Influence of the Iron as a Dopant on the Refractive Index of WO₃

Results on studies of pure tungsten oxide WO₃ and 2, 3 and 4% Fe-doped WO₃ grown on the sapphire substrates by reactive pulsed laser deposition technique are reported. From X-ray diffraction it results that the crystalline structures changed with the substrate temperature and the peaks diffraction having a small shift by the amount of Fe content in WO₃ lattice was noticed. Scanning electron microscopy presented a random behavior of WO₃ nanocrystallites size with substrate temperatures. In the presence of 2% Fe-doped WO₃, the nanocrystallites size varied gradually from 60 nm to 190 nm as substrate temperature increased. The transmission spectra of the pure and 2, 3 and 4% Fe-doped WO₃ films were obtained within the 300-1200 nm spectral range. The refractive index of WO₃ and Fe-doped WO₃ layers were calculated by the Swanepoel method. The refractive index of pure WO₃ shows a variation from 2.35-1.90 and for 2% Fe-doped WO₃ from 2.30-2.00, as the substrate temperature increased. The contents of 3 and 4% Fe-doped WO₃ presented nearly identical values of the refractive index with pure and 2% Fe-doped WO₃, in error limits, at 600 °C. The optical band gap changes with substrate temperature from 3.2 eV to 2.9 eV for pure WO₃ and has a small variation with the Fe.