Study of Shell Thickness-Dependent Charge Transfer Dynamics in Green-Emitting Core/Shell Giant Quantum Dots

The quantum confinement effect and photoenhancement of photoluminescence (PL) of lead sulphide (PbS) quantum dots (QDs) and lead sulphide/manganese sulphide (PbS/MnS) core shell QDs capped with thiol ligands in aqueous solution were investigated. From PL results, the presence of MnS shells gives a strong confinement effect which translates to higher emission energy in PbS/MnS core shell QDs. Increasing MnS shell thickness from 0.3 to 1.5 monolayers (ML) causes a blueshift of PL peak energies as the charge carriers concentrated in the PbS core region. Enhancement of the PL intensity of colloidal PbS and PbS/MnS core shell QDs has been observed when the samples are illuminated above the band gap energy, under continuous irradiation for 40 min. Luminescence from PbS QDs and PbS/MnS core shell QDs can be strongly influenced by the interaction of water molecules and oxygen present in aqueous solution adsorbed on the QD surface. However, PbS/MnS core shell QDs with a shell thickness of 1.5 ML did not show a PL peak energy stability as it was redshifted after 25 min, probably due to wider size distribution of the QDs.

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Coupled Charge Transfer Dynamics and Photoluminescence Quenching in Monolayer MoS2 Decorated with WS2 Quantum Dots

Scientific Reports ◽

10.1038/s41598-019-55776-6 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 3

Author(s):

Larionette P. L. Mawlong ◽

Abhilasha Bora ◽

P. K. Giri

Keyword(s):

Quantum Dots ◽

Charge Transfer ◽

Room Temperature ◽

Chemical Vapor ◽

Kelvin Probe ◽

Photoluminescence Quenching ◽

Force Microscopy ◽

Level Model ◽

Microscopy Analysis ◽

Charge Transfer Dynamics

AbstractHerein, we have investigated the tunability of the photoluminescence (PL) of the monolayer MoS2 (1L-MoS2) by decorating it with WS2 quantum dots (WS2 QD). The direct bandgap 1L-MoS2 and WS2 QDs are grown by chemical vapor deposition and liquid exfoliation methods, respectively. The room temperature PL spectrum of bare 1L-MoS2 is systematically quenched with its decoration with WS2 QDs at different concentrations. A decrease in the work function of 1L-MoS2 with the decoration of WS2 QDs was established from the Kelvin probe force microscopy analysis. A detailed quantitative analysis using the four-energy level model involving coupled charge transfer was employed to explain the redshift and the systematic decrease in the intensity of the PL peak in 1L-MoS2/WS2 QD heterostructure. The modulation of the PL in the heterostructure is attributed to the increase in the formation of negative trions through the charge transfer from WS2 QD to the 1L-MoS2 and thus making the 1L-MoS2 heavily n-type doped, with increase in the electron density by ~1.5 × 1013 cm−2. This study establishes the contribution of defects in the coupled charge transfer dynamics in 1L-MoS2, and it lays out a convenient strategy to manipulate the optical and electrical properties of 1L-MoS2 for various optoelectronic applications.

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Interband Optical Transition Energies in Type-II PbSe/PbS Core/Shell Quantum Dots

Journal of Advanced Physics ◽

10.1166/jap.2017.1297 ◽

2017 ◽

Vol 6 (1) ◽

pp. 80-86

Author(s):

S. N. Saravanamoorthy ◽

A. John Peter

Keyword(s):

Quantum Dots ◽

Optical Properties ◽

Shell Thickness ◽

Optical Transition ◽

Hole Pair ◽

Core Shell ◽

Type Ii ◽

Electron Hole ◽

Transition Energies ◽

Electron Hole Pair

Electronic and optical properties of Type-II lead based core/shell semiconducting quantum dots are reported. Binding energies of electron–hole pair, optical transition energies and the absorption coefficients are investigated taking into account the geometrical confinement in PbSe/PbS core/shell quantum dot nanostructure. The energies are obtained with the increase of shell thickness for various inner core radii. The probability densities of electron and hole wave functions of radial coordinate of the core PbSe and PbS shell quantum dots are presented. The optical transition energy with the spatial confinement is brought out. The electronic properties are obtained using variational approach whereas the compact density matrix method is employed for the nonlinear optical properties. The results show that (i) a decrease in binding energy is obtained when the shell thickness increases due to more separation of electron–hole pair and (ii) the energy band gap decreases with the increase in the shell thickness resulting in the reduction of the higher energy interband transitions.

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