Enhanced photoluminescence properties of electrospun Dy3+‐doped ZnO nanofibres for white lighting devices

Dy³⁺‐doped ZnO nanofibres with diameters from 200 to 500 nm were made using an electrospinning technique. The as‐fabricated amorphous nanofibres resulted in good crystalline continuous nanofibres through calcination. Dy³⁺‐doped ZnO nanofibres were characterized using scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), ultraviolet–visible (UV–vis) light spectroscopy, Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL). XRD showed the well defined peaks of ZnO. UV–vis spectra showed a good absorption band at 360 nm. FTIR spectra showed a Zn–O stretching vibration confirming the presence of ZnO. Photoluminescence spectra of Dy³⁺‐doped ZnO nanofibres showed an emission peak in the visible region that was free from any ZnO defect emission. Emissions at 480 nm and 575 nm in the Dy³⁺‐doped ZnO nanofibres were the characteristic peaks of dopant Dy³⁺ and implied efficient energy transfer from host to dopant. Luminescence intensity was found to be increased with increasing doping concentration and reduction in nanofibre diameter. Colour coordinates were calculated from photometric characterizations, which resembled the properties for warm white lighting devices.     

In-season changes in resistance to insecticides in Helicoverpa armigera (Lepidoptera: Noctuidae) in India

Discriminating doses of fenvalerate, cypermethrin, quinalphos, and endosulfan were determined with an insecticide-susceptible Helicoverpa armigera (Hübner) strain. In-season changes in insecticide resistance were monitored with discriminating dose assays at weekly intervals throughout the cropping season for 6 yr from 1993 to 1999 in central India. Resistance to pyrethroids was high throughout all seasons. Resistance to 0.75 microg of quinalphos was consistent, with seasonal averages ranging from 23 to 27% survival over the 6 yr. Resistance to 10.0 microg of endosulfan was moderately high at an average of 40-47% survival during 1993-1994 and in 1997-1998. It was lower in 1996-1997 at 27%, and in 1998-1999 at 33%. The weekly monitoring data for all seasons were pooled and the consolidated 6-yr seasonal average profile indicated that resistance to quinalphos and endosulfan was low during September at 21 and 27% survival, respectively, but increased to 28 and 37% by the end of November. Resistance levels to organophosphates and endosulfan increased during the season, depending on the use of these compounds. At almost all monitoring sites, the within-season changes in quinalphos resistance for all seasons through the study period followed a trend similar to that of endosulfan. The results suggest the possibility of cross-resistance between these compounds. Based on this study and the existing information on cotton pest management, we have developed a "window strategy" for cotton pest management with specific emphasis on the management of insecticides for effective control of H. armigera. This strategy has contributed to improved control at reduced costs in extensive trials.