Luminescent LaF3:Yb3+/Er3+ crystals with self-assembling microstructures by a facile ionothermal process

LaF3:Yb3+/Er3+ upconversion (UC) crystals with self-assembling microstructures have been synthesized via a simple one-pot ionothermal method. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were used to characterize the samples. The samples crystallize in the pure hexagonal phase and self-assemble into the aligned arrays like a string of pearls. The effects of reaction temperature, reaction time, the volume ratio of ionic liquid (IL)/water in the mixed solvent and solvent composition on the size and morphology of the products have been studied in detail and a possible formation mechanism has also been proposed. The results indicate that the adoption of water-IL solvent mixture as reaction medium facilitates the particle morphology control. Furthermore, a bright yellowish-green emission can be obtained from the LaF3:Yb3+/Er3+ under 980 nm laser excitation. Such a material shows potential applications in color displays, light-emitting diodes, and optical storage.