Size and shape modifications, phase transition, and enhanced luminescence of fluoride nanocrystals induced by doping

Abstract

The synthesis and growth mechanism of well-defined nanostructures are still challenging. In this study, we offer a novel soft chemistry route to modify the size and shape of irregular fluoride crystals by changing the surface charge distribution of the crystal nucleus by Bi³⁺, Al³⁺, Gd³⁺, Yb³⁺, Ba²⁺ and Ca²⁺ ion doping. As a result, irregular BaF₂, SrF₂, GdF₃, and NaGdF₄ alkaline-earth and lanthanide fluorides can be converted into nanoparticles with high yield and controlled size and shape, in which the phase transition from micro-crystals to single-crystalline is also achieved. Enhanced yellow and red emissions of Eu³⁺-doped BaF₂ induced by doping are observed. In conjunction with density functional theory calculations, it shows that the shape and size modifications originate from the surface charge redistribution of the crystal nucleus induced by inner electron charge transfer between the doping ions and lattice cations.