Structural, optical, and photoluminescence properties of CdWO₄ films synthesized by a chemical bath deposition method

Thin cadmium tungstate (CdWO₄) films have gained growing interest in the last few decades because of their high X-ray absorption coefficient and low radiation damage. Various applications are known for CdWO₄, such as sensors in radiation detectors and photocatalytic degradation of organic compounds. In this work, we report a simple and cost-effective chemical bath deposition method of CdWO₄ thin films on glass substrates from one solution. The films were annealed at 600°C for 1 h in air. The scanning electron microscopy/energy-dispersive X-ray spectroscopy analysis revealed a dense structure of the films with multiple defects (cracks and craters), along with a nonstoichiometric W-rich composition. Raman and Fourier transform infrared spectroscopy confirmed the presence of CdWO₄ through v ₁ and v₃ vibrational modes. X-ray diffraction patterns showed a typical monoclinic CdWO₄ structure, along with a minor presence of secondary phases (CdO and WO₃) in the annealed sample at 600°C. UV-vis transmission spectra and the corresponding Tauc plot indicated a direct band gap of 2.62 eV. Reflectance spectra demonstrated intrinsic luminescence under high-energy UV radiation, with a broad emission peak at 500 nm. Preliminary electrochromic tests showed that the films exhibited electrochromic behaviour, with the in situ measured transmittance at 550 nm changing by approximately 55%. With further optimization, CdWO₄ films prepared by this method could be applied for high-energy radiation detectors, such as those for UV and X-ray detection, which will be the subject of future research.