Luminescence in undoped and Nb-doped SrTiO3 crystals: Bulk and surface emission

The luminescence of SrTiO3 depends on the sample type, either doped or stoichiometric, as grown or treated, the excitation conditions, and temperature. The origin of the luminescence emissions, blue, green, and infrared, remains controversial. In particular, the role played by defects, mainly oxygen vacancies, impurities, and selftrapped holes and electrons on the different emissions are far to be elucidated. We present a cathodoluminescence (CL) and photoluminescence (PL) study of undoped and Nb-doped samples. The different excitation conditions of CL and PL permit to distinguish the luminescence emission from the bulk (CL) and from a surface skin region (PL). Significant differences between both techniques are seen for the undoped sample, while the Nb-doped sample presents less differences, highlighting the role played by the surface defects and the doped electrons. The study is complemented by the temperature dependence of the luminescence spectra and the emission due to defects generated by plastic deformation.

Automated summary

The luminescence of SrTiO3 is influenced by factors such as sample type, excitation conditions, and temperature, with the role of different defects on emissions still under debate. Studying undoped and Nb-doped samples through cathodoluminescence and photoluminescence can distinguish emission from bulk and surface regions, revealing the importance of surface defects and doped electrons in luminescence.