Reversible Electrochemical Control over Photoexcited Luminescence of Core/Shell CdSe/ZnS Quantum Dot Film

Abstract

Semiconductor quantum dots (QDs) are widely used in light-emitting diodes and solar cells. Electrochemical modulation is a good way to understand the electrical and optical properties of QDs. In this work, the effects of electrochemical control on photoluminescence (PL) spectra in core/shell CdSe/ZnS QD films are studied. The results show different spectral responses for surface emission and core emission when a negative electrochemical potential is applied: the core emission is redshifted while the surface emission is blueshifted. The former is attributed to the electrostatic expansion of the excitonic wave function, due to the asymmetric distribution of adsorbed cations on the surface of the dots. The latter is attributed to the occupation of lower surface states by the injected electrons, i.e., the photoexcited electrons are more likely to be trapped onto higher surface states, leading to a blueshift of the surface emission. Both the spectral shift and the accompanying PL-quenching processes are reversible by resetting the potential.

Photoexcitation Dynamics in Electrochemically Charged CdSe Quantum Dots: From Hot Carrier Cooling to Auger Recombination of Negative Trions

“…Previous studies have shown that charging can induce surface modifications, which lead to the formation of traps in QDs without inducing significant changes in absorption and photoluminescence . It has also been shown that it is possible to charge QDs without reducing the surface using a passivating ligand or by building core–shell structures to eliminate such surface species. ,, For precise scrutiny of the effect of external bias on the QD assembly, as the main goal of this study, a combination of electrochemistry with spectroscopy is used. Changes of the absorption spectra due to the state filling can further identify the energy levels that are involved in charging. , …”

“…In this work, we combine electrochemistry with ultrafast transient absorption spectroscopy (TA) to monitor changes in the excited state dynamics of the QD under controlled charging. ,− By observing the changes in the steady state absorption during spectroelectrochemistry measurement, we have identified distinct potentials that correspond to the injection of one and two electrons to the QDs. The presence of these negative charges leads to negative trions and tetrons upon excitation by laser light in the TA measurement .…”

Interparticle Spacing Effect among Quantum Dots with High-Pressure Regulation

“…They are band-edge emissions within 435–465 nm for both systems and a long-wavelength emission within 500–600 nm for CdSe/ZnS–QDs, 500–650 nm for CdSe/ZnS–QDs–PMMA. Since phase mismatching induces trap states that will quench instead of enhance emission, long-wavelength emissions may be from surface trap states [ 32 , 33 ]. In CdSe/ZnS–QDs, the trap-state emission is rather weak as compared with a band-edge emission at less than 2.5 GPa.…”

Photoluminescence Lifetime Based Investigations of Linker Mediated Electronic Connectivity Between Substrate and Nanoparticle

“…The aminosilane linker under direct hole quenching and the mercaptosilane linker via indirect charge injection from ITO. Literature shows that the described PL influencing processes are also strongly interconnected to the population of electronic states in the slide (Wehrenberg and Guyot-Sionnest, 2003; Gooding et al, 2008; Li et al, 2017).…”