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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Developing multifunctional nanoparticles in a 1-D coordination polymer of Cd(II)

A simple synthesis for the integration of different nanoparticles (NPs) including Ag, Au, Pd, Cr and mixed (Cu/Fe), has been demonstrated within the nanopores of a non-activated one dimensional porous coordination polymer (PCP) of Cd(II) due to its high flexible structure. There are two different mechanisms (acid formation (HCl/HNO{sub 3}) and redox activity of the framework) elucidated by electron paramagnetic resonance (EPR). Presence of –NO{sub 2} groups of the ligand act as anchoring sites for metal ions of metal precursors leading to NPs growth within the PCP explained by FTIR. High resolution transmission electron microscopy (HRTEM) images provided insight of the chemical and physical characteristics of the NPs within the framework. Ag/AgO NPs exhibit excellent antibacterial properties at extremely low concentrations. The polymer shows potential for sequestration and reduction of hexavalent Cr (highly toxic) to elemental, trivalent and tetravalent Cr (non toxic). This framework is also an excellent template for fabrication and dry storage of nanoparticles synthesized by mixed metal precursors. Ferromagnetic properties have been shown by Ag and Au NPs integrated frameworks while Cu/Fe@Cd-PCP behaves as a paramagnet material at room temperature. - Graphical abstract: Different types of nanoparticles have been synthesized by utilizing a 1D porous coordination polymer of Cd(II) in its as-synthesized state at RT and without use of any reducing agent. Display Omitted - Highlights: • A number of NPs have been synthesized in a 1D PCP without reducing agent. • –NO2 groups act as anchoring sites for the metal ions of metal precursors. • Ag/AgO NPs show excellent antibacterial properties at very low concentrations. • PCP shows potential for sequestration and reduction of Cr(VI) to Cr(0, III and IV).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Magnetic properties and homogeneous distribution of Gd{sup 3+} ions in gadolinium molybdenum borate glass with high Gd{sub 2}O{sub 3} content

Highlights: ► The magnetic susceptibility of Gd{sub 2}O{sub 3}–MoO{sub 3}–B{sub 2}O{sub 3} glass was examined in T = 1.8–300 K. ► The effective magnetic moment was μ{sub eff} = 7.87 μ{sub B}. ► The Weiss constant was θ = −0.7 K. ► Gd{sup 3+} ions are distributed homogeneously as paramagnetic ions down to T = 1.8 K. -- Abstract: The magnetic susceptibility and specific heat of 21.25Gd{sub 2}O{sub 3}–63.75MoO{sub 3}–15B{sub 2}O{sub 3} (mol%) glass showing the crystallization of ferroelastic β′-Gd{sub 2}(MoO{sub 4}){sub 3} crystals are examined in the temperature range of T = 1.8–300 K to clarify magnetic and distribution states of Gd{sup 3+} ions. The magnetic susceptibility obeys the Curie–Weiss law, giving the effective magnetic moment of μ{sub eff} = 7.87 μ{sub B} and the Weiss constant of θ = −0.7 K. Any peak such as λ-type anomaly is not observed in the temperature dependence of specific heat in T = 1.8–5 K. It is suggested that Gd{sup 3+} ions in the glass with a high Gd{sub 2}O{sub 3} content of 21.25 mol% are distributed homogeneously and randomly as paramagnetic ions down to T = 1.8 K without inducing any strong magnetic interaction. The present study suggests that glasses based on the MoO{sub 3}–B{sub 2}O{sub 3} system are good hosts for the homogeneous solubility of a large amount of rare-earth oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effect of Fe and Co doping on electrical and thermal properties of La{sub 0.5}Ce{sub 0.5}Mn{sub 1−x}(Fe, Co){sub x}O{sub 3} manganites

