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

An important economic improvement of white light emitting diode is based on the use of lanthanide­free phosphors 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 defects that 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–up process are expected for industrial applications. Li­doping and polymer surface modifications of ZnO nanoparticles are mainly used in order to reach high PLQY (>30%) but PLQY decay over few days, uses of sophisticated 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 effective chemical solution process to get unique mesospheric self­assembly hybrid ZnO system with intense (PLQY = 40­75%) and stable visible emission. This hierarchical structure revealed to be efficient scatterer , resulting in a significant increase of the light­harvesting capability . W e also demonstrate that the use of mixture of commercial polyacrylic acid­based polymers can provide scalable amounts of ZnO NPs clear water suspensions that can be dried and dispersed again in water without compromising the functional performance (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, molecular weight, concentration, ratio of the P AA­based polymers and self­assembly process­ but also the impacts of transition metal dopings (nature and content) on the enhancement of the efficiency and on the control of the emission colour light of DS thin films in LED technology . Some examples of LED prototypes will also be presented.