Dependence relationship between doping modes and surface plasmon resonance properties of doped ZnO nanocrystals

The use of doped semiconductors to achieve plasmonic frequencies in the middle infrared (mid-IR) has been recently proposed as a promising way to obtain high-quality and tunable plasmonic materials. Plasmonic materials have great static or dynamic tunability. In some cases, choosing a dopant over another is an important trade-off to optimize the plasmonic performance. In this work, trivalent metal ion (M)-doped ZnO nanoparticles (NPs, M=Al, In) were successfully synthesized with highly consistent synthesis conditions. Interestingly, surface plasmon resonance (SPR) can only be observed in Al-doped ZnO (AZO) NPs, but not in In-doped ZnO (IZO) NPs. We used X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman and a first principle calculation to clarify the proper dopant sites (replaceable or interstitial doping) of Al3+ and In3+ in the host nanocrystals of ZnO. In addition, these results assisted by density of states (DOS) analysis indicate that different doping modes influenced the electronic structures in different degrees, and may lead to the opposite SPR phenomenon. Our work deepens the understanding of the relationship between doping sites in the host nanocrystals and SPR properties and give important guidance to the develop the doped semiconductors with plasmonic performance.