Graphical abstract: - Highlights: • Low temperature resistivity minimum contributes to Coulomb and Kondo scattering. • Metallic resistivity shows electron, magnon and phonon scattering are significant. • At high temperatures small polaron conduction mechanism is viable. • Susceptibility measurements show ferromagnetic–paramagnetic transition. - Abstract: The effect of Fe and Co doping on structural, electrical and thermal properties of half doped La{sub 0.5}Ce{sub 0.5}Mn{sub 1−x}(Fe, Co){sub x}O{sub 3} is investigated. The structure of these crystallizes in to orthorhombically distorted perovskite structure. The electrical resistivity of La{sub 0.5}Ce{sub 0.5}MnO{sub 3} exhibits metal-semiconductor transition (T{sub MS} at ∼225 K). However, La{sub 0.5}Ce{sub 0.5}Mn{sub 1−x}TM{sub x}O{sub 3} (TM = Fe, Co; 0.0 ≤ x ≤ 0.1) manganites show semiconducting behavior. The thermopower measurements infer hole as charge carriers and electron–magnon as well spin wave fluctuation mechanism are effective at low temperature domain and SPC model fits the observed data at high temperature. The magnetic susceptibility measurement confirms a transition from paramagnetic to ferromagnetic phase. The observed peaks in the specific heat measurements, shifts to lower temperatures and becomes progressively broader with doping of transition metals on Mn-site. The thermal conductivity is measured in the temperature range of 10–350 K with a magnitude in between 10 and 80 mW/cm K.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Real-space visualization of short-range antiferromagnetic correlations in a magnetically enhanced thermoelectric

Short-range magnetic correlations can significantly increase the thermopower of magnetic semiconductors, representing a noteworthy development in the decades-long effort to develop high-performance thermoelectric materials. Here, we reveal the nature of the thermopower-enhancing magnetic correlations in the antiferromagnetic semiconductor MnTe. Using magnetic pair distribution function analysis of neutron scattering data, we obtain a detailed, real-space view of robust, nanometer-scale, antiferromagnetic correlations that persist into the paramagnetic phase above the Neel temperature $T_N$ = 307 K. In this work, the magnetic correlation length in the paramagnetic state is significantly longer along the crystallographic c axis than within the ab plane, pointing to anisotropic magnetic interactions. Ab initio calculations of the spin-spin correlations using density functional theory in the disordered local moment approach reproduce this result with quantitative accuracy. These findings constitute the first real-space picture of short-range spin correlations in a magnetically enhanced thermoelectric and inform future efforts to optimize thermoelectric performance by magnetic means.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Plasmonic Ag nanocomposite phosphate glasses produced via γ-ray irradiation as reduction route

This paper reports on the impact of γ-ray irradiation (10, 100 kGy) on melt-quenched Ag + -doped phosphate glass and the effects of subsequent thermal processing leading to the production of plasmonic Ag nanocomposites. The γ-irradiated glasses were characterized alongside the pristine by differential scanning calorimetry (DSC), Raman spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, optical absorption, and photoluminescence (PL) spectroscopy. DSC characterization showed consistent glass transition temperatures (T g ) before and after γ-irradiation whereas the crystallization temperatures tended to decrease with increasing γ-ray dose. However, a lack of alteration of the glass network structure was supported by Raman spectroscopy. Room temperature EPR spectra clearly showed the formation of phosphorus oxygen hole center (POHC) defects in the undoped host, in addition to another doublet likely associated with a P 3 defect. The presence of paramagnetic silver species encompassing Ag 2+ and 107/109 Ag 0 atoms was also indicated in the silver-activated glass together with POHC defects. Optical absorption spectra were also consistent with the presence of various radiation-induced centers. Further analyzing the glass absorption edge via Tauc plots suggested the formation of electron center (EC) defects in γ-irradiated samples wherein the silver-doped glass exhibited decreasing band gap energies with increasing γ-ray dose. The PL characterization showed the silver-related radio-PL effect was induced exhibiting broad band emission with two maxima around 500 and 625 nm stemming from various molecular Ag$^{x+}_{n}$ clusters. Emission decay analyses revealed that the longer wavelength emission exhibited slower decay. The highest radiation dose of 100 kGy however resulted in weaker emission and faster decay kinetics attributed to energy transfer between the luminescent silver species and POHC defects. Finally subjecting the γ-irradiated Ag-doped glasses to heat treatment near the T g at 490 °C led to the development of the surface plasmon resonance of Ag nanoparticles (NPs) and the vanishing of the Ag$^{x+}_{n}$ clusters luminescence. In conclusion, the presence of the matrix-related EC defects was deemed accountable for the thermally induced reduction and consequent precipitation of Ag NPs making the plasmonic glasses attractive for photonic applications such as nonlinear optics.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Inversion of dislocation-impurity interactions in α -Fe under magnetic state changes

