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.

Perovskite structures have attracted scientific interest as a promising alternative for water treatment due to their unique structural, high oxidation activity, electronic stability, and optical properties. In addition, the photocatalytic activity of perovskite structures is higher than that of many transition metal compounds. A critical property that determines the high-performance photocatalytic and optical properties is the band gap, lifetime of carrier charge, and band edges relative to the redox potential. Thus, the synthesis/processing and study of the effect on the band gap, lifetime of carrier charge, and band edges relative to the redox potential in the development of high-performance photocatalysts for water treatment are critical. This review presents the basic physical principles of optical band gaps, their band gap tunability, potentials, and limitations in the applications for the water treatment. Furthermore, it reports recent advances in the synthesis process and comparatively examines the band gap effect in the photocatalytic response. In addition to the synthesis, the physical mechanisms associated with the change in the band gap have been discussed. Finally, the conclusions of this review, along with the current challenges of perovskites for photocatalysis, are presented.

Photoluminescence in perovskites can be tuned by varying the CH₂/CH₃ratio controlled by thermal treatment. Thus, organic molecules alter the electronic structure and facilitate the energy transfer from the inorganic to the organic part.

Time-resolved fluorescence spectroscopy (TRFS) is a new tool that can be used to investigate processes of interaction between metal ions and organic matter (OM) in soils, providing a specific analysis of the structure and dynamics of macromolecules. To the best of our knowledge, there are no studies in the literature reporting the use of this technique applied to whole/non-fractionated soil samples, making it a potential method for use in future studies. This work describes the use of TRFS to evaluate the fluorescence lifetimes of OM of whole soils from the Amazon region. Analysis was made of pellets of soils from an oxisol–spodosol system, collected in São Gabriel da Cachoeira (Amazonas, Brazil). The fluorescence lifetimes in the oxisol–spodosol system were attributed to two different fluorophores. One was related to complexation of an OM fraction with metals, resulting in a shorter fluorophore lifetime. A short fluorescence lifetime (2–12 ns) could be associated with simpler structures of the OM, while a long lifetime (19–66 ns) was associated with more complex OM structures. This new TRFS technique for analysis of the fluorescence lifetime in whole soil samples complies with the principles of green chemistry.