Graphitic carbon nitrides (g-C₃N₄) as low-cost, chemically stable, and ecofriendly layered semiconductors have attracted rapidly growing interest in optoelectronics and photocatalysis. However, the nature of photoexcited carriers in g-C₃N₄ is still controversial, and an independent charge-carrier picture based on the band theory is commonly adopted. Here, by performing transient spectroscopy studies, we show characteristics of self-trapped excitons (STEs) in g-C₃N₄ nanosheets including broad trapped exciton-induced absorption, picosecond exciton trapping without saturation at high photoexcitation density, and transient STE-induced stimulated emissions. These features, together with the ultrafast exciton trapping polarization memory, strongly suggest that STEs intrinsically define the nature of the photoexcited states in g-C₃N₄. These observations provide new insights into the fundamental photophysics of carbon nitrides, which may enlighten novel designs to boost energy conversion efficiency.

中文翻译：

---

石墨碳氮化物中本征自俘获激子

石墨氮化碳（g -C ₃ N ₄）作为低成本、化学稳定且环保的层状半导体，引起了人们对光电子学和光催化领域快速增长的兴趣。然而， g -C ₃ N ₄中光生载流子的性质仍存在争议，通常采用基于能带理论的独立载流子图。在这里，通过进行瞬态光谱研究，我们展示了g -C ₃ N ₄纳米片中自俘获激子（STE）的特征，包括宽俘获激子诱导吸收、高光激发密度下不饱和的皮秒激子俘获以及瞬态 STE 诱导刺激排放。这些特征与超快激子俘获偏振存储器一起强烈表明STE本质上定义了g -C ₃ N ₄中光激发态的性质。这些观察结果为氮化碳的基本光物理学提供了新的见解，这可能会启发新颖的设计来提高能量转换效率。