Localized surface plasmon resonance (LSPR) in semiconductor nanocrystals (NCs) that results in resonant absorption, scattering, and near field enhancement around the NC can be tuned across a wide optical spectral range from visible to far-infrared by synthetically varying doping level, and post synthetically via chemical oxidation and reduction, photochemical control, and electrochemical control In this review, we will discuss the fundamental electromagnetic dynamics governing light matter interaction in plasmonic semiconductor NCs and the realization of various distinctive physical properties made possible by the advancement of colloidal synthesis routes to such NCs Here, we will illustrate how free carrier dielectric properties are induced in various semiconductor materials including metal oxides, metal chalcogenides, metal nitrides, silicon, and other materials We will highlight the applicability and limitations of the Drude model as applied to semiconductors considering the complex band structures 

Localized Surface Plasmon Resonance in Semiconductor Nanocrystals

The successful transition of any nanocrystal-based product from the research phase to the commercial arena hinges on the ability to produce the required nanomaterial on large scales. The synthesis of colloidal nanocrystals using a heat-up (non-injection) method is a reliable means to achieve high quality nanomaterials on large scales with little or no batch-to-batch variation. In this class of synthesis precursors are heated within a reaction medium to induce a chemical reaction that yields monomer for nucleation and growth. Use of the heat-up technique circumvents the pitfalls of mixing time and poor heat management inherent to classical “hot-injection” methods. In heat-up syntheses monomer is produced in a more continuous fashion during the heating stage, making it more difficult to separate the nucleation and growth stages of the reaction, a factor that is conventionally considered detrimental toward achieving homogeneous colloidal dispersions. However, through the judicious selection of precursors, st...

The heat-up synthesis of colloidal nanocrystals

Plasmonic doped semiconductor nanocrystals: Properties, fabrication, applications and perspectives

Introducing a few atoms of impurities or dopants in semiconductor nanocrystals can drastically alter the existing properties or even introduce new properties For example, mid-gap states created by doping tremendously affect photocatalytic activities and surface controlled redox reactions, generate new emission centers, show thermometric optical switching, make FRET donors by enhancing the excited state lifetime, and also create localized surface plasmon resonance induced low energy absorption In addition, researchers have more recently started focusing their attention on doped nanocrystals as an important and alternative material for solar energy conversion to meet the current demand for renewable energy Moreover, the electrical and magnetic properties of the host are also strongly altered on doping These beneficial dopant-induced changes suggest that doped nanocrystals with proper selections of dopant-host pairs may be helpful for generating designer materials for a wide range of current technological needs How properties relate to the doping of a variety of semiconductor nanocrystals are summarized in this Review

Luminescence, Plasmonic, and Magnetic Properties of Doped Semiconductor Nanocrystals.

Slowing climate change requires overcoming inertia in political, technological, and geophysical systems. Of these, only geophysical warming commitment has been quantified. We estimated the commitment to future emissions and warming represented by existing carbon dioxide–emitting devices. We calculated cumulative future emissions of 496 (282 to 701 in lower- and upper-bounding scenarios) gigatonnes of CO 2 from combustion of fossil fuels by existing infrastructure between 2010 and 2060, forcing mean warming of 1.3°C (1.1° to 1.4°C) above the pre-industrial era and atmospheric concentrations of CO 2 less than 430 parts per million. Because these conditions would likely avoid many key impacts of climate change, we conclude that sources of the most threatening emissions have yet to be built. However, CO 2 -emitting infrastructure will expand unless extraordinary efforts are undertaken to develop alternatives.

Future CO2 Emissions and Climate Change from Existing Energy Infrastructure

Multifunctional Fe–Sn codoped In2O3 colloidal nanocrystals simultaneously exhibiting localized surface plasmon resonance band, high electrical conductivity, and charge mediated magnetic coupling have been developed. Interactions between Sn and Fe dopant ions have been found critical to control all these properties. Sn doping slowly releases free electrons in the colloidal nanocrystals, after reduction of active complex between Sn4+ and interstitial O2–. Unexpectedly, Fe codoping reduces the free electron concentration. Our X-ray absorption fine structure spectroscopy (XAFS) results show that Fe3+ and Sn4+ substitutes In3+ in the In2O3 lattice for all Fe-doped In2O3 NCs and Sn-doped In2O3 NCs. Interestingly, for Fe–Sn codoped NCs, a smaller fraction of Fe3+ gets reduced to Fe2+ by consuming free electrons produced by Sn doping. Therefore, Fe doping can manipulate free electron concentration in Fe–Sn codoped In2O3 nanocrystals, controlling both plasmonic band and electrical conductivity. Free electrons, on ...

