Abstract
We report on electron spin resonance (ESR) spectroscopy of boron-vacancy (V−B) centers hosted in isotopically engineered hexagonal boron nitride (hBN) crystals. We first show that isotopic purification of hBN with 15N yields a simplified and well-resolved hyperfine structure of V−B centers, while purification with 10B leads to narrower ESR linewidths. These results establish isotopically purified h10B15N crystals as the optimal host material for future use of V−B spin defects in quantum technologies. Capitalizing on these findings, we then demonstrate optically induced polarization of 15N nuclei in h10B15N, whose mechanism relies on electron-nuclear spin mixing in the V−B ground state. This work opens up new prospects for future developments of spin-based quantum sensors and simulators on a two-dimensional material platform.