Structural evolution of Eu-doped hydroxyapatite nanorods monitored by photoluminescence emission

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Strong violet-blue light photoluminescence emission at room temperature in SrZrO3: Joint experimental and theoretical study

Ultrafine ordered and disordered SrZrO3 powders were prepared by the polymeric precursor method. The structural evolution from structural disorder to order was monitored by X-ray diffraction and X-ray absorption near-edge spectroscopy. Complex cluster vacancies [ZrO5 center dot V-O(Z)] and [SrOII center dot V-O(Z)] (where V-O(Z) = V-O(X), V-O(center dot) and V-O(center dot center dot)) were proposed for disordered powders. The intense violet-blue light photoluminescence emission measured at room temperature in the disordered powders was attributed to complex cluster vacancies. High-level quantum mechanical calculations within the density functional theory framework were used to interpret the experimental results. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Interfacial photoluminescence emission properties of core/shell Al2O3/ZrO2

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

First principles calculations on the origin of violet-blue and green light photoluminescence emission in SrZrO3 and SrTiO3 perovskites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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

Complex cluster [TiO5 center dot V-O(z)] and [SrO11 center dot V-O(z)] (where V-O(z)=V-O(X), V-O(center dot), V-O(center dot center dot)) 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 center dot V-O(center dot)] and [SrO11 center dot V-O(center dot)] 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. (C) 2008 American Institute of Physics.

Intense photoluminescence emission at room temperature in calcium copper titanate powders

A study was undertaken about the structural and photoluminescent properties at room temperature of CaCu3Ti4O12 (CCTO) powders synthesized by a soft chemical method and heat treated between 300 and 800 °C. The decomposition of precursor powder was followed by thermogravimetric analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman) and photoluminescence (PL) measurements. XRD analyses revealed that the powders annealed at 800 °C are becoming ordered and crystallize in the cubic structure. The most intense PL emission was obtained for the sample calcined at 700 °C, which is not highly disordered (300-500 °C) and neither completely ordered (800 °C). From the spectrum it is clearly visible that the lowest wavelength peak is placed around 480 nm and the highest wavelength peak at about 590 nm. The UV/vis absorption spectroscopy measurements showed the presence of intermediate energy levels in the band gap of structurally disordered powders. © 2012 Elsevier Ltd and Techna Group S.r.l.

Red shift and higher photoluminescence emission of CCTO thin films undergoing pressure treatment

CCTO thin films were deposited on Pt(1 1 1)/Ti/SiO2/Si substrates using a chemical (polymeric precursor) and pressure method. Pressure effects on CCTO thin films were evaluated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and optical properties which revealed that a pressure film (PF) is denser and more homogeneous than a chemical film (CF). Pressure also causes a decrease in the band gap and an increase in the photoluminescence (PL) emission of CCTO films which suggests that the pressure facilitates the displacement of Ti in the titanate clusters and the charge transference from TiO6 to [TiO5V0z], [TiO5V0z] to [CaO11V0z] and [TiO5V0z] to [CuO4]x. © 2013 Elsevier B.V. All rights reserved.

Photoluminescence emission at room temperature in zinc oxide nano-columns

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Spherical-shaped Y2O3:Eu3+ nanoparticles with intense photoluminescence emission

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Very Intense Distinct Blue and Red Photoluminescence Emission in MgTiO 3 Thin Films Prepared by the Polymeric Precursor Method: An Experimental and Theoretical Approach

MgTiO3 (MTO) thin films were prepared by the polymeric precursor method with posterior spin-coating deposition. The films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates and heat treated at 350 °C for 2 h and then heat treated at 400, 450, 500, 550, 600, 650 and 700 °C for 2 h. The degree of structural order−disorder, optical properties, and morphology of the MTO thin films were investigated by X-ray diffraction (XRD), micro-Raman spectroscopy (MR), ultraviolet− visible (UV−vis) absorption spectroscopy, photoluminescence (PL) measurements, and field-emission gun scanning electron microscopy (FEG-SEM) to investigate the morphology. XRD revealed that an increase in the annealing temperature resulted in a structural organization of MTO thin films. First-principles quantum mechanical calculations based on density functional theory (B3LYP level) were employed to study the electronic structure of ordered and disordered asymmetric models. The electronic properties were analyzed, and the relevance of the present theoretical and experimental results was discussed in the light of PL behavior. The presence of localized electronic levels and a charge gradient in the band gap due to a break in the symmetry are responsible for the PL in disordered MTO lattice.