Doping Controls Plasmonics, Electrical Conductivity, and Carrier-Mediated Magnetic Coupling in Fe and Sn Codoped In2O3 Nanocrystals: Local Structure Is the Key

We prepared Fe- and Sn-codoped colloidal In2O3 nanocrystals (∼6 nm). Sn doping provides free electrons in the conduction band, originating localized surface plasmon resonance (LSPR) and electrical conductivity. The LSPR band can be tuned between 2000 and >3000 nm, depending on the extent and kind of dopant ions. Fe doping, on the other hand, provides unpaired electrons, resulting in weak ferromagnetism at room temperature. Fe doping shifts the LSPR band of 10% Sn-doped In2O3 nanocrystals to a longer wavelength along with a reduction in intensity, suggesting trapping of charge carriers around the dopant centers, whereas Sn doping increases the magnetization of 10% Fe-doped In2O3 nanocrystals, probably because of the free electron mediated interactions between distant magnetic ions. The combination of plasmonics and magnetism, in addition to electronic conductivity and visible-light transparency, is a unique feature of our colloidal codoped nanocrystals.

Multifunctional Sn- and Fe-Codoped In2O3 Colloidal Nanocrystals: Plasmonics and Magnetism.

Thin films of degenerately doped metal oxides such as those of Sn-doped In2O3 (Sn:In2O3) are commercially significant for their broad utilization as transparent conducting electrodes in optoelectro...

Dopant Selection Strategy for High-Quality Factor Localized Surface Plasmon Resonance from Doped Metal Oxide Nanocrystals

Heterovalent dopant ions, such as Sn4+, in In2O3 nanocrystals (NCs) provide free electrons for localized surface plasmon resonance (LSPR). But the same heterovalent dopants act as electron scattering centers, both independently and by forming complexes with interstitial oxygen, thereby increasing LSPR line width. Also, such complexes decrease free carrier density. These detrimental effects diminish the figure-of-merit of LSPR known as the quality factor (Q-factor). Herein, we designed colloidal Cr–Sn codoped In2O3 NCs, where both high carrier density and low carrier scattering can be achieved simultaneously, yielding a high LSPR Q-factor of 7.2, which is a record high number compared to prior reports of doped In2O3 NCs. Q-factors increase systematically from 3.2 for 6.6% Sn doped In2O3 NCs to 7.2 for 23.8% Cr–6.6% Sn codoped In2O3 NCs by increasing the Cr codoping concentration, which is also accompanied by an increase in NC size from 6.7 to 22.1 nm. Detailed characterization and analysis of LSPR spectra ...

Size-Induced Enhancement of Carrier Density, LSPR Quality Factor, and Carrier Mobility in Cr–Sn Doped In2O3 Nanocrystals

Degenerately doped semiconductor nanocrystals (NCs) exhibit strong light–matter interactions due to localized surface plasmon resonance (LSPR) in the near- to mid-infrared region. Besides being readily tuned through dopant concentration introduced during synthesis, this LSPR can also be dynamically modulated by applying an external electrochemical potential. This characteristic makes these materials candidates for electrochromic window applications. Here, using prototypical doped indium oxide NCs as a model system, we find that the extent of electrochemical modulation of LSPR frequency is governed by the depletion width and the extent of inter-NC LSPR coupling, which are indirectly controlled by the dopant density, size, and packing density of the NCs. The depletion layer is a near-surface region with a sharply reduced free carrier population that occurs whenever the surface potential lies below the Fermi level. Changes in the depletion width under applied bias substantially control the spectral modulatio...

Bharat Tandon

Papers

Doping Controls Plasmonics, Electrical Conductivity, and Carrier-Mediated Magnetic Coupling in Fe and Sn Codoped In2O3 Nanocrystals: Local Structure Is the Key

Multifunctional Sn- and Fe-Codoped In2O3 Colloidal Nanocrystals: Plasmonics and Magnetism.

Dopant Selection Strategy for High-Quality Factor Localized Surface Plasmon Resonance from Doped Metal Oxide Nanocrystals

Size-Induced Enhancement of Carrier Density, LSPR Quality Factor, and Carrier Mobility in Cr–Sn Doped In2O3 Nanocrystals

Competition between Depletion Effects and Coupling in the Plasmon Modulation of Doped Metal Oxide Nanocrystals.