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End date: 2023 × Start date: 2022 × Publisher: Amsterdam : Elsevier × WGL Institute: IPHT ×

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    Link to glow - iEDDA conjugation of a Ruthenium(II) tetrazine complex leading to dihydropyrazine and pyrazine complexes with improved 1O2 formation ability
    (Amsterdam : Elsevier, 2022) Müller, Carolin; Wintergerst, Pascal; Nair, Shruthi Santhosh; Meitinger, Nicolas; Rau, Sven; Dietzek-Ivanšić, Benjamin
    The synthesis and photophysical properties of the Ru-polypyridyl type complex [(tbbpy)2Ru(bptz)]2+ (Ru-bptz, tbbpy: 4,4’-di-tert-butyl-2,2’-bipyridine, bptz: 2,6-dipyrido-1,2,4,5-tetrazine), and the complexes [(tbbpy)2Ru(L)]2+ formed by inverse electron demand Diels Alder reaction (iEDDA) of Ru-bptz with with alkenes and alkynes, where L is 3,6-dipyrido-2,5-dihydropyridazine (bpdhpn) or 3,6-dipyrido-pyridazine (bppn) are described. A combination of steady-state and time-resolved spectroscopy complemented by the computation of state-specific absorption properties by means of time-dependent density functional theory reveals that the intense visible absorption band stems from Ru → tbbpy and Ru → L metal-to-ligand charge-transfer (MLCT) excitations. The studies show that lowest-lying L-centered MLCT states (3MLCTL) show comparably low emission quantum yields (3–9%) and lifetimes (90–150 ns). This correlates with the singlet oxygen generation ability, following the trend: Ru-bppn > Ru-bpdhpn > Ru-bptz.
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    (INVITED)Tm:YAG crystal-derived double-clad fibers – A hybrid approach towards high gain and high efficiency Tm lasers
    (Amsterdam : Elsevier, 2022) Leich, Martin; Müller, Robert; Unger, Sonja; Schwuchow, Anka; Dellith, Jan; Lorenz, Adrian; Kobelke, Jens; Jäger, Matthias
    The hybrid approach of combining a Tm:YAG laser crystal with an amorphous fused silica tube is investigated to evaluate the suitability of the resulting crystal-derived fibers for efficient double-clad fiber lasers. The fabrication process and fiber properties of these Tm fibers are investigated, focusing on the dependence of the active fiber properties on the incorporated Tm3+ concentration. Crystal rods with different doping concentrations (TmxY1-x)3Al5O12 (x = 0.02, 0.05 and 0.08) were used as starting core material for fiber drawing. The investigated fibers are mechanically stable and result in a fairly homogenous and amorphous core glass with optical absorption and emission spectra that are similar to conventional Tm:Al doped silica fibers. Regarding laser properties with 790 nm cladding pumping, we could achieve a maximum slope efficiency of 47% with an output power of 4 W. The fiber laser results are compared to a conventionally fabricated double-clad Tm fiber prepared by Modified Chemical Vapor Deposition and solution doping. To the best of our knowledge, we demonstrate the highest laser output and the highest efficiency obtained from a Tm:YAG crystal-derived fiber.