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Correlation between Cr3+ Luminescence and Oxygen Vacancy Disorder in Strontium Titanate under MeV Ion Irradiation

Crespillo, M. L., Graham, J. T., Agulló-López, F., Zhang, Y., Weber, W. J.
The Journal of Physical Chemistry C 2017 v.121 no.36 pp. 19758-19766
ambient temperature, cations, chromium, electrons, guidelines, irradiation, luminescence, models, oxidation, oxides, oxygen, photocatalysis, physical chemistry, physicochemical properties, protons, strontium, trapping
Strontium titanate (SrTiO₃), a model system with a strongly correlated electronic structure, has attracted much attention recently because of its outstanding physicochemical properties and considerable potentials for technological applications. The capability to control oxygen vacancy profiles and their effect on valence states of cations will increase significantly the functionality of devices based on transition metal oxides. This work presents new insights into the near-infrared luminescence emission of Cr³⁺ centers in stoichiometric SrTiO₃ induced using 3 MeV protons at temperatures of 100 K, 170 K, and room temperature. The study covers a wide spectral range, including near-infrared, visible, and near-UV regions. Our main purpose is to investigate the role of the oxygen vacancies introduced by energetic charged particles on the shape and yield of induced luminescence spectra, in particular to explore the interplay between the Cr³⁺ luminescence at 1.55 eV and oxygen disorder. A clear correlation is found between the decay of the Cr luminescence yield during irradiation and the growth of a band at 2.0 eV, well-resolved below 170 K, which has been very recently attributed to d–d transitions of electrons self-trapped as Ti³⁺ in the close vicinity of oxygen vacancies. This correlation suggests irradiation-induced oxidation of the Cr³⁺ (Cr³⁺ → Crⁿ⁺, n > 3) via trapping of irradiation-induced holes, while the partner electrons are self-trapped as Ti³⁺. These new results provide effective guidelines for further understanding the electronic and photocatalytic behavior of STO:Cr³⁺.