Photoluminescence and thermoluminescence of titanium ions in sapphire crystals

Abstract Several titanium species (Ti 3+ , Ti 4+ , Ti 4+ -V Al clusters) were identified in sapphire samples from their optical spectra. In highly reduced samples, we observed only Ti 3+ centres while oxidized samples contain Ti 3+ and Ti 4+ ions as well. The formation of Ti 4+ ions occurs simultaneously with the formation of aluminium-vacancies which are charge compensators for Ti 4+ ions and act as hole traps in charge exchange process. We could observe locally and non-locally compensated Ti 4+ as well. It is shown that Ti 3+ is a deep hole trap while Ti 4+ is a deep electron trap. In the TL process they act as recombination centers for electrons and holes, respectively. However, in TL we observed only the emission of locally compensated Ti 4+ , probably because of spatial correlation.