Plasmonics and Magnetism from Doped Colloidal Indium Oxide Nanocrystals

Abstract

Transparent conducting oxides (TCOs) are metal oxides capable of exhibiting mutually exclusive properties of high electrical conductivity and transparency to the visible light. Through lattice doping, one can either enhance the electrical conductivity of TCOs (which enables their application to different optoelectronic applications) or introduce new functionalities in them. On the other hand, decreasing the size of TCOs to nano-regime allows them to exhibit localized surface plasmon resonance (LSPR) in the near infrared (NIR) region. In this work, we combine the control of size and doping on the properties of a material to yield codoped TCO nanocrystals (NCs). Using In2O3 as the host TCO, we incorporated two dopants, Sn4+ and a transition metal (T.M.), colloidally, to synthesize the codoped In2O3 NCs. While Sn4+ doping provides electrical conductivity and LSPR, T.M. doping is expected to introduce localized magnetic spins giving rise to magnetism. Results show that interactions can indeed be observed between the two dopants in the NC. Through these interactions, we achieve a tunable LSPR, electrical conductivity and magnetism from Fe-Sn codoped In2O3 NCs. By changing the T.M. dopant to Mn2+, we were able to achieve nearly ideal magnetic moment of 5 μB/Mn2+ ion in Mn-Sn codoped In2O3 NCs. On the other hand, we find that Cr-Sn codoped In2O3 NCs exhibit one of the highest figure-of-merit (Q-factors) for LSPR. We used the fundamental understanding to develop a strategy for designing doped TCOs with high LSPR Q-factors and employed them to synthesize Zr-doped In2O3 NCs which exhibit high LSPR Q-factors in the mid-infrared region. In the last chapter, using Cr-Sn codoped In2O3 NCs, we elucidated the primary factors that govern modulation of NIR LSPR under an applied external potential.