Luminescence and Energy Transfer of [Ru(bpy) 3 ] 2+ , [Cr(ox) 3 ] 3- , and [Os(bpy) 3 ] 2+ in Three-Dimensional Oxalato-Networks

Luminescence and energy transfer in [Zn1-xRux(bpy)3][NaAl1-yCry(ox)3] (x ≈ 0.01, y = 0.006 − 0.22; bpy = 2,2‘-bipyridine, ox = C2O42-) and [Zn1-x-yRuxOsy(bpy)3][NaAl(ox)3] (x ≈ 0.01, y = 0.012) are presented and discussed. Surprisingly, the luminescence of the isolated luminophores [Ru(bpy)3]2+ and [Os(bpy)3]2+ in [Zn(bpy)3][NaAl(ox)3] is hardly quenched at room temperature. Steady-state luminescence spectra and decay curves show that energy transfer occurs between [Ru(bpy)3]2+ and [Cr(ox)3]3- and between [Ru(bpy)3]2+ and [Os(bpy)3]2+ in [Zn1-xRux(bpy)3][NaAl1-yCry(ox)3] and [Zn1-x-yRuxOsy(bpy)3] [NaAl(ox)3], respectively. For a quantitative investigation of the energy transfer, a shell type model is developed, using a Monte Carlo procedure and the structural parameters of the systems. A good description of the experimental data is obtained assuming electric dipole−electric dipole interaction between donors and acceptors, with a critical distance Rc for [Ru(bpy)3]2+ to [Cr(ox)3]3- energy transfer of 15 Å and for [Ru(bpy)3]2+ to [Os(bpy)3]2+ energy transfer of 33 Å. These values are in good agreement with those derived using the Förster−Dexter theory.

Simulating Energy Transfer and Upconversion in β-NaYF 4 : Yb 3+ , Tm 3+

The design of upconversion phosphors with higher quantum yield requires a deeper understanding of the detailed energy transfer and upconversion processes between active ions inside the material. Rate equations can model those processes by describing the populations of the energy levels of the ions as a function of time. However, this model presents some drawbacks: energy migration is assumed to be infinitely fast, it does not determine the detailed interaction mechanism (multipolar or exchange), and it only provides the macroscopic averaged parameters of interaction. Hence, a rate equation model with the same parameters cannot correctly predict the time evolution of upconverted emission and power dependence under a wide range of concentrations of active ions. We present a model that combines information about the host material lattice, the concentration of active ions, and a microscopic rate equation system. The extent of energy migration is correctly taken into account because the energy transfer processes are described on the level of the individual ions. This model predicts the decay curves, concentration, and excitation power dependences of the emission. This detailed information can be used to predict the optimal concentration that results in the maximum upconverted emission.

Resonant excitation energy transfer in [Rh(bpy)3][NaCr(ox)3]ClO4

Resonant fluorescence line narrowing of the R1 line of the [Cr(ox)3]3− chromophore in [Rh(bpy)3][NaCr(ox)3]ClO4 at 1.6 K neither gives rise to the usual three-line pattern nor to spectral diffusion. Instead multi-line spectra with spacings equal to the zero-field splitting of the ground state are observed. This phenomenon is attributed to efficient non-radiative resonant energy transfer within the R1 line.

The low-energy β− and electron emitter 161Tb as an alternative to 177Lu for targeted radionuclide therapy

