In recent years, nanowire lasers have emerged as a crucial approach for constructing miniaturized photonic integrated systems due to their advantages, including small footprint, easy integration, low threshold, and low energy consumption. Notably, the incorporation of quantum dots into nanowires, enables flexible adjustment of gain characteristics, resulting in nanowire laser exhibiting superior device performance, such as low threshold and high-temperature stability. Compared with inorganic semiconductor quantum dots, carbon quantum dots (CQDs) offer distinct advantages in terms of low toxicity, low cost, high fluorescence quantum yield, and versatility. Due to their intriguing photophysical properties, low dark toxicity, tunable surface functionality, and adaptable synthesis, CQDs have been harnessed as a gain medium in lasers and successful achievement of multi-wavelength lasers has been demonstrated through surface modification of CQDs.

Our group proposes an approach to achieve tunable narrowband lasing beam output in a specific direction using a self-assembled microstructure. The self-assembled microstructure comprises Au nanoparticles (Au NPs), Ag nanowires (Ag NWs), and a hollow-core metal-cladding resonator (HMCR). Through a chemical reaction, the Au NPs are grown on the surface of Ag NWs, facilitating the localization and confinement of surface plasmon waves (SPW) within a small volume between the nanogap of Au NPs and the Ag NWs surface. This leads to an enhanced density of the electric field power in the gap. Simultaneously, the HMCR allows for effective light confinement in the waveguide with minimal leakage, owing to the free coupling technology. As a result, the interaction between light and matter can be fully realized in the waveguide layer, while the effective refractive index (Neff) of the HMCR is maintained between 0 and 1. The mixture solution of CQDs and Au–Ag nanowires was injected into HMCR. By adjusting the concentration of CQDs, we achieved a wide wavelength tunability in the range of 583–594 nm, with the center wavelength exhibiting a blueshift as the concentration increased. This tunable narrowband CQDs laser, based on self-assembled microstructure, paves the way for the development of miniaturized multi-wavelength laser source and holds potential for integrated multi-wavelength laser sources in the future.

Figure 1. a) The schematic illustration of CQDs and Au-Ag nanowires mixed solutions. Schematic diagrams of the experimental setups: b) Cuvette laser device and d) Hollow-core metal-cladding resonator (HMCR) laser device. c) Lasing emission spectrum from the cuvette e) Lasing emission spectrum from the HMCR.

Figure 2. a) Schematic representation of the optical setup. b) Emission spectra of the CQDs and Au-Ag nanowires composites in the HMCR with increasing pump energy.

Figure 3. a) Schematic diagram of CQDs and Au–Ag nanowires mixture suspension preparation with different CQDs concentrations. b) The lasing emission spectra and photographs of the mixture suspension of CQDs and Au–Ag nanowires composites in the HMCR with different concentrations.

Figure 4. a) TEM picture of Ag nanowire. b) TEM picture of Au–Ag nanowires composites. c–h) The electric field intensity distribution by the incoming field near the pure Ag nanowires and Au–Ag nanowires composites at the excitation wavelength of 532 nm. i–l) TEM picture and energy dispersive X-ray spectroscopy images of the Au–Ag nanowires composites.

This research is published in "Meng Zhang, Hailang Dai, and Xianfeng Chen, Tunable Narrowband Carbon Quantum Dots Laser Based on Self-Assembled Microstructure, Advanced Optical Materials, 2301156 (2023)".

Link: https://onlinelibrary.wiley.com/doi/10.1002/adom.202301156