[Preparation, characterization and upconversion fluorescence of NaYF4 : Yb, Er /graphene oxide nanocomposites].

NaYF4 : Yb, Er/rGO and SiO2-coated NaYF4 : Yb, Er/rGO nanocomposites can be prepared through "one-pot" and directly mixing preparation routes. Various measurement results show that the NaYF4 : Yb, Er in the nanocomposites exhibits a cubic a-type structure and nanoparticle-like morphology with a diameter range of 30-70 nm; the rGO layers are well-dispersed in the nanocomposites, and whereas the rGO obtained from "one-pot" preparation renders relatively better dispersion. Raman spectra demonstrate that there exists a surface coupling action between the two kinds of nanomaterials, and with the increase in the relative rGO content, such action becomes stronger. UC fluorescence measurement results reveal that the rGO has significantly quenching effect and optical-limiting performance on the UC fluorescence, particularly on the red-emission of the NaYFa : Yb, Er or SiO2-coated NaYF4 : Yb, Er nanoparticles. The red-emission intensity gradually decreases with an increase in the rGO content, but the green-emission shows less change. It should be stressed that, in comparison with NaYF4 : Yb, Er/rGO, with a similar rGO content, the red-emission intensity of SiO2-coated NaYF4 : Yb, Er/rGO decreases much obviously due to a stronger light-absorption caused by part rGO aggregation.

Preliminary Research on Conditions of Toxins Produced by Pestalotiopsis photiniae / 微生物学通报

Pestalotiopsis photiniae is one of the predominant pathogens of strawberry root rot disease. Based on preliminary research, it was proved that crude toxins were main pathogenic substances of the pathogen. For further investigation and utilization of toxins produced by this fungus, conditions of producing toxins were analyzed with the leaf disk method in this experiment. The result showed that pH values, cultural time, vibration, and tested temperatures obviously affected the production of toxins, except for light treatment. The most suitable culture conditions for the toxin production were pH 6.2, 25?C, darkness and stillness, for 5 d～7 d. Besides, it was discovered that crude toxins could significantly inhibit seed germination and elongation growth of roots or shoots for maize, rye and mung bean.