Tuning of third-order nonlinear optical susceptibility of Eu3+ doped alkali borate glasses in visible region by embedding gold nanoparticles

Alkali borate-based glasses containing Eu2O3 embedded with different concentration of AuCl3 were fabricated by melting and quenching process. The transmission electron microscopic measurements revealed morphology of the gold nanoparticles (NPs) embedded in glasses. The nonlinear optical features have been studied using Z-scan at 532 nm excitation utilizing nanosecond laser pulses. The nonlinear absorption and refraction features were ascertained by operating the Z-scan technique in open aperture (OA) and closed aperture (CA) configurations, respectively. OA and CA Z-scan signatures unveiled the presence of two-photon absorption and self-focusing refraction nonlinearities, respectively. In the AuCl3 varied glasses, the highest value of the third-order nonlinear susceptibility (χ(3)) (8.01 × 10‒13 esu) was obtained for 0.02 mol% of AuCl3 doped glasses. This optimized system annealed at 450 °C for diverse schedules to tune χ(3) of glass matrices to higher value (for 30 h of annealing, the χ(3) found to be 12.77 × 10‒13 esu). The enhancement in χ(3) with respect to the gold NPs and with respect to heat treatment schedules was regarded to electric field generated by gold NPs near the Eu3+ ions. However, the results were adversely attenuated at higher heat treatment durations (at 40 h) due to non-uniform local field generated by larger size gold NPs. The nonlinear optical results suggest that the heavily AuCl3 loaded glass and heat treated at 450 °C for 30 h durations are beneficial for applications in nonlinear photonic devices in the visible region.