Effect of laser ablated gold nanoparticles on the nonlinear optical properties of π-extended BODIPY dyes

Abstract

Dipyrromethene boron difluoride (BODIPY) and its derivatives have attracted considerable interest due to their remarkable photophysical properties beneficial for developing fluorescent sensors, biolabels, photodynamic therapy agents, photonic materials, and so on. Herein, we report gold nanoparticles (AuNPs) induced modulation of nonlinear optical properties of π-extended BODIPY derivatives BPA and BDIPA. The spherical gold nanoparticles with an average particle size of 11 ± 3.5 nm were synthesized by pulsed laser ablation technique and characterized by transmission electron microscopy and dynamic light scattering. The interaction of AuNPs with the dye molecules was confirmed by UV/vis absorption and steady-state emission spectroscopy studies. Further, the dual-beam thermal lens technique was used to validate dye-nanoparticle interaction. The thermal diffusivity values of the samples at an excitation wavelength of 532 nm were measured and found that the overall heat diffusion was slower in the AuNPs added samples than that of the dye alone sample, corroborating dye-nanoparticle interaction. The third-order nonlinear optical absorption properties of the samples were investigated by using the Z-scan technique in the infrared region (1064 nm). The open aperture configuration shows significant reverse saturable absorption characteristics for all the samples. Determination of nonlinear absorption coefficient for the dye samples at different input intensities identified two-photon absorption as the important mechanism that produces reverse saturable absorption. The AuNPs incorporated dye samples showed a substantial enhancement in the nonlinear optical behavior. The nonlinear absorption coefficient of the AuNPs incorporated dye samples (10 cm/GW) was enhanced almost two times than that of dye alone samples (5 cm/GW). The enhanced nonlinearity is attributed to the intense local field effect of AuNPs.