  Antiferromagnets display enormous potential in spintronics owing to its
intrinsic nature, including terahertz resonance, multilevel states, and absence
of stray fields. Combining with the layered nature, van der Waals (vdW)
antiferromagnets hold the promise in providing new insights and new designs in
two-dimensional (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. 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 luminescence is perpendicular to the
ordered spin orientation in NiPS3. By applying an in-plane magnetic field to
alter the spin orientation, we further manipulate the excitonic emission
polarization. Such strong correlation between exciton and spins provides new
insights for the study of magneto-optics in 2D materials, and hence opens a
path for developing opto-spintronic devices and antiferromagnet-based quantum
information technologies.