Here, in this work, we investigate the dislocation-impurity interaction energies and their profiles for various 3d elements —V, Cr, Mn, Cu, Ni, and Co —in and around 1/2 $\langle111\rangle$ screw dislocations in α -Fe using ab initio methods. We consider the ferromagnetic and paramagnetic states, with the latter being modeled through both the disordered local moment model and a spin-wave approach. Our findings reveal that (1) magnetic effects are large compared to size misfit effects of substitutional impurities, and (2) dislocation-impurity interactions are dependent on the magnetic state of the matrix and thermal lattice expansion. In particular, Cu changes from core-attractive in the ferromagnetic state to repulsive in the paramagnetic state.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Resistivity distribution and donor properties of antimony-doped n -type Czochralski silicon ingots

We investigate antimony (Sb)-doped Czochralski-grown silicon as an alternative n-type substrate for photovoltaic applications, and characterize their axial resistivity distribution, donor properties, and mechanical strength. We find that Sb-doped ingots can achieve a more uniform resistivity distribution along the axial direction compared to P-doped counterparts. Dopant concentration profiles in P-doped ingots can be accurately modelled using the standard Scheil's equation, accounting only for dopant segregation during solidification. In contrast, modelling Sb-doped ingots requires consideration of both dopant segregation and evaporation effects to fit the dopant distribution accurately. Using electron paramagnetic resonance spectroscopy at 9 K, we observe two hyperfine lines in P-doped samples, and six hyperfine lines for Sb 121 and eight for Sb 123 isotopes, with the number of hyperfine lines governed by the nuclear spins. We further identify two-atom Sb clustering in the Sb-doped wafers, confirmed through simulations of the additional weak electron paramagnetic resonance peaks. Finally, we find that 140 μm as-cut planar Sb-doped wafers exhibit slightly higher mechanical strength compared to P-doped wafers.

14 SOLAR ENERGY↗
DOE OSTI2018

U 8 Al 19 Si 6 , A Uranium Aluminide Silicide with a Stuffed Supercell Grown from Aluminum Flux

In this work, U 8 Al 19 Si 6 is formed from the reaction of uranium oxide and silicon in aluminum flux. Growth of this material is dependent on the presence of surface hydroxyl groups on alumina in the crucible. The compound forms as large cuboid crystals with a complex new structure that is a cubic stuffed supercell of UAl 3 (AuCu 3 parent structure type). It features a 4-fold expansion of the unit cell axis and the addition of atoms on two extra positions resulting in Pm$\bar{3n}$ symmetry. The ordered distribution of aluminum and silicon was determined using single crystal neutron diffraction. The magnetic susceptibility shows temperature independent paramagnetic behavior, while heat capacity measurements are consistent with Fermi liquid characteristics at low temperatures where the Sommerfeld constant is enhanced in comparison to that of a conventional metal. Lastly, these bulk thermodynamic properties indicate that U 8 Al 19 Si 6 is an itinerant electron Pauli paramagnet with moderately enhanced mass charge carrier quasiparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Canting of the Magnetic Moments on the Octahedral Site of an Iron Oxide Garnet in Response to Diamagnetic Cation Substitution

Using neutron powder diffraction and magnetic susceptibility measurements, we report on the preparation and characterization of the temperature- and field-dependent properties of CaY2ZrFe4O12, a composition closely related to the high-temperature ferrimagnet Y3Fe5O12. By diluting the concentration of paramagnetic ions on the octahedral sublattice of the garnet structure, we find temperature-dependent canting of the magnetic moments. This reflects the importance of the octahedral sublattice in mediating the magnetic interactions between the tetrahedral sites and offers insight into a large number of competing magnetic interactions in the garnet structure.

