Preparation and Optical Properties of Trivalent Erbium-Doped CaY2O4 Powders Under 980 nm Excitation.

Nanocrystalline CaY2O4:Er3+ up-conversion phosphor was prepared by the sol-gel process. A homogeneous precursor sol was heated on a hot plate and then coagulated gel was prefired at 300 °C for 4 hr in Ar, followed by final annealing at 1,200 °C for 4 h in Ar. The crystallinity of the powders after annealing was confirmed using an X-ray diffraction analysis. The shape and particle size of the powders were observed by field emission-scanning electron microscope and transmission electron microscope. Up-conversion luminescence spectra were recorded with a fluorescent spectrophotometer under a 980-nm excitation. The dependence of the up-converted intensities on pumping powers for powders was obtained by changing the excitation powers at room temperature. X-ray diffraction patterns confirmed the presence of single orthorhombic crystalline CaY2O4 and no impurity peaks were identified. Micrographical images of 3 mol%-doped CaY2O4 powder indicates that the particle size is uniform, and ranges from 100~200 nm. Up-conversion efficiency is the highest when the doping concentration of Er3+ is 3 mol%.

Up-Conversion Photoluminescence of Sol-Gel Derived CaY2O4 Powders Under 980 nm Excitation.

Up-conversion is an anti-stokes process that can convert near-infrared light into visible light. Besides the requirement of high optical conversion efficiency, the thermochemical stability of the host materials is critical for in practical applications, and a stable oxide host material is optimal. CaY2O4 follows the same ordered structure of CaFe2O4, which is composed of an (R2O4)2- (R = rare earth metal) framework of double octahedral moieties with rare earth ions residing within the framework. CaY2O4 is a promising host material due to its favorable characteristics such as high chemical and thermal stability, low-phonon energy, and environment friendliness. Rare earth ion (Er3+ and Yb3+)-doped nano-crystalline phosphors were prepared by a sol-gel process. The synthesized sample was characterized by X-ray diffraction analysis and the crystallite size was confirmed by Scherrer's formula and transmission electron microscopy. The surface morphology of the powders was determined by scanning electron microscopy. X-ray diffraction patterns confirmed their pure orthorhombic structure after annealing at 1,200 °C and the morphology of particles was found to be a nearly spherical shape with a diameter of the order of ~100 nm. Photoluminescence properties of the powders were measured by exciting the samples with a 980 nm diode laser at room temperature. Under the 980-nm laser excitation, the green and red up-conversion emissions were observed at around 520- 540 nm, 540-570 nm and 640-680 nm, which, are attributed to the transitions of ²H11/2 →4I15/2, 4S3/2 →4I15/2 and 4F9/2 →4I15/2 of Er3+ ions, respectively. The up-conversion intensity as a function of laser power shows that the up-conversion mechanism corresponding to green and red emissions occurs via a two-photon process.

Fabrication of Up-Conversion Phosphor Films on Flexible Substrates Using a Nanostructured Organo-Silicon.

Up-conversion phosphors have attracted considerable attention because of their applications in solid-state lasers, optical communications, flat-panel displays, photovoltaic cells, and biological labels. Among them, NaYF4 is reported as one of the most efficient hosts for infrared to visible photon up-conversion of Yb3+ and Er3+ ions. However, a low-temperature method is required for industrial scale fabrication of photonic and optoelectronic devices on flexible organic substrates. In this study, hexagonal ß-NaYF4: 3 mol% Yb3+, 3 mol% Er3+ up-conversion phosphor using Ca2+ was prepared by chemical solution method. Then, we synthesized a nanostructured organo-silicon compound from methyl tri-methoxysilane and 3-glycidoxy-propyl-trimethoxy-silane. The transmittance of the organo-silicon compound was found to be over 90% in the wavelength range of 400~1500 nm. Then we prepared a fluoride-based phosphor paste by mixing the organo-silicon compound with Na(Ca)YF4:Yb3+, Er3+. Subsequently, this paste was coated on polyethylene terephthalate, followed by heat-treatment at 120 °C. The visible emission of the infrared detection card was found to be at 655 nm and 661 nm an excitation wavelength of 980 nm.

Effects of partial middle turbinectomy with varying resection volume and location on nasal functions and airflow characteristics by CFD.

