Hydrothermal Synthesis of Lanthanide Fluorides LnF₃ (Ln = La to Lu) Nano-/Microcrystals with Multiform Structures and Morphologies

Abstract

Lanthanide fluoride LnF3 (Ln = La to Lu) nano-/microcrystals with multiform crystal structures (hexagonal and orthorhombic) and morphologies (separated elongated nanoparticles, aggregated nanoparticles, polyhedral microcrystals) were successfully synthesized by a facile, effective, and environmentally friendly hydrothermal method. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and photoluminescence spectra were used to characterize the samples. The experimental results indicated that the use of NaBF4 is indispensable for obtaining LnF3 crystal structures. Furthermore, the organic additive trisodium citrate (Cit3-) has an obvious impact on the morphologies of the products to some degree. The possible formation mechanisms for LnF3 nano-/microcrystals are presented in detail. Additionally, we systematically investigated the luminescence properties of the LnF3:Eu3+ (Ln = La, Gd, and Lu) samples and found an efficient energy transfer from Gd3+ to Eu3+ in GdF3:Eu3+.