We report the use of targeted $p$- and $n$-type chemical perturbations to manipulate high-${T}_{\mathrm{C}}$ ferromagnetism in ${\mathrm{Mn}}^{2+}\ensuremath{\mathbin:}\mathrm{ZnO}$ ${\mathrm{Co}}^{2+}\ensuremath{\mathbin:}\mathrm{ZnO}$ predictable reproducible ways. demonstrate a clear correlation between nitrogen for an inverse ${\mathrm{Co}}^{2+}\ensuremath{\mathbin:}\mathrm{ZnO}$, both as predicted by recent theoretical models. These reveal rich possibilities exerting external control...

We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots and preparation room-temperature ferromagnetic nanocrystalline thin films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis condensation reaction in DMSO under atmospheric conditions. Synthesis was monitored electronic absorption electron paramagnetic resonance (EPR) spectroscopies. Zn(OAc)2 found to strongly inhibit oxidation Mn2+ O2, allowing be performed aerobically. ions removed from surfaces as-prepared using...

The hypothesis that high-Curie-temperature ferromagnetism in cobalt-doped ZnO (Co2+: ZnO) is mediated by charge carriers was tested controlled introduction and removal of the shallow donor interstitial zinc. Using oriented epitaxial Co2+: films grown chemical vapor deposition, kinetics measurements demonstrate a direct correlation between oxidative quenching diffusion oxidation These results systematic variation key parameter involved and, process, unambiguously reveal this to be dependent...

We report the preparation of spin-coated nickel-doped zinc oxide nanocrystalline thin films using high-quality colloidal diluted magnetic semiconductor (DMS) quantum dots as solution precursors. These show robust ferromagnetism with Curie temperatures above 350K and 300K saturation moments up to 0.1Bohr magnetons per nickel. results demonstrate a step toward use zero-dimensional DMS nanocrystals building blocks for bottom-up construction more complex ferromagnetic nanostructures.

Giving the green light: The connection of two CrIII sensitizers around a central ErIII acceptor in self-assembled cation provides high local metal concentrations that favor efficient nonlinear energy transfer upconversion luminescence (see picture). Upon selective low-energy near-infrared irradiation CrIII-centered transitions, 1 displays an unprecedented molecular two-photon upconverted ErIII-centered emission. Detailed facts importance to specialist readers are published as "Supporting...

We report the discovery that high-TC ferromagnetism in manganese-doped ZnO (Mn2+:ZnO) can be activated by amine binding and calcination. The activation of is attributed to incorporation uncompensated p-type dopants into lattice upon calcination, a process has substantial precedence literature surrounding ZnO. experimental observations are consistent with microscopic mechanism involving formation bound magnetic polarons introduction Mn2+:ZnO. These results clearly demonstrate Mn2+:ZnO...

This work illustrates a simple approach for optimizing long-lived near-infrared lanthanide-centered luminescence using trivalent chromium chromophores as sensitizers. Reactions of the segmental ligand L2 with stoichiometric amounts M(CF(3)SO(3))(2) (M = Cr, Zn) and Ln(CF(3)SO(3))(3) (Ln Nd, Er, Yb) under aerobic conditions quantitatively yield D(3)-symmetrical trinuclear [MLnM(L2)(3)](CF(3)SO(3))(n) complexes Zn, n 7; M 9), in which central lanthanide activator is sandwiched between two...

Absorption and photoluminescence properties of terrylene derivative 7,8,15,16-tetraazaterrylene (TAT) in its solution crystal phases have revealed rather unusual spectral characteristics that defy classification terms simple H- or J-aggregate-coupled systems. TAT readily forms crystalline aggregates by either self-assembly physical vapor deposition, based on π stacks aligned roughly along the crystallographic a axis. Using Holstein-style Hamiltonian including both Frenkel charge-transfer...

Over the past five years, considerable work has been carried out in exploration of candidate diluted oxide magnetic semiconductors with high Curie temperatures. Fueled by early experimental results and theoretical predictions, claims ferromagnetism at above room temperature doped oxides have abounded. In general, neither true nature these materials nor physical causes magnetism adequately determined. It is now apparent that dilute systems are deceptively complex. We consider two...

Conduction band electrons in colloidal ZnO quantum dots have been prepared photochemically and examined by electron paramagnetic resonance spectroscopy. Nanocrystals of 4.6 nm diameter containing single $S$-shell conduction ${g}^{*}=1.962$ a room-temperature ensemble spin-dephasing time $T_{2}{}^{*}=25\text{ }\text{ }\mathrm{ns}$, as determined from linewidth analysis. Increasing the population leads to increased ${g}^{*}$ decreased $T_{2}{}^{*}$, both associated with formation $P$-shell...

