Abstract
Exciton–polariton Bose–Einstein condensation (EP BEC) is of crucial importance for the development of coherent light sources and optical logic elements, as it creates a new state of matter with coherent nature and nonlinear behaviors. The demand for room temperature EP BEC has driven the development of organic polaritons because of the large binding energies of Frenkel excitons in organic materials. However, the reliance on external high-finesse microcavities for organic EP BEC results in poor compactness and integrability of devices, which restricts their practical applications in on-chip integration. Here, we demonstrate room temperature EP BEC in organic single-crystal microribbon natural cavities. The regularly shaped microribbons serve as waveguide Fabry–Pérot microcavities, in which efficient strong coupling between Frenkel excitons and photons leads to the generation of EPs at room temperature. The large exciton–photon coupling strength due to high exciton densities facilitates the achievement of EP BEC. Taking advantages of interactions in EP condensates and dimension confinement effects, we demonstrate the realization of controllable output of coherent light from the microribbons. We hope that the results will provide a useful enlightenment for using organic single crystals to construct miniaturized polaritonic devices.
Highlights
Exciton–polariton Bose–Einstein condensation (EP BEC) is of crucial importance for the development of coherent light sources and optical logic elements, as it creates a new state of matter with coherent nature and nonlinear behaviors
Exciton–polaritons (EPs) arising from strong coupling between excitons and photons can form a macroscopic condensate via bosonic final-state stimulation into the ground state—a process known as Bose–Einstein condensation (BEC) of EPs1,2
N, N′-Bis(2,6-diisopropyl phenol)−3,4,9,10-perylenetetracarboxylic Diimide (PDI-O, Supplementary Fig. 1) was selected to act as the model compound to achieve room temperature polariton condensation for the following two reasons: (1) PDI-O could provide Frenkel excitons with large transition dipole moment and high binding energy owing to the planar, rigid, and extensively πconjugated backbone[33], which is favorable for room temperature strong exciton–photon coupling (Supplementary Figs. 2 and 3); (2) the 2,6-diisopropylphenyl substituents in the imide position of PDI-O (Fig. 1a) can increase face-to-face intermolecular distance and prevent π–π interactions between adjacent molecules[34], which would otherwise cause non-radiative decay that hinders polariton condensation in crystalline structure[35]
Summary
Strong coupling in the organic single-crystal microribbons. N, N′-Bis(2,6-diisopropyl phenol)−3,4,9,10-perylenetetracarboxylic Diimide (PDI-O, Supplementary Fig. 1) was selected to act as the model compound to achieve room temperature polariton condensation for the following two reasons: (1) PDI-O could provide Frenkel excitons with large transition dipole moment and high binding energy owing to the planar, rigid, and extensively πconjugated backbone[33], which is favorable for room temperature strong exciton–photon coupling (Supplementary Figs. 2 and 3); (2) the 2,6-diisopropylphenyl substituents in the imide position of PDI-O (Fig. 1a) can increase face-to-face intermolecular distance and prevent π–π interactions between adjacent molecules[34], which would otherwise cause non-radiative decay that hinders polariton condensation in crystalline structure[35]. The X-ray diffraction (XRD, Supplementary Fig. 7) pattern indicates that the highly crystalline microribbons have a monoclinic crystal structure belonging to P121/n1 space group In this crystal structure, the J-aggregation of PDI-O molecules (Supplementary Fig. 8) would reduce nonradiative decay caused by π–π interactions, which helps to provide high-density Frenkel excitons to strongly couple with microcavity photons[36]. The scattering mechanism is verified by time-resolved PL measurement results, which show that the emission lifetime decreases from 277 to 47 ps when pump fluence is increased above the threshold Such lifetime is much shorter than that of PDI molecules undergoing stimulated emission[44], indicating a transition from exciton reservoir dynamics to an ultrafast decay process corresponding to the stimulated scattering from the exciton reservoir to the condensate.
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