Studies of concentration dependences in the luminescence of Ti-doped Al2O3

Abstract

The variation of luminescence and excitation spectra of titanium doped Al2O3 for the concentration of Ti ranging from 10 to 1000 ppm was investigated using synchrotron radiation. In the lightly doped Al2O3–Ti (<100 ppm) samples we identified several emission bands. These are the emission of the excitons localized at Ti (290 nm), the emission due to F+ centers (325 nm), the band around 420 nm traditionally attributed to F center emission, and the luminescence of Ti3+ ions at 720 nm. The emphasis in this study is on the clarification of the nature of the blue emission band in the samples with high concentration of Ti (≥100 ppm), where the luminescence and excitation spectra of the blue emission exhibit noticeable variability. This is explained by a model of the luminescence process of Ti4+–F centers that includes the photoionization of Ti3+, the subsequent capture of electrons at F+-centers, formation of excited F-centers and, finally, the emission of a blue photon. The quenching of the blue emission with increasing Ti concentration is interpreted in terms of competition between oxygen vacancies and Ti4+ centers in the capture of the electron.