High-resolution spectroscopy and optically detected nuclear magnetic resonance studies of Ho3+ ions in SrF2 crystals containing Ba2+ and Ca2+impurities

Abstract

Optical-RF double-resonance techniques have been used to measure the superhyperfine transition frequencies of two Ho3+ centres of C 4v symmetry present in SrF2:0.001%Ho3+ crystals containing about 0.2% of Ba2+ and Ga2+ as inadvertent impurities. One centre has a charge-compensating 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 attributed 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 contribution arises from the larger host lattice dimension for SrF2. The two sets of nearest-neighbour F- ions have almost identical resonance frequencies for both SrF2 centres while the interstitial F - ion has a substantially reduced resonance frequency in the Ba 2+ 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. Show more