SMARtLEDS

The SMARtLEDs project involves three laboratories in the Auvergne-Rhône-Alpes region (ICCF, LabHC, LMGP) and addresses the LED lighting field. Indeed, this project will allow obtaining a white light emission with stable photometric parameters in agreement with the requirements of the interior lighting in terms of colorimetry (Color Rendering Index (CRI) > 90, color temperature ~ 4000K). Our work will focus on the structuring of Y3Al5O12: Ce3+ (YAG: Ce3+) phosphors (Ps) coatings via their association with ZnO nanowires (NWs) organized in the shape of periodic networks. These will both improve the light extraction and provide the red component to achieve CRI in line with the lighting specifications. It will thus be possible to overcome the use of current red phosphors, expensive and not very stable over time, formulated from rare earth elements doped nitrides or sulfides as well as Mn4+ activated fluorides. YAG: Ce3+ and ZnO compounds will be developed by low cost techniques (sol-gel, hydrothermal and solvothermal synthesis processes). Their combination should lead to a white light emission meeting the lighting requirements. An enhancement of the emission intensity of at least 20% compared to the current devices is being targeted based on first modellings. Different phenomena resulting from these structures will favor the light extraction. Thanks to their nanometric diameter and their high aspect ratio, the NWs will act as nano-antenna guiding the light emitted by the LEDs and converted by the Ps towards the outside. The 3D architectures consisting of NWs will also lead to an increase in the number of the photon’s leaky cones or their angular broadening, thus multiplying the light paths by diffusion within the NWs networks. The dimensionality and periodicity of the NW networks will also be optimized through numerical simulations to reduce internal reflection losses and to control the light’s extraction angles. In addition, ZnO NWs will favor the emission of a light characterized by an optimized CRI, thanks to their spectral contribution in the red region under blue LED excitation. That is absolutely crucial because as aforementioned there are few rare-earth-free phosphors, efficient and stable over time, offering a red emission under excitation by a blue LED. Thus, the use of ZnO NWs to provide this component is a key point of this project. For the self-organized structures, two complementary strategies will be studied in a comparative way: the use of a YAG:Ce coating under the ZnO seed layer or the impregnation of the NWs networks with a YAG:Ce nanoparticles suspension. The originality of the project lies in the proposed association including 1- a low cost lithographic (exposure / development) method based on ZnO sol-gel resists specifically developed for this purpose and compatible with photoetching processes, 2- the localized growth of ZnO NWs on photoetched ZnO networks, 3- YAG:Ce Ps with optimized optical performances and whose selected synthesis processes allow adapted shaping 4- a multifunctional, multi-materials and multi-scale architecture leading to an optimized extraction of the light emitted by the LED and to improved optical and colorimetric performances. A new LED devices concept with increased performances will be proposed at the end of this project and will result in the implementation of a prototype.