Probing Interaction Distance of Surface Quenchers in Lanthanide-Doped Upconversion Core–Shell Nanoparticles

Abstract

Core–shell structures, which employ an optically inert shell to physically separate the emitting core from the surface quenchers, are often designed to optimize the emission efficiency of nanoscale emitters. However, it remains unclear that at what distance the effects of different surface quenchers, such as defects and adsorbed moieties, can be completely screened by the shell. Here, in a model upconversion system, we examine the interaction distance of surface quenchers in core–shell nanoparticles by using upconversion spectroscopy. Steady-state as well as time-resolved spectra show that the quenching effect of surface-adsorbed hydroxyl (OH) group diminishes at a distance (shell thickness) of 3.5 nm in diameter and 8.0 nm in length, which is larger than that for oleate-capped counterparts. With the increase of pumping density, the interaction distance of the surface quenchers does not apparently change, whereas saturation of the surface-related states notably reduces the optimal shell thickness for surface passivation.