Near‐Infrared Excimer Microcavity Lasers Beyond 820 nm

Abstract Near‐infrared (NIR) organic conjugated dyes typically suffer from aggregation‐caused quenching effect, resulting in weak fluorescence in the aggregate state and thus posing a significant challenge in inverting the population between the ground and excited states for stimulated emission above 700 nm in lasers. Here, a unique excimer‐based four‐level system is demonstrated that overcomes the above challenge to achieve NIR organic lasers above 800 nm. Based on a simple emulsion‐solvent‐evaporation method, an anionic cyanine dye (C3‐Py) doped poly(methyl methacrylate) (PMMA) microspheres with multimode monomer and excimer laser emission in the range of 698–823 nm are prepared by tuning the doping content (1–20 wt.%). In particular, a NIR laser emission at ≈820 nm can be successfully achieved at a high doping concentration of 20 wt.%, although the corresponding fluorescence quantum yield is only 0.25%. Luminescence measurements and theoretical calculations reveal that the population inversion occurs between the excimer and the ground state dimers, which is independent of the photophysical properties of the monomer. Further by reducing the size of the microspheres, single‐mode lasers can be realized with emission wavelengths of 698–740 nm. It is believed that excimer will provide new insights into achieving wavelength‐tunable microscale lasers in integrated photonic devices.