Milam-Guerrero, JoAnna↗
DOE OSTI2023

Magnetic Properties of Tetravalent Pu in the Perovskites BaPuO 3 and SrPuO 3

BaPuO 3 and SrPuO 3 were synthesized, and their structures were refined in the orthorhombic space group Pbnm , a common distortion from the classic $Pm\bar{3}$m over barm cubic perovskite. Magnetic-susceptibility measurements, obtained as a function of temperature over the range of 1.8-320 K, exhibit temperature-dependent behavior, with evidence of long-range magnetic order at temperatures higher than their lanthanide and actinide analogues: BaPuO 3 below 164(1) K and SrPuO 3 below 76(1) K. Effective moments of 1.66(10)μ B for BaPuO 3 and 1.84(8)μ B for SrPuO 3 were obtained by fitting their paramagnetic susceptibilities using the Curie-Weiss law. Further, both are below the free-ion value of 2.68 μ B expected for a Pu 4+ 5 $\mid$ 4 ground level. Ab initio wave function calculations, performed at the relativistic complete active space level including spin-orbit coupling and with an embedded cluster approach that neglects interactions between Pu centers, were used to generate embedded-cluster Pu 4+ magnetic susceptibilities. The calculations agree well with experimental data at higher temperatures, providing evidence that a single-ion representation is sufficient to account for the observed paramagnetic behavior without the need to invoke charge transfer, disproportionation, strong covalent bonding, or other more complex electronic behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Influence of Copper Oxidation State on the Bonding and Electronic Structure of Cobalt-Copper Complexes

Heterobimetallic complexes that pair cobalt and copper were synthesized and characterized by a suite of physical methods, including X-ray diffraction, X-ray anomalous scattering, cyclic voltammetry, magnetometry, electronic absorption spectroscopy, electron paramagnetic resonance, and quantum chemical methods. Both Cu(II) and Cu(I) reagents were independently added to a Co(II) metalloligand to provide (py 3 tren)CoCuCl (1-Cl) and (py 3 tren)CoCu(CH 3 CN) (2-CH 3 CN), respectively, where py3tren is the triply deprotonated form of N,N,N-tris(2-(2-pyridylamino)ethyl)amine. Complex 2-CH 3 CN can lose the acetonitrile ligand to generate a coordination polymer consistent with the formula “(py3tren)CoCu” (2). One-electron chemical oxidation of 2-CH 3 CN with AgOTf generated (py 3 tren)CoCuOTf (1-OTf). The Cu(II)/Cu(I) redox couple for 1-OTf and 2-CH 3 CN is reversible at -0.56 and -0.33 V vs Fc + /Fc, respectively. The copper oxidation state impacts the electronic structure of the heterobimetallic core, as well as the nature of the Co–Cu interaction. Quantum chemical calculations showed modest electron delocalization in the (CoCu) +4 state via a Co–Cu σ bond that is weakened by partial population of the Co–Cu σ antibonding orbital. By contrast, no covalent Co–Cu bonding is predicted for the (CoCu) +3 analogue, and the d-electrons are fully localized at individual metals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Complex Topologies from Simple Building Blocks: Uranium(IV) Thiophosphates

Six new uranium thiophosphates Cs 5 Na 6 [U(PS 4 ) 4 ](PS 4 ) (1), Rb 5 Na 3 [U(PS 4 ) 4 ] (2), CsNa[U(PS 4 ) 2 ] (3), Cs 1.67 Na 0.52 I 0.19 [U(PS 4 ) 2 ] (4), Cs 1.033 Na 1.343 I 0.376 [U(PS 4 ) 2 ] (5), and Rb 1.35 Na 0.93 I 0.28 [U(PS 4 ) 2 ] (6) were obtained from halide flux reactions and characterized using single crystal X-ray diffraction. The structures of these compounds consist of a pseudo-tetrahedral uranium unit that in combination with a set of PS 4 group coordination modes can result in an isolated [U(PS 4 ) 4 ] 8– unit, a [U(PS 4 ) 2 ] 2– chain, or a [U(PS 4 ) 2 ] 2– slab. Optical and magnetic properties of 3 and 4 were collected. Both compounds exhibit paramagnetic behavior, and CsNa[U(PS 4 ) 2 ] (3) exhibits a magnetic transition at 200–225 K between two paramagnetic states that both have similar effective magnetic moments of 4.13 and 4.19 µ B /F.U., and strong antiferromagnetic interactions with θ = -183 and -172 K, for the high- and low-temperature states, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Stability, Crystal Chemistry, and Magnetism of U 2+ x Ni 21– x \B 6 and Nb 3– y Ni 20+ y B 6 and the Role of Uranium in the Formation of the Quaternary U 2– z Nb z Ni 21 B 6 and U δ Nb 3-δ Ni 20 B 6 Systems

