Photochromic effect in titanium-doped synthetic sapphire

This study investigates the photochromic behavior of titanium-doped sapphire (Al2O3:Ti4+). The material exhibits reversible photochromism: exposure to light with wavelengths shorter than 290 nm induces a brown coloration, while wavelengths longer than 290 nm restore the sample to colorless. The photochromic color is stable at room temperature but becomes unstable above 150 °C. In situ absorption and photoluminescence spectroscopy were employed to examine the underlying mechanism. The experimental results support the model that the brown coloration arises from electron holes trapped next to cation vacancies. These findings provide more detailed insights into the electron reactions of the photochromic centers in Ti-doped sapphire.