Cobalt sulfide (CoS) is a zero bandgap transition metal chalcogenides (TMCs). However, the bandgap of CoS can be altered when it exists as low-dimensional material, such as quantum dots (QDs), via different preparation methods. In this work, CoS QDs were successfully prepared by liquid-phase ultrasonic exfoliation method and CoS QDs film was obtained by spin coating CoS QDs solution onto a substrate. The morphology, structural, chemical properties, thickness, vibration peaks and chemical bonds of CoS QDs were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), atomic force microscopy (AFM), Raman spectroscopy (Raman) and X-ray photoelectron spectroscopy (XPS). The absorption and fluorescence characteristics of the CoS QDs were studied using ultraviolet-visible-near infrared (UV-Vis-NIR) and fluorescence spectroscopies. Results show that the average size of CoS QDs was 9.1 nm and average thickness was 8.4 nm and CoS QDs solution and film exhibited absorption in the infrared band. With an increase of excitation and emission wavelength, both the photoluminescence (PL) peak and photoluminescence excitation (PLE) peak of CoS QDs solution and film showed red-shift, which demonstrates Stokes shift effect and dependency on wavelength and have near-infrared luminescence characteristics. The infrared absorption and near-infrared luminescence properties of CoS QDs solution and film imply that they can be found important application in the field of infrared detection. Such novel material is expected to play a crucial role in low-cost, high performance infrared photodetector.
Transition metal chalcogenides (TMCs) have wide-ranging applications in nanoelectronics and optoelectronics due to their unique energy band structure and excellent properties. Iron(Ⅱ) sulfide quantum dots (FeS QDs) are environmentally friendly semiconductor material and exhibit excellent near-infrared properties because of their narrow bandgap, which is essential for infrared detectors. In this paper, FeS QDs were prepared by liquid phase ultrasonic exfoliation and the solution of FeS QDs was spin-coated on a quartz substrate to form a film. The morphology, structural and optical properties of FeS QDs solutions and films were studied. FeS QDs demonstrated good dispersion with average particle size and height of approximately 11.7 and 10.4 nm, respectively. The calculated average particle size of FeS QDs was 12.7 nm using the Debye-Scherrer formula, which is in good agreement with the TEM characterization. The ultraviolet-visible-near infrared (UV-Vis-NIR) characterization of the FeS QDs solutions and films exhibited obvious absorption in the ultraviolet to near-infrared wavelength band, and the absorption was stable in the near-infrared wavelength band. The photoluminescence (PL) characterization of the FeS QDs solutions and films revealed luminescence properties in the near-infrared wavelength band, and the peak position appeared to be red-shifted with an increase in excitation wavelength, which suggests excitation wavelength-dependent luminescence properties. The FeS QDs exhibit good infrared characteristics and can potentially be used in infrared photovoltaic and photodetector.
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