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Showing papers on "Photoluminescence published in 2010"


Journal ArticleDOI
TL;DR: The electronic properties of ultrathin crystals of molybdenum disulfide consisting of N=1,2,…,6 S-Mo-S monolayers have been investigated by optical spectroscopy and the effect of quantum confinement on the material's electronic structure is traced.
Abstract: The electronic properties of ultrathin crystals of molybdenum disulfide consisting of N=1,2,…,6 S-Mo-S monolayers have been investigated by optical spectroscopy Through characterization by absorption, photoluminescence, and photoconductivity spectroscopy, we trace the effect of quantum confinement on the material's electronic structure With decreasing thickness, the indirect band gap, which lies below the direct gap in the bulk material, shifts upwards in energy by more than 06 eV This leads to a crossover to a direct-gap material in the limit of the single monolayer Unlike the bulk material, the MoS₂ monolayer emits light strongly The freestanding monolayer exhibits an increase in luminescence quantum efficiency by more than a factor of 10⁴ compared with the bulk material

12,822 citations


Journal ArticleDOI
TL;DR: This observation shows that quantum confinement in layered d-electron materials like MoS(2), a prototypical metal dichalcogenide, provides new opportunities for engineering the electronic structure of matter at the nanoscale.
Abstract: Novel physical phenomena can emerge in low-dimensional nanomaterials. Bulk MoS2, a prototypical metal dichalcogenide, is an indirect bandgap semiconductor with negligible photoluminescence. When the MoS2 crystal is thinned to monolayer, however, a strong photoluminescence emerges, indicating an indirect to direct bandgap transition in this d-electron system. This observation shows that quantum confinement in layered d-electron materials like MoS2 provides new opportunities for engineering the electronic structure of matter at the nanoscale.

7,886 citations


Journal ArticleDOI
TL;DR: The facile one-step alkali-assisted electrochemical fabrication of CQDs with sizes of 1.2– 3.8 nm which possess size-dependent photoluminescence (PL) and excellent upconversion luminescence properties are reported and the design of photocatalysts is demonstrated to harness the use of the full spectrum of sunlight.
Abstract: Carbon nanostructures are attracting intense interest because of their many unique and novel properties. The strong and tunable luminescence of carbon materials further enhances their versatile properties; in particular, the quantum effect in carbon is extremely important both fundamentally and technologically. Recently, photoluminescent carbonbased nanoparticles have received much attention. They are usually prepared by laser ablation of graphite, electrochemical oxidation of graphite, electrochemical soaking of carbon nanotubes, thermal oxidation of suitable molecular precursors, vapor deposition of soot, proton-beam irradiation of nanodiamonds, microwave synthesis, and bottom-up methods. Although small (ca. 2 nm) graphite nanoparticles show strong blue photoluminescence (PL), definitive experimental evidence for luminescence of carbon structure arising from quantum-confinement effects and size-dependent optical properties of carbon quantum dots (CQDs) remains scarce. Herein, we report the facile one-step alkali-assisted electrochemical fabrication of CQDs with sizes of 1.2– 3.8 nm which possess size-dependent photoluminescence (PL) and excellent upconversion luminescence properties. Significantly, we demonstrate the design of photocatalysts (TiO2/CQDs and SiO2/CQDs complex system) to harness the use of the full spectrum of sunlight (based on the upconversion luminescence properties of CQDs). It can be imagined that judicious cutting of a graphite honeycomb layer into ultrasmall particles can lead to tiny fragments of graphite, yielding CQDs, which may offer a straightforward and facile strategy to prepare high-quality CQDs. Using graphite rods as both anode and cathode, and NaOH/EtOH as electrolyte, we synthesized CQDs with a current intensity of 10–200 mAcm . As a reference, a series of control experiments using acids (e.g. H2SO4/EtOH) as electrolyte yielded no formation of CQDs. This result indicates that alkaline environment is the key factor, and OH group is essential for the formation of CQDs by the electrochemical oxidation process. Figure 1a shows a trans-

2,266 citations


Journal ArticleDOI
TL;DR: In this paper, the decoupling of quantum effects on excitation and emission is described, along with the use of quantum dots as sensitizers in phosphors, and the multimodal applications of quantum dot, including in electroluminescence device, solar cell and biological imaging.
Abstract: Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

