Microstructure and upconversion luminescence of Yb 3+ and Ho 3+ co-doped BST thick films
ABSTRACT Ba0.8Sr0.2TiO3 (BST) thick films co-doped with Yb3+ and Ho3+ were fabricated by the screen printing techniques on alumina substrates. The structure and morphology of the BST thick films
were studied by XRD and SEM, respectively. After sintered at 1240 °C for 100 min the BST thick films are polycrystalline with
a perovskite structure. The upconversion luminescence properties of the RE-doped BST thick films under 800 nm excitation at
room temperature were investigated. The upconversion emission bands centered at 470 and 534 nm corresponding to 5F1 → 5I8 and 5F4 → 5I8 transition, respectively were observed, and the upconversion mechanisms were discussed. The dependence of the upconversion
emission intensity upon the Ho3+ ions concentration was also examined; the emission intensity reaches a maximum value in the sample with 2 mol% Yb3+ and 0.250 mol% Ho3+ ions. All the results show that the BST thick films co-doped with Yb3+ and Ho3+ may have potential use for photoelectric devices.
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ABSTRACT: a b s t r a c t 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 morpholog-ical features. With the help of various analyzing techniques like Field Emission Scanning Electron Micros-copy (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 feasi-ble processing of up-conversion rare-earth Y 2 O 3 :Er, Yb phosphors powders are discussed.
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ABSTRACT: The Y2O3:Ho(3+) powder phosphors have been prepared by using low temperature combustion method. Powder X-ray diffraction, scanning electron microscope and transmission electron microscopy techniques were used to characterize the as-prepared phosphor. The UV-Vis-NIR absorption, excitation and emission studies have been performed and the phenomenological Judd-Ofelt intensity parameters which are critically important in calculating the radiative properties and stimulated emission crosssection have been calculated by using Judd-Ofelt theory. Based on the calculated values of the inter electronic parameter, covalency and bonding parameter the bonding between the Ho(3+) ions and surrounding oxygen atoms have been found to be covalent in nature. The color purity has also been verified by using the chromaticity diagram. The analysis shows that the Y2O3:Ho(3+) phosphor may be used for producing the green light emitting diodes and display applications.Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 02/2013; 109C:206-212. DOI:10.1016/j.saa.2013.01.082 · 2.13 Impact Factor
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ABSTRACT: Gadolinium-oxide nanopowders doped with Yb3+ and Ho3+ ions and co-doped with alkali metal ions (Li+ and Na+) were synthesized via polymer complex solution method and their up-conversion emission properties are analyzed. Prepared powders were well crystallized in cubic bixbyite structure, without any impurity phases and with an average crystallite size of about 25 nm, as shown by X-ray powder diffraction analysis. No adsorbed species on the surface of nanoparticles were detected by infrared measurements. The particle morphology was analyzed by transmission electron microscopy, which revealed agglomerated crystalline nanoparticles with irregular, polygonal-like shapes, having a size in the range from 30 to 50 nm. Up-conversion emission properties of Gd2O3:Ho3+,Yb3+ nanopowders were evaluated from photoluminescence emission and decay measurements using 980 nm excitation. Two-photon up-conversion processes produced emissions in visible – near infrared spectral range, with the strongest green emission from 5F4,5S2 . 5I8 Ho3+ electronic transition, and weak red and near infrared from 5F5 - 5I8 and 5F4,5S2 - 5I7 transitions, respectively. In addition, three-photon up-conversion emission was detected in ultra-violet – blue spectral region (5G4 - 5I8, 3D3 - 5I6 and 5G5 - 5I8 transitions). Luminescence measurements were performed on samples with different Ho3+ (0.5 and 1 at. %) and Yb3+ (2, 4 and 6 at%) concentrations to find that 0.5 at% of Ho3+ and 2 at% of Yb3+ provides the most intense upconversion emission. The influence of alkali metal (Li+and Na+) ion co-doping is studied on the sample that showed the most intense up-conversion emission. Increase in the intensity of upconversion emission is observed for both Li+ and Na+ co-doping. The effect is more pronounced with Li+, where addition of 5 at % of Li+ led to more than one order of magnitude emission enhancement. Alkali metal ion co-doping also significantly improved up-conversion color purity through considerably larger increase of green emission compared to red and near infrared.Journal of Luminescence 08/2013; 145. DOI:10.1016/j.jlumin.2013.08.007 · 2.37 Impact Factor