Interaction of lanthanide β-diketonate complexes with polyvinylpyrrolidone: proton-controlled switching of Tb3+ luminescence

A first approach to the use of upconversion nanoparticles to measure fluorescent tracers in water: a proof of concept

In this work we use lanthanide based NaYF₄:Er³⁺, Yb³⁺upconversion nanoparticles (UCNP) to detect ppb-level sensitibity of a xanthene dye, Rhodamine B (RB) dye, under NIR excitation. A static energy transfer was observed between the luminescent UCNP energy donors and RB acceptor in aqueous solution for three different sizes of UCNP. No specific covalent functionalization of the UCNPs was performed providing a direct method of detection, particularly promising in natural systems where the interfering fluorescence background is a detrimental limitation to the performance of the detection method. This procedure is a first approach to be applied in estuarine and coastal zone where the high content of suspended particulate matter prevents the detection of tracers.

Transparent Ion-Exchange Membrane Exhibiting Intense Emission under a Specific pH Condition Based on Polypyridyl Ruthenium(II) Complex with Two Imidazophenanthroline Groups

The development and the photophysical behavior of a transparent ion-exchange membrane based on a pH-sensitive polypyridyl ruthenium(II) complex, [(bpy)2RuII(H2bpib)RuII(bpy)2](ClO4)4 (bpy = 2,2'-bipyridine, H2bpib = 1,4-bis([1,10]phenanthroline[5,6-d]-imidazol-2-yl)benzene), are experimentally and theoretically reported. The emission spectra of [(bpy)2RuII(H2bpib)RuII(bpy)2]@Nafion film were observed between pH 2 and pH 11 and showed the highest relative emission intensity at pH 5 (λmaxem = 594.4 nm). The relative emission intensity of the film significantly decreased down to 75% at pH 2 and 11 compared to that of pH 5. The quantum yields (Φ) and lifetimes (τ) showed similar correlations with respect to pH, Φ = 0.13 and τ = 1237 ns at pH 5, and Φ = 0.087 and τ = 1014 ns and Φ = 0.069 and τ = 954 ns at pH 2 and pH 11, respectively. These photophysical data are overall considerably superior to those of the solution, with the radiative- (kr) and non-radiative rate constants (knr) at pH 5 estimated to be kr = 1.06 × 105 s-1 and knr = 7.03 × 105 s-1. Density functional theory calculations suggested the contribution of ligand-to-ligand- and intraligand charge transfer to the imidazolium moiety in Ru-H3bpib species, implying that the positive charge on the H3bpib ligand works as a quencher. The Ru-Hbpib species seems to enhance non-radiative deactivation by reducing the energy of the upper-lying metal-centered excited state. These would be responsible for the pH-dependent "off-on-off" emission behavior.

Luminescence Tunable Europium and Samarium Complexes: Reversible On/Off Switching and White-Light Emission

Single-molecule functional materials with luminescence tunable by external stimuli are of increasing interest due to their application in sensors, display devices, biomarkers, and switches. Herein, new europium and samarium complexes with ligands having triphenylamine (TPA) groups as the redox center and 2,2'-bipyridine (bpy) as the coordinating groups and diketonate (tta) as the second ligand have been constructed. The complexes show white-light emission in selected solvents for proper mixtures of the emission from Ln³⁺ ions and the ligands. Meanwhile, they exhibit reversible luminescence switching on/off properties by controlling the external potential owing to intramolecular energy transfer from the Ln³⁺ ions to the electrochemically generated radical cation of TPA^•+. Time-dependent density functional theory (TD-DFT) calculations have been performed to study the electronic spectra. The proposed intramolecular energy transfer processes have been verified by density functional theory (DFT) studies.

