Defect states assisted optical nonlinearity of metal nanoparticle incorporated 2D graphene-MoS2 nanocomposites for engineered photonic device applications

Advanced nonlinear materials are engineered with tailored structural, physical and chemical properties to address modern technological demands exhibiting multifunctional potentiality. Here the synergistic behaviour of copper nanoparticles decorated reduced graphene oxide-Molybdenum disulfide (Cu@rGO-MoS₂) hybrid was assessed to estimate the influence of defect states on the nonlinear optical absorption behaviour under intense nanosecond laser excitation. Cu@rGO-MoS₂ hybrids, prepared by hydrothermal synthesis with different concentration of Cu was preliminarily characterized by X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy analysis. The rGO layer stacking upon MoS₂ nanosheets with hexagonal structure, chemical states of all the counterparts, few layer MoS₂ in the hybrid, successful reduction of graphene oxide and fingerprint vibrational bands were confirmed. The scanning electron microscopy images showcased MoS₂ as spherical structure and rGO as layers with Cu initially as dots grow and form wires/rods of varying length and width with increasing Cu concentration in the hybrids. Altogether, the preliminary characteristics probed the presence of enhanced defect states in all the hybrids. The availability of complex sub bandgap states for new pathways in the electronic transition were confirmed using linear ground state absorption analysis. The nonlinear absorption studies were carried out by performing open aperture Z-scan analysis using a Q-switched Nd:YAG laser (532 nm, 10 Hz and 9 ns). All the open aperture Z-scan pattern depicted reverse saturable absorption (RSA) behaviour at all the input on-axis intensities. The RSA was attributed to the sequential two photon absorption mechanism which was underpinned by the intensity dependent Z-scan studies. The carrier dynamics, field enhancements effects, large active surface region, broad light absorption and induced more defects with inclusion of Cu nanoparticles has effectively influenced the nonlinear optical absorption behaviour by tuning the electronic structure making provisions for utilizing the Cu@rGO-MoS₂ hybrid as an efficient optical limiter for laser safety.