In this work, we investigated the U–Ni–B and Nb–Ni–B systems to search for possible new heavy fermion compounds and superconducting materials. The formation, crystal chemistry, and physical properties of U 2 Ni 21 B 6 and Nb 3– y Ni 20+ y B 6 [ternary derivatives of the cubic Cr 23 C 6 -type ( cF 116, $Fm\bar{3}m$)] have been studied; the formation of the hypothetical “U 3 Ni 20 B 6 ” and “Nb 2 Ni 21 B 6 ” has been disproved. U 2 Ni 21 B 6 [ a = 10.6701(2) Å] crystallizes in the ordered W 2 Cr 21 C 6 -type, whereas Nb 3– y Ni 20+ y B 6 [ a = 10.5842(1) Å] adopts the Mg 3 Ni 20 B 6 -type. Ni in U 2 Ni 21 B 6 can be substituted by U, leading to the solid solution U 2+ x Ni 21– x B 6 (0 ≤ x ≤ 0.3); oppositely, Nb in Nb 3 Ni 20 B 6 is partially replaced by Ni, forming the solution Nb 3– y Ni 20+ y B 6 (0 ≤ y ≤ 0.5), none of them reaching the limit corresponding to the hypothetically ordered “U 3 Ni 20 B 6 ” and “Nb 2 Ni 21 B 6 ”. These results prompted us to investigate quaternary compounds U 2– z Nb z Ni 21 B 6 and U δ Nb 3-δ Ni 20 B 6 : strong competition in the occupancy of the 4 a and 8 c sites by U, Nb, and Ni atoms has been observed, with the 4 a site occupied by U/Ni atoms only and the 8 c site filled by U/Nb atoms only. U 2 Ni 21 B 6 , U 2.3 Ni 20.7 B 6 , and Nb 3 Ni 20 B 6 are Pauli paramagnets. Interestingly, Nb 2.5 Ni 20.5 B 6 shows ferromagnetism with T C ≈ 11 K; the Curie–Weiss fit gives an effective magnetic moment of 2.78 μ B /Ni, suggesting that all Ni atoms in the formula unit contribute to the total magnetic moment. The M(H) data at 2 K further corroborate the ferromagnetic behavior with a saturation moment of 10 μ B /fu (≈0.49 μ B /Ni). The magnetic moment of Ni at the 4 a site induces a moment in all of the Ni atoms of the whole unit cell ( 32f and 48h sites), with all atoms ordering ferromagnetically at 11 K. Density functional theory (DFT) shows that the formation of U 2 Ni 21 B 6 and Nb 3 Ni 20 B 6 is energetically preferred. The various electronic states generating ferromagnetism on Nb 2.5 Ni 20.5 B 6 and Pauli paramagnetism on U 2 Ni 21 B 6 and Nb 3 Ni 20 B 6 have been identified.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Etch Products of Copper Atomic Layer Etching by Oxidation and Formic Acid Vapor

Atomic layer etching (ALE) of metals offers a path to greater control of selectivity, etch rate, and etch profile. However, tailoring a process to meet these demands requires an understanding of the volatile etch product, which is challenging to detect due to low product concentrations and the paramagnetism of many metalorganic products. Here, in this work, several complementary analysis techniques were used to determine the volatile etch product and residual surface species of a Cu ALE process based on plasma oxidation and formic acid vapor etching of the oxidized layer. It was shown that the volatile product was copper formate with a Cu 2+ paramagnetic center, in concordance with prior density functional theory (DFT) calculations. While copper formate tetrahydrate was formed, it was determined that the tetrahydrate product was confined to the surface, with anhydrous copper formate being the volatile etch product.

