An ultrasharp photoluminescence line intimately related to antiferromagnetic order has been found in ${\mathrm{NiPS}}_3$, a correlated van der Waals material, opening prospects for magneto-optical coupling schemes and spintronic applications. Here we unambiguously clarify the singlet origin of this excitation, confirming its roots in the spin structure. Based on a comprehensive investigation of the electronic structure using angle-resolved photoemission and $q$-dependent electron energy loss spectroscopy as experimental tools we develop, in a first step, an adequate theoretical understanding using density functional theory (DFT). In a second step the DFT is used as input for a dedicated multiplet theory by which we achieve excellent agreement with available multiplet spectroscopy. Our Letter connects the understanding of the electronic structure and of optical processes in ${\mathrm{NiPS}}_3$ and related materials as a prerequisite for further progress of the field.

• Received 16 May 2023
• Revised 29 September 2023
• Accepted 3 October 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.256504