National Physical Laboratory

About: National Physical Laboratory is a facility organization based out in London, United Kingdom. It is known for research contribution in the topics: Dielectric & Thin film. The organization has 7615 authors who have published 13327 publications receiving 319381 citations.

Förster resonance energy transfer and carbon dots enhance light harvesting in a solid-state quantum dot solar cell

Abstract: A novel yet inexpensive quantum dot solar cell (QDSC) configuration relying on Forster resonance energy transfer (FRET) from electrode bound excited cadmium sulfide (CdS) quantum dots ensconced in zinc sulfide (ZnS) monolayers to unattached copper phthalocyanine (CuPc) molecules, dissolved in a free standing sulfide ion based gel polymeric electrolyte, is presented. Luminescent and conducting carbon dots (C-dots) are incorporated in the anode to improve the electron transfer and transport characteristics of the photoactive assembly. Fluorescence quenching and lifetime measurements provide unambiguous proof of dominant energy and not electron transfer from the blue/green absorbing ZnS/CdS/ZnS donor QDs to the red absorbing CuPc acceptor molecules. The subsequent charge transfer rate from CuPc to the current collector via C-dots in the ZnS/CdS/ZnS/C-dot/CuPc assembly is faster and the electron recombination lifetime (with the oxidized species in the electrolyte, τ) is longer, in contrast with the slower rate and shorter τ in the assembly devoid of C-dots, thus confirming the role of C-dots in facilitating charge propagation. The Forster radius calculated from the overlap integral and the actual separation estimated from high resolution transmission electron microscopy between the CdS and CuPc are close, and the energy transfer efficiency is deduced to be 40%. Incident photon to current conversion efficiency (IPCE) measurements revealed an optimal coverage of the visible spectrum for the cells with both donors and acceptors: the ZnS/CdS/ZnS/C-dot/CuPc assembly shows a 5.76 times increment of photocurrent in the blue/green region in comparison with cells with only donor (ZnS/CdS/ZnS). The demonstration of a quasi solid-state FRET enabled cell not only opens up avenues to use photoactive moieties that do not undergo charge transfer as dictated by conventional energy level offsets, but also shows the viability of producing laminated, cheap QDSCs capable of harvesting broader regions of the visible spectrum.

Gloss as an aspect of the measurement of appearance

Abstract: The perception and measurement of gloss is just one part of the concept of appearance measurement. We describe the comparison between data derived by 20 observers who each scaled the perceived gloss of a set of 84 neutral and colored test samples and measurements of those samples made using a glossmeter and a sphere-based spectrophotometer. With a glossmeter, the relationship between the visual-scaled data and the measured gloss values could be described by a three-part linear fit or, with a higher correlation, a cubic function. For the sphere-based spectrophotometer, the difference in the luminance factor, deltaY, between specular-included and specular-excluded measurements, was found to give a better linear correlation with the observer-scaled data. The color of the samples did not appear to significantly change the perceived gloss of the surface.

Assessment of trace gases, carbon and nitrogen emissions from field burning of agricultural residues in India

Abstract: Field burning of crop residue (FBCR) is becoming a growing environmental concern in developing countries. In this instance, a comprehensive crop-wise and spatially distributed study on the FBCR emissions from India for the period 1980 through 2010 have been undertaken, that covers: residue generation, its types, use pattern, and estimates of carbon, nitrogen, CH4, CO, N2O and NOX emissions; along with associated uncertainties. FBCR contributed about 44 and 14% of the non-biofuel biomass and total biomass burning, respectively in India in the year 2000. The total dry residue generated are estimated as 217, 239 and 253 Tg, of which 45, 60 and 63 Tg of dry biomass are estimated to be subjected to FBCR in the years 1994, 2005 and 2010, respectively. Wheat and rice crops together accounted for about 76% of this. Burning of such huge amount of biomass is estimated to emit 22.4, 24.4 and 26.1 Tg of carbon; 0.30, 0.33 and 0.35 Tg of nitrogen; 4.18, 4.59 and 4.86 Tg carbon dioxide equivalent of greenhouse gases (GHG, viz., CH4 and N2O; which is over 1% of the Indian agriculture sector GHG emissions); 2951, 3,240 and 3,431 Gg of CO; and 120.8, 132.9 and 140.6 Gg NOx emissions in 1994, 2005 and 2010, respectively. Further, the Indian states of U.P, Punjab, Haryana, M.P, Maharashtra, T.N, Karnataka, Andhra Pradesh, Bihar and W.B have been found to contribute maximum to the Indian FBCR emissions. FBCR avoidance and optimum utilization of crop-residue resource is urgently required for agro-ecosystem sustainability in the region.