Smith, Taylor G. [Univ. of California, Los Angeles↗
DOE OSTI2023

T 1 Anisotropy Elucidates Spin Relaxation Mechanisms in an S = 1 Cr(IV) Optically Addressable Molecular Qubit

Paramagnetic molecules offer unique advantages for quantum information science owing to their spatial compactness, synthetic tunability, room-temperature quantum coherence, and potential for optical state initialization and readout. However, current optically addressable molecular qubits are hampered by rapid spin–lattice relaxation ( T 1 ) even at sub-liquid nitrogen temperatures. Here, we use temperature- and orientation-dependent pulsed electron paramagnetic resonance (EPR) to elucidate the negative sign of the ground state zero-field splitting (ZFS) and assign T 1 anisotropy to specific types of motion in an optically addressable S = 1 Cr(o-tolyl) 4 molecular qubit. The anisotropy displays a distinct sin 2 (2θ) functional form that is not observed in S = 1/2 Cu(acac) 2 or other Cu(II)/V(IV) microwave addressable molecular qubits. The Cr(o-tolyl) 4 T 1 anisotropy is ascribed to couplings between electron spins and rotational motion in low-energy acoustic or pseudoacoustic phonons. Our findings suggest that rotational degrees of freedom should be suppressed to maximize the coherence temperature of optically addressable qubits.

magnetic properties↗
DOE OSTI2024

Electrical Control of Magnetic Resonance in Phase Change Materials

Metal–insulator transitions (MITs) in resistive switching materials can be triggered by an electric stimulus that produces significant changes in the electrical response. When these phases have distinct magnetic characteristics, dramatic changes in the spin excitations are also expected. The transition metal oxide La 0.7 Sr 0.3 MnO 3 (LSMO) is a ferromagnetic metal at low temperatures and a paramagnetic insulator above room temperature. When LSMO is in its metallic phase, a critical electrical bias has been shown to lead to an MIT that results in the formation of a paramagnetic resistive barrier transverse to the applied electric field. Using spin-transfer ferromagnetic resonance spectroscopy, we show that even for electrical biases less than the critical value that triggers the MIT, there is magnetic phase separation, with the spin-excitation resonances varying systematically with applied bias. Therefore, voltage-triggered MITs in LSMO can alter magnetic resonance characteristics, offering an effective method for tuning synaptic weights in neuromorphic circuits.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Quantized Electronic Doping towards Atomically Controlled “Charge-Engineered” Semiconductor Nanocrystals

“Charge engineering” of semiconductor nanocrystals (NCs) through so-called electronic impurity doping is a long-standing challenge in colloidal chemistry and holds promise for ground-breaking advancements in many optoelectronic, photonic, and spin-based nanotechnologies. To date, our knowledge is limited to a few paradigmatic studies on a small number of model compounds and doping conditions, with important electronic dopants still unexplored in nanoscale systems. Equally importantly, fine-tuning of charge engineered NCs is hampered by the statistical limitations of traditional approaches. The resulting intrinsic doping inhomogeneity restricts fundamental studies to statistically averaged behaviors and complicates the realization of advanced device concepts based on their advantageous functionalities. We aim to address these issues by realizing the first example of II–VI NCs electronically doped with an exact number of heterovalent gold atoms, a known p-type acceptor impurity in bulk chalcogenides. Single-dopant accuracy across entire NC ensembles is obtained through a novel non-injection synthesis employing ligand-exchanged gold clusters as “quantized” dopant sources to seed the nucleation of CdSe NCs in organic media. Structural, spectroscopic, and magneto-optical investigations trace a comprehensive picture of the physical processes resulting from the exact doping level of the NCs. Gold atoms, doped here for the first time into II–VI NCs, are found to incorporate as nonmagnetic Au + species activating intense size-tunable intragap photoluminescence and artificially offsetting the hole occupancy of valence band states. Fundamentally, the transient conversion of Au + to paramagnetic Au 2+ (5d 9 configuration) under optical excitation results in strong photoinduced magnetism and diluted magnetic semiconductor behavior revealing the contribution of individual paramagnetic impurities to the macroscopic magnetism of the NCs. Altogether, our results demonstrate a new chemical approach toward NCs with physical functionalities tailored to the single impurity level and offer a versatile platform for future investigations and device exploitation of individual and collective impurity processes in quantum confined structures.

36 MATERIALS SCIENCE↗