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Wannier-Mott Excitons in Nanoscale Molecular Ices

Chen, Y-J; Munoz Caro, GM; Aparicio, S; Jimenez-Escobar, A; Lasne, J; Rosu-Finsen, A; McCoustra, MRS; ... Field, D; + view all (2017) Wannier-Mott Excitons in Nanoscale Molecular Ices. Physical Review Letters , 119 (15) , Article 157703. 10.1103/PhysRevLett.119.157703. Green open access

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The absorption of light to create Wannier-Mott excitons is a fundamental feature dictating the optical and photovoltaic properties of low band gap, high permittivity semiconductors. Such excitons, with an electron-hole separation an order of magnitude greater than lattice dimensions, are largely limited to these semiconductors but here we find evidence of Wannier-Mott exciton formation in solid carbon monoxide (CO) with a band gap of >8 eV and a low electrical permittivity. This is established through the observation that a change of a few degrees K in deposition temperature can shift the electronic absorption spectra of solid CO by several hundred wave numbers, coupled with the recent discovery that deposition of CO leads to the spontaneous formation of electric fields within the film. These so-called spontelectric fields, here approaching 4 × 107 V m−1, are strongly temperature dependent. We find that a simple electrostatic model reproduces the observed temperature dependent spectral shifts based on the Stark effect on a hole and electron residing several nm apart, identifying the presence of Wannier-Mott excitons. The spontelectric effect in CO simultaneously explains the long-standing enigma of the sensitivity of vacuum ultraviolet spectra to the deposition temperature.

Type: Article
Title: Wannier-Mott Excitons in Nanoscale Molecular Ices
Open access status: An open access version is available from UCL Discovery
DOI: 10.1103/PhysRevLett.119.157703
Publisher version: http://doi.org/10.1103/PhysRevLett.119.157703
Language: English
Additional information: © 2017 American Physical Society. This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Science & Technology, Physical Sciences, Physics, Multidisciplinary, Physics, SOLID CO, STATES, PEROVSKITE, CRYSTAL, SINGLET
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10040492
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