“…The band gap energy (E g ) was associated with the absorbance and photon energy by following equation hγ α ∝ (hγ -E g ) n , where α is the absorbance, h the Planck constant, γ the frequency, E g the optical band gap and n a constant associated with different types of electronic transition (n = 1/2, 2, 3/2 or 3 for direct allowed, indirect allowed, direct forbidden and indirect forbidden transitions, respectively). 32 Thus, the E g values of BNKTS-100xLi ceramics were evaluated by extrapolating the linear portion of the curve or tail. Our results indicated that an indirect transition which occurred because of n = 2, as shown in Fig.…”