Interfacial Charge Transfer of WO3 Nanorods Decorated with Ag Nanoparticles for a Nonlinear Absorption Modulator
The metal/metal oxide semiconductor materials with special photoelectric properties have been widely used for the development of novel photoelectric devices. However, electron transfers at the interfaces of metal and metal oxide are unclear under a photoexcitation process. Herein, the pure WO3 nanorods and Ag nanoparticles (NPs)-loaded WO3 (AWO) nanorods were synthesized by a hydrothermal technique and a two-step method, which includes hydrothermal and magnetron processes. Their corresponding electron excitation and relaxation properties have been revealed by absorption/emission spectra and transmission curves under nonlinear excitation of an ultrafast laser. The dependence relationship for the morphology and structure of one-dimensional (1D) WO3 nanomaterial orientation on the parameters’ adjustment (reaction time and reactant concentration) and formation mechanism was studied. The 1D WO3 nanomaterials show obvious longitudinal growth in the (200) orientation, as well as lateral growth in the (001) and (110) orientations. The size and distribution effects of Ag NPs on the optical properties of WO3 have also been investigated. On the basis of quantum particle coupling between metal (Ag) and metal oxide materials (WO3 nanorods), electron–hole pairs were generated in the semiconductor and strongly enhanced the radiative recombination. The Z-scan results illustrated that the maximum nonlinear absorption coefficient of the AWO (6 W) nanorods was obtained. When charge transfer happens in Ag NPs, the density of the electronic states in the excited/defect states of the WO3 can be regulated. For AWO nanorods, the ground state of Ag undergoes a saturation absorption process and results in reverse saturation absorption of the excited/defect states. Because of their remarkable nonlinear-optical properties, the proposed AWO nanorods will be potential nanocomposite materials for the development of nonlinear absorption modulator devices.
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