Plasmon-Enhanced Surface-State Emission of CdSe Quantum Dots and Its Application to Microscale Luminescence Patterns

Abstract

In this paper, we report distinct enhancement of surface-state emissions (SSEs) of colloidal CdSe quantum dots (QDs) via coupling to localized plasmons (LPs) in Ag nanostructures. The roles of oleic acid (OA) ligand on QDs in the formation of Ag nanostructures and in the intense enhancement of SSEs of CdSe QDs are explored. We find that OA ligand on CdSe QDs plays a critical role in modifying the morphology of the contacted Ag, which consequently impacts the coupling of QD emitters with LPs in Ag. A systematic study of size effect of QDs on coupling of SSEs with LPs shows that as-deposited small Ag particles favorably enhance the SSEs of small-size CdSe QDs. The OA ligand on QDs yields better Ag crystallinity and clear corners during the annealing process; therefore, it promotes reshaping of small Ag particles into larger ones, favorable to enhance the SSEs of large-size CdSe QDs. The annealed QDs/Ag hybrid structures are more stable than the unannealed ones due to the loss of the OA ligand in the heating process. The selective coupling of QD emitters with LPs in Ag nanostructures allows feasible realization of microscale fluorescent color patterns. The approach of OA-assisted modification of plasmonic properties of Ag nanostructures provides a new route to synthesizing bright luminescence materials and devices that use colloidal QDs.

Designable Luminescence with Quantum Dot–Silver Plasmon Coupler

“…A key issue arises here, namely, can we convert the non‐radiative trap states to radiative ones? Recently, the surface trap states of CdSe QDs have been effectively converted to radiative ones by plasmon‐resonance methods and the QY of these QDs was greatly enhanced . Studies have shown that colloidal QDs with rich surface trap states could be used as white‐light sources because surface trap states can generate a high‐QY broad emission band in the visible region; furthermore, they can be changed by some external parameters …”

“…However, post‐synthesis wet‐chemical treatments usually introduce more defects on the surface of the QDs and form rich‐surface trap states, which usually additionally quench the luminescence. Whereas surface states are dominant routes in the non‐radiative decay of excited electrons, the resonant coupling of QD emitters‐metallic plasmons provides an effective way for extracting the energy of the surface states via radiative decay channels . This physical approach greatly enhances the intensity of SSE.…”

Physical approaches to tuning luminescence process of colloidal quantum dots and applications in optoelectronic devices

“…XRD characterization shows that the Ag films annealed in OA have better crystallinity favorable for the #3 QDs SSE enhancement. Adapted from Hu et al (2012a). enhanced SSEs observed in the QDs/Ag/Si hybrid structures are similar to those of the acceptors in resonance energy transfer systems (Sadhu et al, 2010). SSs on CdSe CQDs are usually thought to be an essential path for nonradiative relaxation (Hines and Guyot-Sionnest, 1996).…”

“…Adapted fromHu et al (2012a). Each row corresponds to one of the three groups of QDs (#1, #2, and #3 from top to bottom).…”

“…Adapted fromHu et al (2012a). (b) The absorption spectra (bold real lines) and PL intensity spectra (dotted lines) of the annealed samples.…”