Growth of hexagonal NaGdF4 nanocrystals based on cubic Ln3+: CaF2 precursors and the multi-color upconversion emissions

•The Ln3+: NaGdF4 nanocrystals were synthesized based on the Ln3+: CaF2 precursors.•The microstructures of nanocrystals were characterized.•The multi-color upconversion emissions were easily realized.

Lanthanide-doped upconversion nanomaterials have attracted great attention recently for their potential applications in the fields of bio-label, three-dimensional display, solar cell and so on. In this article, we report a new strategy to prepare hexagonal Ln3+:NaGdF4 upconversion nanocrystals. Unlike the routine way of synthesizing NaGdF4 nanocrystals through nucleation and growth, the formation of hexagonal NaGdF4 nanocrystals herein is realized based on the Ln3+-doped cubic CaF2 precursors, following a hetero-valence cation exchange process between Gd3+/Na+ and Ca2+. Evidently, Ln3+ dopants in the CaF2 precursors are retained in the finally formed hexagonal NaGdF4 nanocrystals and, subsequently, multi-color upconversion emissions are easily realized by simply adjusting the Ln3+ dopant species and contents in the CaF2 precursors. This novel hetero-valence cation exchange route may open up a new pathway to synthesize nanomaterials that cannot be fabricated directly.

Graphical abstractWe reported a novel hetero-valence cation exchange route to synthesize Ln: NaGdF4 upconversion nanocrystals for the first time.Figure optionsDownload full-size imageDownload as PowerPoint slide