The optical properties of titanium oxide were investigated in relationship with the presence of chemically-optically active centers and their evolution in argon, oxygen and hydrogen ambient. Samples of nanocrystalline TiO₂ powder were annealed at 1100^oC for 30 min., under argon atmosphere. The as-obtained polycrystalline material was further subjected to two types of treatments: i) at 800^oC for 30 and 120 min., respectively, under oxygen, and ii) at 750^oC for 30 and 120 min, respectively, in forming gas with various concentrations in hydrogen, from 10% up to 70%.

The optical emission spectra were measured by cathodoluminescence in the scanning electron microscope (SEM-CL) and analysed in correlation with the structure and morphology of the surface, which were investigated by X-ray diffraction and SEM.

The nanocrystalline TiO₂ powder showed a broad emission spectrum in the visible region with the main emission peak at 450-500 nm and several small peaks situated between 400 and 620 nm. As the effect of the treatment under argon, besides the visible emission at 480-550 nm, a well resolved emission band appears in the near infrared region whose peak is present at 720 nm.

We assign the optical emission bands evidenced in the visible region to oxygen vacancy centers. The peak intensity varies as a function of duration and ambient of the treatment. The emission band at 450 nm was found to be sensitive to treatment in oxygen, while the emission band at 480 nm was highly sensitive to both duration of treatment in hydrogen and the hydrogen content.

The optical emission band situated in the near infrared region is associated with the presence of titanium ions. The treatments in hydrogen and oxygen determines the shift of the peak to 820 nm. The structure of polycrystalline TiO₂ and the growth phenomena of protrusions, terraces and polygonal structures on the polycrystal surfaces as a result of treatments under oxygen and hydrogen are discussed.

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