ZnO nanoparticles: from intense visible emission to Mid IR plasmon
Résumé
The size reduction in ZnO nanoparticles increases the presence of specific crystalline defects (Zn vacancies and O interstitials). These defects can behave as efficient light-emitters. However, the stability in time of their high quantum yield (PL QY) is still challenging. We first show that by controlling the synthesis ambient in the hydrolysis process of ZnEt2 by the addition of some weak polymeric acid (polyacrilic acid) we can design hybrid organic/inorganic ZnO based nanomaterials which exhibit stable PL QY up to 70 % in the green range of the visible spectrum. By carefully controlling the nature and size of the polymeric chains, we are able to synthesize scalable amount of visible light emitters competing with the well-established chalcogenide nano-emitters. ZnO can also be doped by Al or Ga at large concentration (up to few percents). The resulting semiconductor being degenerate, it possesses a free electron gas which exhibits a plasmon resonance. Since the plasmon resonance is related to the electron concentration, the plasmon can be tuned. These materials are promising candidates to transfer the outstanding results of plasmonics achieved with noble metals in the visible range to the IR range. Therefore, in the second part of this contribution, we will present how the dopant concentration can allow tuning the LSPR of nanoparticles in the mid IR range. We will show that degenerate metal oxide nanoparticles, and in particular Ga or Al doped ZnO nanoparticles, are outstanding materials for mid IR plasmonics.