Magnetic-resonance studies of Gd3+ ions in CaO

Two aspects of the ESR spectrum of Gd3+ in CaO are reported. The forbidden transitions in which the electronic spin changes by Delta MS=2, 3, 4 and 5 have been observed at X-band frequencies for the cubic Gd3+ spectrum. Furthermore a spectrum due to Gd3+ in orthorhombic symmetry sites is also reported: apparently the distortion arises when charge compensating defects are located within a few lattice constants of the Gd3+ ion. The ensuing crystal-field splittings are large-comparable with the X-band quantum-and measurements at Q-band frequencies are required for an accurate determination of the crystal-field parameters.