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Expanding the range of available aliovalently doped semiconductor nanocrystals has largely been motivated by the potential for realizing and controlling plasmon-exciton coupling in a single phase. ...

The design of photocatalysts with enhanced efficiency is pivotal to sustainable environmental remediation and renewable energy technologies. Simultaneous optimization of different factors affecting the performance of a photocatalyst, including the density of active surface sites, charge carrier separation, and valence and conduction band redox potentials, remains challenging. Here, we report the synthesis of ternary gallium tin oxide (GTO) nanocrystals (NCs) with variable composition and investigate the role of Ga3+ dopants in altering the electronic structure of rutile-type SnO2 NC lattice using steady-state and time-resolved photoluminescence spectroscopies. Substitutional incorporation of Ga3+ increases the band gap of SnO2 NCs, imparting the reducing power to the conduction band electrons, and causes the formation of acceptor states, which, in conjunction with electron trapping by donors (oxygen vacancies), leads to stabilization of the photoexcited carriers. Combination of a decrease in the charge re...

Semiconductor photocatalysis has emerged as an efficient and sustainable advanced oxidation process for wastewater treatment and other environmental remediation and forms the basis for water splitting and solar-to-fuel conversion. Nanocrystalline metal oxides are particularly promising photocatalysts because of their efficiency, stability, and low toxicity. However, the influence of the crystal structure and defects on the photocatalytic activity of these polymorphic materials is still poorly understood. In this work we investigated the structural dependence of the photocatalytic activity of nanocrystalline Ga2O3. We demonstrate that metastable cubic-phase γ-Ga2O3 prepared from colloidal nanocrystals exhibits an anomalously high photocatalytic activity, which rapidly decreases upon thermally induced transformation to monoclinic β-Ga2O3. Using steady-state and time-resolved photoluminescence measurements we showed that the reduction in photocatalytic activity upon annealing is accompanied by a decrease in ...

Investigation of the origin of high-Curie temperature ferromagnetism in diluted magnetic oxides has become one of the focal points of research on solid-state magnetism. While several possible mechanisms have been proposed theoretically, broader experimental evidence is still lacking. Here we report a comparative study of the electronic structure and magnetic properties of colloidal Fe-doped In2O3 and SnO2 nanocrystals, as building blocks for grain-boundary-rich diluted magnetic oxide films. The dopant ions in both nanocrystal host lattices are principally in 3+ oxidation state, with possibly a minor presence of Fe2+ in In2O3, and no conclusive evidence of the presence of Fe2+ in SnO2 nanocrystals. Subsequently, we found that Fe-doped In2O3 nanocrystalline films exhibit only minor ferromagnetic ordering (with a magnetic moment of less than ca. 0.1 μB/Fe) and decreasing saturation magnetization with increasing doping concentration at room temperature. The saturation magnetic moment of Fe-doped SnO2 nanocrys...

Development of inorganic phosphors capable of generating white light in a homogeneous and reproducible fashion without the use of rare earth elements can lead to an efficient, long-lasting, and sustainable solid state lighting. The design of such phosphors requires that different inorganic components emitting in complementary spectral ranges are electronically coupled to avoid the challenges associated with a multicomponent approach, such as inhomogeneity, poor chromaticity control, and low color rendering index. Here we demonstrate coupling between electronically excited blue-emitting Ga2O3 and orange-red-emitting CdSe/CdS core/shell nanocrystals by surface-enabled Forster resonance energy transfer. This energy transfer process is evident from quenching of Ga2O3 (donor) and an enhancement of CdSe/CdS (acceptor) nanocrystal emission and is further confirmed through the diminished lifetime of Ga2O3 and significantly extended lifetime of CdSe/CdS nanocrystals in the composite films. Controlling the energy t...

The origin of anisotropy at the molecular and electronic structure levels in individual β-Ga2O3 nanowires grown along the crystallographic b direction was studied using linearly polarized X-ray absorption imaging at both gallium L3 and oxygen K edges. The O K-edge spectrum shows significant linear dichroism for the electric field vector of the X-rays oriented parallel and perpendicular to the nanowire long axis. The contributions from the three nonequivalent oxygen sites to the observed spectral anisotropy were elucidated by using FDMNES calculations in the framework of the multiple scattering theory. The role of relevant O and Ga orbitals in the linearly polarized O K-edge absorption was determined based on the point group symmetry arguments. The results of this work suggest mixed covalent and ionic character of the Ga–O bond in individual nanowires, with the dominant contribution of O 2pz orbitals to the absorption spectrum for the electric field vector oriented perpendicular, and O 2px,y orbitals for t...