964 citations


Journal ArticleDOI
TL;DR: What is believed to be the first experimental observation of lasing from the direct gap transition of Ge-on-Si at room temperature using an edge-emitting waveguide device is reported.
Abstract: Monolithic lasers on Si are ideal for high-volume and large-scale electronic-photonic integration. Ge is an interesting candidate owing to its pseudodirect gap properties and compatibility with Si complementary metal oxide semiconductor technology. Recently we have demonstrated room-temperature photoluminescence, electroluminescence, and optical gain from the direct gap transition of band-engineered Ge-on-Si using tensile strain and n-type doping. Here we report what we believe to be the first experimental observation of lasing from the direct gap transition of Ge-on-Si at room temperature using an edge-emitting waveguide device. The emission exhibited a gain spectrum of 1590-1610 nm, line narrowing and polarization evolution from a mixed TE/TM to predominantly TE with increasing gain, and a clear threshold behavior.

902 citations


Journal ArticleDOI
Dengyu Pan1, Jingchun Zhang1, Zhen Li1, Chao Wu1, Xiumei Yan1, Minghong Wu1 
TL;DR: A unique emission that is strongly dependent on pH, solvent, spin, and excitation wavelength was observed in high blue luminescent carbon nanoparticles prepared by a one-step pyrolytic route from ethylenediamine-tetraacetic acid salts.

554 citations


Journal ArticleDOI
Yaping Du1, Bing Xu1, Tao Fu1, Miao Cai1, Feng Li1, Yan Zhang1, Qiangbin Wang1 
TL;DR: Monodisperse Ag(2)S quantum dots synthesized via pyrolysis of Ag(DDTC) in oleic acid, octadecylamine, and 1-octadecene emit near-IR emission at 1058 nm under 785 nm excitation.
Abstract: Monodisperse Ag(2)S quantum dots (QDs) were synthesized via pyrolysis of Ag(DDTC) in oleic acid, octadecylamine, and 1-octadecene. The uniform alkyl-capped Ag(2)S QDs with a size of 10.2 nm emit near-IR emission at 1058 nm under 785 nm excitation.

549 citations


Journal ArticleDOI
TL;DR: Catalyst-free growth of (In)GaN nanowires on (001) silicon substrate by plasma-assisted molecular beam epitaxy is demonstrated and structural characterization by high-resolution transmission electron microscopy (HRTEM) indicates that thenanowires are relatively defect-free.
Abstract: Catalyst-free growth of (In)GaN nanowires on (001) silicon substrate by plasma-assisted molecular beam epitaxy is demonstrated. The nanowires with diameter ranging from 10 to 50 nm have a density of 1−2 × 1011 cm−2. P- and n-type doping of the nanowires is achieved with Mg and Si dopant species, respectively. Structural characterization by high-resolution transmission electron microscopy (HRTEM) indicates that the nanowires are relatively defect-free. The peak emission wavelength of InGaN nanowires can be tuned from ultraviolet to red by varying the In composition in the alloy and “white” emission is obtained in nanowires where the In composition is varied continuously during growth. The internal quantum efficiency varies from 20−35%. Radiative and nonradiative lifetimes of 5.4 and 1.4 ns, respectively, are obtained from time-resolved photoluminescence measurements at room temperature for InGaN nanowires emitting at λ = 490 nm. Green- and white-emitting planar LEDs have been fabricated and characterized. ...

487 citations


Journal ArticleDOI
TL;DR: A two-temperature model describing the electrons and their interaction with strongly coupled optical phonons can account for the experimental observations of significant light emission from graphene under excitation by ultrashort (30-fs) laser pulses.
Abstract: Since graphene has no band gap, photoluminescence is not expected from relaxed charge carriers. We have, however, observed significant light emission from graphene under excitation by ultrashort (30-fs) laser pulses. Light emission was found to occur across the visible spectral range (1.7-3.5 eV), with emitted photon energies exceeding that of the excitation laser (1.5 eV). The emission exhibits a nonlinear dependence on the laser fluence. In two-pulse correlation measurements, a dominant relaxation time of tens of femtoseconds is observed. A two-temperature model describing the electrons and their interaction with strongly coupled optical phonons can account for the experimental observations.

