Fully optical scanning spectroscopy of the anticrossing of electron and nuclear spin levels in a 4H-SiC crystal

Transitions in a system of interacting electron and nuclear spins in color centers with $S = 3/2$ in a 4H-SiC crystal with the natural isotopic composition have been detected by fully optical methods at room temperature. Giant changes in the photoluminescence in a volume of about 1 $\mu$m$^3$ under cw and pulsed laser excitation occur in the region of the anticrossing of electron and nuclear spin levels. An optical manifestation of the flip of the nuclear spin of the $^{29}$Si isotope with the conservation of the projection of the electron spin has been detected. All anticrossing points of the spin sublevels coupled by hyperfine interactions have been identified. This identification enables the observation of such effects in the family of quarter spin centers in other SiC polytypes.