Ytterbium upconversion

Visibly luminescent, NIR (980 nm) excitable Er/Yb-doped nanoparticles have been used for microscopic detection in DNA microarrays [65]. The complete absence of endogenous upconversion luminescence leads to very low backgrounds and enhanced contrast. An NIR luminescent ytterbium(III) complex based on the fluorescein-isothiocyanate motif was demonstrated to be an adequate luminescent label in a sandwich-type in vitro diagnostic test [27]. 

Two simple examples will be given in order to illustrate the instrumentation and the primary data treatment. The discussion is focused on the technical problems and the interpretation of the results is left to a minimum. The first example deals with the resonance energy transfer (RET) from europium to an organic fluorophore. The distance between the donor and acceptor is kept constant by an oligonucleotide. RET is a very common technique in the case of lanthanides, and therefore the discussion is somewhat lengthy and detailed. The second example deals with a sample of upconversion phosphor containing yttrium, ytterbium and erbium. 

Besides triplet-triplet annihilation, a further process for achieving upconversion luminescence emission under continuous wave low-energy irradiation is based oti the use of lanthanide ions, most often erbium, holmium, and thulium (III) cations. In particular, a large variety of phosphors based on an inorganic host doped by lanthanide cations have been developed. The abundance of available states in these cations opens a large variety of paths for upconversion. As an example (Scheme 7.6), upconversion nanoparticles codoped with ytterbium and erbium cations exhibit a green emission due to the transitions from Hn/2 and respectively " Sn/2 excited states to the ground state as well as a red emission from the F9/2 state [10]. 

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