457 citations


Journal ArticleDOI
TL;DR: The function of the emissive dopant in OLEDs was further probed by several physical methods, including electrically detected EPR, cyclic voltammetry, and photoluminescence in the presence of applied current.
Abstract: A highly emissive bis(phosphine)diarylamido dinuclear copper(I) complex (quantum yield = 57%) was shown to exhibit E-type delayed fluorescence by variable temperature emission spectroscopy and photoluminescence decay measurement of doped vapor-deposited films. The lowest energy singlet and triplet excited states were assigned as charge transfer states on the basis of theoretical calculations and the small observed S_1−T_1 energy gap. Vapor-deposited OLEDs doped with the complex in the emissive layer gave a maximum external quantum efficiency of 16.1%, demonstrating that triplet excitons can be harvested very efficiently through the delayed fluorescence channel. The function of the emissive dopant in OLEDs was further probed by several physical methods, including electrically detected EPR, cyclic voltammetry, and photoluminescence in the presence of applied current.

412 citations


Journal ArticleDOI
TL;DR: The photocatalytic performance indicated that Ag deposit acted as not only electron sinks to enhance the separation of photoexcited electrons from holes, but also charge carrier recombination centers, so the optimized amount of Ag deposit was investigated.

Journal ArticleDOI
Luyuan Zhang1, Longwei Yin1, Cheng-Xiang Wang1, Ning Lun1, Yong-Xin Qi1, Dong Xiang1 
TL;DR: ZnO quantum dots with tunable diameters in a range of 22−78 nm were synthesized via a sol−gel route using self-made zinc−oleate complex as a precursor.
Abstract: To get a real understanding on the complexity of origin and mechanism of visible emission for ZnO quantum dots (QDs), we systematically property of visible emission of ZnO QDs with tunable diameters in a range of 22−78 nm synthesized via a sol−gel route using self-made zinc−oleate complex as a precursor It is indicated that the visible emission of ZnO QDs can be ascribed to singly ionized oxygen vacancies, which is associated with the paramagnetic centers with electron paramagnetic resonance (EPR) value of g = 20056 The visible emission property of the ZnO QDs displays highly size-dependent behavior With ZnO QDs size decreasing, the visible emission peaks blue-shift to the positions with shorter wavelength due to quantum size effect, however, is different from that of band gap Quantitative investigation shows that the visible emission can correspond to a transition of holes from the valence band to the preexisting deep donor energy level, which is different from the well-known conclusion that the v

Journal ArticleDOI
TL;DR: The opening of a bandgap in graphene is explained in terms of functionalization of its pristine lattice with oxygen atoms, that is, on the extent of the bandgap opening upon increased functionalisation density.
Abstract: We report a change in the semimetallic nature of single-layer graphene after exposure to oxygen plasma. The resulting transition from semimetallic to semiconducting behavior appears to depend on the duration of the exposure to the plasma treatment. The observation is confirmed by electrical, photoluminescence and Raman spectroscopy measurements. We explain the opening of a bandgap in graphene in terms of functionalization of its pristine lattice with oxygen atoms. Ab initio calculations show more details about the interaction between carbon and oxygen atoms and the consequences on the optoelectronic properties, that is, on the extent of the bandgap opening upon increased functionalisation density.

Journal ArticleDOI
TL;DR: Experimental evidence is reported for a short-lived visible band in the photoluminescence spectrum of silicon nanocrystals that increases in intensity and shifts to longer wavelengths (a redshift) with smaller nanocrystal sizes, which indicates an increased quantum efficiency.
Abstract: Crystalline silicon is the most important semiconductor material in the electronics industry. However, silicon has poor optical properties because of its indirect bandgap, which prevents the efficient emission and absorption of light. The energy structure of silicon can be manipulated through quantum confinement effects, and the excitonic emission from silicon nanocrystals increases in intensity and shifts to shorter wavelengths (a blueshift) as the size of the nanocrystals is reduced. Here we report experimental evidence for a short-lived visible band in the photoluminescence spectrum of silicon nanocrystals that increases in intensity and shifts to longer wavelengths (a redshift) with smaller nanocrystal sizes. This higher intensity indicates an increased quantum efficiency, which for 2.5-nm-diameter nanocrystals is enhanced by three orders of magnitude compared to bulk silicon. We assign this band to the radiative recombination of non-equilibrium electron-hole pairs in a process that does not involve phonons.

