Structural evolution in crystalline MoO3 nanoparticles with tunable size

► Structural evolution of the MoO3 nanoparticles as a function of the crystallite size. ► Tunable optical properties by controlling the MoO3 nanoparticle size. ► The impregnation-decomposition methodology allowed tuning the nanoparticle size. ► The red shift in the band gap of the MoO3 nanoparticles is due to quantum size effect. ► The short-distance order in MoO3 nanoparticle is function to area/volume ratio.