Ultrasmall, white-light CdSe nanocrystals: ligand effects and incorporation into solid-state lighting

Abstract

Due to the declining availability of fossil-fuels and the adverse environmental affects of the same, the world has begun a move to more efficient and longer-lasting solid-state lighting. Ultrasmall CdSe nanocrystals (diameters < 2 nm) emit broad-band white-light, making them a candidate for fabricating white light sources. A portion of the emission from these nanocrystals was found to be pinned at specific wavelengths, due to a phosphonic acid ligand dependent trap state. Modifying the phosphonic acid ligand enabled modulation of the wavelength of this emission. In addition, the quantum yield of both traditionally sized and ultrasmall nanocrystals could be increased through alteration of the ligand chemical structure. The white-light emitting nanocrystals were incorporated into photoluminescent solid-state devices, by coating encapsulated nanocrystals onto a UV LED. Furthermore, electroluminescent devices were fabricated that allowed the nanocrystal to be excited via direct charge injection. Both methods provided devices whose emission yielded white CIE color coordinates and high color-rending indices (93 for photoluminescence and 96.6 for electroluminescence), but with efficiencies (0.19 and 4.8*10-5 lum/watt, respectively) that make them currently commercially unviable.