Journal ArticleDOI
TL;DR: The obtained phosphor exhibits a strong excitation band between 250 and 430 nm, matching well with the dominant emission band of a UV light-emitting-diode (LED) chip.
Abstract: A novel white-light-emitting phosphor Ca9Lu(PO4)7:Eu2+,Mn2+ has been prepared by solid-state reaction. The photoluminescence properties indicate that there is an efficient energy transfer from the Eu2+ to Mn2+ ions via a dipole−quadrupole reaction. The obtained phosphor exhibits a strong excitation band between 250 and 430 nm, matching well with the dominant emission band of a UV light-emitting-diode (LED) chip. Upon excitation of UV light, white light is realized by combining a broad blue-green emission band at 480 nm and a red emission band at 645 nm attributed to the Eu2+ and Mn2+ ions. The energy-transfer efficiency and critical distance were also calculated. Furthermore, the phosphors can generate lights from blue-green through white and eventually to red by properly tuning the relative ratio of the Eu2+ to Mn2+ ions through the principle of energy transfer. Preliminary studies showed that the phosphor might be promising as a single-phased white-light-emitting phosphor for a UV white-light LED.

Journal ArticleDOI
TL;DR: It is demonstrated that this simple methodology can offer a rapid and reliable detection of Cu(2+) with a detection limit as low as 5 nM and a dynamic range up to 100 muM in a fixed fast reaction time of 5 min.
Abstract: Here, we present a simple platform for the use of the enhanced emission of 16-mercaptohexadecanoic acid (16-MHA) capped CdSe quantum dots (QDs) as a probe for ultrasensitive copper(II) detection. In this study, the photoluminescence (PL) of the QDs was first enhanced by Ag nanoprisms which were self-assembled on Si surfaces and then further increased by photobrightening. Using this approach, the control and different analytes could be readily probed all on a single platform using fluorescence microscopy. The enhanced PL intensity of CdSe QDs was selectively quenched in the presence of Cu2+, accompanied by the emergence of a new red-shifted luminescence band. The quenching mechanism was found to be due to a cation exchange mechanism as confirmed by X-ray photoelectron spectroscopy (XPS) measurements. Herein, we have demonstrated that this simple methodology can offer a rapid and reliable detection of Cu2+ with a detection limit as low as 5 nM and a dynamic range up to 100 μM in a fixed fast reaction time o...

Journal ArticleDOI
TL;DR: In this article, the surface plasmon of Au nanoparticles was used to enhance the ultraviolet emission of ZnO nanorods, while the defect-related emission was completely suppressed.
Abstract: The author observe sixfold enhancement in the near band gap emission of ZnO nanorods by employing surface plasmon of Au nanoparticles, while the defect-related emission is completely suppressed. Time-resolved photoluminescence indicates that the decay process becomes much faster by Au capping. The remarkable enhancement of the ultraviolet emission intensities and transition rates is ascribed to the charge transfer and efficient coupling between ZnO nanorods and Au surface plasmons. The suppression of the green emission might be due to a combined effect of Au surface plasmon and passivation of the ZnO nanorod surface traps.

Journal ArticleDOI
TL;DR: Temperature and excitation power dependance of the optical spectra gives a new insight into the excitonic and the phononic properties of this hybrid organic/inorganic semiconductor.
Abstract: We report on optical spectroscopy (photoluminescence and photoluminescence excitation) on two-dimensional self-organized layers of (C6H5C2H4-NH3)2-PbI4 perovskite. Temperature and excitation power dependance of the optical spectra gives a new insight into the excitonic and the phononic properties of this hybrid organic/inorganic semiconductor. In particular, exciton-phonon interaction is found to be more than one order of magnitude higher than in GaAs QWs. As a result, photoluminescence emission lines have to be interpreted in the framework of a polaron model.

Journal ArticleDOI
06 Apr 2010-ACS Nano
TL;DR: Although the analysis of subnanosecond relaxation dynamics in air-exposed NCs is complicated by a significant enhancement in fast carrier trapping, the picosecond PL measurements suggest that air exposure likely has only a weak effect on Auger recombination and also does not significantly affect the efficiency of carrier multiplication.
Abstract: Effects of air exposure on surface properties, electronic structure, and carrier relaxation dynamics in colloidal PbSe nanocrystals (NCs) were studied using X-ray photoelectron spectroscopy, transmission electron microscopy, and steady-state and time-resolved photoluminescence (PL) spectroscopies. We show that exposure of NC hexane solutions to air under ambient conditions leads to rapid oxidation of NCs such that up to 50% of their volume is transformed into PbO, SeO2, or PbSeO3 within 24 h. The oxidation is a thermally activated process, spontaneous at room temperature. The oxidation-induced reduction in the size of the PbSe “core” increases quantum confinement, causing shifts of the PL band and the absorption onset to higher energies. The exposure of NC solutions to air also causes rapid (within minutes) quenching of PL intensity followed by slow (within hours) recovery during which the PL quantum yield can reach values exceeding those observed prior to the air exposure. The short-term PL quenching is ...

