Linear and Nonlinear Optical Characterization of Dye–Polymer Composite Films Based on Methylcellulose Incorporated with Varying Content of Methylene Blue

Compositional dependence of the linear and nonlinear optical characteristics of dye–polymer composite (DPC) films based on methylcellulose-methylene blue (MC-MB) were studied. The absorbance spectra were used to estimate absorption edge, optical density, skin depth, optical band gap energy, and Urbach's parameters for all DPC films. The direct allowed optical band gap energy decreased from 6.29 eV for pure MC to 5.95 eV when doped with 2.5 wt.% of MB. The dispersion of the refractive index is discussed in terms of both the single-oscillator Wemple–DiDomenico and single Sellmeier oscillator models. The nonlinear optical characteristics such as the third-order nonlinear optical susceptibility and nonlinear refractive index were calculated using the dispersive oscillator parameters obtained from the single-oscillator model. The observed improvements in the linear and nonlinear optical characteristics of MC upon incorporating MB make the present DPC a potential candidate for multifunctional applications like optoelectronic and photonic devices.