MXene Quantum Dot Synthesis, Optical Properties, and Ultra‐narrow Photonics: A Comparison of Various Sizes and Concentrations

Abstract Transition metal carbides and nitrides (MXene) quantum dots (QDs) are potentially important for versatile applications, including ultra‐narrow photonics. Here, a simple method for controlling the sizes and solution concentrations of Ti 2 C‐MXene‐QDs are shown, and then their optical properties are systematically investigated and compared. The nonlinear optical characteristics of QDs can be adjusted through the QD size and solution concentration. QDs with smaller sizes of 1–3 nm have stronger absorptivity, larger modulation depth and lower nonsaturable loss, and QDs with higher concentrations have stronger absorptivity and larger modulation depth but higher nonsaturable loss. These QDs are further applied to construct loop‐cavity ultranarrow lasers whose narrowest laser linewidth is 624.5 Hz, highest signal‐to‐noise ratio (SNR) is 77.63 dB and lowest power fluctuation is 0.4%. A comparison of these indicators indicates that smaller and more homogeneous MXene QD solutions with proper concentrations favor ultra‐narrow photonics. The laser power is also amplified to ≈60 mW by an erbium‐doped fiber amplifier (EDFA).