The low-energy β− emitter 161Tb is very similar to 177Lu with respect to half-life, beta energy and chemical properties. However, 161Tb also emits a significant amount of conversion and Auger electrons. Greater therapeutic effect can therefore be expected in comparison to 177Lu. It also emits low-energy photons that are useful for gamma camera imaging. The 160Gd(n,γ)161Gd→161Tb production route was used to produce 161Tb by neutron irradiation of massive 160Gd targets (up to 40 mg) in nuclear reactors. A semiautomated procedure based on cation exchange chromatography was developed and applied to isolate no carrier added (n.c.a.) 161Tb from the bulk of the 160Gd target and from its stable decay product 161Dy. 161Tb was used for radiolabeling DOTA-Tyr3-octreotate; the radiolabeling profile was compared to the commercially available n.c.a. 177Lu. A 161Tb Derenzo phantom was imaged using a small-animal single-photon emission computed tomography camera. Up to 15 GBq of 161Tb was produced by long-term irradiation of Gd targets. Using a cation exchange resin, we obtained 80%–90% of the available 161Tb with high specific activity, radionuclide and chemical purity and in quantities sufficient for therapeutic applications. The 161Tb obtained was of the quality required to prepare 161Tb–DOTA-Tyr3-octreotate. We were able to produce 161Tb in n.c.a. form by irradiating highly enriched 160Gd targets; it can be obtained in the quantity and quality required for the preparation of 161Tb-labeled therapeutic agents.

Energy and charge transfer dynamics in DNA based light harvesting antennae

DNA can serve as a versatile scaffold for chromophore assemblies. For example, light-harvesting antennae have been realized by incorporating phenanthrene and pyrene building blocks into DNA strands. It was shown that by exciting at 320 nm (absorption of phenanthrene), an emission at 450 nm is observed which corresponds to a phenanthrene-pyrene exciplex. The more phenanthrenes are added into the DNA duplex, the higher is the fluorescence intensity with no significant change in quantum yield. This shows that phenanthrene acts as a donor and efficiently transfers the excitation energy to the pyrene. Up to now, the mechanism of this energy transfer and exciplex formation is not known. Therefore, we first aim at studying the photo-cycle of such DNA assemblies through transient absorption spectroscopy. Based on the results, we will explore ways to manipulate the energy transfer by application of intense THz fields. Ground as well as excited state Stark effect dynamics will be investigated.

Factors improving the vibration transfer of the floating mass transducer at the round window

With the placement of a floating mass transducer (FMT) at the round window, a new approach of coupling an implantable hearing system to the cochlea has been introduced. The aim of the present experimental study is to examine the influence of different ways of FMT placement at the round window on the vibration energy transfer to the cochlea.

Enhanced (1)G(4) emission in NaLaF4: Pr3+, Yb3+ and charge transfer in NaLaF4: Ce3+, Yb3+ studied by fourier transform luminescence spectroscopy

A high resolution luminescence study of NaLaF4: 1%Pr3+, 5%Yb3+ and NaLaF4: 1%Ce3+, 5%Yb3+ in the UV to NIR spectral range using a InGaAs detector and a fourier transform interferometer is reported. Although the Pr3+(P-3(0) -> (1)G(4), Yb3+(F-2(7/2) -> F-2(5/2)) energy transfer step takes place, significant Pr3+ (1)G(4) emission around 993, 1330 and 1850 nm is observed. No experimental proof for the second energy transfer step in the down-conversion process between Pr3+ and Yb3+ can be given. In the case of NaLaF4: Ce3+, Yb3+ it is concluded that the observed Yb3+ emission upon Ce3+ 5d excitation is the result of a charge transfer process instead of down-conversion. (C) 2010 Elsevier B.V. All rights reserved.

Excited state interactions between the chiral Au 38 L 24 cluster and covalently attached porphyrin

A protected S-acetylthio porphyrin was synthesized and attached to the Au38(2-phenylethanethiolate)24 cluster in a ligand exchange reaction. Chiral high performance liquid chromatography of the functionalized cluster yielded enantiomeric pairs of clusters probably differing in the binding site of the porphyrin. As proven by circular dichroism, the chirality was maintained. Exciton coupling between the cluster and the chromophore is observed. Zinc can be incorporated into the porphyrin attached to the cluster, as evidenced by absorption and fluorescence spectroscopy, however, the reaction is slow. Quenching of the chromophore fluorescence is observed, which can be explained by energy transfer from the porphyrin to the cluster. Transient absorption spectra of Au38(2-phenylethanethiolate)24 and the functionalized cluster probe the bleach of the gold cluster due to ground state absorption and the characteristic excited state absorption signals. Zinc incorporation does not have a pronounced effect on the photophysical behaviour. Decay times are typical for the molecular behaviour of small monolayer protected gold clusters.