Double-hole aluminium center in α-quartz

EPR studies at ca.25 K of a single crystal of α-quartz, which had been irradiated at 77 K, have disclosed the presence of a new type of impurity center. This is thought to consist of a substitutional aluminium 3+ ion with electron holes at two neighbouring oxygen ions, forming a triplet system. The two primary 27Al hyperfine multiplets as well as the half-field spectrum have been observed, and have led to an approximate spin-Hamiltonian. (author)