Enhancement of the photoluminescence intensity of a single InAs/GaAs quantum dot by separate generation of electrons and holes

7 páginas, 5 figuras.-- PACS numbers: 78.67.Hc, 71.55.Eq, 73.50.GrIt is demonstrated that the microphotoluminescence (μPL) spectrum of a single InAs/GaAs self-assembled quantum dot (QD) undergoes considerable changes when the primary laser excitation is complemented with an additional infrared laser. The primary laser, tuned slightly below the GaAs band gap, provides electron-hole pairs in the wetting layer (WL), as well as excess free electrons from ionized shallow acceptors in the GaAs barriers. An additional IR laser with a fixed energy well below the QD ground state transition generates excess free holes from deep levels in GaAs. The excess electron and hole will experience diffusion separately, due to the time separation between the two events of their generation, to eventually become captured into the QD. Although the generation rates of excess carries are much lower than that of the electron-hole pair generation in the WL, they considerably influence the QD emission at low temperatures. The integrated PL intensity increases by several times as compared to single-laser excitation, and the QD exciton spectrum is redistributed in favor of a more neutral charge configuration. The dependence of the observed phenomenon on the powers of the two lasers and the temperature has been studied and is consistent with the model proposed. The concept of dual excitation could be successfully applied to different low-dimensional semiconductor structures in order to manipulate their charge state and emission intensity.This work was supported by grants from the Swedish Foundation for Strategic Research (SSR) and Swedish Research Council (VR). Financial support from the Wenner-Gren Foundation and the program “Low- Dimensional Quantum Structures” of the Russian Academy of Sciences is acknowledged by E.S.M. V.D. is thankful for financial support from the Swedish Foundation for International Cooperation in Research and Higher Education (STINT) and from the Bulgarian National Science Fund.Peer reviewe

Applications of seaweed extracts in Australian agriculture: past, present and future

A rapidly growing world population has highlighted the need to significantly increase food production in the context of a world with accelerating soil and water shortages as well as climatic stressors. This situation has generated new interest in the application of liquid seaweed extracts because of their potent plant growth-enhancing properties through metabolic benefits, triggering disease response pathways and increasing stress tolerance. The basis for these benefits is complex and poorly understood. Liquid seaweed extracts are complex and have been demonstrated to possess novel mechanisms for increasing crop productivity. The benefits of seaweed extracts to crops have previously been reviewed in the context of the northern hemisphere, but not in the context of Australia, its crops and unique stressors. This review considers the application of seaweed extracts in Australian agriculture by (i) introducing the history of the Australian liquid seaweed extract industry and (ii) focusing on evidence of Australian research related to seaweed extract composition, plant growth properties during plant establishment, pathogenic disease and new approaches to phenotyping the biological efficacy of seaweed extracts. This type of research is essential for future Australian agriculture to develop effective strategies for the use of liquid seaweed extracts