Morphological Tuning of SnO ₂ Nanoparticles and Their Third-Order NLO Behavior in PMMA

In this study, SnO2 nanoparticles with controlled morphologies were synthesized by varying the precursor concentration (0.08 and 0.12 M) using a hydrothermal route and embedded in a PMMA matrix to investigate their third-order nonlinear optical (NLO) properties. X-ray diffraction and Raman spectroscopy confirm the formation of phase-pure tetragonal rutile SnO2. Morphological analysis reveals nanorod-like structures for the 0.08 M sample and spherical to quasi-spherical nanoparticles for the 0.12 M sample. UV-Visible spectroscopy shows a slight increase in optical band gap with increasing precursor concentration. The NLO properties were evaluated using the open and closed aperture Z-scan technique using a linearly polarized He-Ne laser operating at a wavelength of 632.8 nm with an output power of 10 mW. The 0.12 M SnO2-PMMA nanocomposite exhibits enhanced nonlinear absorption (β = 3.42 × 10−6 cm/W) and nonlinear refractive index (n2 = 3.54 × 10−4 cm2/W) compared to the 0.08 M sample (β = 2.14 × 10−6 cm/W, n2 = 3.00 × 10−4 cm2/W). These results demonstrate the effectiveness of precursor concentration in tailoring NLO performance for photonic applications.