A new sonication-assisted ionic liquid-based route to microcrystals of lanthanide fluorides and their photoluminescent properties

• Microcrystals of lanthanide fluorides were prepared by sonication-assisted IL-based route.
• It is a fast, simple, green and mild method to get lanthanide fluoride microcrystals.
• The microcrystals are uniform, monodisperse, well-shaped and phase-pure.
• IL served as reaction medium, fluoride source as well as template.
• Sonication helped to accelerate reaction and get monodisperse uniform microcrystals.

We introduce an ionic liquid-based method for the synthesis of uniform lanthanide fluoride microcrystals with the assistance of a sonication-accelerated reaction system. It is a fast, simple and mild process to get uniform monodisperse spherical lanthanide fluoride microcrystals in large scale. Homogeneous precipitation in a biphasic system of ethanol solution of lanthanide nitrates and ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6] led to the uniform LnF3 microcrystals. The method was applied to the preparation of pure LnF3 (Ln = La, Ce, Pr, Nd) and Eu3+-doped LaF3, Tb3+-doped CeF3. SEM images indicated highly uniform cotton-like spherical microcrystals were obtained. HRTEM image indicated that the microcrystals were aggregated by nanocrystals of 6–10 nm due to agglomeration effect of the ionic liquid. The uniformity and dispersility of LaF3 decreased with the increasing of the molar ratio of [C4mim][PF6] to La(NO3)3·6H2O. Diameter of the microcrystal decreased from La to Nd. Photoluminescence properties of Eu3+-doped LaF3 and Tb3+-doped CeF3 were also studied.