Engineering Relaxation-Paths of C-Exciton for Constructing Band Nesting Bypass in WS<sub>2</sub> Monolayer.
basic_science · Level V
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- Record sourced from PubMed, PMID 35481760.
- Also identified by DOI 10.1021/acs.nanolett.2c00509.
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Abstract
Transition-metal dichalcogenides exhibit strong photon absorption characteristics in the band nesting region (denoted as C-exciton) due to intrinsic van Hove singularities despite being atomically thin. However, because of unique parallel band structure and ineluctably unfavorable recombination process, only a small fraction of the hot carriers from C-excitons are converted into optically active band-edge excitons via inherent relaxation-paths. The resultant photoluminescence quantum yield (PLQY) is severely suppressed for the resonant excitation of C-exciton. To overcome this limitation, we have designed double type-I band alignments to construct a band nesting bypass in a monolayer WS<sub>2</sub>/CdS quantum dot heterostructure for cooling the C-excitons. Transient optical measurements confirmed that the hot carriers from the C-excitons were effectively transferred from WS<sub>2</sub> to CdS with an efficiency of 50% and subsequently back to the WS<sub>2</sub> band-edge to form A-excitons over an ultrafast subpicosecond time scale, accompanied by a record high PLQY of ∼11.1% for near-resonance C-exciton excitation.