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.

The effect of surface trap states on band edge recombination in CdSe, CdS and CdS x Se 1-x alloy nanocrystals has been determined using fluorescence upconversion spectroscopy. These measurements reveal that there is both a size and composition dependence on the short-lived (τ 1 ) and long-lived (τ 2 ) components of fluorescence lifetime at the band edge. An increase in nanocrystal diameter, ranging from 23 to 60 Å, is accompanied by an increase in τ 1 . This behavior is explained by the decrease in accessible trap sites through a reduction in surface-to-volume ratio. Similarly, τ 2 is found to increase with increasing nanocrystal size. However, with increasing sulfur concentration in the alloy nanocrystals, both a reduction in the magnitude of τ 1 and a reversal in the trend for τ 2 are observed. These changes in lifetimes associated with the addition of sulfur are explained by increased trapping on the nanocrystal surface. These results indicate that carrier dynamics may be controlled not only through size, but also through composition of the nanocrystals. Compositional variation has been shown not only to affect carrier dynamics, but also to affect the optical properties of nanocrystals. An increase in the Stokes shift is observed for CdS x Se 1-x alloy nanocrystals as compared to CdSe and CdS nanocrystals. This indicates that the Stokes shift is highly influenced by the nonlinear effects of alloying.

We report pinning of the emission spectrum in ultrasmall CdSe nanocrystals with a diameter of 1.7 nm and smaller. It was observed that the first emission feature ceased to blueshift once the band edge absorption reached 420 nm, though the band edge absorption continued to blueshift with decreasing nanocrystal diameter.

Electrophoretic deposition was used to deposit CdSe nanocrystals on TiO2 for use in photovoltaic cells. The deposition current underwent a simple exponential decay, consistent with the current being comprised of charge transfer from charged nanocrystals to the electrodes. Rutherford backscattering spectroscopy showed the composition of the deposited films depended on the polarity of the electrode on which the film formed. A solar cell constructed using electrophoretic deposition exhibited a photovoltaic response from the region in which nanocrystals were deposited, with an efficiency of ∼10−6%. The low efficiency was primarily due to the planar geometry employed for the TiO2 subsrate.