LAUSR

In the past few decades, there has been a long-standing pursuit to exploring emergent materials with robust optical gain and superior light-matter interacting properties for the development of photonic and optoelectronic devices including but not limited to micro-lasers, single photon emitters, light-emitting-diodes, photo-detectors and so on. Pioneering efforts have been devoted to advanced optical gain materials, covering from classical IIVI/III-V semiconductors, emergent two-dimensional semiconducting materials, organic dyes to halide perovskites, which hold great promise for optimizing the device performance and expanding the frontier photonics/optoelectronics. Meanwhile, the scientific and engineering challenges, forging these materials into powerful tools for fundamental sciences and industrial technologies, still remain. The rapid evolution of this area necessitates a highlight of the recent advances and challenges, which is the aim of this timely themed issue on “Optical Gain Materials towards Enhanced Light-Matter Interactions” organized by Science China Materials. This highlight was partly motivated by a symposium organized during the 10th International Conferences on Materials for Advanced Technologies (ICMAT 2019) held in Singapore, co-chaired by all the guest editors. The wide applicability of optical gain materials highly depends on the intrinsic crystalline and optical quality, and cannot be separated from advanced fabrication techniques. The review by Liu et al. [1] concentrates on the recent studies of various growth methods in halide perovskite semiconductors. Especially, Chen et al. [2] propose the continuous-flow fabrication of doped perovskite nanocrystals in a microfluidic reactor, which enables efficient physical mixing of the precursor ions in the confined micro-channels with stable and closed environment towards high-quality synthesis. Controlled growth of plasmonic heterostructures with a specific composition, morphology, size, and structural symmetry, as well as their optical-related applications are covered by Wang et al. [3]. The progress report by Xiao et al. [4] provides a comprehensive summary of colloidal crystals spheres self-assembly into periodic patterns for optical applications. For typical third-generation semiconductors, Liu et al. [5] overview the development on the design and growth of GaN-based laser diodes. With advanced optical gain materials and well-designed structures, novel optical and photonic properties resulting from enhanced light-matter interactions can be expected. From a basic scientific perspective, Chen et al. [6] highlight the booming GaAs-based nanowires, especially in the aspect of optical properties and lasing, towards potential infrared laser in integrated optoelectronics. In specific researches, the article by Wang et al. [7] realizes the plasmon-enhanced second-harmonic generation up to 617.7-fold in asymmetric Ag@CdSe hetero-nanorods, enabling high-resolution detection in the biological sensing. An ultrafast formation (<100 fs) of dihydrogen defects in YHxOy, which is responsible for the transparentto-opaque photochromic transition with the state stability strongly dependent on the concentration of oxygen, is presented by Cao et al. [8] by using excited-state density functional theory simulation. In the contribution by Pan et al. [9], the strong optical anisotropy of deep-ultraviolet fluorooxoborates with designed possible anionic groups is systematically analyzed to check the influence on birefringence towards developing novel nonlinear optical crystals. Another strategy to enrich the understanding of ideal nonlinear optical crystals, theoretical modeling and simulation, is reported by Lin et al. [10], covering seven potential structures in the deep-ultraviolet region predicted for the first time. For two-dimensional GeS na-