Rare-earth doped glasses and light managing in solar cells

Glasses doped with rare earth elements possess unique photoluminescence properties. They find application in several devices, such as lasers, optical amplifiers, and sensors. More recently, rare-earth doped glass thin films have been the subject of investigation for the development of frequency-converting layers able to increase the efficiency of silicon solar cells. Another approach to the improvement of the performance of a solar cell is based on the capture of a larger flux of light by the detector, which can be obtained by surface texture, plasmonics, or waveguide structures. Here, the recent advances in this area will be briefly reviewed

Sol-gel processing of hybrid ZnO nanophosphors self-assembled in mesospheres for WLED application.

International audienc

ZnO nanoparticles as a luminescent down-shifting layer for photosensitive devices

International audienc

Hybrid ZnO nanophosphors assembled in mesosphere for LED application.

National audienc

Metal oxide nanoparticles as phosphors for white light emitting diodes

International audienceZinc oxide is a direct and wide band gap semiconducting material (3.37 eV at room temperature), which has usually been used for the optoelectronic applications in the UV spectral range [1, 2]. A good crystalline quality of ZnO is mandatory to obtain high luminescent efficiency, but the recombination on the inevitable intrinsic defects in ZnO crystal lattice is competing with the excitonic emission, lowering the efficiency of ZnO-based UV devices. Scientists have dedicated a considerable effort to reduce the presence of these undesirable defects, but at present they are attracting a growing interest, as they are at the origin of a broad range light emission from blue to IR. This is especially true in the case of the nanoparticles, where the presence of the surface defects strongly contributes to the white light emission. Complete understanding of the causes of this visible emission is still lacking, but several reviews have summed up the state-of-the art knowledge [3, 4]. Another major result is that the photoluminescent quantum efficiency (PL QE) is highly dependent on the quantum dot size: the smaller the size, the larger the PL QE. Thus, very high QY have only been reached for very small (~ some nm in diameter) ZnO nanoparticles (NPs). When incorporated into appropriate host polymer matrices, ZnO NPs can be applied as phosphors in white light emitting diodes (WLEDs). In addition, rare earth-free (RE) materials applied to WLEDs are attractive and necessary from the viewpoint of the uneven distribution of RE in the modern world, as it is China who covers 95 % of their global demand.We demonstrate broadband white light emission from rare earth (RE)-free ZnO NPs and layers (pure or doped with metallic ions) and synthesized with easy to scale up chemical routes [5]. The RE-free ZnO-based NPs exhibit white light emission, maintaining a high value of PL QE. It should also be noted that that the peak wavelength of the broad light emission (and thus the emission color) can be tuned by or the amount or valence of the incorporated metallic ion. We demonstrate the use of these phosphors in a novel organic-inorganic WLED in combination with a solid state UV light-emitting source. References:1.Ü. Özgür, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, Ş. D. Doğan, V. Avrutin, S.-J. Cho and H. Morkoç, Journal of Applied Physics 98, 041301, 2005.2. S. J. Pearton, D. P. Norton, K. Ip, Y. W. Heo, T. T. Steiner, Progress in Materials Science 34, 293, 2005.3.A. B. Djurišić, Y. H. Leung, Small 2, 944, 2006.4.M. Willander, O. Nur, J. R. Sadaf, M. I. Qadir, S. Zaman, A. Zainelabdin, N. Bano, Materials 3, 2643, 2010.5.Y. Zhu, A. Apostoluk, P. Gautier, A. Valette, T. Cornier, J.-M. Bluet, K. Masenelli-Varlot, S. Danièle, B. Masenelli, Scientific Reports 6, pp. 23557 (1-11), 2016

The Influence of the thickness of nanographitic coatings fabricated by electrophoretic deposition on ethanol electro-oxidation

International audienceThe catalyst support layer is fabricated by applying a DC electrophoretic deposition on a colloid consisting of dispersed nanographitic flakes along with magnesium ions in isopropyl alcohol. The thickness and conductivity of the deposited layers are controlled by varying the time of the voltage application in the electrophoretic deposition EPD technique. The catalyst supports are decorated by sputtering palladium nanostructures serving as the catalyst. The fabricated support layer with the optimum thickness exhibits an improved conductivity and electro-oxidation performance attaining 800 mA/cm2 per mg of palladium

Sol-gel processing of hybrid ZnO quantum dots mesospheres for LED applications

SSCI-VIDE+CDFA+SDA:TCO:LOMInternational audienceAn important economic improvement of white light emitting diode is based on the use of lanthanide­freephosphors that are supposed to convert UV light into visible one, thanks to down­conversion (DS) process.ZnO nanoparticles (NPs) have aroused an increasing interest since they possess a variety of intrinsic defectsthat provide light emission in the visible range without the introduction of any additional impurity . However ,high photoluminescent quantum yield (PLQY), green/yellow emission, stable dispersion and easy scale–upprocess are expected for industrial applications. Li­doping and polymer surface modifications of ZnOnanoparticles are mainly used in order to reach high PLQY (>30%) but PLQY decay over few days, uses ofsophisticated polymers or multi­step reactions are the main issues for industrial implementation.Recently , we developed and patented an industry­capable (in terms of legislation concerns) and cost effectivechemical solution process to get unique mesospheric self­assembly hybrid ZnO system with intense (PLQY= 40­75%) and stable visible emission. This hierarchical structure revealed to be efficientscatterer , resulting in a significant increase of the light­harvesting capability . W e also demonstrate that theuse of mixture of commercial polyacrylic acid­based polymers can provide scalable amounts of ZnO NPsclear water suspensions that can be dried and dispersed again in water without compromising the functionalperformance (e.g. transparency and PLQY) of the final DS layer.Herein, we will address the effects of the ZnO NPs surface functionalization ­ such as nature, molecularweight, concentration, ratio of the P AA­based polymers and self­assembly process­ but also the impacts oftransition metal dopings (nature and content) on the enhancement of the efficiency and on the control of theemission colour light of DS thin films in LED technology . Some examples of LED prototypes will also bepresented

Solution processing of hybrid ZnO quantum dots assembled in mesosphere for light emitting diode applications

International audienc

Solution processing of hybrid ZnO nanophosphors assembled in mesosphere for LED application

SSCI-VIDE+CDFA+SDA:LOM:TCOInternational audienceAn important economic improvement of white light emitting diode (LED) is based on the use of lanthanide-free phosphors that are supposed to convert UV light into visible one, thanks to down-conversion (DS) process. ZnO nanoparticles have aroused an increasing interest since they possess a variety of intrinsic defects that provide light emission in the visible range without the introduction of any additional impurity. Our recent patented industry-capable (in terms of legislation concerns) and cost effective chemical solution approach (PCT WO 2016/038317 A1) led to mesospheric self-assembly hybrid ZnO-PAA nanomaterials (PAA = polyacrylic acid) that can be used as original nanostructured material which revealed to be efficient scatterer, resulting in a significant increase of the light-harvesting capability and emission performance. Herein, we will address the use of such self-assembly nanostructured ZnO materials as luminophor for LED devices. We will demonstrate how and why optimizations of (i) the set-up of the synthesis (reaction and washing steps), (ii) the molecular weight of the commercial polymers PAAH and PAANa (1800-250000) and the ratio of their mixture, (iii) cationic doping and (iv) core-shell structure lead to remarkable efficiency of white emission light of DS thin films in LED technolog