  High-frequency pulse electron paramagnetic resonance (EPR) and electron
nuclear double resonance (ENDOR) were used to clarify the electronic structure
of the color centers with an optically induced high-temperature spin-3/2
alignment in hexagonal 4H-, 6H- and rhombic 15R- silicon carbide (SiC)
polytypes. The identification is based on resolved ligand hyperfine
interactions with carbon and silicon nearest, next nearest and the more distant
neighbors and on the determination of the spin state. The ground state and the
excited state were demonstrated to have spin S = 3/2. The microscopic model
suggested from the EPR and ENDOR results is as follows: a paramagnetic
negatively charged silicon vacancy that is noncovalently bonded to a
non-paramagnetic neutral carbon vacancy, located on the adjacent site along the
SiC symmetry c-axis.
