HgI2@CsI core/shell nanoparticles: Synthesis,characterization, and application in photosensors

Due to their excellent characteristics such as carrier transport ability, high electrical conductivity, and mobility, core/shell nanostructure photovoltaic devices have received a lot of interest. In this study, HgI₂@CsI core/shell nanoparticles were synthesized by using two-step pulsed laser ablation in liquid (PLAL) at laser fluences of 12.7 and 33.1 J/cm². The structural and optical properties of the samples were examined using X-ray diffraction (XRD), zeta potential (ZP), energy dispersive X-ray (EDX), transmission electron microscope (TEM), UV–Vis absorption, and photoluminescence spectra. The XRD data conforms to the formation of cubic CsI and tetrahedral and orthorhombic HgI₂. The zeta potential results show that the sample prepared at 33.1 J/cm² has the highest stability. TEM images show the formation of core-shell morphology and the thickness of the shell depends on the laser fluence. UV–Vis results show that the band gap of the core/shell was 3.22 and 3.23 eV for 12.7 and 33.1 J/cm², respectively. The fluorescence spectra show two emission peaks for two laser fluences. The current-voltage characteristics of the HgI₂@CsI/Si heterojunction were measured at dark and illumination, and the maximum On/Off ratio was about 167 for a photodetector prepared at 12.7 J/cm². The figures of merit of the photodetectors, including responsivity, external quantum efficiency, and detectivity, are measured at room temperature. A responsivity as high as 0.7 W/A at 400 nm was obtained for a photodetector fabricated at 12.7 J/cm².