Silica shell growth on lanthanide-doped upconversion nanoparticles.

Upconversion nanoparticles (UCNPs) combining both dye sensitization and core/shell enhancement are of great interest for their ability to boost the excitation efficiency of upconversion systems. Here, we report and investigate a 20-fold upconversion luminescence enhancement in dye-sensitized core/active shell UCNPs compared to that in nonsensitized core-only UCNPs. We observe a two-component luminescence rise dynamics in the upconversion kinetics of dye-sensitized UCNPs, distinctly different from the one-component rise dynamics of the nonsensitized UCNPs. For dye-sensitized UCNPs, the fast sub-microsecond component of the upconversion luminescence rise time is attributed to the radiative pumping of Er3+ ions from the dye, whereas the slow sub-millisecond component is due to the nonradiative energy transfer from the dye predominantly to Yb3+ ions, followed by the energy migration and the nonradiative energy transfer from Yb3+ to Er3+ ions. Our studies provide an insight into the interplay between radiative and nonradiative energy transfer as well as into the role of energy migration across the active shell of dye-sensitized core/active shell UCNPs.

Gold nanoparticles, or colloidal gold (AuNP), represent one of the most significant and established forms of sub-micron inorganic structures to be researched in recent years. AuNP physical and chemical properties...

Lanthanide doped Upconversion Nanoparticles (UCNPs) are a class of nanomaterials with excellent luminescence properties. The practical use of UCNPs, however, has been hindered by their relatively low upconversion (UC) quantum...

Lanthanide-doped upconversion nanoparticles have emerged as attractive candidates for biomedical applications. This is due to their excitation and emission wavelengths, which lay the foundation for deeper penetration depth into biological tissue, higher resolution due to reduced scattering and improved imaging contrast as a result of a decrease in autofluorescence background. Usually, their encapsulation within a biocompatible silica shell is a requirement for their dispersion within complex media or for further functionalization of the upconversion nanoparticle surface. However, the creation of a silica shell around upconversion nanoparticles can be often challenging, many times resulting in partial silica coating or nanoparticle aggregation, as well as the production of a large number of silica particles as a side product. In this work we demonstrate a method to accurately predict the experimental conditions required to form a high yield of silica-coated upconversion nanoparticles, regardless of their shape and size.