Abstract: Mo-doped titania excited by a 978nm diode laser exhibits a visible broadband emission which can be controlled by high-temperature chemical redox. The
luminescence has been assigned to the transitions from the excited states ³T₁, ³T₂ to the ground state ¹A₁ of the [MoO₄]^2- radicle. FTIR spectrum
confirms the presence of the [MoO₄]^2- complexes, while XPS measurement suggests the concurrent existence of lower valent Mo species. The intermediate states
available for upconversion are supposed to be related to the lower valent Mo species through which the external chemical redox modifies the luminescence.

Key words: upconversion, TiO2, [MoO₄]^2-