TY - JOUR A1 - Lange, M. A. A1 - Khan, I. A1 - Dören, R. A1 - Ashraf, M. A1 - Qurashi, A. A1 - Prädel, L. A1 - Panthöfer, M. A1 - von der Au, Marcus A1 - Cossmer, Antje A1 - Pfeifer, Jens A1 - Meermann, Björn A1 - Mondeshki, M. A1 - Tahir, M. N. A1 - Tremel, W. T1 - High-speed solid state fluorination of Nb2O5 yields NbO2F and Nb3O7F with photocatalytic activity for oxygen evolution from water N2 - Solid state reactions are slow because the diffusion of atoms or ions through the reactant, intermediate and crystalline product phases is the rate-limiting step. This requires days or even weeks of high temperature treatment, and consumption of large amounts of energy. We employed spark-plasma sintering, an engineering technique that is used for high-speed consolidation of powders with a pulsed Electric current passing through the sample to carry out the fluorination of niobium oxide in minute intervals. The approach saves time and large amounts of waste energy. Moreover, it allows the preparation of fluorinated niobium oxides on a gram scale using poly (tetrafluoroethylene) (®Teflon) scrap and without toxic chemicals. The synthesis can be upscaled easily to the kg range with appropriate sintering equipment. Finally, NbO2F and Nb3O7F prepared by spark plasma sintering show significant photoelectrocatalytic (PEC) oxygen evolution from water in terms of photocurrent density and incident photon-to-current Efficiency (% IPCE), whereas NbO2F and Nb3O7F prepared by conventional high temperature chemistry show little to no PEC response. Our study is a proof of concept for the quick, clean and energy saving production of valuable photocatalysts from plastic waste. KW - Fluorination KW - Nb2O5, NbO2F, Nb3O7F KW - Photocatalytic activity PY - 2021 U6 - https://doi.org/10.1039/d1dt00533b VL - 50 IS - 19 SP - 6528 EP - 6538 PB - Royal Society of Chemistry AN - OPUS4-52439 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meijer, M. S. A1 - Rojas-Gutierrez, P. A. A1 - Busko, D. A1 - Howard, I. A. A1 - Frenzel, Florian A1 - Würth, Christian A1 - Resch-Genger, Ute A1 - Richards, B. S. A1 - Turshatov, A. A1 - Capobianco, J. A. A1 - Bonnet, S. T1 - Absolute upconversion quantum yields of blue-emitting LiYF4:Yb3+,Tm3+ upconverting nanoparticles N2 - The upconversion quantum yield (QY) is an essential parameter for the characterization of the optical performance of lanthanoid-doped upconverting nanoparticles (UCNPs). Despite its nonlinear dependence on excitation power density, it is typically reported only as a single number. Here, we present the first measurement of absolute upconversion quantum yields of the individual emission bands of blue light-emitting LiYF4:Yb3+,Tm3+ UCNPs in toluene. Reporting the quantum yields for the individual emission bands is required for assessing the usability of UCNPs in various applications that require upconverted light of different wavelengths, such as bioimaging, photocatalysis and phototherapy. Here, the reliability of the QY measurements is demonstrated by studying the same batch of UCNPs in three different research groups. The results show that whereas the total upconversion quantum yield of these UCNPs is quite high - typically 0.02 at a power density of 5 W/cm2 — most of the upconverted photon flux is emitted in the 794 nm upconversion band, while the blue emission band at 480 nm is very weak, with a much lower quantum yield of 6 times 10^5 at 5 W/cm2. Overall, although the total upconversion quantum yield of LiYF4:Yb3+,Tm3+ UCNPs seems satisfying, notably for NIR bioimaging, blue-light demanding phototherapy applications will require better-performing UCNPs with higher blue light upconversion quantum yields. KW - Core-shell nanoparticles KW - Lanthanide-doped nayf-4 KW - Near-infrared light KW - Upconverting nanoparticles KW - Photocatalytic activity KW - Nanocrystals KW - Photosensitizer PY - 2018 U6 - https://doi.org/10.1039/c8cp03935f VL - 20 IS - 35 SP - 22556 EP - 22562 PB - Royal Society of Chemistry AN - OPUS4-46370 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -