Influence of heat treatment and γ-irradiation on the optical properties of methylene blue trihydrate thin films

Physics department, Faculty of Education, Ain Shams University, Roxy 11757 Cairo, Egypt

Corresponding author: dr.a.eldeeb@gmail.com

Received: 28 May 2007
Revised: 24 October 2007
Accepted: 26 October 2007
Published online: 5 February 2008

Abstract

Structural and optical properties of thermally evaporated methylene blue trihydrate thin films up to a film thickness of 165 nm have been investigated. The lattice constants and the crystallite size were calculated. The optical parameters were obtained using spectrophotometric measurements of the transmittance and reflectance at normal incidence of light in the wavelengths range 200–2500 nm. Below the absorption edge, subgap absorption in the energy range 0.75–1.4 eV was observed and interpreted in terms of defect states induced absorption phenomena and act as deep traps for charge carriers. The type of optical transition was found to be an indirect allowed transition. The values of the optical gap E_opt, the transport gap E_t, the exciton binding energy E_B, the Urbach's energy E_u and the dispersion parameters for as-deposited, annealed and irradiated films with different doses of γ-irradiation were estimated and discussed their influenced by heat treatment and irradiation.