Journal ArticleDOI
TL;DR: It is demonstrated that photoluminescence emission enhancement from CdSe quantum dots (QDs) can be obtained in the absence of any excitation enhancement near single silver nanoprisms, and the spectral dependence of the radiative and nonradiative decay rate of the QDs closely follows the silver nanoparticle plasmon scattering spectrum.
Abstract: The near-field effects of plasmonic optical antennas are being explored in applications ranging from biosensors to solar cells. We demonstrate that photoluminescence emission enhancement from CdSe quantum dots (QDs) can be obtained in the absence of any excitation enhancement near single silver nanoprisms. The spectral dependence of the radiative and nonradiative decay rate of the QDs closely follows the silver nanoparticle plasmon scattering spectrum. Using both experiment and theory we show that, in the absence of excitation enhancement, the ratio of radiative to nonradiative decay rate enhancement is proportional to the silver nanoparticle scattering efficiency. These results provide guidelines both for separating excitation and emission enhancement effects in sensing and device applications and for tailoring emission enhancement effects using plasmonic nanostructures.

Journal ArticleDOI
07 Apr 2010-Langmuir
TL;DR: Photoluminescence decay and transient absorption measurements reveal the role of surface bound MPA in altering the photophysical properties of CdSe quantum dots.
Abstract: Ligand exchange with 3-mercaptopropionic acid (MPA) has been successfully used to tune the emission intensity of trioctylphosphineoxide/dodecylamine-capped CdSe quantum dots. Addition of 3-mercaptopropionic acid (MPA) to CdSe quantum dot suspension enhances the deep trap emission with concurrent quenching of the band edge emission. The smaller sized quantum dots, because of larger surface/volume ratio, create a brighter trap emission and are more easily tuned. An important observation is that the deep trap emission which is minimal after synthesis is brightened to have a quantum yield of 1−5% and can be tuned based on the concentration of MPA in solution with the quantum dots. Photoluminescence decay and transient absorption measurements reveal the role of surface bound MPA in altering the photophysical properties of CdSe quantum dots.

Journal ArticleDOI
TL;DR: In this article, the effect of surfaces on the optical properties of GaAs nanowires is evidenced by comparing Nanowires with or without an AlGaAs capping shell as a function of the diameter.
Abstract: The effect of surfaces on the optical properties of GaAs nanowires is evidenced by comparing nanowires with or without an AlGaAs capping shell as a function of the diameter. We find that the optical properties of unpassivated nanowires are governed by Fermi-level pinning, whereas, the optical properties of passivated nanowires are mainly governed by surface recombinations. Finally, we measure a surface recombination velocity of 3 x 10(3) cm s(-1) one order of magnitude lower than values previously reported for (110) GaAs surfaces. These results will serve as guidance for the application of nanowires in solar cell and light emitting devices.

Journal ArticleDOI
TL;DR: Results indicate that the luminescence processes in both anatase and rutile TiO(2) have a close relationship with trap states, as well as the photocatalytic activity under stationary illumination.
Abstract: Anatase and rutile TiO2 were investigated with photoluminescence techniques under the weak excitation condition, where trap states play a vital role in carrier dynamics. The visible emission of anatase and near-infrared (NIR) emission of rutile both exhibit extremely long lifetimes up to milliseconds. The decay processes can be well described by the power-law decay which corresponds to the trapping–detrapping effect. These results indicate that the luminescence processes in both anatase and rutile TiO2 have a close relationship with trap states. The visible emission band was assigned to the donor–acceptor recombination. Oxygen vacancies and hydroxyl groups mainly serve as the donor and acceptor sites, respectively. The NIR luminescence is originated from the recombination of trapped electrons with free holes, while the trapped electrons were formed through two paths, direct trapping or trap-to-trap hopping. The trap states in anatase and rutile TiO2 may largely influence the photocatalysis process of TiO2 and determine the photocatalytic activity under stationary illumination.

