Rutile is the most common TiO 2 mineral with extensive application in the field of optical materials, and trivalent cations can significantly substitute Ti 4+ with charge balanced by protonation. Several M 3+ -doped (M = Al, Ni, Co, Cr, Ga, Fe, and Mn) rutile samples were synthesized at 3 GPa (gigapascal) and 1273 K. The MO 6 -octahedral distortion model provides a reasonable explanation for the order of the M 3+ concentrations. The total Cr 3+ concentration was measured to be as high as 6.8 at % (atomic percentage) since the Cr 3+ O 6 distortion is very close to that of Ti 4+ O 6 . This high Cr content significantly affects the Ti−O bonds and the lattice vibrations, and a quarter of the doped Al 3+ and Cr 3+ populations are identified in the interstitial sites. The M 3+ effect on OH-stretching vibration was investigated by Fourier transform infrared (FTIR) spectra, which is useful for studying hydration mechanism in natural rutile samples with complex cationic substitutions. Besides, the doped-M 3+ effect on the optical properties, including absorption, loss function, reflectivity, and refractive index, was studied by theoretical calculation. Incorporation of transition metal cations, especially Mn 3+ , significantly improves its optical performance in the visible light region, which is also confirmed by micro ultraviolet−visible−near infrared (UV−vis−NIR) spectra.

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