A two-step synthetic route to GdOF:Ln3+ nanocrystals with multicolor luminescence properties

Abstract

GdOF:Ln³⁺ (Ln = Eu, Tb, Eu/Tb, Ce/Tb, Yb/Er, and Yb/Tm) nanocrystals with a hexagonal prism morphology have been readily synthesized by a novel topotactic transformation route. The Gd(OH)₂F precursor was first synthesized and structurally analyzed by the Rietveld refinement method. It has been found that the Gd(OH)₂F precursor was formed by a novel type of ion-exchange from the brucite-like Gd₂(OH)₅NO₃·0.9H₂O (LGdH). Such an ion-exchange behavior is different from the traditional case for the layered double hydroxides (LDHs) in which the intercalated anions are exchanged by the external ions. The detailed structural analysis showed that GdOF prefered [0001] epitaxial growth direction of Gd(OH)₂F due to the structural matching of [0001]Gd(OH)₂F//[110]GdOF. Furthermore, the potential application of the as-prepared nanocrystals as phosphors is emphasized by demonstrating strong multicolor emissions including both down-conversion and upconversion, and energy transfer (Ce–Tb) processes by GdOF:Ln³⁺ in detail. Our nonorganic green synthetic strategy based on the novel ion-exchange for the LDHs may enrich the synthetic methodology for nanomaterials.