Solution
processing of semiconductor nanocrystal (NC) solids represents
an attractive platform for the development of next-generation optoelectronic
devices. In search of enhanced light-emitting performance, NC solids
are typically designed to have large interparticle gaps that minimize
exciton diffusion to dissociative sites. This strategy, however, reduces
electrical coupling between nanoparticles in a film, making the injection
of charges inefficient. Here, we demonstrate that bright emission
from nanocrystal solids can be achieved without compromising their
electrical conductivity. Our study shows that solids featuring a low
absorption-emission spectral overlap (J) exhibit
an intrinsically slower exciton diffusion to recombination centers,
promoting longer exciton lifetimes. As a result, enhanced emission
is achieved despite a strong electronic coupling. The observed phenomenon
was found consistent with a decreased resonant energy transfer in
films exhibiting a reduced J value. The inverse correlation
between film luminescence and J was revealed through
a comparative analysis of CdSe/CdS and ZnSe/CdS solids and further
confirmed in two control systems (ZnTe/CdSe and Mn2+-doped
ZnCdSe/ZnS). Exceptionally slow exciton diffusion (∼0.3 ms)
and high brightness were observed for Mn2+-doped Zn1–x
Cd
x
Se/ZnS
NC films exhibiting a nearly vanishing J parameter.
We expect that the demonstrated combination of electrical coupling
and bright emission in nanocrystal solids featuring low J can benefit the development of nanocrystal light-emitting technologies.
We demonstrate a general strategy for the synthesis of colloidal semiconductor nanocrystals (NCs) exhibiting size dispersion below 5%. The present approach relies on the sequential deposition of fully saturated cationic and anionic monolayers onto small-diameter clusters, which leads to focusing of nanocrystal sizes with the increasing particle diameter. Each ionic layer is grown through a room-temperature colloidal atomic layer deposition process that employs a two-solvent mixture to separate the precursor and nanocrystal phases. As a result, unreacted precursors can be removed after each deposition cycle, preventing the secondary nucleation. By using CdS NCs as a model system, we demonstrate that a narrow size dispersion can be achieved through a sequential growth of Cd 2+ and S 2− layers onto starting CdS cluster "seeds". Besides shape uniformity, the demonstrated methodology offers an excellent batch-to-batch reproducibility and an improved control over the nanocrystal surface composition. The present synthesis is amenable to other types of semiconductor nanocrystals and can potentially offer a viable alternative to traditional hot-injection strategies of the nanoparticle growth.
An efficient method for covalently linking of cellulose and clay using a click chemistry based strategy is reported. Azide and alkynyl derivatives of silane were synthesized and used for silanization of cellulose and clay respectively. Functionalized cellulose and clay were then coupled using Cu(I) catalyzed azide-alkyne cycloaddition reaction, resulting in a covalent linkage between them. Successful synthesis of the silane derivates was established using Fourier transform infrared (FTIR) and nuclear magnetic resonance. Silanization of cellulose and clay with azide and alkynyl derivatives and the formation of a triazole linkage were confirmed using FTIR.
Graphical AbstractKeywords Micro crystalline cellulose (MCC) Á Kaolinite Á Silanization Á Click chemistry Á Azidealkyne cycloadditionEthyl acetate EDC.HCl 1-Ethyl-3-(3-dimethyllaminopropyl) carbodiimide hydrochloride Electronic supplementary material The online version of this article (
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