Exploring polylactide/poly(butylene adipate-co-terephthalate)/rare earth complexes biodegradable light conversion agricultural films

In this work, rare earth europium was combined with different organic ligands to obtain two kinds of rare earth conversion agents, Eu(DBM)₄CPC and Eu(TTA)₃(TPPO)₂. Two kinds of conversion films were successfully prepared by combining them with polylactide and poly(butylene adipate-co-terephthalate). Results showed that the film has excellent light conversion ability and high color purity, and rare earth complexes improved melt flowing property and decreased melt viscosity of blend. At the same time, the elongation at break of the film increased greatly, which could up to 595.0/460.9% in the both machine direction (MD) and transverse direction (TD). The results of GPC show that rare earth complexes can make main chain of PLA scission, which causes rapid molecular weight reduction, and the effect of Eu(DBM)₄CPC on the molecular weight of PLA was more significant than Eu(TTA)₃(TPPO)₂. SEM shows that the complicity of PLA and PBAT has been improved, the dispersed phase of the blend is more uniform. DSC shows that both rare earth complexes can improve the crystallization capacity of PLA. And with the addition of cetylpyridinium chloride could improve the compatibility of rare earth complexes and polymer materials, the light transmittance and hydrophilicity of the film also increased obviously.

Sensitized green emission of terbium with dibenzoylmethane and 1, 10 phenanthroline in polyvinyl alcohol and polyvinyl pyrrolidone blends

Tb doped polyvinyl alcohol: polyvinyl pyrrolidone blends with dibenzoylmethane (DBM) and 1, 10 Phenanthroline (Phen) have been prepared by solution cast technique. Bond formation amongst the ligands and Tb³⁺ ions in the doped polymer has been confirmed employing Fourier Transform Infrared (FTIR) techniques. Optical properties of the Tb³⁺ ions have been investigated using UV-Vis absorption, excitation and fluorescence studies excited by different radiations. Addition of dimethylbenzoate and 1, 10 Phenanthroline to the polymer blend increases the luminescence from Tb³⁺ ions along with energy transfer from the polymer blend itself. Luminescence decay curve analysis affirms the non-radiative energy transfer from DBM and Phen to Tb³⁺ ions, which is identified as the reason behind this enhancement. The fluorescence decay time of PVA-PVP host decreases from 6.02ns to 2.31ns showing an evidence of energy transfer from the host blend to the complexed Tb ions. Similarly the lifetime of DBM and Phen and both in the blend reduces in the complexed system showing the feasibility of energy transfer from these excited DBM and Phen to Tb³⁺ and is proposed as the cause of the above observations. These entire phenomena have been explained by the energy level diagram.

Critical Role of Energy Transfer Between Terbium Ions for Suppression of Back Energy Transfer in Nonanuclear Terbium Clusters

Lanthanide (Ln(III)) complexes form an important class of highly efficient luminescent materials showing characteristic line emission after efficient light absorption by the surrounding ligands. The efficiency is however lowered by back energy transfer from Ln(III) ion to the ligands, especially at higher temperatures. Here we report a new strategy to reduce back energy transfer losses. Nonanuclear lanthanide clusters containing terbium and gadolinium ions, Tb_nGd_9−n clusters ([Tb_nGd_9−n(μ-OH)₁₀(butylsalicylate)₁₆]⁺NO₃⁻, n = 0, 1, 2, 5, 8, 9), were synthesized to investigate the effect of energy transfer between Tb(III) ions on back energy transfer. The photophysical properties of Tb_nGd_9−n clusters were studied by steady-state and time-resolved spectroscopic techniques and revealed a longer emission lifetime with increasing number of Tb(III) ions in Tb_nGd_9−n clusters. A kinetic analysis of temperature dependence of the emission lifetime show that the energy transfer between Tb(III) ions competes with back energy transfer. The experimental results are in agreement with a theoretical rate equation model that confirms the role of energy transfer between Tb(III) ions in reducing back energy transfer losses. The results provide a new strategy in molecular design for improving the luminescence efficiency in lanthanide complexes which is important for potential applications as luminescent materials.

A facile synthetic route to convert Tb(iii) complexes of novel tetra-1,3-diketone calix[4]resorcinarene into hydrophilic luminescent colloids

Luminescent hydrophilic core–shell nanoparticles are synthesized through reprecipitation and polyelectrolyte deposition techniques from Tb(iii) complexes.