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Spin-Triplet-Mediated Up-Conversion and Crossover Behavior in Single-Molecule Electroluminescence
Gong Chen1,2, Yang Luo1, Hongying Gao1
1International Center for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China.
Physical Review Letters
|May 21, 2019
Summary
We observed up-conversion electroluminescence from a single phthalocyanine molecule, ruling out intermolecular mechanisms. This breakthrough reveals new insights into molecular light emission and its underlying physics.
Area of Science:
- Molecular spectroscopy
- Scanning probe microscopy
- Optoelectronics
Background:
- Scanning tunneling microscope-induced light emission (STM-IL) is crucial for studying molecular optical properties.
- Molecular up-conversion electroluminescence mechanisms are debated, with triplet-triplet annihilation and plasmonic pumping as leading theories.
Purpose of the Study:
- To experimentally realize and investigate up-conversion electroluminescence in a single phthalocyanine molecule.
- To unambiguously identify the microscopic mechanisms governing this phenomenon.
- To explore novel characteristics of molecular light emission.
Main Methods:
- Single-molecule scanning tunneling microscopy-induced light emission spectroscopy.
- Bias-dependent current-intensity measurements.
- Development of a microscopic theoretical model.
Main Results:
- Demonstrated up-conversion electroluminescence from a single phthalocyanine molecule.
- Ruled out intermolecular coupling mechanisms for up-conversion.
- Identified three distinct regions in bias-dependent emission intensity with unique nonlinear current dependences.
- Attributed observed behavior to the interplay of inelastic electron scattering and carrier injection.
Conclusions:
- The study provides definitive evidence against intermolecular mechanisms in single-molecule up-conversion electroluminescence.
- A microscopic model elucidates the role of intermediate spin-triplet states in the observed phenomenon.
- This work opens new avenues for understanding and manipulating molecular light emission at the single-molecule level.
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