Bandgap Engineering of Erbium-Metallofullerenes toward Switchable Photoluminescence.

Jin, Huaimin; Xin, Jinpeng; Xiang, Wenhao; Jiang, Zhanxin; Han, Xinyi; Chen, Muqing; Du, Pingwu; Yao, Yang-Rong et al. · Adv Mater · 2023

basic_science · Level V

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Abstract

Encapsulating photoluminescent lanthanide ions like erbium (Er) into fullerene cages affords photoluminescent endohedral metallofullerenes (EMFs). Few reported photoluminescent Er-EMFs are all based on encapsulation of multiple (two to three) metal atoms, whereas mono-Er-EMFs exemplified by Er@C<sub>82</sub> are not photoluminescent due to its narrow optical bandgap. Herein, by entrapping an Er-cyanide cluster into various C<sub>82</sub> cages to form novel Er-monometallic cyanide clusterfullerenes (CYCFs), ErCN@C<sub>82</sub> (C<sub>2</sub> (5), C<sub>s</sub> (6), and C<sub>2</sub> <sub>v</sub> (9)), the photoluminescent properties of CYCFs are investigated, and obvious near-infrared (NIR) photoluminescence only is observed for ErCN@C<sub>2</sub> (5)-C<sub>82</sub> . Combined with a comparative photoluminescence study of three medium-bandgap di-Er-EMFs, including Er<sub>2</sub> @C<sub>s</sub> (6)-C<sub>82</sub> , Er<sub>2</sub> O@C<sub>s</sub> (6)-C<sub>82</sub> , and Er<sub>2</sub> C<sub>2</sub> @C<sub>s</sub> (6)-C<sub>82</sub> , this study proposes that the optical bandgap can be used as a simple criterion for switching the photoluminescence of Er-EMFs, and the bandgap threshold is determined to be between 0.83 and 0.74 eV. Furthermore, the photoluminescent patterns of these three di-Er-EMFs differ dramatically. It is found that the location of the Er atom within the same C<sub>s</sub> (6)-C<sub>82</sub> cage is almost fixed and independent on the endo-unit; thus the previous statement on the key role of metal position in photoluminescence of di-Er-EMFs seems erroneous, and the geometric configuration of the endo-unit, especially the bridging mode of two Er ions, is decisive instead.