A facile synthesis of water-soluble BaYF 5 :Ln 3 + NCs with excellent luminescent properties as promising contrast agent for dual-modal bioimaging

Monodisperse, water-dispersible lanthanide (Ln3+)-doped BaYF5 nanocrystals (NCs) are synthesized through a fast, facile and environmentally–friendly microwave-assisted modified polyol process with polyethyleneimine as the surfactant. The TEM images illustrate the sphere-like and flower-like morphologies of the obtained NCs. Intense multicolor down conversion (DC) luminescence is also achieved in Ce3+/Ln3+ (Ln=Tb, Dy) doped BaYF5 NCs. Then, upon excitation at 980nm, upconversion (UC) luminescent properties of BaYF5:Yb3+/Ln3+ (Ln=Er, Tm, Ho) NCs and energy transfer between Yb3+ and Ln3+ are systematically surveyed. Furthermore, a layer of SiO2 is coated on the surface of the NCs and the methyl thiazolyl tetrazolium (MTT) assays are performed to test the cytotoxicity of BaYF5:Ln3+ NCs. Due to the X-ray absorption property of Ba element, a proof-of-concept CT imaging with BaYF5:Ln3+ NCs is conducted. These results indicate that the obtained NCs have great potential as optical/CT bioprobe.