M. F. C. Gurgel

Structural conditions that leads to photoluminescence emission in SrTiO3: An experimental and theoretical approach

Complex cluster [TiO5⋅VOz] and [SrO11⋅VOz] (where VOz=VOX, VO•, VO••) vacancies were identified in disordered SrTiO3 powders prepared by the polymeric precursor method, based on experimental measurements by x-ray absorption near edge structure spectroscopy. The paramagnetic complex states of [TiO5⋅VO•] and [SrO11⋅VO•] with unpaired electrons were confirmed by electron paramagnetic resonance spectroscopy. The disordered powders showed strong photoluminescence at room temperature. Structural defects of disordered powders, in terms of band diagram, density of states, and electronic charges, were interpreted using high-level quantum mechanical calculations in the density functional framework. The four periodic models used here were consistent with the experimental data and explained the presence of photoluminescence.

Intense visible photoluminescence in Ba(Zr0.25Ti0.75)O3 thin films

Photoluminescence at room temperature in Ba(Zr0.25Ti0.75)O3 thin films was explained by the degree of structural order-disorder. Ultraviolet-visible absorption spectroscopy, photoluminescence, and first principles quantum mechanical measurements were performed. The film annealed at 400°C for 4h presents intense visible photoluminescence behavior at room temperature. The increase of temperature and annealing time creates [ZrO6]–[TiO6] clusters in the lattice leading to the trapping of electrons and holes. Thus, [ZrO5]–[TiO6]∕[ZrO6]–[TiO6] clusters were the main reason for the photoluminescence behavior.

Photoluminescence in disordered sm-doped PbTiO3: Experimental and theoretical approach

Sm-doped PbTiO3 powder was synthesized by the polymeric precursor method, and was heat treated at different temperatures. The x-ray diffraction, photoluminescence, and UV-visible were used as a probe for the structural order degree short-, intermediate-, and long-range orders. Sm3+ ions were used as markers of these order-disorder transformations in the PbTiO3 system. From the Rietveld refinement of the Sm-doped PbTiO3 x-ray diffraction data, structural models were obtained and analyzed by periodic ab initio quantum mechanical calculations using the CRYSTAL 98 package within the framework of density functional theory at the B3LYP level. This program can yield important information regarding the structural and electronic properties of crystalline and disordered structures. The experimental and theoretical results indicate the presence of the localized states in the band gap, due to the symmetry break, which is responsible for visible photoluminescence at room temperature in the disordered structure.