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Updated: May 24, 2025
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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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Abnormal Slow Phonon Dynamics Toward Prolonging Excited States Dynamics Enabled by Crystalline-Assembling
Yipeng Tang1, Heejae Kim2, Kwang-Sup Lee2
1Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, 37996, USA.
Advanced Materials (Deerfield Beach, Fla.)
|March 3, 2025
Summary
Researchers discovered that arranging donor-acceptor (D-A) molecules into a dipolar crystal significantly slows down phonon dynamics. This slow relaxation of lattice vibrations unusually prolongs the excited states and photoluminescence in light-emitting materials.
Area of Science:
- Materials Science
- Solid State Physics
- Photophysics
Background:
- Phonon dynamics critically influence optical properties of excited states in light-emitting materials.
- Controlling lattice vibrations is key to tuning material optoelectronic behavior.
Purpose of the Study:
- To investigate the effect of assembling donor-acceptor (D-A) molecules into a dipolar crystal on phonon dynamics.
- To explore the relationship between slow phonon relaxation and prolonged excited-state lifetimes.
Main Methods:
- Utilized photoexcitation-modulated Raman spectroscopy to monitor crystalline-lattice vibrations.
- Employed a 785 nm Raman-scattering laser and a 343 nm photoexcitation beam.
- Investigated photoluminescence (PL) decay dynamics at room temperature and 77 K.
Main Results:
- Observed unusually slow relaxation of photoexcited lattice vibrations on the scale of seconds in dipolar AC crystals.
- Demonstrated that photoluminescence (PL) exhibits prolonged decay, lasting 10 ms after photoexcitation.
- Confirmed that suppressing phonon dynamics by freezing D-A molecular liquid into a solid at 77 K significantly prolongs PL to 1 s.
Conclusions:
- Crystalline assembly of D-A molecules into a dipolar crystal enables extremely slow phonon dynamics.
- Slow phonon dynamics are hypothesized to be a key mechanism for unusually prolonging excited-state dynamics.
- This finding offers a pathway to engineer materials with extended excited-state lifetimes for advanced optical applications.
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