01 Jan 2010
TL;DR: In this article, the authors show that when the MoS2 crystal is thinned to monolayer, strong photoluminescence emerges, indicating an indirect to direct bandgap transition in this d-electron system.
Abstract: Novel physical phenomena can emerge in low-dimensional nanomaterials. Bulk MoS2, a prototypical metal dichalcogenide, is an indirect bandgap semiconductor with negligible photoluminescence. When the MoS2 crystal is thinned to monolayer, however, a strong photoluminescence emerges, indicating an indirect to direct bandgap transition in this d-electron system. This observation shows that quantum confinement in layered d-electron materials like MoS2 provides new opportunities for engineering the electronic structure of matter at the nanoscale.

Journal ArticleDOI
TL;DR: In this article, the authors reported the correlated d(0) ferromagnetism and photoluminescence in undoped single-crystalline ZnO nanowires synthesized by using a vapor transport method.
Abstract: We report the correlated d(0) ferromagnetism and photoluminescence in undoped single-crystalline ZnO nanowires synthesized by using a vapor transport method. We systematically tune the oxygen deficiency in the ZnO nanowires from 4% to 20% by adjusting the growth conditions, i.e., selecting different catalyst (Au or Ag) and varying the growth temperature. Our study suggests that oxygen vacancies induce characteristic photoluminescence and significantly boost the room-temperature ferromagnetism. Such undoped ZnO nanowires with tunable magnetic and optical properties are promising to find applications in multifunctional spintronic and photonic nanodevices.

Journal ArticleDOI
TL;DR: In this article, the potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed.
Abstract: Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce3+ and Eu2+, the luminescence can be varied over the entire visible region by appropriately choosing the composition of the sulfide host. Main application areas are flat panel displays based on thin film electroluminescence, field emission displays and ZnS-based powder electroluminescence for backlights. For these applications, special attention is given to BaAl2S4:Eu, ZnS:Mn and ZnS:Cu. Recently, sulfide materials have regained interest due to their ability (in contrast to oxide materials) to provide a broad band, Eu2+-based red emission for use as a color conversion material in white-light emitting diodes (LEDs). The potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed. Finally, this review concludes with the size-dependent luminescence in intrinsic colloidal quantum dots like PbS and CdS, and with the luminescence in doped nanoparticles.

Journal ArticleDOI
TL;DR: In this paper, the free-ion Hamiltonian model and Judd-Ofelt theory have been used to analyze the energy level scheme and spectral intensities of Dy 3+ ions in CFB glasses.

Journal ArticleDOI
TL;DR: A simple, cost-effective, two-step method was proposed for preparing single-phase SnO polycrystalline thin films on quartz and it was demonstrated that the average transmittance of both the as-deposited and the annealed SnO thin films was up to 70%.
Abstract: A simple, cost-effective, two-step method was proposed for preparing single-phase SnO polycrystalline thin films on quartz. X-ray diffraction (XRD) analysis demonstrated that the annealed films were consisted of polycrystalline α-SnO phase without preferred orientation, and chemical composition analysis of the single phase in nature was analyzed using X-ray photoelectron spectroscopy (XPS). Transmittance spectra in UV−vis−IR range indicated that the average transmittance of both the as-deposited and the annealed SnO thin films was up to 70%. The optical band gap decreased from 3.20 to 2.77 eV after the annealing process, which was attributed to the crystalline size related quantum size effect. Photoluminescence (PL) spectrum of the annealed film showed only a weak peak at 585 nm, and no intrinsic optical transition emission was observed. Moreover, the p-type conductivity of SnO film was confirmed through Hall effect measurement, with Hall mobility of 1.4 cm2 V−1 s−1 and hole concentration of 2.8 × 1016 cm−3.

Journal ArticleDOI
TL;DR: In this paper, a new and simple method to directly synthesize stable and crystalline pure phase CeO 2 nanoparticles has been developed using cationic surfactant (cetyltrimethylammonium bromide, CTAB) and cerium chloride (CeCl 3 ) at room temperature.

Journal ArticleDOI
TL;DR: It is shown that excitons can dissociate, without the aid of an external bias or chemical potential gradient, via tunneling through a potential barrier when the coupling energy is comparable to the exciton binding energy.
Abstract: Internanocrystal coupling induced excitons dissociation in lead salt nanocrystal assemblies is investigated. By combining transient photoluminescence spectroscopy, grazing incidence small-angle X-ray scattering, and time-resolved electric force microscopy, we show that excitons can dissociate, without the aid of an external bias or chemical potential gradient, via tunneling through a potential barrier when the coupling energy is comparable to the exciton binding energy. Our results have important implications for the design of nanocrystal-based optoelectronic devices.