Principles upconversion

The methods discussed so far, fluorescence upconversion, the various pump-probe spectroscopies, and the polarized variations for the measurement of anisotropy, are essentially conventional spectroscopies adapted to the femtosecond regime. At the simplest level of interpretation, the information content of these conventional time-resolved methods pertains to populations in resonantly prepared or probed states. As applied to chemical kinetics, for most slow reactions (on the ten picosecond and longer time scales), populations adequately specify the position of the reaction coordinate intermediates and products show up as time-delayed spectral entities, and assignment of the transient spectra to chemical structures follows, in most cases, the same principles used in spectroscopic experiments performed with continuous wave or nanosecond pulsed lasers. 

The principle of upconversion is schematically given in Fig. 10.1. This figure shows the energy level structure of an ion with ground state A and excited levels B and C. The energy differences between levels C and B and levels B and A are equal. Excitation... 

Kg. 10.1. The principle of upconversion. The infrared excitation radiation (lOOOO cm ) is converted into green emission (20000 cm )... 

Fig. 14 Principle of the homogeneous enzyme-activity assay based on an internally quenched double-labeled substrate (a) without upconversion (conventional assay) or (b) with a UCNP donor. The hydrolytic enzyme reaction separates the fluorophore (F) and quencher (Q) located at the two ends of the substrate, and so the emission of the fluorophore is recovered. Intact substrates remain...

The other upconversion pathways are foremost relevant in doped inorganic materials. Multiionic mechanisms can be developed based on those fimdamental principles. The most frequent lanthanide ions for upconversion in inorganic materials are Pr +, Er +, and Tm +. Most of those inorganic materials use f- f transitions to achieve excited state absorptions. Lanthanide ions having both NIR and visible emission are thus needed. This limitation does not occur for two-photon absorption, which may use any lanthanide ion. For more details, the reader can refer to specific reviews. ... 

Wright, J.C., 1976, Upconversion and Excited State Energy Transfer in Rare-Earth Doped Materials, in Fong, F.K., ed.. Radiationless Processes in Molecules and Crystals, Vol. 15 (Springer-Verlag, Heidelberg, Germany). Wybourne, B.G., 1970, Symmetry Principles and Atomic Spectroscopy (Wiley, New York). Yamada, N., S. Shionoya, and T. Kashida, 1972, J. Phys. Soc. Japan 32, 1577. 

Hischemdller A., C. Walter, V. Weiler, H. Hummel, T. Thepen, M. Huhn, S. Barth, W. HoheiseL K. Kohler, D. Dimova-Landen, C. Bremer, M. Haase and J. Waldeck, Labeling of Anti-MUC-1 Binding Single Chain Fv Fragments to Surface Modified Upconversion Nanoparticles for an Initial in Vivo Molecular Imaging Proof of Principle Approach, Int. J. Mol. Set, 13,4153-4167 (2012). 

The first two chapters of this work cover theoretical and practical aspects of the emission process, the spectroscopic techniques and the equipment used to characterize the emission. Chapter 3 introduces and reviews the property of circularly polarized emission, while Chapter 4 reviews the use of lanthanide ion complexes in bioimaging and fluorescence microscopy. Chapter 5 covers the phenomenon of two-photon absorption, its theory as well as applications in imaging, while Chapter 6 reviews the use of lanthanide ions as chemo-sensors. Chapter 7 introduces the basic principles of nanoparticle upconversion luminescence and its use for bioimaging and Chapter 8 reviews direct excitation of the lanthanide ions and the use of the excitation spectra to probe the metal ion s coordination environment in eoordination compounds and biopolymers. Finally, Chapter 9 describes the formation of heterobimetallic complexes, in whieh the lanthanide ion emission is promoted through the hetero-metal. 

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