Synthesis and characterization of lanthanide-doped upconversion nanoparticle

Abstract

Their near-infrared (NIR) absorption capabilities, stable optical emission and a high degree of biocompatibility， have made lanthanide-doped upconversion nanoparticle (UCNP) a popular choice towards developing the next-generation phosphorescence element. From biological labelling，to becoming the gain media for optical communications, there are many possible potential applications for a UCNP product.

Lanthanide-doping functions to further enrich and tune the optical properties of the host crystal. Commonly persisting as a trivalent ion，the inherently unfilled 4f orbitals of lanthanides, and the shielding effect it provides, makes them the ideal optical doping element to be incorporated across many different materials. Though amongst the available lanthanides, only ytterbium, erbium and thulium found the most frequent usage off. Ytterbium (Yb^3+) with its single excited state functions to absorb the initial excitation, which would then be transferred to either of the available erbium (Er^3+) and thulium (Tm^3+) emitter, where their many intermediate states allows for a wide-range of emission product.

While doping profiles are the main factor in dictating the optical behavior of a UCNP，there are certainly additional external factors that also play a considerable part as well. As such，this study would aim to give an overview and discussed some of the major factors that may affect the observed luminescence of a UCNP. This is accomplished by fabricating three different NaYF_4 core-shell UCNP that is co-doped with Yb/Er and Yb/Tm doping. These sample would represent the three of the common possible emission colors of a UCNP，which are: red, green and blue.