Nanoparticles and fluorescence

Abstract

Nanoparticles of three different categories of condensed matter, namely, metal, semiconductor, and insulator, exhibit fluorescence through radiative recombination of charge carriers though the origin and mechanism of light emission is vastly different. Whereas fluorescence from metal nanoparticles, e.g., Au and Ag, falls in the visible region due to sp-d band transition of electrons, the fluorescence gets enhanced due to interaction with localized surface plasmon. Semiconductor quantum dots form a special class of fluorescent materials where the emission color can be tuned by tailoring the particle size as a manifestation of quantum confinement effect. Doped semiconductor nanoparticles offer another category of multifunctional materials with tunable emission and desired electronic/magnetic properties. Rare earth-doped insulators are conventionally used as phosphors for various display and lighting applications. Nanoparticles of various rare earth-doped complex insulators emit intense monochromatic light and can be synthesized by various techniques such as sol-gel, wet chemistry, coprecipitation, hydrothermal, etc. Synthesis and elimination of surface states by passivation/capping play an important role in arresting non-radiative pathways to augment fluorescence efficiency of nanoparticles.