Europium‐activated rare earth fluoride (LnF3:Eu3+–Ln = La,Gd) nanocrystals prepared by using ionic liquid/NH4F as a fluorine source via hydrothermal synthesis

Lanthanide (Ln) fluorides are considered exceptional luminescent rigid host matrices for various optical active Ln³⁺ ions due to their high refractive index, high chemical stability and low phonon energy, leading to the low probability of non‐radiative decay, which results in higher photoluminescence quantum yield (PLQY) (usually higher than oxide hosts). In this study, Eu³⁺‐activated Ln fluorides (LnF₃:Eu³⁺–Ln = La, Gd) are synthesized by the hydrothermal method using 1‐butyl‐3‐methylimidazolium tertrafluoroborate BMIBF₄] and NH₄F as fluorine precursors. The synthesized nanocrystals (NCs) are structurally and morphologically characterized, and their optical properties investigated using spectrofluorometry. The X‐ray diffraction (XRD) patterns of Eu³⁺‐substituted and ‐unsubstituted LnF₃ (prepared from a different fluorine source) are indexed based on the hexagonal and orthorhombic crystal structure, respectively. Average crystalline sizes are calculated using the Scherrer equation and it is found that the synthesized NCs have an average crystalline size of 12–35 nm. Transmission electron microscopy (TEM) images reveal that the NCs are well dispersed and nearly ellipsoid, with an average size of ~ 5 nm. Eu³⁺‐activated NCs show characteristic excitation and emission spectra. The emission spectra show both magnetic (⁵D₀–⁷F₁) and electric (⁵D₀–⁷F₂) dipole transition with appropriate CIE color coordinates; however, the intensity of the magnetic dipole transition is high, which is in accordance with local site symmetry. Owing to their unique size and excellent optical properties, the synthesized NCs may have potential application in the fields bio‐imaging and solar concentrators. Copyright © 2016 John Wiley & Sons, Ltd.