Radial Dopant Placement for Tuning Plasmonic Properties in Metal Oxide Nanocrystals

Abstract

Doped metal oxide nanocrystals that exhibit tunable localized surface plasmon resonances (LSPRs) represent an intriguing class of nanomaterials that show promise for a variety of applications from spectroscopy to sensing. LSPRs arise in these materials through the introduction of aliovalent dopants and lattice oxygen vacancies. Tuning the LSPR shape and energy is generally accomplished through controlling the concentration or identity of dopants in a nanocrystal, but the lack of finer synthetic control leaves several fundamental questions unanswered regarding the effects of radial dopant placement, size, and nanocrystalline architecture on the LSPR energy and damping. Here, we present a layer-by-layer synthetic method for core/shell nanocrystals that permits exquisite and independent control over radial dopant placement, absolute dopant concentration, and nanocrystal size. Using Sn-doped InO (ITO) as a model LSPR system, we synthesized ITO/InO core/shell as well as InO/ITO core/shell nanocrystals with varying shell thickness, and investigated the resulting optical properties. We observed profound influence of radial dopant placement on the energy and linewidth of the LSPR response, noting (among other findings) that core-localized dopants produce the highest values for LSPR energies per dopant concentration, and display the lowest damping in comparison to nanocrystals with shell-localized or homogeneously distributed dopants. Inactive Sn dopants present on ITO nanocrystal surfaces are activated upon the addition of a subnanometer thick undoped InO shell. We show how LSPR energy can be tuned fully independent of dopant concentration, relying solely on core/shell architecture. Finally, the impacts of radial dopant placement on damping, independent of LSPR energy, are explored.

Moving the Plasmon of LaB6 from IR to Near-IR via Eu-Doping

“…Vacancies also play a large role in tuning the optical properties of such materials, having a significant influence on free carrier density and doping constraints [ 6 , 7 ]. It′s even possible to fully tune the plasmon independent of dopant concentration in core-shell indium-tin-oxide nanoparticles [ 8 ] and by reducing holes in the valence band in copper sulfide [ 9 ].…”

Tuning infrared plasmon resonances in doped metal-oxide nanocrystals through cation-exchange reactions

“…We further expanded this study to other types of extrinsically doped metal-oxide NCs. ITO NCs represent another widely studied example of degenerately doped metal-oxide NCs 13,15,20,41,53 . Reactions between ITO NCs and CuCl 2 were performed in a manner analogous to the Cu-exchange reactions on ICO NCs.…”

Tunable Charge Transport in Hybrid Superlattices of Indium Tin Oxide Nanocrystals and Metal Phthalocyanines—Toward Sensing Applications

“…An estimate of the carrier concentration ( N ) in the ITO NCs used in this work is obtained through the following equationwhere ω p is the plasma frequency, e is the elementary charge, m e is the effective mass, and ε 0 is the vacuum permittivity. Applied to the spectroscopic data displayed in Figure S9 in the Supporting Information, we estimate the charge carrier concentration as 9 × 10 18 cm −3 , which is well placed in the range (10 18 –10 22 cm −3 ) often reported for n‐type conductive metal oxides …”