Layer-Tunable Nonlinear Optical Characteristics and Photocarrier Dynamics of 2D PdSe in Broadband Spectra.

Layered 2D transition metal dichalcogenides (TMDCs) exhibited fascinating nonlinear optical (NLO) properties for constructing varied promising optoelectronics. However, exploring the desired 2D materials with both superior nonlinear absorption and ultrafast response in broadband spectra remain the key challenges to harvest their greatest potential. Here, based on synthesizing 2D PdSe films with the controlled layer number, the authors systematically demonstrated the broadband giant NLO performance and ultrafast excited carrier dynamics of this emerging material under femtosecond visible-to-near-infrared laser-pulse excitation (400-1550 nm). Layer-dependent and wavelength-dependent evolution of optical bandgap, nonlinear absorption, and photocarrier dynamics in the obtained 2D PdSe are clearly revealed. Specially, the transition from semiconducting to semimetallic PdSe induced dramatic changes of their interband absorption-relaxation process. This work makes 2D PdSe more competitive for future ultrafast photonics and also opens up a new avenue for the optical performance optimization of various 2D materials by rational design of these materials.