Multifunctional Hybrid Nanomaterials from Water Dispersible CaF₂:Eu³⁺, Mn²⁺ and Fe₃O₄ for Luminescence and Hyperthermia Application

Abstract

CaF₂ nanoparticles doped with 1 at. % Eu³⁺and codoped with Mn²⁺ ions (1, 2, and 3 at. %) were synthesized at 180 °C by using ethylene glycol as a capping agent and solvent medium. The emission spectra of these nanomaterials show two main peaks at 590 and 612 nm after excitation at 240 or 394 nm. Enhancement in luminescence is found upon codoping of Mn²⁺. Parts of Eu³⁺ ions are substituted into Ca²⁺ sites (having a symmetry environment), which is reflected in the higher probability of magnetic dipole transition over that of electric dipole transition. The polymer film of polyvinyl alcohol incorporated with CaF₂:1Eu shows the red emission. The prepared nanomaterials are highly water dispersible. The hybrid of CaF₂:1Eu and Fe₃O₄ shows the heating ability up to 42 °C under an AC magnetic field. This is suitable for cancer therapy through hyperthermia. A very high specific absorption rate (SAR) of 283 W/g is observed. This can be ascribed to the increased magnetocrystalline anisotropy and Brownian relaxation. Biocompatibility of hybrid nanoparticles up to 75% in HeLa cells is observed. Also, this hybrid shows the red emission, and thus, it will be useful in tracing of magnetic nanoparticles through in vivo and in vitro optical imaging applications. Interestingly, the new exciton band at 300 nm is found in such a hybrid material