Synthesis of Pr³⁺-doped WO₃ particles: correlation between photoluminescent and photocatalytic properties

The WO₃ and WO₃:Pr³⁺ particles were successfully synthesized by the co-precipitation method. The XRD analysis with Rietveld refinement revealed the formation of a monoclinic phase for WO₃ and for doped samples, this result was later confirmed by Raman spectroscopy studies. The presence of Pr³⁺ in the WO₃ crystalline lattice induced structural and optical changes in the particles, increasing the crystallite size, distorting the clusters (shortening of the W-O bonds), favoring the crystallinity and changing the optical gap. The predominant morphology of the particles of WO₃ and WO₃:Pr³⁺ obtained was nanocubes constituted by the superposition of plates of nanometric thicknesses. The photoluminescence of WO₃ and WO₃:Pr³⁺ was produced by the existence of surface defects in the particles. The increase in the concentration of Pr³⁺ promoted an increase in the intensity of PL, due to the increase in the rate of recombination of electron/hole charges. The WO₃ sample exhibited emission in the white region due to the adjustment of simultaneous electronic transitions in the blue, green and red regions, characteristic of the broadband spectrum. The interval of the 2.65 eV gap band and the high efficiency in the separation of the photogenerated charges (e^-/h⁺) with the low recombination rate contributed to the photocatalytic degradation of Crystal Violet (CV) by the catalyst. The WO₃:4% Pr³⁺ sample showed the best photocatalytic efficiency, degrading 73% of the CV dye in 80 minutes. This result was associated with a reduction in particle size and density of oxygen vacancies on the material surface.