A large red-shift in the photoluminescence emission of Mg1-xSrxTiO3

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effect of pressure-assisted heat treatment on photoluminescence emission of α-Bi2O3 needles

Materials with high photoluminescence (PL) intensity can potentially be used in optical and electronic devices. Although the PL properties of bismuth(III) oxide with a monoclinic crystal structure (α-Bi2O3) have been explored in the past few years, methods of increasing PL emission intensity and information relating PL emission to structural defects are scarce. This research evaluated the effect of a pressure-assisted heat treatment (PAHT) on the PL properties of α-Bi2O3 with a needlelike morphology, which was synthesized via a microwave-assisted hydrothermal (MAH) method. PAHT caused an angular increase between the [BiO6]-[BiO6] clusters of α-Bi2O3, resulting in a significant increase in the PL emission intensity. The Raman and XPS spectra also showed that the α-Bi2O3 PL emissions in the low-energy region (below ∼2.1 eV) are attributed to oxygen vacancies that form defect donor states. The experimental results are in good agreement with first-principles total-energy calculations that were carried out within periodic density functional theory (DFT).

Structural evolution of Eu-doped hydroxyapatite nanorods monitored by photoluminescence emission

This paper reports the synthesis of Eu-doped hydroxyapatite (HA:Eu) resulting in particles with nanorod diameters from 9 to 26 nm using the microwave hydrothermal method (HTMW). Eu3+ ions were used as a marker in the HA network by basic hydrolysis followed by the HTMW treatment. The crystalline HA:Eu nanorod nature in a short-range order was detected by photoluminescence (PL) measurements from Eu3+ emission into the HA matrix. Thus, was possible to verify that HA crystallization is favored in a short structural order when the HTMW treatment time was increased from 0 to 40 min and that the Eu3+ substitution in the HA lattice is site-selective. (C) 2012 Elsevier B.V. All rights reserved.

Structural XANES characterization of Ca0.99Sm0.01TiO3 perovskite and correlation with photoluminescence emission

In this work, CaTiO3:Sm (CT:Sm) were prepared by a soft chemical processing at different annealing temperatures starting with a disordered structure and reaching an ordered one, with the propose to understand the relationship between structural order-disorder and photoluminescence emission. The samples were characterized by titanium K-edge, Titanium L-II and L-III-edge XANES, electron paramagnetic resonance (EPR) and photoluminescence (PL) measurements. XANES results clearly point the presence of local distortion in [TiO6] octahedral clusters until the crystallization was completed. The interactions of the network clusters that form the CT:Sm structures provides favorable structural and electronic conditions for the appearance of PL phenomena. (C) 2012 Published by Elsevier B.V.

Very Intense Distinct Blue and Red Photoluminescence Emission in MgTiO3 Thin Films Prepared by the Polymeric Precursor Method: An Experimental and Theoretical Approach

MgTiO3 (MTO) thin films were prepared by the polymeric precursor method with posterior spin-coating deposition. The films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates and heat treated at 350 degrees C for 2 h and then heat treated at 400, 450, 500, 550, 600, 650 and 700 C for 2 h. The degree of structural order disorder, optical properties, and morphology of the MTO thin films were investigated by X-ray diffraction (XRD), micro-Raman spectroscopy (MR), ultraviolet-visible (UV-vis) absorption spectroscopy, photoluminescence (PL) measurements, and field-emission gun scanning electron microscopy (FEG-SEM) to investigate the morphology. XRD revealed that an increase in the annealing temperature resulted in a structural organization of MTO thin films. First-principles quantum mechanical calculations based on density functional theory (B3LYP level) were employed to study the electronic structure of ordered and disordered asymmetric models. The electronic properties were analyzed, and the relevance of the present theoretical and experimental results was discussed in the light of PL behavior. The presence of localized electronic levels and a charge gradient in the band gap due to a break in the symmetry are responsible for the PL in disordered MTO lattice.