E. C. Paris

Photoluminescence of disordered ABO3 perovskites

Intense photoluminescence in highly disordered (amorphous) BaTiO3, PbTiO3, and SrTiO3 prepared by the polymeric precursor method was observed at room temperature. The emission band maxima from the three materials are in the visible region and depend on the exciting wavelength. The origin of the photoluminescence was not exactly identified. However, the line shape indicates that confinement effects are not probable. The experimental results indicate that it could be related to the disordered perovskite structure.

Amorphous lead titanate: a new wide-band gap semiconductor with photoluminescence at room temperature

This paper describes a new amorphous wide-band gap semiconductor with photoluminescence (PL) at room temperature. The amorphous PbTiO3 was prepared by a sol–gel-like process in powder and thin film form. The optical property and the PL behaviour showed a direct relation to the amorphous structure. The PL peak energy can be controlled by the change of the exciting surge energy. Copyright

Synthesis of PbTiO3 by use of polymeric precursors

Lead titanate powders were synthesized through the use of polymeric precursors according to the Pechini Process. The polymeric precursor was calcined at temperatures ranging from 300 to 600°C for 1 or 2 h. X-ray diffraction (XRD) showed that lead titanate crystallizes from the precursor at temperatures as low as 400°C. No intermediate carbonate phase was detected by Fourier transform infrared spectroscopy (FTIR) or by XRD. A powder with mean particle size of 150 nm was obtained after calcination of the precursor at 600°C for 1 h.

Photoluminescent behavior of SrBi2Nb2O9 powders explained by means of β-Bi2O3 phase

Photoluminescence (PL) behavior of SrBi2Nb2O9 (SBN) powders was explained by means of β-Bi2O3 phase on the SBN lattice. Oxygen vacancies and recombination of electrons holes in the valence band lead to the formation of [NbO5∙VOx], [NbO5∙VO•] and [NbO5∙VO••] complex clusters which are the main reason for the PL at room temperature. X-ray diffraction and Fourier transform Raman spectroscopy were used as tools to investigate the structural changes in SBN lattice allowing to correlate [NbO5∙VO•]∕[NbO6]′ ratio with the evolution of the visible PL emission in the SBN powders.

The origin of photoluminescence in amorphous lead titanate

We discuss the nature of visible photoluminescence at room temperature in amorphous lead titanate in the light of the results of recent experimental and theoretical calculations. Experimental results obtained by XANES and EXAFS revealed that amorphous lead titanate is composed of a Ti-O network having fivefold Ti coordination and NBO-type (non-bridging oxygen) defects. These defects can modify the electronic structure of amorphous compounds. Our calculation of the electronic structure involved the use of first-principle molecular calculations to simulate the variation of the electronic structure in the lead titanate crystalline phase, which is known to have a direct band gap, and we also made an in-depth examination of amorphous lead titanate. The results of our theoretical calculations of amorphous lead titanate indicate that the formation of fivefold coordination in the amorphous system may introduce delocalized electronic levels in the HOMO (highest occupied molecular orbital) and the LUMO (lowest unoccupied molecular orbital). A comparison of the experimental and theoretical results of amorphous compounds suggests the possibility of a radiative recombination (electron-hole pairs), which may be responsible for the emission of photoluminescence.

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.