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In our globalizing world, the geographical locations of food production and consumption are becoming increasingly disconnected, which increases reliance on external resources and their trade. We quantified to what extent water and land constraints limit countries' capacities, at present and by 2050, to produce on their own territory the crop products that they currently import from other countries. Scenarios of increased crop productivity and water use, cropland expansion (excluding areas prioritized for other uses) and population change are accounted for.We found that currently 16% of the world population use the opportunities of international trade to cover their demand for agricultural products. Population change may strongly increase the number of people depending on ex situ land and water resources up to about 5.2 billion (51% of world population) in the SRES A2r scenario. International trade will thus have to intensify if population growth is not accompanied by dietary change towards less resource-intensive products, by cropland expansion, or by productivity improvements, mainly in Africa and the Middle East. Up to 1.3 billion people may be at risk of food insecurity in 2050 in present low-income economies (mainly in Africa), if their economic development does not allow them to afford productivity increases, cropland expansion and/or imports from other countries.

Innovative materials for phosphor converted white light-emitting diodes are in high demand owing to the huge potential of the light-emitting diode technology to reduce energy consumption worldwide. As the primary blue diode is already highly optimized, the conversion phosphors are of crucial importance for any further improvements. We report on the discovery of the high performance red phosphor Sr[Li 2 Al 2 O 2 N 2 ]:Eu 2+ meeting all requirements for a phosphor’s optical properties. It combines the optimal spectral position for a red phosphor, as defined in the 2016 Research & Development-plan of the United States government, with an exceptionally small spectral full width at half maximum and excellent thermal stability. A white mid-power phosphor-converted light-emitting diode prototype utilising Sr[Li 2 Al 2 O 2 N 2 ]:Eu 2+ shows an increase of 16% in luminous efficacy compared to currently available commercial high colour-rendering phosphor-converted light-emitting diodes, while retaining excellent high colour rendition. This phosphor enables a big leap in energy efficiency of white emitting phosphor-converted light-emitting-diodes.

Biomass from cellulosic bioenergy crops is expected to play a substantial role in future energy systems, especially if climate policy aims at stabilizing greenhouse gas concentration at low levels. However, the potential of bioenergy for climate change mitigation remains unclear due to large uncertainties about future agricultural yield improvements and land availability for biomass plantations. This letter, by applying a modelling framework with detailed economic representation of the land and energy sector, explores the cost-effective contribution of bioenergy to a low-carbon transition, paying special attention to implications for the land system. In this modelling framework, bioenergy competes directly with other energy technology options on the basis of costs, including implicit costs due to biophysical constraints on land and water availability.As a result, we find that bioenergy from specialized grassy and woody bioenergy crops, such as Miscanthus or poplar, can contribute approximately 100 EJ in 2055 and up to 300 EJ of primary energy in 2095. Protecting natural forests decreases biomass availability for energy production in the medium, but not in the long run. Reducing the land available for agricultural use can partially be compensated for by means of higher rates of technological change in agriculture. In addition, our trade-off analysis indicates that forest protection combined with large-scale cultivation of dedicated bioenergy is likely to affect bioenergy potentials, but also to increase global food prices and increase water scarcity. Therefore, integrated policies for energy, land use and water management are needed.

The current model for understanding trapping of charge carriers to the surface of semiconductor nanocrystals is inconsistent with experimental evidence indicating that carriers can thermally de-trap from surface sites. A proper understanding of the microscopic details of charge trapping would guide chemical design of the nanocrystal surface for applications such as charge transport, sensing, or photochemistry. This thesis presents a model of surface charge trapping in which transitions to surface state are governed by rates derived from semiclassical electron-transfer theory. In this picture, trapping to the surface induces a strong polarization in the nanocrystal, resulting in a trapped state with strong electron-phonon coupling via the Frölich mechanism. This trapped state then emits over a broad energy range due to a Franck-Condon vibronic progression. This model is shown to be consistent with the temperature-dependence of core and surface emission as well as the spectral properties of surface emission. The strong coupling of the surface state is validated by independent experiments, and the model is shown to hold promise for explaining the experimental data regarding the trapping of hot (excess energy) carriers.iii RésuméLe modèle prévalent concernant le piégeage des porteurs de charges à la surface de nanocrystaux semi-conducteurs est inconsistant avec certains résultats expérimentaux indiquant que les charges peuvent subir une relaxation thermique depuis les états de surfaces. Une bonne compréhension des aspects microscopiques du processus de piégeage des porteurs de charges permettrait de guider le design de la surface des nanocrystaux en vue d'applications comme le transport de charges, la détection ou la photo-chimie.Ce travail de doctorat propose un modèle du piégeage des charges où les taux de transition vers des états de surface sont basés sur la théorie semi-classique du transfert d'électrons. Dans ce modèle, le piégeage à la surface crée une forte polarisation dans le nanocrystal, ce qui résulte en un état piégé avec un grand couplage électron-phonon via le mécanisme de Fröhlich. Cet état piégé émet dans une large bande spectrale due à la progression vibronique de Franck-Condon. Le modèle proposé est consistent avec la dépendance en température du spectre d'émission du centre et de la surface ainsi que des propriétés spectrales d'émission de la surface. Le couplage fort de l'état de surface est validé par des expériences indépendantes et il est montré que le modèle est prometteur pour l'analyse d'expériences sur le piégeage des porteurs de charges chauds (ayant un excès d'énergie).iv