Ni2+ ion and hence the luminescence of the doped glass could be associated with the d–d optical transitions 3A2g (F)- 3
T1g (F), 1Eg(D) and 3T1g (P), 1T2g (D)- 3T1g (F) and 3T2g (F), so the energy levels of the excitation states of Ni2+ are different with the matrices change [29–32]. Usually, two kinds of environments around Ni2+ are proposed as octahedral and tetrahedral sites. In this system, the site symmetry around Ni2+ can be ascribed to the former case that Ni2+ is an ion with an exceptionally large crystal field stabilization energy (CFSE), particularly in an octahedral field. In fact, the d–d transitions of the tetrahedral complexes are electric dipole allowed; whereas those of the octahedral complexes are electric dipole forbidden, and which