Wet‐Chemically Synthesized Colloidal Semiconductor Nanostructures as Optical Gain Media

Ong, Xuanwei; Zhi, Min; Gupta, Shashank; Chan, Yinthai

doi:10.1002/cphc.201500975

Cited by 6 publications

(5 citation statements)

References 65 publications

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“…Semiconductor nanostructures, with tunable optical and excitonic properties as variations of geometries, sizes, and compositions, are applied in optical and electronic devices. , To pursue high efficiencies of light harvesting and energy conversion for solar cells, narrow line width within a wide spectral region for light emission diodes, and low threshold with high optical gain for microlasers, core/shell heterostructures with a near unit quantum yield (QY) from surface passivation or long lifetime carriers from a charge-separated state become hot topics. − All of the interesting properties and potential applications are based on distributions and transfers of electrons and holes in the nanostructures, which can be disclosed by time-resolved spectroscopies such as transient absorption (TA) spectroscopy, fluorescence decay measurements, 2D time-resolved spectroscopy, etc. − …”

Section: Introductionmentioning

confidence: 99%

Quasi-Type II Carrier Distribution in CdSe/CdS Core/Shell Quantum Dots with Type I Band Alignment

et al. 2018

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Band alignments are essential for understanding the optical properties and carrier transfer of core/shell QDs. As CdSe/CdS core/shell QDs with increasing shell thickness represent red-shifted absorption and luminescence spectra, weakened oscillator strength of the lowest electronic transition, and elongated luminescence lifetime, they are assigned to quasi-type II band alignment. However, femtosecond transient absorption spectroscopy with state-selective excitation revealed a type I band alignment of the CdSe/CdS QDs with a thin CdS shell, in which the excited electron is localized in the CdSe core with core excitation while delocalized in the whole QDs with shell excitation, even though a quasi-type II carrier distribution was observed with steady-state spectroscopy. In the type I core/shell QDs, the CdS shell acts as an energy barrier in surface electron and hole-trapping processes. The time constant of the hole-trapping process of the CdSe core (∼10 ps) was elongated 10 times owing to a tunnel effect through the high energy barrier of the CdS shell, which was estimated from the decay related to the biexcitonic induced spectral shift. The biexcitonic spectral shift induced by a ∼100 ps hole-trapping process was also observed at the 1S(e)–2S3/2(h) transition. Our results from transient absorption spectroscopy with state-selective excitation are useful to clarify band alignment and carrier distribution of hetero-nanostructures, which could help to objectively extract charge carriers in photovoltaic applications.

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Section: Introductionmentioning

confidence: 99%

Quasi-Type II Carrier Distribution in CdSe/CdS Core/Shell Quantum Dots with Type I Band Alignment

et al. 2018

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“…Due to its anisotropic shape, such NRs exhibit unique properties compared to the typical spherical core-shell semiconductor nanocrystals (NCs). [15][16][17][18][19][20] Fluorescence from these NRs originates from the radiative recombination of excitons in the CdSe core while photon absorption at shorter wavelengths is dominated by the rod-like CdS shell. 15 Consequently, the absorption cross-section of NRs can be altered by changing the length of the NR while its emission wavelength exhibits little to no change.…”

Section: Introductionmentioning

confidence: 99%

A robust low data solution: Dimension prediction of semiconductor nanorods

Liu

et al. 2021

Computers & Chemical Engineering

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“…QD thin films have attracted attention in the field of optoelectronic devices, including light emitting devices, solar cells, photodetectors, and gain medium for laser applications. − Especially, QD films in a large area have a quite high potential for display applications such as QD film display, QD color-filter display, and QD-LED display. , However, fabricating homogeneous self-assembled QD monolayers (QD-SAMs) over large areas is still challenging. Several methods have been proposed to fabricate QD-SAMs. , Coe–Sullivan et al proposed a method to form large-area ordered monolayers of QDs by spin-casting a mixed solution of aromatic organic materials and aliphatically capped QDs .…”

Section: Introductionmentioning

confidence: 99%

Tuning the Emission Colors of Self-Assembled Quantum Dot Monolayers via One-Step Heat Treatment for Display Applications

Leng

Chan

et al. 2020

ACS Appl. Nano Mater.

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Homogeneously self-assembled colloidal semiconductor quantum dot monolayers (QD-SAMs) over large areas are promising materials for thin film optoelectronic device applications, especially for display. Although tuning of emission colors from QDs is generally achieved during wet chemical synthesis and before monolayer formation, we propose in this study a simple and effective method to adjust emission colors after the formation of QD-SAMs by a simple one-step heat treatment. CdSe-based core/shell or core/double shell structured QDs (CdSe/ZnS, CdSe/CdZnS, and CdSe/CdS/ZnS) covered with an optimal set of hydrophobic ligands can form homogeneous and stable QD-SAMs at the air−water interface. The QD-SAMs are subsequently transferred onto hydrophobized glass substrates by the Langmuir−Schaefer (LS) method and thermally treated in air. We found a blueshift of more than 35 nm for the emission wavelength (red to green) by a thermal treatment at 280 °C for 150 min with CdSe/ZnS QD-SAMs. The color can be adjusted by changing the heating temperature and the treatment time. The wavelength shift is in the order of CdSe/ZnS(4L) > CdSe/ZnS(6L) = (CdSe/CdZnS) > (CdSe/CdS/ZnS). The energy dispersive X-ray (EDX) microanalysis of a single QD reveals that the blueshift is mainly caused by atomic diffusion-induced alloying of core/ shell type QDs. The main problem of this method is the decreasing emission intensity caused by oxidation during the heat treatment; however, this problem can be solved with the use of a SiO 2 protective coating on the QD-SAMs. We believe that this simple technique is useful for manufacturing RGB-colored ultrathin QD-SAM films for QD displays such as QD film display, QD color-filter display, and QD light emitting diode.

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Wet‐Chemically Synthesized Colloidal Semiconductor Nanostructures as Optical Gain Media

Cited by 6 publications

References 65 publications

Quasi-Type II Carrier Distribution in CdSe/CdS Core/Shell Quantum Dots with Type I Band Alignment

Quasi-Type II Carrier Distribution in CdSe/CdS Core/Shell Quantum Dots with Type I Band Alignment

A robust low data solution: Dimension prediction of semiconductor nanorods

Tuning the Emission Colors of Self-Assembled Quantum Dot Monolayers via One-Step Heat Treatment for Display Applications

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