Structural, optical and X-ray attenuation properties of Tb3+:BaxCe1−xF3−x (x = 0.18–0.48) nanospheres synthesized in polyol medium

Abstract

Uniform Ba_0.18Ce_0.82F_2.82 nanospheres have been obtained after aging a solution of barium and cerium nitrates and sodium tetrafluoroborate in a mixture of ethylene glycol and water at 120 °C for 20 hours. The diameter of the spheres could be tailored from 65 nm to 80 nm by varying the NaBF₄ concentration while maintaining their colloidal stability in aqueous suspension. Increasing the aging temperature led to a phase transformation from hexagonal to cubic symmetry and to a concomitant increase of the Ba/Ce ratio, which reached a value close to the nominal one (50/50) at 240 °C. The same method was successful in obtaining Tb³⁺-doped nanospheres with homogeneous cation distribution and the same morphological features as the undoped material. An intense green emission was observed after the excitation of the Tb³⁺-doped samples through the Ce³⁺–Tb³⁺ energy transfer (ET) band. The ET efficiency increased with increasing Tb content, the maximum emission being observed for the 10% Tb-doped nanospheres. Aqueous suspensions of the latter sample showed excellent X-ray attenuation values that were superior to those of an iodine-based clinically approved contrast agent. Their fluorescence and X-ray attenuation properties make this material a potential dual bioprobe for luminescence bioimaging and X-ray computed tomography.