Red emitting cubic Y 2 O 3 :Eu 3+ nanophosphor with an average particle size in the range of 10-20 nm was synthesized using a more facile gel-polymer pyrolysis process. The maximum relative luminescence yield obtained for the nanophosphor prepared with a urea and PVA combination is about 30% in relation to the bulk Y 2 O 3 :Eu 3+ industrial red phosphor. The photoluminescence excitation spectrum monitoring the dominant hypersensitive 5 D 0 f 7 F 2 red emission of Eu 3+ comprises two parts, viz., the dominant Eu 3+ -O 2 chargetransfer band and a weak excitonic band (or its tail) corresponding to the Y 3+ -O 2-host matrix absorption. The relative strengths of these two bands have a strong dependence on the particle size. Furthermore, in this nanocrystalline insulator system having a band gap of about 6 eV, it is possible to observe a size dependent blue shift (∼600 cm -1 ) in the photoluminescence excitation band corresponding to the Urbach tail region of the yttria host matrix. Both the bulk and nanocrystalline Y 2 O 3 :Eu 3+ show storage luminescence, a phenomenon previously unknown in this system. The mechanisms responsible for this appear to be different in these systems. The storage luminescence in the bulk system can be attributed to lattice defects, whereas that in the nanocrystalline counterpart is from a meta-stable, photoinduced surface-states arising from chemisorbed species.

Metal pins used to apply skeletal traction or external fixation devices protruding through skin are susceptible to the increased incidence of pin site infection. In this work, we tried to establish the photokilling effects of titanium dioxide (TiO2) nanoparticles on an orthopedic implant with an in vitro study. In these photocatalytic experiments, aqueous TiO2 was added to the tested microorganism. The time effect of TiO2 photoactivation was evaluated, and the loss of viability of five different bacteria suspensions (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus hirae, and Bacteroides fragilis) was examined by the viable count procedure. The bactericidal effect of TiO2 nanoparticle-coated metal plates was also tested. The ultraviolet (UV) dosage used in this experiment did not affect the viability of bacteria, and all bacteria survived well in the absence of TiO2 nanoparticles. The survival curve of microorganisms in the presence of TiO2 nanoparticles showed that nearly complete killing was achieved after 50 min of UV illumination. The formation of bacterial colonies above the TiO2 nanoparticle-coated metal plates also decreased significantly. In this study, we clearly demonstrated the bactericidal effects of titanium dioxide nanoparticles. In the presence of UV light, the titanium dioxide nanoparticles can be applicable to medical facilities where the potential for infection should be controlled.

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Recombination dynamics of photoluminescence (PL) in colloidal CdSe/ZnS quantum dots (QDs) were studied using time-resolved PL measurements. The PL intensity shows a biexponential decay at 9 K, consisting of a fast component (∼1 ns) and a slow component (∼6.3 ns). Based on the emission-energy and temperature dependence of carrier lifetimes, we suggest that the fast and slow PL decay of colloidal CdSe/ZnS QDs originates from recombination of the delocalized carriers in the internal core states and the localized carriers at the interface, respectively.

Luminescent Y3Al5O12: Ce3+ [yttrium aluminum garnet (YAG):Ce3+] nanoceramics (5–50 nm) have been prepared through a facile sol-gel pyrolysis route. A blueshift of about 720 cm−1 in the reflectance spectra near the absorption edge can be observed for YAG:Ce3+ nanoparticles (having an average particle size around 5 nm) with respect to the submicron powders (∼0.9 μm). Furthermore, the scope of application for this important luminescent system can be extended by isostructural substitution with heavier cations such as Ba2+. This substitution giving rise to an oxygen-vacancy defect complex, that exhibits certain size-sensitive exciton-impurity energy-transfer property in YAG:Ce3+ nanoparticles.

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The dissolution behavior and kinetics of spinel lithium manganate LiMn2O4 with different particle sizes have been investigated in this study. The dissolution of manganese cations from LiMn2O4 is confirmed to occur when LiMn2O4 particles are immersed in the electrolytes. The amount of dissolved manganese ions markedly increases with a rise in temperature and a decrease in particle size, which implies that the capacity fading of LiMn2O4 at elevated temperatures is associated with manganese dissolution. On the basis of the isothermal analysis of reaction kinetics, the rate of manganese dissolution from LiMn2O4 is dominated by the rate of dissolution reaction. Smaller particles exhibit a larger reaction rate constant and higher activation energy of the dissolution process than the larger ones. Therefore, an increase in temperature has a more pronounced effect on the dissolution reaction of small particles than on that of large particles.