CsPbX3 (X = Cl, Br, I) perovskites have attracted a great deal of interest due to their bright, narrow emission, high photoluminescence quantum yields, tunable band gap, and defect tolerance. Trivalent lanthanides have been successfully incorporated, allowing for novel properties such as narrow line emission and quantum cutting. However, the structure and chemistry of lanthanide dopants within the perovskite lattice are not well understood. Yb3+, in particular, is known to be incorporated at relatively high concentrations and shows great promise as a component of solar down-converters. Based on optical spectroscopy measurements and structural simulations, Yb3+ is hypothesized to exist in various charge-compensated structures including a prominent charge-neutral cluster having two substitutional Yb3+ ions compensated by a single Pb2+ vacancy. There is no direct structural evidence to support either this or alternative defect structures, however. To investigate the structure and oxidation state of the Yb dopant site in CsPbCl3 perovskites, we performed X-ray absorption and X-ray total scattering measurements on 0.9% and 7.4% Yb-doped CsPbCl3. XANES shows the oxidation state of Yb to be exclusively 3+, and a combination of Yb L3 and Pb L3 EXAFS shows Yb3+ to substitute exclusively at Pb2+ sites, with a similar octahedral coordination of Cl- atoms. These data also show a contracted Yb-Cl bond distance of 2.6 Å, supported by PDF analysis of our X-ray total scattering data. PDF data also indicate the presence of Pb vacancies, consistent with the previous hypotheses of charge compensation of Yb3+ substitution. Together, these data provide a deeper view into the structural properties of this important doped perovskite.

X-ray probes of Yb3+ dopants in perovskite cesium lead chloride

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