  Composite quasi-particles with emergent functionalities in spintronic and
quantum information science can be realized in correlated materials due to
entangled charge, spin, orbital, and lattice degrees of freedom. Here we show
that by reducing the lateral dimension of correlated antiferromagnet NiPS3
flakes to tens of nanometers, we can switch-off the bulk spin-orbit entangled
exciton in the near-infrared (1.47 eV) and activate visible-range (1.8 to 2.2
eV) transitions with charge-transfer character. These ultra-sharp lines (<120
ueV at 4.2 K) share the spin-correlated nature of the bulk exciton by
displaying a Neel temperature dependent linear polarization. Furthermore,
exciton photoluminescence lineshape analysis reveals a polaronic character via
coupling with at-least 3 phonon modes and a comb-like Stark effect through
discretization of charges in each layer. These findings augment the knowledge
on the many-body nature of excitonic quasi-particles in correlated
antiferromagnets and also establish the nanoscale platform as promising for
maturing integrated magneto-optic devices.
