Abstract
The podand-type ligand L, based on a tertiary amine substituted by three pyridyl-6-phosphonic acid functions, forms hydrated complexes with Ln3+ cations. The luminescence properties of the YbL complex were studied in D2O as a function of the pD and temperature. In basic conditions, increases in the luminescence quantum yield and the excited state lifetime of the Yb centered emission associated with the 2F5/2 → 2F7/2 transition were observed and attributed to a change in the hydration number from two water molecules in the first coordination sphere of Yb at acidic pH to a single one in basic conditions. Upon the addition of TbCl3 salts to a solution containing the YbL complex in D2O, heteropolynuclear Yb/Tb species formed, and excitation of the Yb at 980 nm resulted in the observation of the typical visible emission of Tb as a result of a cooperative upconversion (UC) photosensitization process. The UC was further evidenced by the quadratic dependence of the UC emission as a function of the laser power density.
Highlights
IntroductionThe upconversion (UC) phenomenon is an anti-Stokes process in which low-energy photons are converted into higher energy ones
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The upconversion (UC) phenomenon is an anti-Stokes process in which low-energy photons are converted into higher energy ones
Summary
The upconversion (UC) phenomenon is an anti-Stokes process in which low-energy photons are converted into higher energy ones. This generally results in the observation of visible-to-NIR emission upon excitation in the NIR domain [1,2]. This process is useful for applications in biology, as the excitation and emission wavelengths match the biological window where the background is low. It provides a low autofluorescence background and a high penetration depth [3,4,5]
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