Low Threshold Room Temperature Polariton Lasing from Fluorene‐Based Oligomers

Mengjie Wei,Ebinazar B Namdas,Ifor D W Samuel,Atul Shukla,Ilene Allison,Graham A Turnbull,Shih‐Chun Lo,Van T N Mai,Arvydas Ruseckas

doi:10.1002/lpor.202100028

Mengjie Wei, Ebinazar B Namdas + Show 7 more

Open Access

https://doi.org/10.1002/lpor.202100028

Copy DOI

Abstract

AbstractOrganic semiconductors possessing tightly bound Frenkel excitons are known to be attractive candidates for demonstrating polariton lasing at room temperature. As polariton lasing can occur without inversion, it is a potential route to very low threshold coherent light sources. However, so far, the thresholds of organic polariton lasers have generally been much higher than those of organic photon lasers. Here this problem has been addressed by investigating two new organic molecules with a structure combining fluorene and carbazole groups. The materials are readily deposited from solution and exhibit high photoluminescence quantum yields, high absorption coefficients, and large radiative decay rates in neat films. Room temperature polariton lasing is realized in both materials with incident thresholds of 13.5 and 9.7 µJ cm−2, corresponding to absorbed thresholds of 3.3 and 2.2 µJ cm−2, respectively. These are the lowest values reported to date for polariton lasing in organic semiconductor materials, and approach typical values for organic photon lasers. The step‐like power dependent blue‐shift of polariton modes indicates an interplay between different depletion channels of the exciton reservoir. This work brings practical room temperature polaritonic devices and future realization of electrically driven polariton lasers a step closer.

Highlights

(LPB) and the upper polariton branch are known to be attractive candidates for demonstrating polariton lasing (UPB), inherit characteristics from both at room temperature
It is worthwhile noting that the photoluminescence quantum yields (PLQYs) of BSTFCz in neat films is close to the lower boundary of the values reported in ref.[27] and the emission peak of 0–0 is weaker, which may be attributed to different processing conditions used
Evidence for nonlinearity was presented in the angle-resolved PL spectra, including a nonlinear increase of PL intensity with increasing pump fluence, accompanied by a spectral linewidth narrowing of more than an order of magnitude and a step-like blue-shift at polariton lasing threshold, which is a signature of the interplay between the stimulated exciton relaxation and intermolecular energy transfer

Summary

Results and Discussion

We anticipate further reducing the polariton lasing thresholds by optimizing the chemical structure of these laser dyes to increase neat film PLQYs, fine tuning the LPB to have a better overlap with the emission peak for more efficient radiative pumping of the LP states, and by increasing photonic confinement in an improved cavity configuration, such as 0D cavities, for higher quality factor. Another signature of polariton lasing is the blue-shift of emission peaks with increasing pump fluence, which we observe in both BSFCz and BSTFCz cavities.

Conclusion

Experimental Section

Data Availability Statement