Crystal Structure, Vibrational Spectra on Trivalent-Cation-Doped Rutile and Application in Optical Materials

Abstract

Rutile is the most common TiO2 mineral with extensive application in the field of optical materials, and trivalent cations can significantly substitute Ti4+ with charge balanced by protonation. Several M3+-doped (M = Al, Ni, Co, Cr, Ga, Fe, and Mn) rutile samples were synthesized at 3 GPa (gigapascal) and 1273 K. The MO6-octahedral distortion model provides a reasonable explanation for the order of the M3+ concentrations. The total Cr3+ concentration was measured to be as high as 6.8 at % (atomic percentage) since the Cr3+O6 distortion is very close to that of Ti4+O6. This high Cr content significantly affects the Ti–O bonds and the lattice vibrations, and a quarter of the doped Al3+ and Cr3+ populations are identified in the interstitial sites. The M3+ 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-M3+ effect on the optical properties, including absorption, loss function, reflectivity, and refractive index, was studied by theoretical calculation. Incorporation of transition metal cations, especially Mn3+, significantly improves its optical performance in the visible light region, which is also confirmed by micro ultraviolet–visible–near infrared (UV–vis–NIR) spectra.