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Type: Article × Subject: Cryogenic temperatures ×

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    Davydov splitting and singlet fission in excitonically coupled pentacene dimers
    (Cambridge : RSC, 2019) Basel, Bettina Sabine; Hetzer, Constantin; Zirzlmeier, Johannes; Thiel, Dominik; Guldi, Rebecca; Hampel, Frank; Kahnt, Axel; Clark, Timothy; Guldi, Dirk Michael; Tykwinski, Rik R.
    Singlet fission (SF) allows two charges to be generated from the absorption of a single photon and is, therefore, potentially transformative toward improving solar energy conversion. Key to the present study of SF is the design of pentacene dimers featuring a xanthene linker that strictly places two pentacene chromophores in a rigid arrangement and, in turn, enforces efficient, intramolecular π-overlap that mimics interactions typically found in condensed state (e.g., solids, films, etc.). Inter-chromophore communication ensures Davydov splitting, which plays an unprecedented role toward achieving SF in pentacene dimers. Transient absorption measurements document that intramolecular SF evolves upon excitation into the lower Davydov bands to form a correlated triplet pair at cryogenic temperature. At room temperature, the two spin-correlated triplets, one per pentacene moiety within the dimers, are electronically coupled to an excimer state. The presented results are transferable to a broad range of acene morphologies including aggregates, crystals, and films. © 2019 The Royal Society of Chemistry.
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    Spectroscopy and 2.1 µm laser operation of Czochralski-grown Tm3+:YScO3 crystals
    (Washington, DC : Soc., 2022) Suzuki, Anna; Kalusniak, Sascha; Tanaka, Hiroki; Brützam, Mario; Ganschow, Steffen; Tokurakawa, Masaki; Kränkel, Christian
    We report on growth, temperature-dependent spectroscopy, and laser experiments of Tm3+-doped YScO3 mixed sesquioxide crystals. For the first time, cm3-scale laser quality Tm3+:YScO3 crystals with 2.2 at.% and 3.1 at.% doping levels were grown by the Czochralski method from iridium crucibles. We reveal that the structural disorder in the mixed crystals allows for broad and smooth spectral features even at cryogenic temperatures. We obtained the first continuous wave laser operation in this material at wavelengths around 2100 nm using a laser diode emitting at 780 nm as a pump source. A maximum slope efficiency of 45% was achieved using a Tm3 + (3.1 at.%):YScO3 crystal. Our findings demonstrate the high potential of Tm3+-doped mixed sesquioxides for efficient ultrafast pulse generation in the 2.1 µm range.