Objective  TMCs have been widely used in photocatalysis, solar cells, lasers and other fields because of their excellent optical, electrical and photoelectric properties. As a typical TMCs material, CoS QDs have excellent near-infrared absorption properties due to their narrow band gap and are expected to be used in infrared technology. CoS QDs are expected to be an important material for infrared detector preparation. In order to improve the optical properties and processing properties of CoS QDs, CoS QDs were further prepared into nanocomposite films to expand their application range. At present, the research work on CoS mainly focuses on CoS NPs, and there are few reports on quantum dot composite films. Therefore, the CoS QDs prepared by liquid phase ultrasonic exfoliation method are blended with PDMS, and the infrared properties of CoS QDs /PDMS nanocomposite films are studied. In order to expand the application of CoS QDs in infrared optics.

  Methods  CoS QDs solution was prepared by liquid phase ultrasonic exfoliation method. The preparation steps were as follows: 0.15 g CoS powder (purity ≥99.5%) was weighed and put into a mortar and fully ground for2 h; The ground CoS powder was evenly mixed with 50 mL of anhydrous ethanol (purity ≥99.7%) dispersant, and placed in the ultrasonic instrument at 90 W power for 2 h; The ultrasonic solution was centrifuged at a rotational speed of 500 r/min for 5 min. Taking out the supernatant, CoS QDs solution was obtained. The CoS QDs solution is dried for later use. CoS QDs/PDMS nanocomposite films were prepared by blending method. 5 mLof the basic component A of PDMS and 0.5 mL of the curing agent B were transferred to the beaker, and appropriate amount of the dried CoS QDs powder was added, stirred with a magnetic stirrer for 5 min, and then transferred to the petri dish and heated at 30 ℃ until film formation. The size, morphology, structure and elemental components of CoS QDs were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and energy dispersive spectrometry (EDS). The phase composition and bonding properties of CoS QDs were analyzed by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy (Raman); the optical properties of CoS QDs and CoS QDs/PDMS composite films were tested by UV-Vis spectrophotometer and fluorescence spectrometer.

  Results and Discussions   Both CoS QDs and CoS QDs/PDMS nanocomposite films have obvious absorption and luminescence characteristics in infrared band, and the infrared absorption characteristics of the composite films are better than that of CoS QDs films (Fig.4(a)-(c)). With the increase of excitation wavelength, the PL peak of CoS QDs/PDMS nanocomposite films shows a redshift, which shows obvious Stokes shift effect and excitation wavelength dependence (Fig.4(k)).

  Conclusions  The spherical CoS QDs with good dispersion, uniform particle size and average particle size of about 5 nm were successfully prepared by liquid phase ultrasonic stripping method, and the CoS QDs/PDMS nanocomposite films were prepared by blending CoS QDs and PDMS. After UV-Vis test, it was found that CoS QDs solution and CoS QDs/PDMS nanocomposite films have absorption from ultraviolet to infrared band(200-2200 nm). Compared with CoS QDs films, the infrared absorption characteristics of CoS QDs/PDMS nanocomposite films are effectively enhanced. Moreover, the absorption strength of the film samples hardly changed after six months. The PL test shows that CoS QDs and CoS QDs/PDMS nanocomposite films have PL phenomenon in infrared band, PL peak has obvious redshift phenomenon, Stokes shift effect, and both have wavelength dependence. On the other hand, CoS QDs/PDMS nanocomposite films have excellent infrared optical properties, especially the absorption and luminescence characteristics in the infrared band, and the optical properties are very stable, indicating that the composite material has important potential application value in the fields of infrared detectors, nano-photonic devices, flexible displays, infrared lasers and so on.