A topotactic structural transformation synthetic route for β-NaYF4 upconversion nanocrystals from YF3 at room temperature

Abstract

Phase engineering is a crucial issue in nano science and technology, because the physiochemical properties of nanomaterials are first determined by their phase structures besides their size, shape, and surface chemistry. Herein, we described a new topotactic structural transformation synthetic route for hexagonal phase β-NaYF₄ upconversion nanocrystals to address the unavoidable formation of intermediate cubic phase α-NaYF₄ in the early stage during the aqueous-based nanogrowth process. We found that the high topotactic structural matching of [010]YF₃//[0001]β-NaYF₄ induced the in situ topotactic transformation from YF₃ to β-NaYF₄, bypassing the formation of the α-NaYF₄ intermediate phase at room temperature. Besides, we also studied the effects of synthetic parameters on the nanogrowth of β-NaYF₄ nanocrystals, and the upconversion emission properties were also investigated. Our synthetic strategy shows that topotactic structural transformation can act as an efficient tool towards phase engineering for modern nanomaterial science.