Plasmonics with Doped Quantum Dots

Abstract

We review the discovery of localized surface plasmon resonances (LSPRs) in doped semiconductor quantum dots (QDs), an advance that has extended nanoplasmonics to materials beyond the classic gamut of noble metals. The initial demonstrations of near‐infrared LSPRs in QDs of heavily self‐doped copper chalcogenides and conducting metal oxides are setting the broad stage for this new field. We describe the key properties of QD LSPRs. Although the essential physics of plasmon resonances are similar to that in metal nanoparticles, the attributes of QD LSPRs represent a paradigm shift from metal nanoplasmonics. Carrier doping of quantum dots allows access to tunable LSPRs in the wide frequency range from the THz to the near‐infrared. Such composition or carrier density tunability is unique to semiconductor quantum dots and not achievable in metal nanoparticles. Most strikingly, semiconductor quantum dots allow plasmon resonances to be dynamically tuned or switched by active control of carriers. Semiconducting quantum dots thus represent the ideal building blocks for active plasmonics. A number of potential applications are discussed, including the use of plasmonic quantum dots as ultrasmall labels for biomedicine and electrochromic materials, the utility of LSPRs for probing nanoscale charge dynamics in semiconductors, and the exploitation of strong coupling between photons and excitons. Further advances in this field necessitate efforts toward generalizing plasmonic phenomena to a wider range of semiconductors, developing strategies for achieving controlled levels of doping and stabilizing them, investigating the spectroscopy of these systems on a fundamental level, and exploring their integration into optoelectronic devices.

Doped Nanocrystals as Plasmonic Probes of Redox Chemistry

“…[8,9] Others have shown similar LSPRs in nanocrystals of copper(I) selenide and copper(I) telluride. [10][11][12][13][14][15][16] LSPR tunability by variation of the copper vacancy concentration has also been demonstrated by the Alivisatos and Manna groups: the greater the vacancy concentration, the higher the LSPR frequency. [9,10] Metal nanoparticles do not possess such tunability, as their free carrier concentrations are large and difficult to perturb appreciably.…”

Control of Plasmonic and Interband Transitions in Colloidal Indium Nitride Nanocrystals

“…28,33,35,36,38,41,54 Equation 1 was used to calculate the plasma frequency, ω p , from the LSPR frequency, ω LSPR (both in untis of cm −1 ), with ε ∞ being the permittivity of free space and ε m the high frequency dielectric constant of the material (6.7 for InN). 1, 55 We ignore γ, the correction factor for inhomogeneity and scattering, because of the difficulty in estimating this term for NC samples as has been discussed elsewhere.…”

Shape-Dependent Field Enhancement and Plasmon Resonance of Oxide Nanocrystals

“…4,22,23 In metallic nanocrystals (NCs), the LSPR is mostly limited to the visible part of the spectrum and determined at the stage of synthesis. The LSPR frequency range of metallic nanostructures can be further extended to the near-infrared (NIR), but this requires larger sized particles with complex shapes such as nanorods 16 (>50 nm in length) or nanoshells 17,18 (>60 nm in diameter).…”

“…The ability to modify the plasmon resonance of NCs less than 20 nm in size to precise resonant absorption lines and with resonances within the biological window in the NIR 19 would be beneficial for numerous applications, such as enhancement spectroscopies in the near-infrared, 5,6,20 sensing, or photothermal therapies. 21,22 More recently, intense interest has been focused on a new type of plasmonic nanomaterials offering exactly these tunable properties, namely doped semiconductor NCs. 23,24 These are comprised of vacancy doped semiconductors such as copper chalcogenides, 25−27 tungsten oxides, 28,29 or doped metal oxide nanocrystals.…”

“…nanoparticle bulk (22) where h is the heat transfer coefficient, a is the surface area, and T bulk determines the temperature in the surrounding medium. The heat transfer coefficient for a spherical particle immersed in a pool of surrounding medium is given by h = (k s /R), where k s is the thermal conductivity of the medium and R is the radius of the particle.…”