(Digital Presentation) Engineering Band Gap of Chalcogenide Nanomaterial-Polymer Composites
Authors: Fatemi Ali , Rasouli Milad 
Published: July 2022

Over the last two decades, engineering the optical properties of nanoscale structures (nanowires, quantum dots, and nanotubes), i.e., band gap, absorption, and photoluminescence radiation, which can be manipulated in sulfide-based semiconductor materials, has received a lot of attention. Due to their tunable characteristics, these materials were introduced for potential applications ranging from medicine and communications to energy and various sensors (1). In addition, chemical synthesis methods provide the desired structure, material, reproducibility, and possibility of large-scale production, along with sustainable industrialization and foster innovation of these material systems. Polyvinyl-alcohol (PVA) is one of the functional polymers, in addition to the ability to stabilize the nanomaterial solution, which can change the optical properties of the material (2). Currently, the majority of sulfide-based nanomaterials are cadmium, lead, and silver, which have shown a wide range of applications. Here, PVA/CdS, PVA/PbS, and PVA/Ag2S nanocomposites were investigated as the desired composites. For optical studies, band gap, absorption, and photoluminescence irradiation of these material systems were performed. The structural and morphological properties were examined by scanning electron microscopy, DLS, and X-ray diffraction. The band gap value of synthesized nanoparticles in the polymer bed was 3.48, 3.08, and 2.27 eV for PVA/CdS, PVA/PbS, and PVA/Ag2S, respectively, whereas for pure PVA the band gap value was 4.75 eV. As shown in Figure 1, with the entry of nanoparticles into the polymer, a shift in the composite band gap can be seen that corresponds to an increase in absorption. Photoluminescence irradiations for polymer-nanoparticle composites showed that silver-polymer nanoparticles have intense irradiance at 405nm, while cadmium-polymer and lead-polymer composites have intense irradiance at 430nm and 500nm, respectively. An X-ray diffraction pattern was indicated for each of the crystals, confirming the presence of the expected crystal structure. The DLS of materials represents sizes of 150, 125, and 175 nm for PVA/CdS, PVA/PbS, and PVA/Ag2S. Besides, the structure of the material systems was examined by FE-SEM microscopy, which showed a homogeneous distribution of particles in the polymer and a cubic nanoparticle structure for PVA/PbS and a spherical for PVA/Ag2S and PVA/CdS. Our findings show that polymer-nanomaterial composites are potential candidates for use in sensors and solar energy cells, especially non-toxic Ag2S nanomaterials (3) that have already been documented as an emerging platform for in-vivo imaging.
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Figure 1