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

Abstract A series of W 1− x Mo x O 3 ⋅0.33H 2 O ( x  = 0, 0.25, 0.50, 0.75) nano/microstructures and MoO 3 ⋅0.55H 2 O with elongated morphology were prepared by using hydrothermal technique. Aqueous acidified solutions of ammonium metatungstate hydrate ((NH 4 ) 6 H 2 W 12 O 40 ⋅XH 2 O) and ammonium heptamolybdate tetrahydrate ((NH 4 ) 6 Mo 7 O 24 ⋅4H 2 O) were hydrothermally reacted to yield the desired nano/microstructures. In the WO 3 ⋅0.33H 2 O 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, W 1− x Mo x O 3 ⋅0.33H 2 O 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.