Optical limiting and two-photon absorption in transition metal and rare earth-doped CeO2 nanoparticles

Abstract

CeO₂(Cerium Oxide), CeO₂: Cu, CeO₂: Zn, CeO₂: Co, CeO₂: Ag and CeO₂: Eu nanoparticles at 11 mol% concentration are synthesized by solution combustion method using Aloe vera gel extract as a green reducing agent. The as-formed samples are calcined at 600 °C for 3 h. Bragg reflections of CeO₂ confirms the formation of cubic fluorite structure. No such additional phases/diffraction peaks corresponding to the dopant are observed. The crystallite size calculated from Scherrer’s method varies from 20 to 10 nm respectively. The energy band gap was tuned from 2.2 eV to 3.5 eV . The optical nonlinearity of the specimens was studied using the open aperture Z-scan technique, revealing reverse saturable absorption attributed to a two-photon absorption process. The non linear nonlinear non-linear absorption coefficient of C, C–Ag, C–Cu, C–Co, C–Eu, and C–Zn were found to be 0.60, 0.74, 1.40, 1.25, 0.6,1, and 0.68 respectively. The optical limiting threshold were found to be 4.27, 3.09, 1.22, 1.55, 4.03, and 3.80 x 10¹² Wm⁻². A higher non-linear absorption coefficient and lower limiting threshold indicate better optical limiting action. A higher $\Delta$E${}_U$ enhances defect-mediated transitions, strengthening nonlinear absorption ($\beta$) and lowering the optical limiting threshold (OLT), though excessive $\Delta$E${}_U$ may introduce scattering losses. Optimizing the bandgap ($\Delta$E${}_g$) through controlled doping facilitates multiphoton absorption, enhancing $\beta$ and minimizing OLT for advanced NLO applications. Urbach energy analysis reveals tunable structural properties in CeO${}_2$-based materials, with CeO${}_2$-Zn exhibiting the lowest Urbach energy (0.28858 eV), reflecting high crystallinity. In contrast, CeO${}_2$-Ag and CeO${}_2$-Cu show higher values (5.19454 eV and 3.76634 eV), suggesting significant structural disorder and potential for enhanced NLO(non-linear optics) performance. Overall, the C–Cu sample emerges as an ideal material for fabricating optical limiters designed for green lasers.