties, however it is challenging to achieve lanthanide-based upconversion luminescence in these materials. Here, 1,3,5-benzenetricarboxylic acid (BTC) and trivalent Yb³⁺ ions were used to generate crystalline Yb-BTC MOF 1D-microrods with upconversion luminescence under near infrared excitation via cooperative luminescence. Subsequently, the Yb-BTC MOFs were doped with a variety of different lanthanides to evaluate the potential for Yb³⁺-based upconversion and energy transfer. Yb-BTC MOFs doped with Er³⁺, Ho³⁺, Tb³⁺, and Eu³⁺ ions exhibit both the cooperative luminescence from Yb³⁺ and the characteristic emission bands of these ions under 980 nm irradiation. In contrast, only the 497 nm upconversion emission band from Yb³⁺ is observed in the MOFs doped with Tm³⁺, Pr³⁺, Sm³⁺, and Dy³⁺. The effects of different dopants on the efficiency of cooperative luminescence were established and will provide guidance for the exploitation of Ln-MOFs exhibiting upconversion.     

Fluorescence of rare earth ions adsorbed on porous vycor glass

Fluorescence of rare earth (RE) ions arising from f—f transitions in Pr³⁺, Eu³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺ and Tm³⁺ was observed front the ions adsorbed on porous Vycor glass or on pressed discs of fumed silica. The non-radiative relaxations of the excited states were depressed as a result of a strong chemical bond between the ions and silica acting as a ligand.     

Liquid Membrane Transport of Heavier Rare Earth Metal Ions Based on CPC Results with Di(2-Ethylhexyl) Phosphoric Acid

Abstract

The behaviors of heavier rare earth metal ions in bulk liquid membrane transport systems were examined for Gd³⁺, Tb³⁺, Dy³, Ho³⁺, Er³⁺, Tm³, Yb³⁺ and Lu³⁺ ions. The liquid membrane transport system was constructed by aq. HCl/CHCl₃ containing Di (2-ethylhexyl) phosphoric acid/aq. HCl. The optimum concentration of HCl in the aqueous phase with respect to the rate of transport for these ions increased with the atomic number of the rare earth elements. This trend of transport behaviors was on the same line observed for lighter rare earth ions in the preceding work. Difference in the rate of transport can be used for selective liquid membrane transport of several sets of combination with these ions.     

Thermal analysis of rare-earth metal(III) hexa(isothiocyanato)chromate(III) complexes with ɛ-caprolactam

Thermal decomposition of the complexes [LnL₈][Cr(NCS)₆] (Ln = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, Lu³⁺; L = ɛ-C₆H₁₁NO) in air and in inert atmosphere was studied by thermogravimetry, X-ray phase analysis, IR spectroscopy, and mass spectrometry. The compositions of gaseous and solid thermolysis products were established. A reversible thermochromic effect was found on heating to 200–210°C.     

新型希土4-羟基-7-三氟甲基-3-喹啉基甲酸乙酯配合物的光物理性质

首次合成了五种新型希土(Eu³⁺, Tb³⁺, Gd³⁺, Sm³⁺, Dy³⁺)配合物。配体为带有喹啉环的4-羟基-7-三氟甲基-3-喹啉基甲酸乙酯。并用元素分析、红外光谱和热分析方法确定了配合物的组成。通过测定钆配合物的低温磷光光谱表明4-羟基-7-三氟甲基-3-喹啉基甲酸乙酯的三重态能级为22000 cm^-1。配合物的光物理性质表明配体的三重态能级适于希土Eu³⁺, Sm³⁺, Dy³⁺和Tb³⁺，特别是Tb³⁺的发光。     

Vacuum ultraviolet and near-infrared excited luminescence properties of Ca3(PO4)2:RE, Na (RE=Tb, Yb, Er, Tm, and Ho)