We report the preparation and investigation of charged colloidal Co2+:ZnO Mn2+:ZnO nanocrystals. Although both magnetically doped semiconductor nanocrystals have been reported previously, as described herein not. Conduction band electrons were introduced into ZnO diluted magnetic (DMS) photochemically, resulting TM2+-e-CB interactions observed by electron paramagnetic resonance spectroscopy (TM2+ = Co2+ or Mn2+). This new motif reveals attractive opportunities for studying spin effects in...

Colloidal reduced ZnO nanocrystals are potent reductants for one-electron or multielectron redox chemistry, with reduction potentials tunable via the quantum confinement effect. Other methods tuning of these unusual reagents desired. Here, we describe synthesis and characterization a series colloidal Zn(1-x)Mg(x)O Zn(0.98-x)Mg(x)Mn(0.02)O in which Mg(2+) substitution is used to tune nanocrystal potential. The effect doping on band-edge was investigated using electronic absorption,...

Colloidal ZnO semiconductor nanocrystals have previously been shown to accumulate multiple delocalized conduction-band electrons under chemical, electrochemical, or photochemical reducing conditions, leading emergent semimetallic characteristics such as quantum plasmon resonances and raising prospects for application in multielectron redox transformations. Here, we demonstrate a dramatic enhancement the capacitance of colloidal through aliovalent Fe3+-doping. Very high areal volumetric...

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTTunable Electronic Structure and Surface Defects in Chromium-Doped Colloidal SrTiO3−δ NanocrystalsWilliam L. Harrigan, Samuel E. Michaud, Keith A. Lehuta, Kevin R. Kittilstved*View Author Information Department of Chemistry, University Massachusetts Amherst, 710 N. Pleasant Street, 01003, United States*K. Kittilstved. E-mail: [email protected]Cite this: Chem. Mater. 2016, 28, 2, 430–433Publication Date (Web):January 7, 2016Publication History...

Cobalt-doped ZnO (Co2+:ZnO) films were studied by magnetic circular dichroism (MCD) spectroscopy. A broad 300K ferromagnetic MCD signal was observed between 1.4 and 4.0eV after exposure of paramagnetic Co2+:ZnO to zinc metal vapor, attributed low-energy photoionization transitions originating from a spin-split donor impurity band in n-type Co2+:ZnO.

Electronic absorption, magnetic circular dichroism (MCD), photoconductivity, and valence-band x-ray photoelectron (XPS) spectroscopic measurements were performed on epitaxial ${\text{Zn}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{O}$ films to investigate the origin of mid-gap band that appears upon introduction ${\text{Mn}}^{2+}$ into ZnO lattice. Absorption MCD spectroscopies reveal ${\text{Mn}}^{2+}$-related intensity at energies below first excitonic transition ZnO, tailing well visible...

The ground state electronic structure of Fe³⁺ dopants in colloidal ZnO nanocrystals is studied by EPR spectroscopy and reveals multiple coordination environments during nanocrystal growth.

The fundamental properties of electrons in the prototypical n-type oxide nanocrystal, Al3+-doped ZnO, have been studied at both ensemble and single-particle levels by spectroscopic electron force microscopic techniques. We developed implemented a new synthetic methodology that enables tunable incorporation Al3+ ZnO nanocrystal an "etching–regrowth–doping" (ERD) strategy single-pot reaction. ensemble-averaged evolution speciation were using electronic absorption spectroscopy powder X-ray...

The effects of photodoping on the electronic structure Fe(3+)-doped ZnO colloidal nanocrystals are presented. We observe disappearance spectroscopic signatures attributed to both substitutional Fe(3+) and interstitial in host as a function time, which precede appearance well-known localized surface plasmon resonance from conduction band electrons nanocrystals. These results suggest that oxidation state defects can be reversibly switched

High-temperature magnetic ordering in Mn2+- and Co2+-doped ZnO diluted semiconductors has been predicted theoretically confirmed experimentally to have different charge-carrier requirements. This paper summarizes some of these experimental theoretical results relates the carrier polarity requirements for 300K ferromagnetism Mn2+:ZnO Co2+:ZnO differences charge-transfer electronic structures two materials.

The local environment of Cr3+ during the sol–gel synthesis 1% and 5% Cr3+-doped SrTiO3 (Cr3+:SrTiO3) bulk powders was systematically studied by structural characterization techniques dopant-specific spectroscopies. After calcination at 800 °C, precursors were annealed between 850 °C 1050 for up to 6 h. We observe formation numerous phases in addition final product SrTiO3. One these is a metastable Ruddelsden–Popper phase (Sr2TiO4) that forms when precursor less than 2 Electron paramagnetic...