ESR of Ni2+in AgCl and AgBr

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Abstract
Previous ESR studies of AgCl:Ni and AgBr:Ni at low temperatures have identified divalent nickel ions in octahedral and axial sites, which were attributed to substitutional nickel ions without and with charge-compensating vacancies in next-nearest cation positions. Another angular dependent ESR spectrum, present with lower intensity in both crystals, has now been found to have orthorhombic symmetry. This centre is attributed to a substitutional divalent nickel ion with a charge-compensating vacancy in a nearest cation location. A microwave power-dependent line with resolved super-hyperfine structure superimposed on the octahedral nickel ESR line is believed to be a double quantum transition. Other more complex centres, produced by low-temperature annealing, have been observed but not identified.