Electron nuclear double resonance of the trapped hole center in α-Al2O3:Mg2+

The superhyperfine (shf) interactions of trapped hole centers with 27Al neighbor nuclei in α-Al2O3 doped with Mg2+ are resolved with electron nuclear double resonance (ENDOR). The hole is localized at an O2- ion. With electron nuclear triple resonance (double ENDOR) it could be established that one of the two next nearest neighbor Al3+ ions is missing, but no ENDOR lines due to a Mg2+ impurity can be identified. The isotropic shf interaction constants of the nearest and next nearest Al3+ neighbors are negative. The shf interactions are quantitatively interpreted by taking into account transferred exchange polarization at the oxygen ion. From this, it seems more likely than not that the Al3+ vacancy is filled by a Mg2+ ion. (author)