Biocompatible and surfactant-free Er, Yb doped fluorapatite upconversion nanoparticles for biomedical applications

There is growing attention on developing upconversion nanoparticles because of their potential biomedical applications. The key focus is on the efficiency and biocompatibility of the materials used. Even though many efficient host materials have been reported, biocompatibility must be addressed more. Fluorapatite (FAp) is an ideal choice for this purpose. The main concern in the synthesis of FAp upconversion nanoparticles is controlling their size on high-temperature annealing. Mostly, surfactants are used during synthesis which can control particle size. Even though a high annealing temperature is essential to activate the erbium center, in most reports the annealing temperature is kept below 800°C to prevent aggregation of particles. Increasing the annealing temperature to 1200°C will significantly improve the luminescence intensity. Activating the Er centre at a high annealing temperature without affecting the particle size is challenging. This work discusses the synthesis of PEI-modified Er, Yb-doped fluorapatite nanoparticles with an annealing temperature of 1200°C. The Nanoparticles are highly luminescent and dispersible in water.