Two-dimensional light-emitting materials: preparation, properties and applications

The past decade has witnessed tremendous research efforts devoted to two-dimensional (2D) materials and great progress made in both their fundamental studies and technique development. 2D light-emitting materials such as transition-metal dichalcogenides (TMDs) and phosphorene are receiving particular attention as a result of their intriguing electronic, optical and optoelectronic properties. The ability to tune their layer numbers, engineer their dielectric environment, form alloys, create van der Waals heterostructures, etc. provides further means to modulate their properties which have led to a number of interesting luminescence features and potential applications in lighting, imaging and sensing. As the map of 2D materials has expanded over the past few years, 2D organic and organic-inorganic hybrid materials, such as 2D polymers, metal-organic frameworks (MOFs), and organic-inorganic hybrid perovskites, have also emerged with merits of low cost, chemical versatility and solution processibility. Importantly, the wide tunability of their functional properties is enabled by the rational design and controlled modification of their compositions and structures at the molecular level. Herein, we present a critical review of 2D light-emitting materials by categorizing them into three main groups, namely 2D inorganic light-emitting materials, 2D organic light-emitting materials, and 2D organic-inorganic hybrid light-emitting materials. Within each group, we will describe their preparation methods and discuss their structural and chemical properties. Significant emphasis will be placed on strategies that can tune their luminescence properties, and their potential applications in various fields. Finally, we will summarize by stating the current challenges and future opportunities in the development of 2D light-emitting materials.