Optical spin initialization of nitrogen vacancy centers in a $^{28}$Si-enriched 6H-SiC crystal for quantum technologies

High-spin defect centers in crystal matrices are used in quantum computing technologies, highly sensitive sensors, and single-photon sources. In this work, optically active nitrogen-vacancy color centers NV$^-$ in a $^{28}$Si-enriched (nuclear spin $I = 0$) 6H-$^{28}$SiC crystal have been studied using the photoinduced ($\lambda = 980$ nm) high-frequency ($94$ GHz, $3.4$ T) pulsed electron paramagnetic resonance method at a temperature of $T = 150$ K. Three structurally nonequivalent types of NV$^-$ centers with axial symmetry have been identified and their spectroscopic parameters have been determined. Long spin–lattice, ${T}_{1} = 1.3$ ms, and spin–spin, ${{T}_{2}} = 59$ $\mu$s, ensemble relaxation times of NV$^-$ centers with extremely narrow ($450$ kHz) absorption lines allow highly selective excitation of resonant transitions between sublevels $m_I$ caused by the weak hyperfine interaction ($A \approx 1$ MHz) with $^{14}$N ($I = 1$) nuclei for the quantum manipulation of the electron spin magnetization.