Structural, morphological and luminescence properties of nanocrystalline up-converting Y1.89Yb0.1Er0.01O3 phosphor particles synthesized through aerosol route

Nanocrystalline up-converting Y₂ O₃Yb³⁺ Er³⁺ phosphor particles were processed in a dispersed system-aerosol, generated ultrasonically at 1.3 MHz from common nitrate precursor solution having fixed ytterbium-to-erbium concentration ratio. The appropriate process parameters: residence time 21 s, carrier gas (air) flow rate 1.6 dm3/min, synthesis temperature 900 °C, led to the formation of un-agglomerated spherical nanostructured secondary particles, having mean particle size of approx 450 nm, composed of primary nanoscaled (20 nm) subunits. In order to reach targeting phase crystallinity, the as-prepared particles were additionally annealed at 1100 °C in air for 12, 24 and 48 h, respectively. Particle structure, morphology and purity were analyzed by X-ray powder diffraction (XRPD), scanning electron microscopy (FESEM/SEM), analytical and high resolution transmission electron microscopy (TEM/HRTEM) in combination with energy dispersive X-ray analysis and Fourier Transform Infrared Spectroscopy (FTIR). All samples crystallized in a cubic bixbyte-structure, space group Ia-3. The crystallite size changed with annealing time from 30 nm in as-prepared sample to 135 nm in sample annealed for 48 h, respectively. Emission spectra were assigned to the following trivalent erbium f–f electronic transitions: ²H₉/₂ → ⁴I₁₅/₂ (blue: 407–420 nm), (²H₁₁/₂̦ ⁴S₃/₂) → ⁴I₁₅/₂ (green: 510–590 nm), and ⁴F₉/₂ → ⁴I₁₅/₂ (red: 640–720 nm). The significant improvement of the emission decay times were observed after thermal treatment and this effect is correlated further with the structural and morphological particles characteristics. For the anneal-ing time of 12 h a quite high emission decay times were achieved (blue: 0.14 ms, green: 0.32 ms and red: 0.39 ms).This research is financially supported through the Project #172035 of the Ministry of Science and Education of the Republic of Serbia. OM especially acknowledge the University Carlos III, Madrid, Spain-Santander Bank Chairs of Excellence program and JSPS 2011/2012 fellowship, Japan.Publicad

Aerosol route as a feasible bottom-up chemical approach for up-converting phosphor particles processing

Proocedings of: Fourth Conference on the Characterization and Control of Interfaces for High Quality Advanced Materials. Kurashiki, Japan, 02-05 September 2012.The opportunities of the hot wall aerosol synthesis, i.e. conventional spray pyrolysis (CSP) method are demonstrated for the generation of highly spherical three-dimensional (3D) nanostructured phosphor particles with uniformly distributed components, phases and nano-clustered inner structure. With the presumption that certain particle morphology is formed during the evaporation/drying stage, the aerosol transport properties and powder generation are correlated with the particles structural and morphological features. With the help of various analyzing techniques like Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM) coupled with energy dispersive X-ray Analysis and STEM mode (TEM/EDS), X-ray Powder Diffraction (XRPD) and fluorescence measurements the feasible processing of up-conversion rare-earth Y2O3:Er, Yb phosphors powders are discussed.The financial support for this work is provided by the Ministry of Education, Science and Technological Development of the Republic of Serbia Project No. 172035 and JSPS fellowship, 2011/2012 (O.M.).Publicad

Palladium microfiber network as a platform for hydrogen sensing applications

In this study, we developed a hydrogen sensor based on a palladium microfiber network on a paper substrate. A 60-nm pure palladium film was deposited on photocopy paper using a vacuum evaporation technique. The photocopy paper was employed as the sensor substrate because of its low cost and the simple and rapid fabrication process. The texture of the microfiber network on the paper greatly increased the surface area to volume ratio for the palladium thin film, which is crucial for rapid response sensors. The experimental results showed that the hydrogen sensor exhibited a rapid response and linear gas response characteristics at room temperature and pressure. The gas response of the papersubstrate sensor was much higher compared with the glass substrate

Size effect of Au nanoparticles on TiO2 crystalline phase of nanocomposite thin films and their photocatalytic properties

This work focuses on the size effects of Au nanoparticles (AuNPs) on the TiO2 crystalline phase of nanocomposite AuNPs-embedded TiO 2 (Au-TiO2) thin films, their adsorption ability, and photocatalytic activity. Au-TiO2 films were synthesized through a sol-gel method using polyvinylpyrrolidone-protected AuNPs (AuNPs@PVP). The mean diameters of AuNPs@PVP dispersed in a sol solution were 2.0 ± 0.7 or 7.9 ± 3.1 nm and the heat-treatment temperature of the films was 400-900 °C. XRD and Ti L3,2-edge X-ray absorption near-edge structure (XANES) analysis revealed that AuNPs doping could suppress an anatase to rutile phase transformation. In addition, the larger size of AuNPs doped in TiO 2 film tended to prevent the transformation more effectively. The film doped with the smaller AuNPs@PVP and annealed at 500 °C showed the highest photocatalytic activity among the obtained films because it had the well-crystallized anatase phase and the high adsorption ability, which was attributed to the existence of a five-coordinated Ti site that was revealed from Ti K-edge XANES measurements