ESR Study of Hole Centers in MgF_2 Crystals Irradiated with γ-Rays and Neutrons at Low Temperatures

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The hole centers produced in MgF_2 crystals irradiated with γ-rays and neutrons at low temperatures have been studied by electron spin resonance. Two kinds of centers were observed in neutron-irradiated crystal and designated as H_N and V_N, respectively. The H_N center has been already assigned to be an interstitial F atom which forms an asymmetric (F^<-0.4>-F^<-0.6>) molecular ion with a lattice F ion, while the V_N center is nearly [011]-oriented F_2^- molecular ion; a hole trapped by the ions interacts equivalently with each F nucleus. The H_N and V_N centers decay at about 560 K and 185 K, respectively. In γ-rayed crystal a hole center like the V_N canter was produced and named as V_γ center. The V_γ center is also F_2^- molecular ion whose bond-axis tilts by several degrees from that of the V_N center. This center decays at around 145 K.
1976-10-15