Time resolved and temperature dependence of the radiative properties of thiol-capped CdS nanoparticles films

In this work, we present the temperature-dependence and time-resolved photoluminescence (PL) of CdS nanoparticles capped independently with three different ligands thiophenol, thioglycerol, and l-cysteine over a broad temperature range from 10 to 300 K. The respective nanoparticles sizes in the three systems studied in this work are 1.5, 4, and 2 nm as determined from X-ray diffraction (XRD). From the analysis of AFM images, it was found that the lateral particle sizes of capped CdS nanoparticles are greater than those deduced from XRD or optical absorption measurements. The aim of this study is the investigation of the impact of the organic ligands on the radiative recombination dynamics in organically capped CdS nanoparticles. From the PL study and based on the temperature-dependence and time-resolved emission spectroscopy, we conclude that the emission of CdS QDs film originates from recombination of the delocalized carriers in the internal core states with a small contribution of the localized carriers at the interface. The PL decay reveals a biexponential behavior for the entire three samples at all temperatures. One of the two exponential components decays rapidly with a time τ(1) in the range 0.5–0.8 ns, whereas the other decays much more slowly, with a time τ(2) in the range 1–3 ns. The weak activation energy (32–37 meV) deduced from the temperature dependence of the PL intensity suggests the involvement of shallow traps. The analysis of the experimental results reveals a relatively narrow size distribution, an efficient surface passivation, and a satisfactory thermal stability of CdS nanocrystals

Effect of CdS nanocrystals on the photoluminescence of Eu3+-doped silicophosphate sol gel glass

In this work, we investigate the effect of co-doping with CdS nanoparticles on the photoluminescence properties of Eu3+ doped silicophosphate glass prepared via the sol gel method. Infrared spectroscopy (FTIR) revealed the insertion of phosphorus within the silicate network. XRD and TEM analyses revealed the presence of CdS nanoparticles dispersed in the glass matrix. Based on the optical study and the effective mass theory for spherical quantum dots, it was found that CdS nanocrystals have a gap of nearly 3.53 eV and a size of 2.42 nm. The enhancement of Eu3+ emission induced by CdS nanocrystals and thermal annealing was assigned to either an energy transfer via defect states or structural alteration of the glass network around the rare earth ions

Chemical composition of 8 <it>eucalyptus</it> species' essential oils and the evaluation of their antibacterial, antifungal and antiviral activities

<p>Abstract</p> <p>Background</p> <p>In 1957, Tunisia introduced 117 species of <it>Eucalyptus</it>; they have been used as fire wood, for the production of mine wood and to fight erosion. Actually, <it>Eucalyptus</it> essential oil is traditionally used to treat respiratory tract disorders such as pharyngitis, bronchitis, and sinusitis. A few investigations were reported on the biological activities of <it>Eucalyptus</it> oils worldwide. In Tunisia, our previous works conducted in 2010 and 2011 had been the first reports to study the antibacterial activities against reference strains. At that time it was not possible to evaluate their antimicrobial activities against clinical bacterial strains and other pathogens such as virus and fungi.</p> <p>Methods</p> <p>The essential oils of eight <it>Eucalyptus</it> species harvested from the Jbel Abderrahman, Korbous (North East Tunisia) and Souinet arboreta (North of Tunisia) were evaluated for their antimicrobial activities by disc diffusion and microbroth dilution methods against seven bacterial isolates: <it>Haemophilus influenzae</it>, <it>Klebsiella pneumoniae</it>, <it>Pseudomonas aeruginosa</it>, <it>Staphylococcus aureus</it>, <it>Streptococcus agalactiae</it>, <it>Streptococcus pneumoniae</it> and <it>Streptococcus pyogenes</it>. In addition, the bactericidal, fungicidal and the antiviral activities of the tested oils were carried out.</p> <p>Results</p> <p>Twenty five components were identified by GC/FID and GC/MS. These components were used to correlate with the biological activities of the tested oils. The chemical principal component analysis identified three groups, each of them constituted a chemotype. According to the values of zone diameter and percentage of the inhibition (zdi, % I, respectively), four groups and subgroups of bacterial strains and three groups of fungal strains were characterized by their sensitivity levels to <it>Eucalyptus</it> oils. The cytotoxic effect and the antiviral activity varied significantly within <it>Eucalyptus</it> species oils.</p> <p>Conclusions</p> <p><it>E. odorata</it> showed the strongest activity against <it>S. aureus</it>, <it>H. influenzae</it>, <it>S. agalactiae</it>, <it>S. pyogenes</it>, <it>S. pneumoniae</it> and against all the tested fungal strains. In addition, <it>E. odorata</it> oil showed the most cytotoxic effect. However, the best antiviral activity appeared with <it>E. bicostata</it>. Virus pretreatment with <it>E. bicostata</it> essential oil showed better antiviral activity (IC₅₀ = 0.7 mg/ml, SI = 22.8) than cell-pretreatment (IC₅₀ = 4.8 mg/ml, SI = 3.33). The essential oil of <it>E. astringens</it> showed antiviral activity only when incubated with virus prior to cell infection. This activity was dose-dependent and the antiviral activity diminished with the decreasing essential oil concentration.</p