General Synthesis of Layered Rare-Earth Hydroxides (RE = Sm, Eu, Gd, Tb, Dy, Ho, Er, Y) and Direct Exfoliation into Monolayer Nanosheets with High Color Purity

Abstract

Layered rare-earth hydroxides (LREHs) are promising optical and magnetic materials, while it is hard to obtain monolayer nanosheets through a direct exfoliation. In this study, organic dodecyl sulfate (C₁₂H₂₅SO₄^-, DS^-) was used to prepare LREHs. In-plane lattice parameters of the LREHs decreased from Sm³⁺ to Er³⁺, correlating well with the monotonically decreasing ionic radius. Conversely, the interlayer spacing slightly increased with the increase of host layer charge density and corresponding intercalated DS^- contents. By a direct sonication of the LREHs in formamide, nanosheets were obtained with a thickness of ∼1 nm and size of ∼500 nm. Compared to the bulk crystals, exfoliation resulted in a slight elongation of in-plane lattice constants and a more asymmetric coordination environment. The suspension of europium hydroxide nanosheets exhibited a remarkably high red-light emission purity (91.4%). This work demonstrated an important strategy toward an efficient synthesis of well-defined LREH nanosheets with high color purity.