Role of nickel ion coordination on spectroscopic and dielectric properties of ZnF2–As2O3–TeO2:NiO glass system

20ZnF2–30As2O3–(50 − x)TeO2:xNiO (0 ≤ x ≤ 2.0) glasses were synthesized. The glasses were characterized by X-ray diffraction, scanning electron microscopy, EDS and DSC techniques. A variety of properties, i.e. optical absorption, infrared, magnetic susceptibilities and dielectric properties (constant ϵ′, loss tan δ, a.c. conductivity σac over a wide range of frequency and temperature) of these glasses have been carried out. The analysis of results of all these studies has indicated that the nickel ions occupy both octahedral and tetrahedral positions and the gradual increase of NiO content in the glass matrix causes growing proportions of Ni2+ ions that occupy octahedral positions. The luminescence spectra of these glasses have exhibited a broad emission band in region 1200–1450 nm identified due to 3T2(3F) → 3A2(3F) octahedral transition of Ni2+ ions. The luminescence efficiency and cross section have been found to be the highest for the glass containing highest concentration of NiO. Finally it is concluded that the higher the concentration of octahedrally positioned Ni2+ ions, the higher is the luminescence efficiency.