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

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 [C 4 mim][PF 6 ] led to the uniform LnF 3 microcrystals. The method was applied to the preparation of pure LnF 3 (Ln   =   La, Ce, Pr, Nd) and Eu 3+ -doped LaF 3 , Tb 3+ -doped CeF 3 . 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 LaF 3 decreased with the increasing of the molar ratio of [C 4 mim][PF 6 ] to La(NO 3 ) 3 ·6H 2 O. Diameter of the microcrystal decreased from La to Nd. Photoluminescence properties of Eu 3+ -doped LaF 3 and Tb 3+ -doped CeF 3 were also studied.