Nonlinear photonics in CdSe-based nanoplatelets and related colloidal nanomaterials

Abstract

The nonlinear optical (NLO) properties of semiconductor nanomaterials are of growing interest due to their relevance in ultrafast photonics and optoelectronic applications. In this work, we investigate the third-order and higher-order NLO responses of colloidal cadmium selenide (CdSe) nanoplatelets (NPLs) and core/shell CdSe/CdS structures in toluene using femtosecond Z-scan and optical Kerr gate (OKG) techniques. Our results reveal strong agreement between both methods and demonstrate complex intensity-dependent behavior, including sign reversal in nonlinear refraction and evidence of effective three-photon absorption. Time-resolved measurements show ultrafast orientational dynamics, with sub-picosecond responses modulated by nanostructure design. Under resonant excitation, both saturable absorption and enhanced self-focusing effects were observed, particularly in CdSe NPLs. The CdSe/CdS core/shell structures exhibit broader absorption features and higher saturation thresholds, indicative of inhomogeneous broadening. Comparatively, CsPbBr3 halide perovskite quantum dots show strong Kerr-type nonlinearities at low intensities, which saturate under stronger excitation due to excitonic state filling and strong nonlinear solvent contribution. These findings highlight the crucial role of quantum confinement and structural engineering in optimizing nonlinear optical behavior, providing insights for the development of advanced photonic materials.