Novel Two‐Step Topotactic Transformation Synthetic Route Towards Monodisperse LnOF:Re,³⁺ (Ln = Y, Pr–Lu) Nanocrystals with Down/Upconversion Luminescence Properties

A novel two‐step topotactic transformation (TT) synthetic route, Y₂(OH)₅NO₃•nH₂O (LYH)→Y(OH)_2.02F_0.98→YOF, is first developed for the monodisperse YOF:Re³⁺ (Re = Eu, Tb, Yb/Er, and Yb/Tm) nanostructure with bundle, tube, and atomically thick sheet morphologies. The intermediate Y(OH)_2.02F_0.98 precursor is synthesized from the starting point of the {0001} plane, which forms by a novel type of ion‐exchange from the brucite‐like LYH due to the structural similarity between the [Y₂(OH)₅(H₂O)_n]⁺ unit layer and the Y(OH)_2.02F_0.98 {0001} plane. Such ion‐exchange behavior is different from the traditional case for LYH exchanging the intercalated anions. The detailed structural characterization reveals that the formation of YOF is attributed to an in situ TT with the structural matching of [0001]Y(OH)_2.02F_0.98//[110]YOF. Moreover, this novel synthetic route can be also extended to other lanthanides oxyfluorides series (LnOF, Ln = Pr–Lu), and the as‐prepared YOF:Re³⁺ products exhibit intense characteristic down/upconversion luminescence. Our synthetic strategy dovetails well with the green concept in the current nanoscience and nanotechnology, which may bring new opportunity to LRHs and open a new avenue in the synthetic methodology for micro/nanomaterials.