Facile and Controllable Synthesis of Monodisperse CaF2 and CaF2:Ce3+/Tb3+ Hollow Spheres as Efficient Luminescent Materials and Smart Drug Carriers

Highly uniform and well-dispersed CaF2 hollow spheres with tunable particle size (300-930 nm) have been synthesized by a facile hydrothermal process. Their shells are composed of numerous nanocrystals (about 40 nm in diameter). The morphology and size of the CaF2 products are strongly dependent on experimental parameters such as reaction time, pH value, and organic additives. The size of the CaF2 hollow spheres can be controlled from 300 to 930 nm by adjusting the pH value. Nitrogen adsorption-desorption measurements suggest that mesopores (av 24.6 nm) exist in these hollow spheres. In addition, Ce3+/Tb3+-codoped CaF2 hollow spheres can be prepared similarly, and show efficient energy transfer from Ce3+ to Tb3+ and strong green photoluminescence of Tb3+ (541 nm, D-5(4)-> F-7(5) transition of Tb3+, the highest quantum efficiency reaches 77%). The monodisperse CaF2:Ce3+/Tb3+ hollow spheres also have desirable properties as drug carriers. Ibuprofen-loaded CaF2:Ce3+/Tb3+ samples still show green luminescence of Tb3+ under UV irradiation, and the emission intensity of Tb3+ in the drug-carrier system varies with the released amount of ibuprofen, so that drug release can be easily tracked and monitored by means of the change in luminescence intensity. The formation mechanism and luminescent and drug-release properties were studied in detail.