ZrS2 quantum dots:Preparation, structure, and optical properties

 In recent years, transition metal chalcogenides（TMDs）have attracted extensive attention of researchers due to their unique electronic structure and excellent photoelectric properties. In this paper, hexagonal structure1 T-ZrS₂ quantum dots（QDs）having a monodisperse grain size of around 3.1 nm is prepared by the ultrasonic exfoliation method.

The preparation includes the following steps: ZrS₂ powder is ground, followed by ultrasonic exfoliation in 1-methyl-2-pyrrolidone（NMP）, and 1 T-ZrS₂ QDs are collected after centrifugation. The structure,morphology and optical properties of the QDs are studied in detail. The structure, morphology, size distribution, and elemental composition of 1 T-ZrS₂ QDs are studied by using X-ray diffractomete（XRD）,transmission electron microscopy（TEM）, atomic force microscopy（AFM）, and scanning electron microscopy（SEM）. The chemical bonds of 1 T-ZrS₂ QDs are characterized by X-ray photoelectron microscopy（XPS） and Fourier transform infrared spectrometer（FTIR）. The TEM and AFM results show that the 1 T-ZrS₂ QDs are spherical in shape with uniform size distribution.

The sizes of the 1 T-ZrS₂ QDs follow a Gaussian fitted distribution with an average diameter of WC = 3.1 nm and the FWHM is 1.3 nm. The XRD diffraction pattern of 1 T-ZrS₂ QDs show wide dispersed diffraction peaks, which is the characteristic of QDs. The diffraction peak at 2 q = 32.3°（d = 0.278 nm） corresponds to the（101） crystal plane, and the weak diffraction peak at 2 q =56.8°（d = 0.167 nm） belongs to the（103） crystal plane. The grain size is also calculated by using the DebyeScherrer formula, and the calculated value（2.9 nm） is consistent with the result of TEM（3.1 nm.

Two Raman vibration modes(E1 g and A_1g) are observed. The E1 g（507.3 cm–1） and A_1g(520.1 cm^–1) modes relate to the inplane and out-of-plane vibration respectively. The Raman intensity of the A_1g vibration mode is stronger than that of E1 g. The UV-Vis and photoluminescence（PL and PLE） characterizations exhibit that the 1 T-ZrS₂ QDs have two UV absorption peaks at 283 nm and 336 nm, respectively. The Stokes shift is ～130 nm, the fluorescence quantum yield reaches up to 53.3%. The results show that the 1 T-ZrS₂ QDs have the excellent fluorescence performance and unique optical properties, which make the 1 T-ZrS₂ QDs an important material for developing photodetectors, multi-color luminescent devices, and other devices.