Tb³⁺, Yb³⁺, Tm³⁺, Er³⁺, and Ho³⁺ doped Ca₃(PO₄)₂ were synthesized by solid-state reaction, and their luminescence properties were studied by spectra techniques. Tb³⁺-doped samples can exhibit intense green emission under VUV excitation, and the brightness for the optimal Tb³⁺ content is comparable with that of the commercial Zn₂SiO₄:Mn²⁺ green phosphor. Under near-infrared laser excitation, the upconversion luminescence spectra of Yb³⁺, Tm³⁺, Er³⁺, and Ho³⁺ doped samples demonstrate that the red, green, and blue tricolored fluorescence could be obtained by codoping Yb³⁺-Ho³⁺, Yb³⁺-Er³⁺, and Yb³⁺-Tm³⁺ in Ca₃(PO₄)₂, respectively. Good white upconversion emission with CIE chromaticity coordinates (0.358, 0.362) is achieved by quadri-doping Yb³⁺-Tm³⁺-Er³⁺-Ho³⁺ in Ca₃(PO₄)₂, in which the cross-relaxation process between Er³⁺ and Tm³⁺, producing the ¹D₂-³F₄ transition of Tm³⁺, is found. The upconversion mechanisms are elucidated through the laser power dependence of the upconverted emissions and the energy level diagrams.     

DNA Intercalating Near-Infrared Luminescent Lanthanide Complexes Containing Dipyrido[3,2-a:2′,3′-c]phenazine (dppz) Ligands: Synthesis,Crystal Structures,Stability, Luminescence Properties and CT-DNA Interaction

In order to create near-infrared (NIR) luminescent lanthanide complexes suitable for DNA-interaction, novel lanthanide dppz complexes with general formula [Ln(NO₃)₃(dppz)₂] (Ln = Nd³⁺, Er³⁺ and Yb³⁺; dppz = dipyrido[3,2-a:2′,3′-c]phenazine) were synthesized, characterized and their luminescence properties were investigated. In addition, analogous compounds with other lanthanide ions (Ln = Ce³⁺, Pr³⁺, Sm³⁺, Eu³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Tm³⁺, Lu³⁺) were prepared. All complexes were characterized by IR spectroscopy and elemental analysis. Single-crystal X-ray diffraction analysis of the complexes (Ln = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Eu³⁺, Er³⁺, Yb³⁺, Lu³⁺) showed that the lanthanide’s first coordination sphere can be described as a bicapped dodecahedron, made up of two bidentate dppz ligands and three bidentate-coordinating nitrate anions. Efficient energy transfer was observed from the dppz ligand to the lanthanide ion (Nd³⁺, Er³⁺ and Yb³⁺), while relatively high luminescence lifetimes were detected for these complexes. In their excitation spectra, the maximum of the strong broad band is located at around 385 nm and this wavelength was further used for excitation of the chosen complexes. In their emission spectra, the following characteristic NIR emission peaks were observed: for a) Nd³⁺: ⁴F_3/2 → ⁴I_9/2 (870.8 nm), ⁴F_3/2 → ⁴I_11/2 (1052.7 nm) and ⁴F_3/2 → ⁴I_13/2 (1334.5 nm); b) Er³⁺: ⁴I_13/2 → ⁴I_15/2 (1529.0 nm) c) Yb³⁺: ²F_5/2 → ²F_7/2 (977.6 nm). While its low triplet energy level is ideally suited for efficient sensitization of Nd³⁺ and Er³⁺, the dppz ligand is considered not favorable as a sensitizer for most of the visible emitting lanthanide ions, due to its low-lying triplet level, which is too low for the accepting levels of most visible emitting lanthanides. Furthermore, the DNA intercalation ability of the [Nd(NO₃)₃(dppz)₂] complex with calf thymus DNA (CT-DNA) was confirmed using fluorescence spectroscopy.     

Adducts of lanthanide β-diketonates with 2,4,6-tri(2-pyridyl)-1,3,5-triazine: Synthesis,structural characterization,and photoluminescence studies

Adducts of lanthanide β-diketonates of the general formula LnL₃(TPTZ) were synthesized and structurally characterized by single crystal X-ray diffraction [Ln = Eu³⁺, Tb³⁺, Er³⁺; L is the conjugate base of dibenzoylmethane (DBM), 1-benzoylacetone (BA), thenoyltrifluoroacetone (TTA), or 4,4,4-trifluoro-1-phenyl-1,3-butanedione (BTFA); TPTZ = 2,4,6-tri(2-pyridyl)-1,3,5-triazine, a rigid Lewis base with a large π system]. The lanthanide ion in each of these complexes is nonacoordinate with six β-diketonate oxygen atoms and three TPTZ nitrogen atoms, forming a coordination polyhedron best describable as a monocapped square antiprism. Characteristic red, green, and near infrared luminescence was observed for the Eu³⁺, Tb³⁺, and Er³⁺ complexes, respectively. All complexes showed significantly enhanced luminescence quantum yields when compared with the corresponding aqua analogues, with one of the Eu³⁺ complexes displaying a quantum yield of 69.7% in chloroform.     

