Photoluminescence and Z-scan studies of green-synthesized silver nanoparticles for photonic applications

Green synthesis of metal nanoparticles has emerged as a sustainable alternative to conventional chemical routes, offering improved biocompatibility and reduced environmental impact. The present study reports the green production of silver nanoparticles (AgNPs) using Terminalia arjuna bark extract, functioning as both the reducer and stabilizer. Phytochemical constituents of the extract promote swift reduction of Ag⁺ ions, as indicated by a noticeable color change and the appearance of a sharp SPR band at 430 nm in the UV–Vis spectrum. Structural analysis using X-ray diffraction verified the face-centered cubic crystalline structure of the NPs, with an average crystallite size of 12.72 ± 0.08 nm. Morphological studies carried out with high-resolution transmission electron microscopy further showed predominantly spherical particles exhibiting lattice fringes corresponding to the Ag (220) planes. Fourier-transformed infrared spectroscopic analysis confirmed the participation of hydroxyl, carbonyl, and amide groups in the capping and stabilization of the NPs. Dynamic light scattering and zeta potential measurements further revealed moderate colloidal stability, with a zeta potential of –25.62 mV. Photoluminescence studies demonstrated a sharp and intense emission peak at 425 nm (when excitation was provided at 400 nm) with a high color purity of 95.9%, corresponding to blue-violet light, making these biosynthesized AgNPs promising candidates for blue emission devices and optoelectronic applications. Nonlinear optical measurements performed at 632.8 nm using the Z-scan technique demonstrated reverse saturable absorption and a self-defocusing effect, confirming third-order optical nonlinearity governed by thermal and plasmonic contributions. The extracted parameters including a nonlinear refractive index n2≈2.66±0.43×10-12m2/W, nonlinear absorption coefficient βeff≈2.16±0.05×10-5m/W, and third-order susceptibility χ(3)≈3.30±0.54×10-6esu highlight strong nonlinear responses, underscoring the NPs’ suitability for applications in all-optical switching, optical limiting, and photonic modulation.