Carbon Nanodots as Active Media for Tunable Laser and Random Laser Applications

After making their appearance at the beginning of the century as a newborn in the wide family of carbon-based nanomaterials, carbon dots (CDs) are now well-established as zero-dimensional C-based nanoparticles capable of bright and tunable visible fluorescence. Because of their fascinating optical properties, very uncommon in other C-based nanomaterials such as CNTs and graphene, CDs are very appealing for light emitting devices and several other applications in photonics and photochemistry. Broadly speaking, CDs can be seen as a carbon-based equivalent of inorganic quantum dots, endowed with specific advantages due to their water solubility, ease of functionalization, low cost, low toxicity, and lack of rare or critical chemical elements. However, the optical response of CDs still needs to be optimized to fulfill the requirements of many real-world applications. In particular, only a few types of CDs are capable of optical gain, still limiting their use as active media in lasers.<br/><br/>In a series of recent works [1-3], our group has demonstrated the use of CDs as versatile active media for laser and random laser action. We used different synthesis routes to obtain various types of CDs capable of bright fluorescence and optical gain in the green and red region of the visible spectrum. Aqueous solutions of these CDs are shown to behave as active media inside Fabry-Pérot-like optical resonators, yielding an efficient narrowband and directional emission very similar to that of a dye laser [1,2]. In addition, we recently demonstrated [2-3] that the same CDs can also be used as active media in random lasers (RLs). RLs are a class of devices which are attracting a growing interest in photonics as laser-like sources featuring specific benefits over traditional lasers for some applications, such as speckle-free imaging and omnidirectional emission [3]. Our CD-based RLs characteristically display ultra-narrow (~ 0.70 nm) emission lines over a comparatively broader (~10 nm) background. The relative weight of these two types of emissions can be controlled by an appropriate choice of experimental conditions, allowing to tune the characteristics of RL light.<br/><br/>The results demonstrate the potential of CDs as a viable alternative to environmental unfriendly, scarce, or chemically unstable nanomaterials as laser gain media with customizable emissions.<br/><br/>1. A. Sciortino et al. <b>Chem. Mater.</b> 30, 1695 (2018)<br/>2. A. Madonia et al. <b>ACS Nano</b> 17, 21274 (2023)<br/>3. A Pramanik et al. <b>ACS Photonics, </b>in press (2024)