HIGH-RESOLUTION SPECTROSCOPY AND OPTICALLY DETECTED NUCLEAR-MAGNETIC-RESONANCE STUDIES OF HO3+ IONS IN SRF2 CRYSTALS CONTAINING BA2+ AND CA2+ IMPURITIES

Optical-RF double-resonance techniques have been used to measure the s uperhyperfine transition frequencies of two Ho3+ centres of C4v symmet ry present in SrF2:0.001%Ho3+ crystals containing about 0.2% of Ba2+ a nd Ca2+ as inadvertent impurities, One centre has a charge-compensatin g F- ion located in the nearest-neighbour interstitial position along the (100) axis while the other has an additional Ba2+ ion also located on this axis. The superhyperfine transition frequencies are about 60% smaller than those reported for CaF2:Ho3+ and these decreases are att ributed principally to the decreased Ho3+ ground-state magnetic moment resulting from the increased energy separation between the ground and first excited state Ho3+ electronic energy levels. Another contributi on arises from the larger host lattice dimension for SrF2. The two set s of nearest-neighbour F- ions have almost identical resonance frequen cies for both SrF2 centres while the interstitial F- ion has a substan tially reduced resonance frequency in the Ba2+ modified centre. These trends correlate with those in the relevant crystal-field parameters. Some qualitative conclusions are drawn about the positions of the Ho3 and F- ions in these centres.