Solid‐State Red Laser with a Single Longitudinal Mode from Carbon Dots

Abstract Miniaturized solid‐state lasers with a single longitudinal mode are vital for various photonic applications. Here we prepare red‐emissive carbon dots (CDs) with a photoluminescence quantum yield (PLQY) of 65.5 % by combining graphitic nitrogen doping and surface modification. High‐concentration doping alters the CDs’ emission from blue to red, while the electron‐donating groups and polymer coating on their surfaces improve the PLQY and photostability. The CDs exhibit excellent stimulated emission characteristics, with a low threshold of amplified spontaneous emission (ASE) and long gain lifetime. A planar microcavity with only one resonant mode, which fitted with the CDs’ ASE peak, was constructed. Combining the CDs and microcavity produced a solid‐state laser with a single longitudinal mode, a linewidth of 0.14 nm and a signal‐to‐noise ratio of 14.8 dB (Q∼4600). Our results will aid the development of colorful solid‐state micro/nano lasers with potential use in practical photonics.