Figure 13.

Plots of the Kubelka–Munk function vs photon energy of the specimens synthesized at different temperatures showing the optical E_g estimated using the Tauc procedure. The dashed lines represent the x-axis intercept of the line tangent to the inflection point for each dataset. (a) Indirect E_g model, [F(R_∞)hν]^1/2, γ = 2. The insets show the systematic changes in E_g with increasing synthesis temperature and resulting NP size. (b) Directly allowed E_g model—[F(R_∞)hν]², γ = 1/2; the red dashed lines are drawn as a guide for the eye, showing an approximately exponential trend for the evolution of the optical E_g with the increase in the synthesis temperature.