Systematic evaluation of pre-heating temperature-dependent gas sensing performance of V2O5 thin films

This study investigates the influence of four distinct pre-heating temperatures (150 °C, 200 °C, 250 °C and 300 °C) on the V 2 O 5 thin films synthesized via the sol-gel spin coating method. Structural analysis using XRD revealed mixed orthorhombic phases of α- V 2 O 5 and V 4 O 9 , with crystallite sizes varying from 18.5 to 24.3 nm depending on pre-heating conditions. While SEM confirmed the uniform grain morphology, EDAX corroborated the elemental composition. Optical studies indicated the bandgap values are nearly 2.40 eV and subtle variations in Urbach energy, with the lowest disorder observed at 250 °C. Photoluminescence spectra exhibited a non-monotonic trend, where pre-heating to 250 °C suppresses deep-level defect emissions (DLE) centred at 565 nm while eliminating non-radiative quenching pathways to produce a strong near-band-edge (NBE) emission at 459 nm. XPS analysis confirmed that pre-heating at 250 °C promotes the recovery process of coordination deficient defects, increasing the percentage of structured lattice oxygen from 56.10% to 58.50% and maintaining a dominant V 5+ oxidation state. The chemiresistive measurements demonstrated a maximum response of 25.1% towards 5 ppm of H 2 S gas and a practical limit of detection (LOD) of 1 ppm at an optimized operating temperature of 300 °C for the V 2 O 5 thin films preheated at 250 °C. These findings identify 250 °C as the optimal pre-heating temperature for producing stoichiometric, defect-engineered V 2 O 5 films for environmental monitoring.