Solution thermodynamics of Lanthanide–Cryptand 222 complexation processes

The thermodynamics of trivalent cations (Y³⁺, La³⁺, Pr³⁺, Nd³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Ho³⁺, Er³⁺, Yb³⁺) and cryptand 222 in acetonitrile at 298.15?K is discussed. Recent reports regarding the behavior of lanthanide(III) trifluoromethane sulfonate salts in acetonitrile are considered. Thus, the experimental work was carried out under conditions in which ions (M³⁺) are predominantly in solution. Therefore, conductiometric titrations were carried out to establish the composition of the cation–cryptand 222 complexes and their ionic behavior in solution. Stability constants and derived standard Gibbs energies, enthalpies and entropies were determined by competitive titration microcalorimetry. Previously reported thermodynamic data for the complexation of cryptand 222 and a few lanthanide cations (La³⁺, Pr³⁺ and Nd³⁺) in acetonitrile are revisited. The medium effect on the stability of complex formation in acetonitrile relative to N,N-dimethylformamide is demonstrated. Thus, a drop in stability by a factor of 8 × 10¹⁰ is observed for the latter relative to the former solvent. The selectivity of cryptand 222 for these cations relative to La³⁺ in acetonitrile is discussed.     

NMR study of monophthalocyaninatolanthanide (III) compounds

The variation of ¹H NMR shifts of monophthalocyaninatolanthanide (III) compounds of nine rare earth elements from Sm³⁺ to Lu³⁺ (except Gd³⁺) was studied. It was found that a “triad effect” appears in the sign alteration of the induced chemical shifts of α, β protons in the phthalocyanine rings for the second half of the rare earth series, that is, ¹H NMR spectra shift upfield for Tb³⁺, Dy³⁺ and Ho³⁺ compounds, while for Er³⁺, Tm³⁺ and Yb³⁺ the spectra shift downfield. The largest alteration of the chemical shifts appears in the compound with Tb³⁺. This is in agreement with the regularity obtained theoretically by Bleaney. The ¹³C NMR spectra of several monophthalocyaninatolanthanide compounds have also been recorded. The variation of the chemical shifts was discussed.     

Visible and near-IR luminescence via energy transfer in rare earth doped mesoporous titania thin films with nanocrystalline walls

Selected photoluminescence in the wavelength range of 600-1540 nm is generated by energy transfer from a light-gathering mesostructured host lattice to an appropriate rare earth ion. The mesoporous titania thin films, which have a well-ordered pore structure and two-phase walls made of amorphous titania and TiO₂ nanocrystallites, were doped with up to 8 mol% lanthanide ions, and the ordered structure of the material was preserved. Exciting the titania in its band gap results in energy transfer and it is possible to observe photoluminescence from the crystal field states of the rare earth ions. This process is successful for certain rare earth ions (Sm³⁺, Eu³⁺, Yb³⁺, Nd³⁺, Er³⁺) and not for others (Tb³⁺, Tm³⁺). A mechanism has been proposed to explain this phenomenon, which involves energy transfer through surface states on titania nanocrystals to matching electronic states on the rare earth ions.     

Significant effect of lanthanide doping on the texture and properties of nanocrystalline mesoporous TiO2

A systematic study of microstructure and photocatalytic properties of lanthanide doping of nanocrystalline mesoporous titanium dioxide is performed. The anatase-to-rutile (A-R) phase transformation of nanosized TiO₂ was significantly inhibited by lanthanide doping and the inhibitory effect was enhanced with the increase of the rare earth radius, i.e., La³⁺>Gd³⁺>Yb³⁺ for different lanthanide dopants. At high calcination temperatures, different texture lanthanide titanium oxides of Ln₄Ti₉O₂₄ (La³⁺, Pr³⁺, Nd³⁺), Ln₂Ti₂O₇ (Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Er³⁺), and Yb₂TiO₅ were developed, respectively, revealing that the structures of lanthanide titanium oxide developed in Ln/TiO₂ depend on the lanthanide radius. Larger radius lanthanides prefer to form higher coordination number lanthanide titanium oxide. In addition, the thermal stability of mesoporous structures of TiO₂ was remarkable improved by lanthanide doping. The photocatalytic properties were studied by employing the photodegradation of Rhodamine B (RB) as a probe reaction. The results indicate that the lanthanide doping could bring about significant improvement to the photoreactivity of TiO₂, and the improvement was sensitive to the atomic electronic configuration.     

