Electronic Absorption Spectrum of Ni2+ Doped in NH4Cl Single Crystal

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Abstract
The absorption spectrum of Ni2+ doped ammonium chloride is studied in the temperature range of 293–77°K. From the observed spectrum it is concluded that Ni2+ goes interstitially. Different possible coordinations at the metal ion site are discussed. It is suggested that the divalent nickel ion has very likely a fourfold chlorine coordination associated with two neutral water molecules at the first‐neighbor NH4+ sites along 〈100〉 direction. An abrupt blue shift of about 100–150 cm−1 is observed at 235°K in the positions of the band maxima and is attributed to the anomalous lattice contraction of the host lattice at this temperature.