Cathodoluminescence and Crystal Growth of Sapphire

Even though the luminescence process in sapphire has been widely investigated, the relation between the presence of specific impurities such as titanium and iron, and the way the crystal grows up, is enlightened here thanks to the cathodoluminescence (CL) approach. The role of each impurity, taking into account its different valence states and the correlation between all the possible ions, i.e. Ti4+, Ti4+, Fe3+, and Fe2+ is tentatively explained: Ti4+ will act as a blue emitting centre, Ti3+ as a red one in a complex luminescence process, while Fe2+ will act as a quenching centre. Thus, the crystal growth process, Verneuil process, can be totally described as for the distribution of the impurities needed to generate the sapphires. Particularly, growth bands find an explanation regarding these distributions of iron and titanium in their different valence states.