Enhanced optical properties of W1−XMoxO3⋠0.33H2O solid solutions with tunable band gaps

A series of W1−xMoxO3⋅0.33H2O (x = 0, 0.25, 0.50, 0.75) nano/microstructures and MoO3⋅0.55H2O with elongated morphology were prepared by using hydrothermal technique. Aqueous acidified solutions of ammonium metatungstate hydrate ((NH4)6H2W12O40⋅XH2O) and ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24⋅4H2O) were hydrothermally reacted to yield the desired nano/microstructures. In the WO3⋅0.33H2O crystal lattice can be substituted with up to 75% Mo without structural alterations. When the Mo atoms increase, from 0 to 75 at. %, the band gap of the, as-prepared, W1−xMoxO3⋅0.33H2O material decreases from 2.55 to 2.15 eV. In order to corroborate experimental data, first-principle calculations using DFT and DFT + U framework were employed which revealed indirect band gap semiconductors up to x = 0.75. We suggest that the increase in the Mo fraction (25%, 50% and 75%) by hydrothermal synthesis (pressure and temperature) is responsible for the narrowing of the band gap.