Hybrid Z‑scan simultaneously probes nonlinear absorption and fluorescence competition in xanthene dye systems with...

A hybrid Z-scan setup with a grating spectrometer and CCD capable of recording light transmission, fluorescent intensity, and elastic scattering is designed to study five xanthene dyes such as Rose Bengal, Rhodamine B, Rhodamine 6G, Eosin-B, and Erythrosine-B mixed with citrate-stabilized silver and platinum nanoparticles. Fluorescence and light scattering recorded at two positions, the focal point and out-of-focus reference revealed systematic fluorescence suppression at the focal point, directly demonstrating competition between nonlinear absorption and fluorescence via energy level transitions. The nonlinear absorption coefficient (β) exhibited inverse correlations with both optical bandgap and fluorescence intensity-to-absorption ratio. Rhodamine 6G uniquely displayed a transition from reverse saturation absorption to saturation absorption upon silver nanoparticle addition, while platinum nanoparticle uniformly enhanced β across all dyes. Rose Bengal, Eosin-B, and Erythrosine-B dyes demonstrate higher fluorescence quenching due to plasmonic nanoparticle interaction.