AgI nanostructure development in sputter-disordered and Al-doped Ag films probed by XRD,SEM, optical absorption and photoluminescence

By use of thermal evaporation and rf magnetron sputtering 300 and 500 Å thick Ag and Ag (Al) films were prepared. γ-AgInanoparticles were formed during (a) short time (2–5 min) iodization of undoped thermally evaporated Ag films, (b) longer time (12 h) iodization of undoped rf sputtered Ag films and (c) short time (2–15 min) iodization of thermally evaporated Ag_0.95Al_0.05 and Ag_0.90Al_0.10 films of 500 and 300 Å thickness respectively. Both rf sputtered and Al doped Ag films yielded ～20 to ～60 nm sized γ-AgI particles upon iodization. Optical absorption spectra reveal Z_1,2 and Z₃ exciton transitions with increased broadening of γ-AgI nanoparticles, suggesting the effect of disorder produced during film formation. Blue shift observed with increasing film thickness could be the effect of decreasing particle size, thereby increasing the quantum confinement effects. Photoluminescence studies show that the donor-acceptor recombination rate, enhanced by 25% for Ag_0.95Al_0.05I film relative to that of undoped AgI, is due to the tight binding of Al to surface defect sites.