Surfactant-Free Synthesis, Luminescent Properties, and Drug-Release Properties of LaF3 and LaCO3F Hollow Microspheres

Uniform LaF3 and LaCO3F hollow microspheres were successfully synthesized through a surfactant-free route by employing La(OH)CO3 colloidal microspheres as a sacrificial template and NaBF4 as the fluorine source. The synthetic process consists of two steps: the preparation of a La(OH)CO3 precursor via a facile urea-based precipitation and the following formation of lanthanide fluoride hollow microspheres under aqueous conditions at low temperature (50 degrees C) and short reaction time (3 h), without using any surfactant and catalyst. The formation of hollow spheres with controlled size can be assigned to the Kirkendall effect. It is found that the phase and structure of the products can be simply tuned by changing the pH values of the solution. Time-dependent experiments were employed to study the possible formation process. N-2 adsorption/desorption results indicate the mesoporous nature of LaF3 hollow spheres. Yb3+/Er3+ (Ho3+) and Yb3+/Tm3+-doped LaF3 hollow spheres exhibit characteristic up-conversion (UC) emissions of Er3+ (Ho3+) and Tm3+ under 980 nm laser-diode excitation, and Ce3+/Tb3+-doped LaF3 and LaCO3F emit bright yellow-green and near-white light under UV irradiation, respectively. In particular, LaF3:Yb/Er and LaCO3F:Ce/Tb hollow microspheres exhibit obvious sustained and pH-dependent doxorubicin release properties. The luminescent properties of the carriers allow them to be tracked or monitored during the release or therapy process, suggesting their high potential in the biomedical field.