Synthesis and characterization of monodisperse spherical SiO2@RE2O3 (RE=rare earth elements) and SiO2@Gd2O3:Ln (Ln=Eu, Tb, Dy, Sm, Er, Ho) particles with core-shell structure

Spherical SiO₂ particles have been coated with rare earth oxide layers by a Pechini sol-gel process, leading to the formation of core-shell structured SiO₂@RE₂O₃ (RE=rare earth elements) and SiO₂@Gd₂O₃:Ln³⁺ (Ln=Eu, Tb, Dy, Sm, Er, Ho) particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence spectra as well as lifetimes were used to characterize the resulting SiO₂@RE₂O₃ (RE=rare earth elements) and SiO₂@Gd₂O₃:Ln³⁺ (Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺, Er³⁺, Ho³⁺) samples. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size ca. 380 nm), smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (40 nm for two deposition cycles). Under the excitation of ultraviolet, the Ln³⁺ ion mainly shows its characteristic emissions in the core-shell particles from Gd₂O₃:Ln³⁺ (Eu³⁺, Tb³⁺, Sm³⁺, Dy³⁺, Er³⁺, Ho³⁺) shells.     

Magneto-optic and luminescent properties of tellurite glass TeO<Subscript>2</Subscript>-ZnCl<Subscript>2</Subscript> doped with rare-earth elements

Tellurite glasses were synthesized on the basis of the binary system composed of 70 mol % TeO₂ and 30 mol % ZnCl₂ and doped with Nd³⁺, Pr³⁺, Tb³⁺, Er³⁺, Yb³⁺, Ho³⁺. The physicochemical, luminescent, and magneto-optic properties of these glasses were studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 8, 2004, pp. 1262–1265.Original Russian Text Copyright © 2004 by Grishin, Gurev, Intyushin, Elliev, Pavlova, Savikin.     

Crystal Structures of the Lanthanum(III), Europium(III), and Terbium(III) Cryptates of Tris(bipyridine) Macrobicyclic Ligands

The crystal structures of the La^III, Eu^III, and Tb^III complexes of macrobicyclic [bpy.bpy.bpy] ligands, [La³⁺ ? 1 ]3 Cl^? ( = 3- La), [Tb³⁺ ? 1 ]3 Cl^? ( = 3- Tb), and [Eu³⁺ ? 2 ]3 C1^? ( = 3- Eu), have been determined. They confirm the cryptate nature of these species, the cations being bound to the eight N-sites of the ligand. The macrobicycle presents two open faces, thus allowing additional coordination of two species, Cl^? ions or H₂O molecules, to the bound cations. These data provide structural support for the photophysical studies of the luminescent properties of the Eu^III and Tb^III cryptates, which indicated residual coordination of H₂O molecules.     

Synthesis and trivalent lanthanide ion complexation studies of new macrocyclic receptors based lactam ionophores

This study is the first report on the design, synthesis and photophysical properties of three new macrocyclic receptors based receptors containing two amide bridges. Their binding properties towards trivalent lanthanide ions such as La³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Er³⁺ and Yb³⁺ were investigated by using spectroscopic techniques. With respect to emission intensity changes upon trivalent lanthanide ion complexation, macrocyclic receptors based lactam ionophores showed higher selectivity towards Yb³⁺ and/or Er³⁺ ion over other ions. Presence of proximal two amide groups in macrocyclic lactam receptors having different cavity size were observed to play an important role in exhibiting its lanthanide ion binding.     

