ABSTRACTThe addition of high refractive index (RI) inorganic nanoparticles (NPs) to LED encapsulation materials can lead to higher light extraction efficiency. In addition, the NPs can be carriers for additional functionality such as color conversion. Using a simple “grafting-to” approach, bimodal polydimethylsiloxane (PDMS) brushes were grafted onto high-RI ZrO2 NPs. Subsequently, an organic phosphor, 6-[fluorescein-5(6)-carboxamido]hexanoic acid (FCHA), was attached onto the PDMS-grafted ZrO2 NPs via a facile ligand exchange process. The bimodal polymer brush design enables homogenous dispersion of the surface functionalized NPs within the silicone matrix. The functionalized NPs with ∼53 wt% ZrO2 core have a ∼0.08 higher RI than neat silicone, and the NP-filled silicone nanocomposites exhibit a transparency of ∼ 90% in the 550-800 nm wavelength range. In addition, the nanocomposites could be excited at a wavelength around 455 nm by a blue LED and undergo secondary yellow emission at around 571 nm. It is expected that the prepared nanocomposites can be used as high-efficiency, non-scattering, color-tuned materials for advanced LED encapsulation.
Directed self-assembly of inorganic nanoparticles at air/liquid interfaces