Linear and non-linear optical parameters of polycarbonate reinforced inorganic bismuth nitrate pentahydrate salt composite

Abstract

The effect of dispersinga filler on the optical properties of polycarbonate (PC) was studied using UV–Visible spectroscopy. The composite films with different weights of bismuth nitrate pentahydrate (Bi (NO3)3·5H2O or BNP) in the PC matrix (from 0.1 wt% up to 5 wt%) were prepared by solution casting technique using dichloromethane (DCM) as the solvent of PC. Tauc's equation was used to obtain the optical band gap and the type of electronic transition occurring on absorption of a suitable photon of electromagnetic radiation. Significant decrease in the optical band gap was noticed for PC/BNP composite containing 0.75 wt% of BNP, when compared to pure PC. Important optical parameters like dielectric constant (ϵr and ϵi), refractive index (n) and optical conductivity (σ) of the PC/BNP composites are significantly improved with the addition of BNP in the PC matrix. Interestingly, the composite sample with filler level (FL) 5 wt % showed the highest optical conductivity (9.90 × 109 s-1) at 4.56 eV (incident photon energy) the prepared composite films. The theoretical Wemple-DiDomenico single oscillator model was used to estimate various dispersion parameters (average oscillator energy (Eo), oscillator dispersion energy (Ed), optical spectral moments (M-1 and M-3), static refractive index (no), and static dielectric constant (ϵs)) of the prepared composites. The average oscillator strength (So), average oscillator wavelength (λo) and high frequency dielectric constant (ϵ∞1) were determined by using the Sellmeier single oscillator model. Also, the ratio of free carriers to effective mass (N/m*), lattice dielectric constant (ϵL) and plasma frequency (ωp) have been calculated. The values of (N/m*) increased from 3.79 × 1037 kg−1 m-3 to 24.86 × 1037 kg−1 m-3 with increasing FL (from 0 wt % up to 2.5 wt %). The volume energy loss function (VELF) and surface energy loss function (SELF) were determined using real and imaginary part of dielectric constant. The non-linear third order optical susceptibility (χ(3)) and non-linear second order refractive index (n2) were determined using simple semiempirical relations. The photo-induced changes in the optical parameters are significant due to an interaction between the incident light and electrons of the composite, and thus, detailed analysis of these optical parameters of PC composites may find applications in optical devices.