Understanding the electronic properties of BaTiO3 and Er3+ doped BaTiO3 films through confocal scanning microscopy and XPS: the role of oxygen vacancies.

Photonic and electronic properties exist inherently in ferroelectric barium titanate (BaTiO₃); severe luminescence quenching also exists due to the insufficient confinement of excitons. In this sense, high optical emission can only be achieved by its chemical and structural modification. Thin BaTiO₃ and Er:BaTiO₃ films were grown by the spin coating method on a glass substrate at room temperature. Self-trapping of excitons in the thin BaTiO₃ film and its structural modification due to the doping with Er³⁺ ions (Er:BaTiO₃) are verified using scanning confocal fluorescence microscopy (SCFM), where self-trapping excitons never occured in its pure state. By thermal treatment and doping (BaTiO₃ and Er:BaTiO₃) we obtained localization of the excitons, which would further induce lattice strain around the surface defects, to accommodate the self-trapped excitons. With such a self-trapped state, the structure of BaTiO₃ generates broadband emission of several overlapping bands between 1.95 and 2.65 eV at room temperature, while the structure Er:BaTiO₃ showed defined emission bands at 2.24 and 2.35 eV, with very weak contributions of the emission due to the self-trapping state. The influence of the variation of the excitation wavelength using 1PE and 2PE on the emission bands of BaTiO₃ and Er:BaTiO₃ is also investigated. The results of enhanced emission bands suggest a clear dependence of the emission intensity on the excitation energy, where a ∼3 fold enhancement in emission has been demonstrated under Er³⁺ (1.55 eV) excitation, which can be attributed to effective energy transfer between the Er³⁺ ions. As a result, it is concluded that the developed BaTiO₃ and Er:BaTiO₃ can pave the way for future photonic devices. [ABSTRACT FROM AUTHOR]