Abstract
Polariton lasing is coherent emission that originates from macroscopic accumulation of polariton population in the ground state and is a promising route toward efficient coherent light sources as population inversion is not necessary. Unlike most Wannier–Mott excitons in inorganic semiconductors, Frenkel excitons created in organic semiconductors have high oscillator strength and high exciton binding energy, which sustain stable exciton–polaritons at room temperature. Herein, room temperature polariton lasing from a novel class of ladder‐type oligo(p‐phenylene)s is demonstrated. The polariton lasers exhibit a nonlinear increase of their spectrally integrated emission, a reduction in spectral linewidth, blueshift of emission peaks, and long‐range spatial coherence when the pump fluence is increased above threshold. By tuning the π‐conjugation length of the molecular structure, the polariton lasing wavelength can be changed from 430 to 457 nm. Optically pumped thresholds of 12 and 17 μJ cm−2 are observed, which are among the lowest values reported for polariton lasing in organic semiconductors.
Highlights
Exciton–polaritons are quasi-particles that arise from strong coupling between excitons and cavity photons.[1]
The lowest energy excitonic transition is at 421 nm with an full width at half maximum (FWHM) of 18 nm, and its vibronic replica is at 399 nm with a linewidth of 26 nm, whereas the emission is symmetrical with the absorption spectrum, with peaks are at 438 and 463 nm
The absorbed thresholds for 2L-F and 4L-F cavities are 12 and 17 μJ cmÀ2, respectively, which are comparable to the lowest absorbed threshold that has been reported for organic semiconductors in a planar cavity structure.[20]
Summary
Exciton–polaritons are quasi-particles that arise from strong coupling between excitons and cavity photons.[1] Under appropriate energy (of several hundreds of meV) and high oscillator strength. These attractive properties enable demonstration of strong coupling at room temperature.[16] In addition, their simple fabrication and broadband tunability can help realize large area and multi-purpose polariton devices. The fused phenylene rings give extensive π-conjugation along the rigid backbone, whereas solubilizing side groups enable simple processing from solution. These structural properties result in narrow and well-defined exciton transi-. We find that the thresholds of these cavities are relatively low and comparable with the lowest threshold that has been reported for organic semiconductors.[20]
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