Exciton Recycling in Graded Gap Nanocrystal Structures

Abstract

We propose a cascaded energy transfer structure made of semiconductor nanocrystals. Funnel-like band gap profiles are realized applying layer-by-layer assembly to CdTe nanocrystals of distinct sizes. Optical excitations efficiently transfer along the band gap gradient and are finally captured by the largest nanocrystals. The photoluminescence yield from the center layer is surprisingly high. The stepwise passing on of excitation energy avoids hot carriers, and the funnel structure recycles otherwise trapped and lost electron−hole pairs.

Surface plasmon enhanced Förster resonance energy transfer between the CdTe quantum dots

“…2 A cascaded FRET in artificial solids formed by layers of QDs has also been demonstrated. 3 Efforts to improve the FRET process have been focused on structures with reduced donor-acceptor QDs' separation, improved spectral overlap of the donor emission and acceptor absorption spectra, and increased packing density of the layers. 4…”

“…2 A cascaded FRET in artificial solids formed by layers of QDs has also been demonstrated. 3 Efforts to improve the FRET process have been focused on structures with reduced donor-acceptor QDs' separation, improved spectral overlap of the donor emission and acceptor absorption spectra, and increased packing density of the layers. 4 Metal nanoparticles ͑NPs͒ have been used to modify some of the fundamental optical processes such as Raman scattering 5 and radiative processes 6 in chemical species in a characteristic way.…”

“…This causes an increase in the donor decay rate with reduced PL lifetime and an increase in the acceptor lifetime, which is a clear signature of the FRET process. [2][3][4] When the layer of mixed QDs is in proximity to the Au NPs, the donor lifetime decreased further from 4.40 ns ͑on quartz͒ to 2.06 ns and the acceptor lifetime is modified from 10.70 ͑on quartz͒ to 7.52 ns. The average lifetime values of donor and acceptor dots are also shown to be distance dependent.…”

Structural tuning of color chromaticity through nonradiative energy transfer by interspacing CdTe nanocrystal monolayers

“…In another structure, alternating layers of NCs and polyelectrolytes have been assembled to form a funnel-like bandgap variation toward the center NC layer for efficient energy harvesting. 17 Also, LbL structures have been constructed by directly attaching oppositely charged NCs without using any linker polymer for further increased energy transfer rates. 18 These previous studies have demonstrated FRET and related dynamics in these engineered LbL NC structures.…”

Quantum efficiency enhancement in nanocrystals using nonradiative energy transfer with optimized donor-acceptor ratio for hybrid LEDs

“…9 To address this problem, the recycling of trapped excitons into the quantum dots by using nonradiative energy transfer ͑ET͒, which is also known as Förster resonance energy transfer, provides a possible solution to enhance the quantum efficiency of these NC solid films. Although Förster ET for colloidal NC emitters are investigated in various studies, [10][11][12][13][14][15][16][17][18] the dependence of quantum efficiency enhancement on the donor-acceptor variation in the solid film and its optimization have not been investigated for hybrid LEDs to date.…”