Strong visible emissions of Er3+ resulting from two-photon absorption and energy transfer from the host YVO4 were observed in nanocrystalline Er3+-doped YVO4, which was prepared by a hydrothermal method using a citrate−yttrium−vanadate complex as the precursor. The nanocrystals were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), UV−visible absorption spectra, and photoluminescence (PL) spectra. The highly crystalline YVO4:Er3+ nanoparticles, with an average diameter of 35 nm, have a tetragonal zircon structure and can redisperse in water because of the presence of citrate ligands. We discussed in detail the visible upconversion mechanism and temperature dependence of the upconversion emission for the Er3+ ions in the YVO4 nanocrystals.

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Helicobacter pylon is a pathogen associated with type B gastritis, peptic ulcer disease, gastric atrophy, and stomach cancer. H. pylori exists in two morphological forms, spirals and coccoids. The latter has been described as viable but non-cultivable. The role of the coccoid form in the pathogenesis of gastric disease is disputed. Some authors consider the coccoid form to be a degenerative or dead form of H.pylori, while others consider it a resting but still metabolically active form.This study reports the conversion fiom spiral to coccoid form ultrastructurally. Dense material is accumulated in the periplasmic space, the spiral bacteria bend and the outer membrane is separated from the inner cell wall layer. Remodeling of inner structures takes place, ending in the coccoid form of the bacteria with preserved light polyphosphate areas. Reduction of surface takes place by production of surface membrane vesicles, which later are squeezed off. The finding of preserved subcellular structures +d intact double membranes in combination with degenerative forms suggests that some of the coccoids are viable. Scanning electron microscopy (SEM) demonstrates coccoid form of bacteria with slightly ruffled surfaces but no spiral forms.