Doping-Induced Tuning of Ultrasharp Exciton Emission in NiPS3: Unveiling Sensitivity to Spin-Structure Interplay.*

Metal phosphorus trichalcogenides (MPX₃, M = Mn, Fe, Ni; X = S, Se) have gained prominence in spintronics and quantum technologies. In particular, NiPS₃ emitting a sharp photoluminescence (PL) peak at 1.476 eV, which is attributed to the spin-orbit entangled exciton (SO-X) state, has generated a lot of excitement recently. We examined Ni_1-xMn_xPS₃ and NiPS_3-ySe_y compounds to understand how changes in magnetic order affect this SO-X emission. Increasing Mn impurity concentration from 0 to 22% leads to a reduction in the intensity of SO-X and broadening of the linewidth from 0.4 to 4.2 meV. Whereas Se doping introduced a new PL peak at 1.472 eV, and also broadened the linewidth of SO-X emission. Notably, the sharp peak disappeared beyond x or y of 0.2. Furthermore, we analyzed the polarization-resolved PL of Ni_1-xMn_xPS₃ alloys. At 5 K, increase of Mn concentration leads to decrease in degree linear polarization. In parallel, Raman spectroscopy of Ni_1-xMn_xPS₃ revealed the two magnon scattering peak, a key indicator of correlated antiferromagnetism in NiPS₃, exhibited a shift towards lower energies and suppression when x is increased from 0 to 0.2. This correlates with our findings in the PL spectrum further underscores the pivotal role of Mn impurities in disrupting the AFM order of NiPS₃ system. This study unveils the interplay between impurity induced disruption in spin structures and PL and Raman characteristics in NiPS₃, shedding light on their potential for future application.