DNA binding and antibacterial properties of ternary lanthanide complexes with salicylic acid and phenanthroline

Twelve ternary lanthanide complexes RE(sal)₃phen (RE³⁺ = La³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Tm³⁺, Yb³⁺, Lu³⁺, sal = salicylic acid, phen = phenanthroline) were prepared. Interactions between the complexes and calf thymus DNA (ct‐DNA) were investigated using UV–visible spectrophotometry, fluorescence quench experiment and viscosity measurement. Hypochromicity and red shift of the absorption spectra of complexes were observed in the presence of DNA. The enhanced emission intensity of ethidium bromide (EB) in the presence of DNA was quenched by the addition of lanthanide complexes, which indicated that the lanthanide complexes displaced EB from its binding sites in DNA. Based on the systematic research of the binding constant (K_b) and the fluorescence quenching constant (K_q) of the 12 complexes, we found that the complexes with smaller lanthanide ion radius had stronger binding abilities with DNA. Viscosity measurement showed that the relative viscosity of the DNA solution was enhanced with increasing the amounts of the complexes. All these results suggested that the complexes could bind to DNA and the major binding mode was intercalative binding. Moreover, all these complexes exhibited excellent antibacterial abilities against Escherichia coli. Also, the antibacterial activities of complexes with heavy rare earth were higher than those of complexes with light rare earth. Copyright © 2014 John Wiley & Sons, Ltd.     

Luminescent-technique study on the structure of cation subsystem in the ionic conductor Na5RESi4O12 (RE is a rare-earth cation Tb3+, Ho3+, Er3+, Gd3+, Eu3+)

Results of experimental studies of luminescence in a group of materials with common formula Na₅RESi₄O₁₂ (RE is a rare-earth cation Tb³⁺, Ho³⁺, Er³⁺, Gd³⁺, Eu³⁺ entering the stoichiometric formula of the substance) are summarized. The luminescence spectra give information on the mobile-cation sublattice structure and dynamics. It follows from experimental results that the current opinion on the disordering of mobile sublattice is not quite correct. At relatively low temperatures (T < 100 K), a small number of typical local configurations of cations can be elucidated, which in aggregate can describe the Na⁺ cation sublattice to rather high degree of accuracy. At higher temperatures, the number of spectral lines and their positions change, which formally corresponds to changes in the symmetry of sites of the lattice, hence, is the sign of a second order phase transition. This phenomenon is given an explanation based on a suggestion on the local dynamic averaging of the mobile cation electrical fields.     

Energy transfer and heat-treatment effect of photoluminescence in Eu-doped TbPO4 nanowires

We have successfully synthesized Eu³⁺-doped TbPO₄ nanowires, which are orderly organized to form bundle-like structure. A thermal treatment up to 600 °C does not modify the size, shape and structure of as-synthesized sample. Due to the energy overlap between Tb³⁺ and Eu³⁺, an efficient energy transfer occurs from Tb³⁺ to Eu³⁺. The effects of Eu³⁺ concentration and thermal treatment on the luminescent properties of Eu³⁺ are investigated. The increase of Eu³⁺ concentration leads to the increase of the energy transfer efficiency from Tb³⁺ to Eu³⁺, but also enhances the probability of the interaction between neighboring Eu³⁺, which results in the concentration quenching. With the heat-treatment, the luminescence of Eu³⁺ presents an obvious increase, but almost no change for the luminescence of Tb³⁺. This difference is explained based on the TGA, DTA, and fluorescent decay dynamics analyses.     

Photophysical Properties of Metal Ion Functionalized NaY Zeolite

A series of luminescent ion exchanged zeolite are synthesized by introducing various ions into NaY zeolite. Monometal ion (Eu³⁺, Tb³⁺, Ce³⁺, Y³⁺, Zn²⁺, Cd²⁺, Cu²⁺) exchanged zeolite, rare‐earth ion (Eu³⁺, Tb³⁺, Ce³⁺) exchanged zeolite modified with Y³⁺ and rare‐earth ion (Eu³⁺, Tb³⁺, Ce³⁺) exchanged zeolite modified with Zn²⁺ are discussed here. The resulting materials are characterized by Fourier transform infrared spectrum radiometer (FTIR), XRD, scanning electronic microscope (SEM), PLE, PL and luminescence lifetime measurements. The photoluminescence spectrum of NaY indicates that emission band of host matrix exhibits a blueshift of about 70 nm after monometal ion exchange process. The results show that transition metal ion exchanged zeolites possess a similar emission band due to dominant host luminescence. A variety of luminescence phenomenon of rare‐earth ion broadens the application of zeolite as a luminescent host. The Eu³⁺ ion exchanged zeolite shows white light luminescence with a great application value and Ce³⁺ exchanged zeolite steadily exhibits its characteristic luminescence in ultraviolet region no matter in monometal ion exchanged zeolite or bimetal ions exchanged zeolite.