The major optical behavior of a material is linked with the imaginary part of dielectric function ( 2 ( )) (Eqns. ). The 2 ( ) describes the inter-band transitions by analyzing the major peaks. All the optical inter-band transitions are essentially due to the orbitals of F, B, and N atoms which can be described by analyzing PDOS (Fig. ). The major sharper peaks (Fig. ) arise at 9.16 and 9.95 ( blue-shifted) in E‖x, and 7.95 , 8.59 and 11.88 (red-shifted) in E‖z displays earlier interband trasitions in FBNF. The higher number and larger intensity in spectra indicates the multiple inter-band transitions and enhanced optical response of FBNF than the pristine counterpart.