Surface-Enhanced Infrared Absorption Spectroscopy by Resonant Vibrational Coupling with Plasmonic Metal Oxide Nanocrystals.

Coupling between plasmonic resonances and molecular vibrations in nanocrystals (NCs) offers a promising approach for detecting molecules at low concentrations and discerning their chemical identities. Metallic NC superlattices can enhance vibrational signals under far-field detection by generating a myriad of intensified electric field hot spots between the NCs. Yet, their effectiveness is limited by the fixed electron concentration dictated by the metal composition and inefficient hot spot creation due to the large mode volume.

Thermal Activation of Anti-Stokes Photoluminescence in CsPbBr Perovskite Nanocrystals: The Role of Surface Polaron States.

Optically driven cooling of a material, or optical refrigeration, is possible when optical up-conversion via anti-Stokes photoluminescence (ASPL) is achieved with near-unity quantum yield. The recent demonstration of optical cooling of CsPbBr perovskite nanocrystals (NCs) has provided a path forward in the development of semiconductor-based optical refrigeration strategies. However, the mechanism of ASPL in CsPbBr NCs is not yet settled, and the prospects for cooling technologies strongly depend on details of the mechanism.

Wavelength Tunable Infrared Perfect Absorption in Plasmonic Nanocrystal Monolayers.

The ability to efficiently absorb light in ultrathin (subwavelength) layers is essential for modern electro-optic devices, including detectors, sensors, and nonlinear modulators. Tailoring these ultrathin films' spectral, spatial, and polarimetric properties is highly desirable for many, if not all, of the above applications. Doing so, however, often requires costly lithographic techniques or exotic materials, limiting scalability.

Dipolar Ligands Tune Plasmonic Properties of Tin-Doped Indium Oxide Nanocrystals.

Surface functionalization with dipolar molecules is known to tune the electronic band alignment in semiconductor films and colloidal quantum dots. Yet, the influence of surface modification on plasmonic nanocrystals and their properties remains little explored. Here, we functionalize tin-doped indium oxide nanocrystals (ITO NCs) via ligand exchange with a series of cinnamic acids with different electron-withdrawing and -donating dipolar characters.

Modular mixing in plasmonic metal oxide nanocrystal gels with thermoreversible links.

Gelation offers a powerful strategy to assemble plasmonic nanocrystal networks incorporating both the distinctive optical properties of constituent building blocks and customizable collective properties. Beyond what a single-component assembly can offer, the characteristics of nanocrystal networks can be tuned in a broader range when two or more components are intimately combined. Here, we demonstrate mixed nanocrystal gel networks using thermoresponsive metal-terpyridine links that enable rapid gel assembly and disassembly with thermal cycling.

Optically Cooling Cesium Lead Tribromide Nanocrystals.

One photon up-conversion photoluminescence is an optical phenomenon whereby the thermal energy of a fluorescent material increases the energy of an emitted photon compared with the energy of the photon that was absorbed. When this occurs with near unity efficiency, the emitting material undergoes a net decrease in temperature, so-called optical cooling. Because the up-conversion mechanism is thermally activated, the yield of up-converted photoluminescence is also a reporter of the temperature of the emitter.

The role of gold oxidation state in the synthesis of Au-CsPbX heterostructure or lead-free CsAuAuX perovskite nanoparticles.

Here, we report that the oxidation state of gold plays a dominant role in determining the reaction products when gold halide salts are mixed with all-inorganic lead halide perovskite nanocrystals. When CsPbX nanocrystals react with Au(i) halide salts, Au nanoparticles are deposited on the surface of the perovskites through the reduction of Au ions by the surfactant ligand shell, to produce Au-CsPbX heterostructures. These heterostructures preserve comparably high photoluminescence quantum yield (PLQY) and show identical XRD diffractograms as the parent CsPbX nanocrystals.

The role of mid-gap states in all-inorganic CsPbBr nanoparticle one photon up-conversion.

CsPbBr3 nanoparticles that have been treated with NH4SCN to produce essentially trap-free surfaces show an increase of one photon up-conversion quantum yield with little change to the up-conversion energy of activation, as estimated using an Arrhenius analysis. This suggests that mid-gap trap states constitute a loss pathway, and may not be integral to the one-photon excitation mechanism.

Au Exchange or Au Deposition: Dual Reaction Pathways in Au-CsPbBr Heterostructure Nanoparticles.

We have designed a facile synthetic strategy for the selective deposition of Au metal on all-inorganic CsPbBr perovskite nanocrystals that includes the addition of PbBr salt along with AuBr salt. PbBr is necessary because the addition of Au to solutions of CsPbBr nanocrystals otherwise results in the exchange of Au ions from solution with Pb cations within the nanocrystal lattice to produce CsAuAuBr nanocrystals with a tetragonal crystal structure and a band gap of about 1.6 eV, in addition to Au metal deposition.

Exciton-to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals.

We report the one-pot synthesis of colloidal Mn-doped cesium lead halide (CsPbX) perovskite nanocrystals and efficient intraparticle energy transfer between the exciton and dopant ions resulting in intense sensitized Mn luminescence. Mn-doped CsPbCl and CsPb(Cl/Br) nanocrystals maintained the same lattice structure and crystallinity as their undoped counterparts with nearly identical lattice parameters at ∼0.2% doping concentrations and no signature of phase separation.