Antiferromagnets display enormous potential in spintronics owing to its intrinsic nature, including terahertz resonance 1,2 , multilevel states 3,4 , and absence of stray fields 5,6 . Combining with the layered nature, van der Waals (vdW) antiferromagnets hold the promise in providing new insights and new designs in twodimensional (2D) spintronics. The zero net magnetic moments of vdW antiferromagnets strengthens the spin stability, however, impedes the correlation between spin and other excitation elements, like excitons 7,8 . Such coupling is urgently anticipated for fundamental magneto-optical studies and potential opto-spintronic devices. Here, we report an ultra-sharp excitonic emission with excellent monochromaticity in antiferromagnetic nickel phosphorus trisulfides (NiPS3) from bulk to atomically thin flakes. We prove that the linear polarization of the excitonic

Germanium Selenide (GeSe) is a van der Waals-bonded layered material with promising optoelectronic properties, which has been experimentally synthesized for 2D semiconductor applications. In the monolayer, due to reduced dimensionality and, thus, screening environment, perturbations such as the presence of defects have a significant impact on its properties. We apply density functional theory and many-body perturbation theory to understand the electronic and optical properties of GeSe containing a single selenium vacancy in the −2 charge state. We predict that the vacancy results in mid-gap "trap states" that strongly localize the electron and hole density and lead to sharp, low-energy optical absorption peaks below the predicted pristine optical gap. Analysis of the exciton wavefunction reveals that the 2D Wannier-Mott exciton of the pristine monolayer is highly localized around the defect, reducing its Bohr radius by a factor of four and producing a dipole moment along the out-of-plane axis due to the defect-induced symmetry breaking. Overall, these results suggest that the vacancy is a strong perturbation to the system, demonstrating the importance of considering defects in the context of material design.

Electronic Raman scattering activates the investigation of d-d excitations and electron-spin coupling in 2D antiferromagnets.

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