Comprehensive study of -Alanine passivated colloidal gold nanoparticles and GNP-PVP thin films: Linear optical properties and very large nonlinear refractive index, absorption coefficient, third-order nonlinear susceptibility measurements and effect of passivation

Abstract We synthesized gold nanoparticles (GNPs) stabilized in various concentration of l -alanine by chemical reduction method. We measured NLO responses of GNPs when they are dispersed in the l -alanine stabilizer with 1, 2.5 and 5 m M concentrations and when they are implanted into the PVP matix, by using single beam Z- Scan technique with 632 nm He–Ne CW laser for excitation. GNPs exhibited blue shift in localised surface plasmon resonance (LSPR) peak with the l -alanine concentration. The fcc structured GNPs of reducing size with the stabilizer concentration were obtained and characterized by the TEM as well as XRD. The FTIR spectral investigation revealed the formation of strong bond between the surface of GNPs and the l -alanine functional groups and established that l -alanine is very good candidate for stabilization of MNPs. It was observed that these samples show very large nonlinear refractive index, absorption coefficient and third-order nonlinear susceptibility in the order of 10 − 8 c m 2 W − 1 , 10 − 6 c m W − 1 and 10 − 9 e s u respectively for colloidal suspension of GNPs, and for the GNP-PVP thin films these parameter values were found in the order of 10 − 6 c m 2 W − 1 , 10 − 5 c m W − 1 and 10 − 6 e s u respectively. The thermally stimulated, l -alanine concentration dependant, very large NLO responses attributed to the local field effect from Mie resonance and thermal lensing effect originated from thermo-optic phenomenon. The obtained results validate the influence of the stabilizer ( l -alanine) on NLO properties.