Effect of different synthesis parameters on the structural, morphological and optical properties of hydrothermally synthesized tungsten diselenide (WSe2) nanostructures: Experimental and theoretical validation

Abstract

In this study, tungsten diselenide (WSe<inf>2</inf>) nanostructures were synthesized via a hydrothermal route using sodium tungstate dihydrate (Na<inf>2</inf>WO<inf>4</inf>.<inf>2</inf>H<inf>2</inf>O) and selenium (Se) powder as precursors. Particular attention was given to the influence of synthesis parameters, namely reaction temperature and growth duration, as these play a decisive role in crystallite size, morphology, and the presence of impurities. To systematically evaluate their impact, WSe<inf>2</inf> samples were prepared under different conditions and examined for structural, morphological, and optical variations. The as-synthesized samples were characterized by using X-ray diffraction (XRD), Raman spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray Analysis (EDAX), High Resolution Transmission Electron Microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Ultraviolet-Visible (UV-Vis) spectroscopy and Photoluminescence (PL) spectroscopy. The bonding structure and the vibrational modes of Raman spectrum were validated by Density Functional Theory (DFT) calculation using the B3LYP/LANL2DZ mode. The XRD and Raman spectroscopy measurements confirmed the formation of the hexagonal phase (2H-WSe<inf>2</inf>). The morphology transitioned from aggregated particles to flake-like nanostructures with increasing temperature, while reaction time influenced the crystal refinement and stacking. A significant decrement in the value of the energy band gap for most pure exfoliated WSe<inf>2</inf> was observed from the UV-Vis absorption spectra. PL spectra revealed indirect and excitonic transitions with emission peaks in the near-IR region (∼1.3 and ∼1.5 eV). Further, the PL spectra of exfoliated bulk WSe<inf>2</inf> exhibited a clear blue-shift of the emission peak, indicating effective material thinning from multilayered to few-layered WSe<inf>2</inf>. These optical properties indicate a possible optoelectronic potential of WSe<inf>2</inf>. © 2025 Elsevier Ltd