One-step surfactant-free synthesis of KSc2F7 microcrystals: controllable phases, rich morphologies and multicolor down conversion luminescence properties

Abstract

Homogeneous KSc₂F₇ microcrystals with controlled and abundant morphologies were prepared by a one-step hydrothermal route without employing any templates or surfactants. Particularly, uniform and well-defined KSc₂F₇ crystals with rod, sheet, flower-like, thin rectangular, xylitol-like and thin plate morphologies were achieved by manipulating the different environments of crystal growth, such as increasing the concentration of F⁻, changing pH and adding different surfactants. In addition, a phase transformation from monoclinic ScF₃ to orthorhombic KSc₂F₇ was observed at different molar ratios of F/Sc and pH values, respectively. A more interesting thing is that the KSc₂F₇ crystals doped with 5% Ln³⁺ (Ln = La, Ce, Sm, Eu, Gd, Tb and Lu) showed rich morphologies and various sizes. The obtained KSc₂F₇:Ln³⁺ products showed multicolor emission with red (Eu³⁺), green (Tb³⁺) and blue (Ce³⁺), respectively. And the best emission conditions for KSc₂F₇ crystals are F/Sc/K = 3.5 : 1 : 3, pH = 7 and without any surfactants. The synthetic KSc₂F₇:Eu³⁺/Tb³⁺/Ce³⁺ phosphors may potentially be used for multicolor illumination and displays.