Emission and Reflectance Spectroscopy Study of Excitonic Behaviors in 2D CrCl₃

Two-dimensional chromium(III) chloride (CrCl₃) offers the opportunity for applications in various fields including optoelectronic devices and magnetic sensors because of its intrinsic magnetism down to monolayer limit and strong visible absorption of its bulk form. In this work, we studied the excitonic behaviors of few-layer to bulk CrCl₃. Absorption/photoluminescence (PL) spectroscopy and time-correlated single-photon counting (TCSPC) were used to elucidate its electronic structure and excitonic lifecycle, respectively. There was no significant spectral change with the number of layers in Raman, absorption, and PL signals. Surprisingly, however, the PL lifetime showed a drastic reduction from 1940 ns to 2 ns with decreasing thickness from 61 to 3 nm. Comparison with the samples sandwiched between hexagonal BN confirmed that the ambient stability of the sample affects the excitonic lifetime. The origins for the accelerated relaxation in 2D forms will be discussed based on the control experiments to address the effects of ambient instability and possible photoinduced reactions.