Abstract
Ni^<2+> ions occupy the tetrahedral(4), trigonal bipyramid(5) and octahedral(6) sites in glasses and glass-ceramics. The color changes depending on coordination number, typically pink for tetrahedral site, brown for trigonal bipyramidal and tetrahedral sites and green to blue for octahedral site, respectively. The broad NIR emission peaking at around 1220 nm was observed only for octahedral Ni^<2+> ions. This emission is due to 3^T_2(F)→3^A_2(F) transition.
