Learning by Research

Thesis Title: New materials for eco-efficient white LEDs : ZnO nanowire-based heterostructures and rare-earth-free aluminium borates phosphors

The widespread implementation of white light-emitting diodes (wLEDs), based on the blue electroluminescence of an LED and the yellow photoluminescence of a phosphor, represents a major opportunity to reduce global energy consumption. The performances of wLEDs are based on materials considered as critical, such as gallium and gallium/indium nitrides for the blue LED, and cerium doped yttrium aluminium garnet for the phosphor. The synthesis of these materials require costly and high-temperature physical and chemical deposition techniques. In this context, new non-critical materials have been studied and manufactured by soft chemistry methods: ZnO nanowires array as n-type semiconductor, and aluminoborate powders as phosphor. On the one hand, the mechanisms of the extrinsic doping and related modification of the growth of ZnO nanowires deposited by chemical bath deposition were investigated, showing the dominant roles of pH and precursor concentrations. Defects and complex defects incorporated in ZnO nanowires, crucial from an application point of view, greatly modify their optical and electrical proprieties. Their epitaxial growth on p-type GaN thin films forms heterojunctions whose electroluminescence properties are evaluated. On the other hand, aluminoborate-based phosphors powders were synthesized by the Pechini method, by substituting yttrium, usually present in the amorphous particles. The optimization of the new chemical compositions and thermal annealing offers a broad emission whose internal quantum luminescence efficiency exceeds 60 %. This study provides a better understanding of the trapping of carbon species, and their role in the luminescence. Eventually, consumer interest in such structures without critical materials and with low embodied energy is measured and offers optimistic prospects for their development.

Cette étude permet une meilleure compréhension du piégeage d’espèces carbonées, et de leur rôle dans la luminescence. Finalement, l’intérêt des consommateurs pour de telles structures sans matériaux critiques et à basse énergie grise est mesuré et offre des perspectives optimistes pour leur développement.

Key Words: LED lighting, ZnO nanowires, Aluminoborate phosphors, Semiconductors, Heterostructures, Critical materials

Doctoral School:  ED I-MEP² - Ingénierie - Matériaux, Mécanique, Environnement, Énergétique, Procédés, Production
Research Laboratory:  Laboratoire des Matériaux et du Génie Physique (LMGP, CNRS/Grenoble INP-UGA)
Thesis Supervision: Vincent CONSONNI, Estelle APPERT and Mathieu SALAÜN

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