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Sm 3+ doped SiO 2 -Gd 2 O 3 composites were obtained by a sol-gel process, and the ideal percentage of Sm 3+ was evaluated for bioimaging applications. By XRD, a formation of Gd 2 O 3 cubic materials was observed, and TEM shows that Gd 2 O 3 particles are dispersed in a SiO 2 lattice. PLE spectra confirm the main absorption bands in the UV region and emission shows the most efficient excitation at 275 nm. PL results reveal the incorporation of Sm 3+ in Gd 2 O 3 structures and lead to the understanding of the efficient energy transfer between Gd 3+ and Sm 3+ in the materials. The mechanism is proposed and discussed. CIE plotting shows color coordinates in the orange and red regions, mainly dependent on the excitation source. Sm 3+ positions in Gd 2 O 3 are discussed using the results obtained in the emission spectra. Materials presented high lifetime values, between 1.53 and 1.82 ms. The phosphors show tunability properties and better performance as red phosphors when excited at 275 nm. Cell viability was performed and the material is non-toxic. The materials were evaluated as biological markers, and present fluorescence under rhodamine emission filters. SiO 2 -Gd 2 O 3 :Sm 3+ demonstrates a good viability index and co-localizes with membrane cell markers, showing a promising material for cell tracking. The material also demonstrates potential for cancer targeting.

This paper presents an evaluation of photoluminescent and structural properties of Eu 3+ -doped TiO 2 materials in powder form prepared by sol–gel process. The increase of heat-treatment temperature of synthesis results in the TiO 2 phase transition, obtaining anatase, rutile and sometimes brookite, examined by Raman and XRD techniques. Crystallite size as well as microstrains in the crystal structure were evaluated as a function of Eu 3+ and heat-treatment temperature. It was found that when Eu 3+ is introduced in anatase phase an intense color emission is observed under excitation at 394 and 463 nm. The rutile phase presents inversion center symmetry, and apparently the Eu 3+ tends to occupy this site, which decreases the intensity of the emission assigned to the 5 D 0 → 7 F 2 transition. The materials obtained at 700 °C showed most intensity of emission in the red region, verified by the ratio between 5 D 0 → 7 F 2 / 5 D 0 → 7 F 1 transitions of Eu 3+ . The results showed that the materials are interesting absorber in the ultraviolet and red region and can be used for improvement of energy conversion in solar cells devices.

Herein we report on the crystallized nanoparticles based on Eu 3+ -doped Y 2 O 3 with 5 mol% using citric acid as precursor. The heating temperatures were evaluated in order to obtain the best crystallized nanoparticles with size around 12 nm and with highest red intense photoluminescence emission. Nanocrystallite size was calculated by Scherrer׳s equation based on diffractogram of the material heated at 750 °C for 4 h, obtaining size around 8 nm. The low photoluminescence intense emissions were attributed to the presence of quenchers remaining from precursors used in the synthesis. In general the photoluminescence properties were evaluated based on emission and excitation spectra profile. Rietveld refinement was performed based on the diffractogram of the material annealed at 750 °C for 4 h, and the visualization of the cubic structure was obtained. The centered cubic crystalline structure of Y 2 O 3 was obtained and the photoluminescence properties of Eu 3+ ion in Y 2 O 3 host lattice was verified as being dependent on the temperature of heating and C 2 and S 6 site of symmetry present in the cubic structure. CIE chromaticity diagram was obtained with x and y being 0.682 and 0.316, respectively, for material with the highest relative photoluminescence intensity.

The preparation of Y2O3 doped with different amounts of Eu 3 þ ions obtained via a precipitation method using oxalic acid as precursor is reported here. The precursors were calcined at different temperatures to obtain the polycrystalline ceramic materials in order to verify the influence of temperature on the photoluminescence emission properties of the materials. The efficient incorporation of Eu 3 þ ions in Y2O3 host matrix was verified by X-ray diffraction. Based on the diffractograms obtained, using Scherrer’s equation the increase of the crystallite size as a function of annealing temperature was verified. All materials obtained showed intense photoluminescence emission in the red region ( � 611.5 nm), assigned to the f–f intraconfigurational transition of the Eu 3 þ ions. The CIE chromaticity diagrams were built based on the photoluminescence emission spectra with X and Y coordinates being 0.672 and 0.325, respectively, indicating the pure color emission of the material. The materials obtained are excellent absorbers in the UV–vis region (bellow 250, around � 394 and � 463 nm) with intense emission in the red region (� 611.5 nm). Two lifetime values are observed indicating that the Eu 3 þ ions are located in at least two sites of symmetry, C2 and S6. The lifetime values obtained are on the order of ms, being relatively long and interesting for contribution to solar cell efficiency improvement. The fact that these materials absorb ultraviolet radiation very well, resulting in intense emission in the red region, make them excellent candidates to for applications in solar cells. & 2014 Elsevier Ltd and Techna Group S.r.l All rights reserved.

Ceramic matrix composites (CMCs) were prepared from a polysiloxane network filled with rice husk ash (RHA), a reactive filler. CMCs were obtained by pyrolysis at 1000 and 1600 °C of green bodies prepared from a mixture of polysiloxane network and RHA at a weight ratio of 4:1, respectively. The RHA and the CMCs were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), in addition to density and mechanical measurements. The CMCs were obtained without macroscopic defects, and their initial observed porosity was reduced by polymeric infiltrations cycles of the polymeric precursor, which improved their flexural strength and modulus up to 100%.