Intersystem crossing and exciton-defect coupling of spin defects in hexagonal boron nitride

Despite the recognition of two-dimensional (2D) systems as emerging and scalable host materials of single-photon emitters or spin qubits, the uncontrolled and undetermined chemical nature of these quantum defects has hindered further development. Leveraging the design of extrinsic defects can circumvent these issues. Here, we establish a complete first-principles theoretical framework to accurately and systematically design quantum defects in wide-bandgap 2D systems, considering essential static and dynamical properties for spin qubit discovery. Many-body interactions, such as defect–exciton couplings, are vital for excited-state properties in ultrathin 2D systems. Nonradiative processes, including phonon-assisted decay and intersystem crossing (ISC), are evaluated alongside radiative processes. Through first-principles screening, we identify promising single-photon emitters (SiV) and spin qubits (TiVV and MoVV) in hexagonal boron nitride (h-BN). This work provides a comprehensive framework for defect design in 2D materials.