43181 2017 eng lecture 0 -- -- -- Upconversion nanoparticles (UCNPs) offer new strategies for luminescence-based sensing and imaging. One of the best studied materials are ..-NaYF4 UCNPs doped with 20 % Yb3+ and 2 % Er3+, which efficiently convert 976 nm light to photons emitted at 540 nm, 655 nm, and 845 nm, respectively, reveal long luminescence lifetimes (> 100 µs), are photostable and chemically inert. Their upconversion (UC) luminescence (UCL) properties are, however, strongly influenced by particle size, surface chemistry, and microenvironment. In addition, the multiphotonic absorption processes responsible for UCL render UCL excitation power density (..) dependent. This makes quantitative UCL measurements as well as the determination of UC quantum yields (.UC) very challenging. The rational design of brighter UCNPs particle architectures and the interest in identifying optimum particle architectures for FRET-based sensing and imaging schemes, which often rely on core-only UCNPs to minimize donor-acceptor distances, encouraged us to assess the influence of particle size and P on UCL. Here, we present the photophysical properties of a series of hexagonal NaYF4 UCNPs with sizes from 10 to 43 nm with different surface ligands dispersed in organic solvents and water studied by steady state and time-resolved fluorometry as well as quantitatively by integrating sphere spectrometry with P varied over about three orders of magnitude. Our results underline the need for really quantitative luminescence studies for mechanistic insights and the potential of high P to compensate for UCL quenching due to high energy phonons and surface effects. 15th Conference on Methods and Applications in Fluorescence Bruges, Belgium 10.09.2017 13.09.2017 0 Ute Resch-Genger eng uncontrolled Upconversion eng uncontrolled Nanoparticle eng uncontrolled Absolute fluorometry eng uncontrolled Integrating sphere spectroscopy eng uncontrolled NIR eng uncontrolled IR eng uncontrolled Fluorescence eng uncontrolled Surface chemistry eng uncontrolled Deactivation pathways eng uncontrolled Photophysics eng uncontrolled Quantum yield Analytische Chemie Ingenieurwissenschaften und zugeordnete Tätigkeiten Datei im Netzwerk der BAM verfügbar ("Closed Access") Präsentation