We report a quantitative analysis and development of hybrid white-light-emitting nanoconjugates, prepared by functionalizing colloidal γ-Ga2O3 nanocrystals with selected organic fluorophores. Using the Forster resonance energy transfer (FRET) formalism, we studied the coupling of native defect states in Ga2O3 nanocrystals, as energy donors, with different orange-red-emitting fluorophores bound to nanocrystal surfaces, as energy acceptors. Variations in the average nanocrystal size and dye surface coverage were used to characterize the efficiency of the energy transfer process and the corresponding donor–acceptor separations. The results show that for approximately three rhodamine B molecules per nanocrystal the energy transfer efficiency increases from 23% to 49% by decreasing the NC size from 5.3 to 3.6 nm. These FRET efficiencies correspond to the estimated donor–acceptor distances of 3.55 ± 0.02 and 2.99 ± 0.03 nm, respectively. Similar trends were observed for ATTO 590-conjugated Ga2O3 nanocrystals, a...

Understanding the mechanisms of defect-related photoluminescence in colloidal transparent conducting oxide nanocrystals is important for the development of new multifunctional nanostructures and devices. Here we report a study of the role of NC size, structure, defects, and surface capping on the photoluminescence energy, efficiency, and dynamics of colloidal γ-Ga2O3 nanocrystals. A strong blue emission (quantum yield ∼25%) is associated with the presence of the vacancy-defect sites, and assigned to the donor–acceptor pair (DAP) recombination. The emission energy and lifetime are generally determined by the donor and acceptor binding energies (which are dependent on the NC structure) and the attractive Coulombic interactions between charged donor and acceptor sites (which are dependent on the defect concentration). Variable temperature photoluminescence measurements reveal that binding energies of the donor and acceptor levels are also size-dependent; in 6.0 ± 1.0 nm γ-Ga2O3 nanocrystals donor binding ene...

We report the synthesis and separation of colloidal indium tin oxide (ITO) nanocrystals in the stable cubic bixbyite (bcc-ITO) and metastable corundum (rh-ITO) phase under identical conditions, based on the size−structure correlation. Both phases are obtained in the same reactions, with nanocrystals below ca. 5 nm in size having corundum crystal structure. This bimodal size distribution allows for the separation of the nanocrystal phases by size selective precipitation. A comparative study of bcc-ITO and rh-ITO nanocrystals reveals a dramatic difference in their optical and electrical properties. Unlike smaller rh-ITO nanocrystals, bcc-ITO nanocrystals exhibit a strong absorption in the near-infrared (NIR) region arising from the plasmon oscillations due to the presence of free electrons. The difference in the free electron concentration in bcc-ITO and rh-ITO nanocrystals is related to the different electronic structure of the donor states, associated with Sn4+ dopants, in these two nanocrystal allotropic...

Doping semiconductor nanocrystals is crucial for enhancing and manipulating their functional properties, but the doping mechanism and the effects of dopants on the nanocrystal growth and structure ...

Colloidal free-standing Cr3+-doped In2O3 nanocrystals were synthesized in oleylamine from indium (III) and chromium (III) acetylacetonate precursors. The nanocrystals were treated with trioctylphosphine oxide to remove surface-bound dopant ions and ensure internal doping. The lattice resolved transmission electron microscopy images reveal that nanocrystals are faceted and highly crystalline, with no evidence of a secondary phase formation. The average doping concentration estimated with energy dispersive X-ray spectroscopy at the single nanocrystal level agrees with the average doping concentration from the analogous nanocrystal ensemble measurement. Ligand-field electronic absorption spectroscopy suggests that Cr3+ dopants are preferentially substituted for In3+ ions in their trigonally distorted octahedral (b) sites in In2O3 nanocrystals. Nanocrystalline films, prepared under mild conditions using colloidal Cr3+-doped In2O3 nanocrystals as building blocks, exhibit robust room temperature ferromagnetism....