Spectroscopic aspects for the Yb3+ coordination compound with a large energy gap between the ligand and Yb3+ excited states


We present the experimental and theoretical results that made it possible to propose the energy transfer mechanism for a Yb complex with a large energy gap between the ligand and Yb excited states using a theoretical model and experimental data. Absorption and emission spectroscopy in the 300-4 K range is used for the study of the Yb3+ compound with N-phosphorylated sulfonamide (Na[YbL4]), which, despite the large energy gap, is characterized by high emission sensitization efficiency (eta(sens) = 40%) and relatively long Yb3+ emission lifetime (27 mu s). The crystal structure of Na[YbL4], radiative lifetime (930 mu s), refractive index (1.46), intrinsic (3.0%), and overall (1.3%) emission quantum yield were determined. To obtain the electronic properties of the Na[YbL4], a time-dependent density functional theory (TD-DFT) was performed. The intramolecular energy transfer (IET) rates from the excited states S-1 and T-1 to the Yb3+ ion as well as between the ligand and the ligand-to-metal charge transfer (LMCT) states were calculated. Once the intersystem crossing S-1 -> T-1 is not so effective due to a large energy gap between S-1 and T-1 (approximate to 10000 cm(-1)), it has been shown that the LMCT state acts as an additional channel to feed the T-1 state. Then, the T-1 can transfer energy to the Yb3+ 2F5/2 energy level (W-T), where W-T is dominated by the exchange mechanism. Based on IET and a rate equation model, the overall emission quantum yield Q(Ln)(L) was simulated with and without the LMCT, this also confirmed that the pathway S-1 -> LMCT -> T-1 -> Yb3+ is more likely than the S-1 -> T-1 -> Yb3+ one. (C) 2022 Published by Elsevier B.V.



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Kasprzycka, E; Neto, ANC; Trush, VA; Malta, OL; Jerzykiewicz, L; Amirkhanov, VM; Legendziewicz, J; Gawryszewska, P

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The authors wish to acknowledge support through the grant of Minister of Science and Higher Education POIG.01.01.02e02e006/09. This work was developed within the scope of the projects CICECO-Aveiro Institute of Materials (UIDB/50011/2020 & UIDP/50011/2020) financed by Portuguese funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. The support of the European Union's Horizon 2020 FET Open program under grant agreement No. 801305 (NanoTBTech) is also acknowledged. We thank Dr. Pawel Gluchowski and Dr. Boguslaw Macalik from Institute of Low Temperature and Structure Research-Polish Academy of Sciences for measuring the decay times of Yb3+ emission and the dependence of refractive index of Na[YbL4] vs. wavelength, respectively. The authors are very grateful for the comments raised by Reviewer #1, especially for calling our attention to the possibility of the cross-relaxation process involving the S1? T1 and 2F7/2? 2F5/2 transitions.

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