Encapsulated white-light CdSe nanocrystals as nanophosphors for solid-state lighting

Abstract

White-light emitting ultra-small CdSe nanocrystals present exciting possibilities in the area of solid-state lighting technology. In this work, thirteen dissimilar polymers were examined as potential encapsulants for these single-sized nanocrystals. Films of the encased nanocrystals were characterized in terms of nanocrystal aggregation and changes to the nanocrystals' natural emission. The Hildebrand and Hansen solubility parameters of each encapsulant were found to be correlated to the quality of nanocrystal encapsulation achieved. Encapsulants with cyclosiloxane or bisphenol-A type epoxy structures caused extensive aggregation of the nanocrystals at low loading levels (<0.5% w/w) due to the solubility difference between the polymer structure and the nanocrystals' ligands. Of the encapsulants tested, the most robust, color stable, and homogenous encapsulation was obtained using a biphenylperfluorocyclobutyl polymer. In this polymer, nanocrystal loading levels up to 18% w/w were achieved. White-light emitting CdSe nanocrystals encapsulated in the biphenylperfluorocyclobutyl polymer were coated on various UV-LEDs creating a white light source with chromaticity coordinates of (0.324, 0.322) and a high color-rendering index of 93.