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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
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Wannier-Mott Excitons in Nanoscale Molecular Ices
Y-J Chen1, G M Muñoz Caro2, S Aparicio3
1Department of Physics, National Central University, Jhongli District, Taoyuan City 32054, Taiwan.
Physical Review Letters
|October 28, 2017
Summary
Researchers discovered Wannier-Mott excitons in solid carbon monoxide (CO), challenging previous understanding. This finding explains the sensitivity of CO
Area of Science:
- Solid-state physics
- Materials science
- Optical properties of materials
Background:
- Wannier-Mott excitons are crucial for optical and photovoltaic properties in low band gap, high permittivity semiconductors.
- These excitons, characterized by large electron-hole separation, were previously thought to be confined to such materials.
Purpose of the Study:
- To investigate the formation of Wannier-Mott excitons in solid carbon monoxide (CO).
- To explain the observed temperature-dependent spectral shifts in solid CO's electronic absorption spectra.
- To elucidate the role of spontelectric fields in solid CO's optical properties.
Main Methods:
- Analysis of electronic absorption spectra of solid CO at varying deposition temperatures.
- Measurement and modeling of spontaneous electric fields (sponelectric fields) within CO films.
- Application of an electrostatic model incorporating the Stark effect.
Main Results:
- Evidence for Wannier-Mott exciton formation in solid CO, a material with a wide band gap (>8 eV) and low permittivity.
- Observed spectral shifts of several hundred wave numbers due to minor temperature changes (few degrees K).
- Sponelectric fields, reaching ~4x10^7 V/m, were found to be temperature-dependent and correlate with spectral shifts.
Conclusions:
- Wannier-Mott excitons can form in materials beyond traditional low band gap semiconductors, specifically in solid CO.
- The Stark effect, influenced by temperature-dependent spontelectric fields, explains the observed spectral shifts.
- This work resolves the long-standing mystery of vacuum ultraviolet spectral sensitivity to deposition temperature in solid CO.
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