Insights into the growth mechanism of REF3 (RE = La–Lu, Y) nanocrystals: hexagonal and/or orthorhombic

Abstract

The synthesis of REF₃ (RE = La–Lu, Y) nanocrystals with controlled phase structures has so far remained a challenge. Herein we have developed a one-for-all synthetic procedure that allows the successful synthesis of REF₃ nanocrystals in a controlled manner. Experimental results showed that the radius of RE ions determines the phase structure: pure hexagonal REF₃ (RE = La–Eu), a mixture of hexagonal and orthorhombic REF₃ (RE = Gd), and pure orthorhombic REF₃ (RE = Tb–Lu, Y) nanocrystals are obtained along with the decrease of the ionic radius. As Gd is positioned exactly in the middle of the lanthanides row, GdF₃ nanocrystals were used as a model to further investigate how the molar ratio of F⁻ : Gd³⁺, the doping of RE ions with different ionic radii, and the doping concentration of certain RE ions affects the crystal structure of the final product.