The hydrothermal synthesis method was employed for the fabrication of pristine tungsten trioxide (WO3) and that of varying dopant percentages (1, 3 and 5% m/m) of magnesium (Mg-WO3). The optical and structural properties of the synthesized materials were characterized using DRS, XRD, FTIR, TEM, BET, FESEM, XPS, PL, and Raman. Rectangular shaped nanostructures were observed through FESEM, wherein confirmed as monoclinic with the aid of XRD, FTIR and Raman analysis. Visualization of the doping was carried out using HRTEM imagery, which was also confirmed by a slight increase (0.0069 nm) of d spacing. As a consequence, band gaps were diminished and band edge positions were shifted. Band edge position shifts were confirmed via XPS analysis (0.08 eV). The point of zero charge was observed to shift towards positive upon doping at working pH 1 and 3.75 pH was the highest recorded. The rate of recombination was greatly reduced upon doping was observed through PL analysis. This was supported by DFT calculations, in which case the reduction of the rate of recombination was attributed to the introduction of Mg orbital. An improved efficiency was observed via the photo reduction of Cr(VI) metal ion in waste water, in which case, 97% reduction was attained.