10.1021/acs.chemmater.9b02917.s001 Bharat Tandon Bharat Tandon Sandeep Ghosh Sandeep Ghosh Delia J. Milliron Delia J. Milliron Dopant Selection Strategy for High-Quality Factor Localized Surface Plasmon Resonance from Doped Metal Oxide Nanocrystals American Chemical Society 2019 High-Quality Factor Localized Surface Plasmon Resonance dopant activation 2 O 3 lattice LSPR line width metal oxide NC systems 2 O 3 NCs exhibit Zr donor level Doped Metal Oxide Nanocrystals Dopant Selection Strategy mid-infrared region LSPR Q-factors metal oxides model aliovalent dopant LSPR Q-factor surface plasmon resonance 2 O 3 LSPR peak energy LSPR energy aliovalent cationic dopants 2 O 3 NCs 2019-09-09 19:14:17 Journal contribution https://acs.figshare.com/articles/journal_contribution/Dopant_Selection_Strategy_for_High-Quality_Factor_Localized_Surface_Plasmon_Resonance_from_Doped_Metal_Oxide_Nanocrystals/9788408 Thin films of degenerately doped metal oxides such as those of Sn-doped In<sub>2</sub>O<sub>3</sub> (Sn:In<sub>2</sub>O<sub>3</sub>) are commercially significant for their broad utilization as transparent conducting electrodes in optoelectronic devices. Over the past decade, nanocrystals (NCs) of Sn:In<sub>2</sub>O<sub>3</sub> and other doped metal oxides have also attracted interest for localized surface plasmon resonance (LSPR) that occurs in the near- to mid-infrared region. The suitability of this LSPR for some applications depends on its capacity to concentrate light in small regions of space, known as near-field hot spots. This efficiency to create near-field hot spots can be judged through an LSPR figure-of-merit such as Quality factor (Q-factor), defined as the ratio of LSPR peak energy to its line width. The free electron density determines the LSPR peak energy, while the extent of electron scattering controls the LSPR line width; hence, these factors together essentially dictate the value of the Q-factor. An unfortunate trade-off arises when dopants are introduced since the aliovalent dopants generating the free electrons (increasing LSPR energy) also act as centers of scattering of electrons (increasing LSPR line width), thereby decreasing the LSPR Q-factor. Dopant selection is hence of paramount importance to achieve a high value of LSPR Q-factor. Here, we describe the properties of aliovalent cationic dopants that allow both high LSPR energy and low LSPR line width and, subsequently, high LSPR Q-factor. In this context, we identify Zr<sup>4+</sup> as a model aliovalent dopant for high LSPR Q-factor in the In<sub>2</sub>O<sub>3</sub> lattice. The resulting Zr-doped In<sub>2</sub>O<sub>3</sub> NCs exhibit one of the highest LSPR Q-factors reported in the mid-infrared region while also performing equivalently to the recognized materials for either high dopant activation (Sn:In<sub>2</sub>O<sub>3</sub> NCs) or low LSPR line width (Ce-doped In<sub>2</sub>O<sub>3</sub> NCs) simultaneously. The Zr donor level is positioned well inside the conduction band of In<sub>2</sub>O<sub>3</sub>, and Zr doping is surface segregated, both minimizing electron scattering. The combination of this low electron scattering and high dopant activation of Zr<sup>4+</sup> ions is responsible for the high LSPR Q-factors. These strategies can be used to design a variety of doped metal oxide NC systems exhibiting high LSPR Q-factors.