Novel nanostructures and optical properties of silver doped sodium phosphate thin films

(50-x)Na2O-50P2O5-xAgCl (x = 0 to 15 mol%) glasses in bulk form were synthesized using melt-quenching technique. Thin films of these silver doped sodium phosphate glasses were deposited by thermal evaporation process. The influence of deposition of these glasses in thin film form and subsequent annealing at 600 degrees C on the structure and optical properties such as transmittance, reflectance, refractive index and band gap have been investigated in detail. X-ray diffraction studies of the as-deposited films show the films to be amorphous whereas annealed films show existence of orthorhombic and monoclinic phase of NaPO3 along with crystalline cubic phase of AgCl in doped glasses. Structural investigations of these annealed films show unique morphologies (needle-like and granular) at nano-scale. Both as-fabricated and annealed films are poor reflectors but show high transmittance in the entire spectral region under consideration, which is a direct consequence of particle size effects. Indirect band gap narrowing and variation in refractive index upon annealing is consistent with nanostructural transformations in these samples.