As a highly anticipated transition metal dichalcogenide (TMDC) material, tungsten disulfide nanosheet (WS? nanosheet) exhibits a series of excellent optical property due to its unique layered structure and is widely used in the manufacture of high-performance devices such as photodetectors, solar cells and optical sensors.
Light absorption characteristics
Broadband light absorption: Tungsten disulfide nanosheet exhibits a wide range of light absorption capabilities in the visible to near-infrared region. This characteristic is mainly due to its complex internal electronic transition mechanism, including direct transitions (from valence band to conduction band) and indirect transition processes related to defects and impurities in the material.
Effect of the number of layers on absorption: The light absorption capacity of tungsten disulfide nanosheet is closely related to number of layers. As the number of layers decreases, the quantum confinement effect is significantly enhanced, resulting in a blue shift in the absorption spectrum, that is, the absorption peak moves toward the short wavelength direction. For example, a single-layer WS? nanosheet has stronger absorption in the visible light region than a multi-layer structure. This is because the binding energy of electrons and holes in the single-layer structure is larger, and it can absorb photon energy more efficiently.
Light emission characteristics
Fluorescence emission phenomenon: Under certain conditions, WS? nanosheet can produce fluorescence emission. When excited by light, electrons jump from the valence band to the conduction band to form electron-hole pairs, and then release photons through the recombination process to produce fluorescence. Its fluorescence emission peak is usually located in the visible light region, and the position of the emission peak is closely related to the number of layers of the material. The fluorescence quantum efficiency of a single-layer WS? nanosheet is relatively high, which makes it have significant application potential in fields such as fluorescence imaging and light-emitting diodes.
Electroluminescence characteristics: Tungsten disulfide nanosheet can achieve electroluminescence under the action of an electric field. By integrating WS? nanosheet with materials such as electrodes and constructing a suitable device structure, when current passes through, electrons and holes are injected and recombine in the nanosheet, thereby producing a luminescence phenomenon. This characteristic provides new possibilities for the application of WS? nanosheet in fields such as display technology.
Nonlinear optical property
Saturation absorption phenomenon: Tungsten disulfide nanosheet exhibits significant nonlinear saturation absorption characteristics. Under strong light irradiation, its absorption coefficient will gradually decrease with the increase of light intensity, showing saturated absorption behavior. This property enables it to be used as a saturable absorber in ultrafast laser technology to achieve operations such as laser mode locking and pulse compression.
Second harmonic generation capability: Due to the low symmetry of the crystal structure of tungsten disulfide nanosheet, it also has the nonlinear optical effect of second harmonic generation. Under the action of high-intensity laser, WS? nanosheet can double the frequency of the incident light and generate second harmonic signals. This property has important potential application value in the fields of nonlinear optical imaging, optical communications, etc.
