A comprehensive review on upconversion nanoparticles: From synthesis strategies to multifunctional applications

Upconversion nanoparticles (UCNPs) have garnered significant attention in recent years due to their unique ability to convert near-infrared light into visible or ultraviolet emission. This review provides a comprehensive overview of the synthesis methods, optical, electronic, and biological properties of UCNPs. We discuss the various techniques employed for synthesizing UCNPs, including thermal decomposition, solvothermal, and hydrothermal methods. The optical properties of UCNPs, including their upconversion mechanisms, emission spectra, and quantum yields, are also examined. The biocompatibility and cytotoxicity of UCNPs are also discussed, highlighting their potential for biomedical applications. Finally, we review the applications of UCNPs in various fields, including bioimaging, photodynamic therapy, solar cells, and optoelectronic devices. The purpose of this review is to provide an in-depth understanding of UCNPs and their potential for advancing various technologies.