Kofod Nicolaj, Arppe-Tabbara Riikka, Sørensen Thomas Just
Department of Chemistry & Nano-Science Center , University of Copenhagen , Universitetsparken 5 , 2100 København Ø , Denmark.
J Phys Chem A. 2019 Apr 4;123(13):2734-2744. doi: 10.1021/acs.jpca.8b12034. Epub 2019 Feb 20.
Dysprosium(III) ions are the third most luminescent lanthanide(III) ions. Dy(III) is used as dopant in optical fibers and as shift reagent in NMR imaging and is the element at the forefront of research in single-molecule magnets. Nonetheless, the excited state manifold of the dysprosium(III) ion is not fully mapped and the nature of the emitting state has not been unequivocally assigned. In the work reported here, the photophysical properties of dysprosium(III) triflate dissolved in HO, MeOH, and DMSO have been studied in great detail. The solvates are symmetric, all oxygen donor atom complexes where the coordination number is 8 or 9. By comparing protonated and deuterated solvents, performing variable temperature spectroscopy, and determining the excited state lifetimes and luminescence quantum yields, the solution structure can be inferred. For the three complexes, the observed electronic energy levels were determined using absorption and emission spectroscopy. The Dy(III) excited state manifolds of the three solvates differ from that reported by Carnall, in particular for the low lying F-states. It is shown that dysprosium(III) complexes primarily luminesce from the F state, although thermal population of, and subsequent luminescence from the I state is observed. The intrinsic luminescence quantum yield is moderate (∼10%) in DMSO- d and is significantly reduced in protonated solvent as both C-H and O-H oscillators act as efficient quenchers of the F state. We are able to conclude that the emitting state in dysprosium(III) is F, that the m levels must be considered when determining electronic energy levels of dysprosium(III), and that scrutiny of the transition probabilities may reveal the structure of dysprosium(III) ions in solution.
镝（III）离子是第三大具有发光特性的镧系（III）离子。Dy（III）用作光纤中的掺杂剂以及核磁共振成像中的位移试剂，并且是单分子磁体研究的前沿元素。尽管如此，镝（III）离子的激发态多重态尚未完全确定，并且发射态的性质也尚未明确归属。在本文报道的工作中，对溶解在H₂O、MeOH和DMSO中的三氟甲磺酸镝（III）的光物理性质进行了详细研究。这些溶剂化物是对称的，都是氧供体原子配合物，配位数为8或9。通过比较质子化和氘代溶剂、进行变温光谱分析以及测定激发态寿命和发光量子产率，可以推断溶液结构。对于这三种配合物，使用吸收光谱和发射光谱确定了观察到的电子能级。这三种溶剂化物的Dy（III）激发态多重态与Carnall报道的不同，特别是对于低能级的F态。结果表明，镝（III）配合物主要从F态发光，尽管也观察到了I态的热布居及其随后的发光。在氘代二甲亚砜中，其固有发光量子产率适中（约10%），而在质子化溶剂中显著降低，因为C-H和O-H振荡器都作为F态的有效猝灭剂。我们能够得出结论，镝（III）中的发射态是F态，在确定镝（III）的电子能级时必须考虑m 能级，并且对跃迁概率的仔细研究可能揭示溶液中镝（III）离子的结构。
