The present research work reports on the fabrication of ultraviolet (UV) photodetectors using bismuth ferrite (BiFeO_3, BFO) thin films with varying thickness. Using the spray pyrolysis technique, BFO thin films were deposited on the glass substrate at 673 K. The deposited BFO thin films were characterized by Raman and FTIR spectroscopic analysis. The morphological analysis reveals uniform grain distribution for the prepared BFO samples. The optical analysis reveals that transmittance value decreases upon an increase in the thickness of BFO thin films and the calculated optical band gap value lies between 2.0 to 2.3 eV. The varying thickness of the BFO active layer was stacked between ITO and Al electrodes and the current–voltage (I–V) characteristics of the fabricated ITO/BFO/Al devices were studied under dark and UV illumination (λ = 365 nm). It was observed that BFO with an optimum thickness (365 nm) exhibits higher photoresponsivity of 110 mA/W with an external quantum efficiency (EQE) of 37.30%. The impact of different thickness of the BFO active layer, the role of adsorption and desorption of oxygen (O₂) molecules upon the surface of BFO layers towards UV photoresponse characteristics were investigated.

Gadolinium doped bismuth ferrite (Gd:BFO) nanoparticles were synthesized using an auto combustion method. The structural analysis of the prepared Gd: BFO nanoparticles showed that all samples exhibit a rhombohedral structure. The optical analysis shows the doping of Gd ions reduces the band gap value of BFO from 2.21 eV to 2.17 eV. The presence of Fe-O stretching vibrations is confirmed by Fourier transform infrared (FTIR) spectroscopic analysis. The magnetic hysteresis (M-H) analysis shows a weak ferromagnetic nature for the prepared BFO samples and the value of saturation magnetization (M_s) increases upon an increase in the Gd doping concentration. The dielectric analysis shows that the doping of Gd ions in BFO has a notable control in the dielectric loss of the prepared BFO nanoparticles. It was observed the Gd (2 wt%) doped BFO nanoparticles exhibit 84.5% degradation toward crystal violet (CV) dye under visible light irradiation. The formation of trap levels due to Gd 4f state and the role of superoxide anion ( $O_2^{-}$) and OH^o radicals toward the degradation of CV dye were analyzed.