Year: 2021
Type: article
Abstract: Semiconductor nanoplatelets (NPLs), with their large exciton binding energy, narrow photoluminescence (PL), and absence of dielectric screening for photons emitted normal to the NPL surface, could be expected to become the fastest luminophores amongst all colloidal nanostructures. However, super‐fast emission is suppressed by a dark (optically passive) exciton ground state, substantially split from a higher‐lying bright (optically active) state. Here, the exciton fine structure in 2–8 monolayer (ML) thick Csn − 1PbnBr3n + 1 NPLs is revealed by merging temperature‐resolved PL spectra and time‐resolved PL decay with an effective mass model taking quantum confinement and dielectric confinement anisotropy into account. This approach exposes a thickness‐dependent bright–dark exciton splitting reaching 32.3 meV for the 2 ML NPLs. The model also reveals a 5–16 meV splitting of the bright exciton states with transition dipoles polarized parallel and perpendicular to the NPL surfaces, the order of which is reversed for the thinnest NPLs, as confirmed by TR‐PL measurements. Accordingly, the individual bright states must be taken into account, while the dark exciton state strongly affects the optical properties of the thinnest NPLs even at room temperature. Significantly, the derived model can be generalized for any isotropically or anisotropically confined nanostructure.
Source: Advanced Science
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $5,000
Funders: U.S. Department of Energy, American Society for Engineering Education, Solar Technologies go Hybrid, Center for Hybrid Organic Inorganic Semiconductors for Energy, Deutsche Forschungsgemeinschaft, Office of Science, Office of Naval Research, Basic Energy Sciences, H2020 European Research Council
OpenAlex ID: W3203206681