The surgical term "turbinectomy" encompasses many variations in the location and extent of removal. As a systemic approach to consider the negative impact of middle turbinectomy(MT), such as the excessive removal of turbinate, airflows inside a pre-surgery model and a series of virtual surgery models were numerically analyzed and compared. These models simulate three variations of partial MT(three bilateral and three unilateral) with varying resection volume and location. Each middle turbinectomy results in alterations of flow and thermal parameters, such as nasal resistance (NR), velocity, temperature, wall shear stress(WSS) and wall heat transfer(WHT). WSS distributions were also considered in connection with mucosal secretion. The tendency of changes in nasal functions and airflow characteristics was identified with respect to resection volume and location. A counter-rotating vortical structure was seen in the region of widened middle airway for the case of total resection of middle turbinate. Maximum velocity and WSS near sphenopalatine ganglion, which was a possible explanation for headache after total resection of middle turbinate, was increased. Changes in NR and WHT for bi-lateral resection cases were greater than those for unilateral resection cases. While the physiological changes in four partial MT models were insignificant, changes in near total resection model was prominent. Although our surgical simulation was done for a single case, we postulate that the removal of the anterior inferior part of middle turbinate while preserving posterior margin will not alter airflow characteristics extensively. These findings will help designing surgical plans for partial MT.

Morphologic factors of biliary trees are associated with gallstone-related biliary events.

AIM: To determine the risk factors for gallstone-related biliary events. METHODS: This retrospective cohort study evaluated magnetic resonance cholangiopancreatography images from 141 symptomatic and 39 asymptomatic gallstone patients who presented at a single tertiary hospital between January 2005 and December 2012. RESULTS: Logistic regression analysis showed significant differences between symptomatic and asymptomatic patients with gallstones in relation to the number of gallstones, the angle between the long axis of the gallbladder and the cystic duct, and the cystic duct diameter. Multivariate analysis showed that the number of gallstones (OR = 1.27, 95%CI: 1.03-1.57; P = 0.026), the angle between the long axis of the gallbladder and the cystic duct (OR = 1.02, 95%CI: 1.00-1.03; P = 0.015), and the diameter of the cystic duct (OR = 0.819, 95%CI: 0.69-0.97; P = 0.018) were significantly associated with biliary events. The incidence of biliary events was significantly elevated in patients who had the presence of more than two gallstones, an angle of > 92° between the gallbladder and the cystic duct, and a cystic duct diameter < 6 mm. CONCLUSION: These findings will help guide the treatment of patients with asymptomatic gallstones. Clinicians should closely monitor patients with asymptomatic gallstones who exhibit these characteristics.

Epitaxially-Grown Europium-Doped Barium Titanate Films on Various Substrates for Red Emission.

Intense red photoluminescence under ultraviolet excitation was observed in epitaxially-grown europium-doped perovskite BaTiO3 thin films deposited on the SrTiO3 (100), MgO (100) and sapphire (0001) substrates using metal carboxylate complexes. Precursor films prepared by spin coating were pyrolyzed at 250 °C for 120 min in argon, followed by final annealing at 850 °C for 60 min in argon. Crystallinity and epitaxy of the films were analyzed by X-ray diffraction θ-2θ scan and pole-figure analysis. Photoluminescence of the thin films at room temperature under 254 nm was confirmed by a fluorescent spectrophotometer. The obtained epitaxial BaTiO3 thin films on the SrTiO3 (100) and MgO (100) substrates show an intense red-emission lines at 615 nm corresponding to the (5)D0 --> (7)F2 transitions on Eu(3+) with broad bands at 595 and 650 nm.

Hydroxyapatite forming ability of electrostatic spray pyrolysis derived calcium phosphate nano powder.

A novel fabrication technique, i.e., electrostatic spray pyrolysis (ESP), has been used in this study to prepare calcium phosphate nano powders. Final annealing was done at 400 degrees C for 30 min in air. The hydroxyapatite-forming ability of the annealed powder has been investigated in Eagle's minimum essential medium solution. X-ray diffracton, field emission scanning electron microscope, energy dispersive X-ray spectroscope, and Fourier transform infrared spectroscope were employed to characterize the annealed powders after immersion. The powder with an amorphous structure induced hydroxyapatite formation on their surfaces after immersion for 15 days.