EPR of Mo5+ in amorphous MoO3 thin films

Mo⁵⁺ centres in amorphous thin films of MoO₃ have been studied as a function of optical density using EPR techniques. Measurements were made for over an order of magnitude change in optical density and down to helium temperatures. A direct correlation between the optical density and the number of Mo⁵⁺ centres is found for low optical densities but further colouration does not continue to increase the number of Mo⁵⁺ centres. A model is proposed to explain the results.