The Fluoride Host: Nucleation, Growth, and Upconversion of Lanthanide-Doped Nanoparticles

The rapid ascent of nanoscience has garnered significant attention in recent years. Much of the interest generated has dealt with the integration of nanoparticles in various applications ranging from automotive and textiles to bioimaging and nanomedicine. In order for the realization of this potential, their synthesis and chemistry need to be thoroughly understood. One particularly interesting class of nanoparticles comprises a lanthanide-doped inorganic matrix. Due to their physicochemical and optical properties, these lanthanide-doped nanoparticles are undergoing widespread investigation in many fields, particularly for in vitro and in vivo imaging, as well as theranostics. They offer significant advantages in biological applications, particularly the extension of the system applicability to deep tissue regions of the body, a reduced scattering of the excitation wavelength, reduction of autofluorescence, and decrease in thermal loading and photodamage to the system under study. Specifically, lanthanide-doped fluoride hosts are being propelled to the forefront of the current research efforts as they offer several advantages relative to other studied upconverting host materials. This review will take an in-depth look at lanthanide-doped upconverting fluoride nanoparticles with a particular emphasis on the synthesis, nucleation, and growth mechanisms and, finally, the potential to tailor particle properties.