(Invited) Lanthanide Doped Nanoparticles and Their Applications

Abstract

Since approximately 2000, lanthanide doped nanoparticles have received significant attention due to their interesting luminescent properties. At the core of this interest is their ability to convert near-infrared excitation light (typically 980 or 800 nm) to higher energies spanning the ultraviolet, visible and near-infrared regions of the spectrum through a multiphoton process known as upconversion. Upconversion differs from conventional multiphoton excitation in other materials where no real intermediate states are present necessitating the use of ultrafast lasers (in the femtosecond regime) for simultaneous excitation to the upper emitting state. The lanthanide ions possess a multitude of 4f electronic states that have long lifetimes (micro- to millisecond) thus act as population reservoirs in the upconversion process. Hence, upconversion occurs through real, long-lived intermediate states through a sequential photon absorption process. This eliminates the need for ultrafast excitation and as a result, upconversion can be observed using inexpensive, continuous wave diode lasers. Upconversion luminescence can be exploited for a number of applications in nanomedicine, theranostics, photovoltaics, photocatalysis, as well as many others.While their upconversion luminescence has been studied in great detail, lanthanide doped nanoparticles can also emit in the near-infrared through a direct Stokes (down-shifted) luminescence process. Of particular importance is that these near-infrared emissions lie within the biological windows where biological tissues are optically transparent. For obvious reasons, a great deal of the work on the nanomedicine and theranostics applications of lanthanide doped nanoparticles has shifted to their near-infrared luminescence properties.In this presentation, we will demonstrate the synthesis of these nanoparticles, establish how changing their nanoscale architecture can affect their luminescence properties (both upconversion and near-infrared), and discuss their potential applications, particularly in nanomedicine.