Showing papers on "Photoluminescence published in 2008"
TL;DR: This work shows that the "giant" NQDs (g-NQDs) are functionally distinct from standard core-only, core/shell and even core/multishell NQds, and are substantially less sensitive to changes in surface chemistry.
Abstract: Semiconductor nanocrystal quantum dots (NQDs) comprise an important class of inorganic fluorophores for applications from optoelectronics to biology. Unfortunately, to date, NQD optical properties (e.g., their efficient and particle-size-tunable photoluminescence) have been susceptible to instabilities at the bulk and single-particle levels. Specifically, ensemble quantum yields (QYs) in emission are dependent upon NQD surface chemistry and chemical environment, while at the single-particle level, NQDs are characterized by significant fluorescence intermittency (blinking) that hinders applications as single-photon light sources for quantum informatics and biolabels for real-time monitoring of single biomolecules. Furthermore, while NQDs are significantly more photostable than their organic dye counterparts, traditional NQDs photobleach over periods of seconds to many minutes. Here, we demonstrate for the first time that by encapsulating the NQD core in a sufficiently thick inorganic shell, we are able to divorce NQD function from NQD surface chemistry and chemical environment. We show that our "giant" NQDs (g-NQDs) are functionally distinct from standard core-only, core/shell and even core/multishell NQDs. g-NQDs are substantially less sensitive to changes in surface chemistry. They do not photobleach under continuous laser excitation over periods of several hours repeated over several days, and they exhibit markedly different blinking behavior; >20% of the g-NQDs do not blink, while >40% have on-time fractions of >80%. All of these observations are in stark contrast with control samples comprising core-only and standard, thinner core/multishell NQDs.
887 citations
TL;DR: A new approach for photoluminescence imaging in vitro and in vivo has been shown utilizing near infrared to near infrared (NIR-to-NIR) up-conversion in nanophosphors, which results in high contrast optical imaging due to absence of an autofluorescence background and decreased light scattering.
Abstract: A new approach for photoluminescence imaging in vitro and in vivo has been shown utilizing near infrared to near infrared (NIR-to-NIR) up-conversion in nanophosphors. This NIR-to-NIR up-conversion process provides deeper light penetration into biological specimen and results in high contrast optical imaging due to absence of an autofluorescence background and decreased light scattering. Aqueous dispersible fluoride (NaYF4) nanocrystals (20−30 nm size) co-doped with the rare earth ions, Tm3+ and Yb3+, were synthesized and characterized by TEM, XRD, and photoluminescence (PL) spectroscopy. In vitro cellular uptake was shown by the PL microscopy visualizing the characteristic emission of Tm3+ at ∼800 nm excited with 975 nm. No apparent cytotoxicity was observed. Subsequent animal imaging studies were performed using Balb-c mice injected intravenously with up-converting nanophosphors, demonstrating the high contrast PL imaging in vivo.
849 citations
TL;DR: The demonstrated photoluminescence adds another dimension to the versatility of carbon-based emitters, and is suggested that the tethered modifier stabilizes the surface of the carbon nanoparticles helping to generate energy traps that emit light when stimulated.
Abstract: Quantum dots are semiconductor nanocrystals that inherently fluoresce at specific wavelengths in the visible, enabling a number of potential applications to be realized. However, conventional quantum dots are based on metallic elements, which has raised concerns over toxicity, stability and high cost. As a result, the search for more benign substitutes is a worthwhile yet challenging undertaking. Recently a new type of visible emitters has been reported exclusively based on functionalized carbon nanoparticles. The carbon dots were 5 nm in diameter and were produced via laser ablation of graphite. Surface oxidation with nitric acid and subsequent covalent grafting of organic moieties afforded light-emitting derivatives. Notably, the light emitted by these dots depends on the wavelength of light used for excitation. It was suggested that the tethered modifier stabilizes the surface of the carbon nanoparticles helping to generate energy traps that emit light when stimulated, an effect described as emission from passivated surfaces. Because of its origin the emission is size-dependent, i.e., the smaller the size of the dots the better their photoluminescence efficiency. In another intriguing approach, photoluminescent carbon dots 3 nm in size were directly fabricated by electrochemical shocking of multi-wall carbon nanotubes. The demonstrated photoluminescence adds another dimension to the versatility of carbon-based
765 citations
TL;DR: In this paper, the authors present a review of recent work on the origin of the concept of enhanced multiple electron-hole pair (i.e. exciton) production in semiconductor quantum dots (QDs).
646 citations
TL;DR: A comparison of the photophysics of a series of polythiophenes with ionization potentials with an excellent correlation between the free energy difference for charge separation and yield of the long-lived charge generation, with efficient charge generation requiring a much larger deltaG(CS)rel than that required to achieve efficient PL quenching.
Abstract: We report herein a comparison of the photophysics of a series of polythiophenes with ionization potentials ranging from 4.8 to 5.6 eV as pristine films and when blended with 5 wt % 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]C61 (PCBM). Three polymers are observed to give amorphous films, attributed to a nonplanar geometry of their backbone while the other five polymers, including poly(3-hexylthiophene), give more crystalline films. Optical excitation of the pristine films of the amorphous polymers is observed by transient absorption spectroscopy to give rise to polymer triplet formation. For the more crystalline pristine polymers, no triplet formation is observed, but rather a short-lived (∼100 ns), broad photoinduced absorption feature assigned to polymer polarons. For all polymers, the addition of 5 wt % PCBM resulted in 70−90% quenching of polymer photoluminescence (PL), indicative of efficient quenching of polythiophene excitons. Remarkably, despite this efficient exciton quenching, the yield of dissoc...
631 citations
TL;DR: The electro-optical properties of thin films of electron donor-acceptor blends of a fluorene copolymer and a fullerene derivative were studied and it is shown that in these films nanocrystalline PCBM clusters are formed at high PCBM content.
Abstract: The electro-optical properties of thin films of electron donor−acceptor blends of a fluorene copolymer (PF10TBT) and a fullerene derivative (PCBM) were studied. Transmission electron microscopy shows that in these films nanocrystalline PCBM clusters are formed at high PCBM content. For all concentrations, a charge transfer (CT) transition is observed with absorption spectroscopy, photoluminescence, and electroluminescence. The CT emission is used as a probe to investigate the dissociation of CT excited states at the donor−acceptor interface in photovoltaic devices, as a function of an applied external electric field and PCBM concentration. We find that the maximum of the CT emission shifts to lower energy and decreases in intensity with higher PCBM content. We explain the red shift of the emission and the lowering of the open-circuit voltage (V OC) of photovoltaic devices prepared from these blends with the higher relative permittivity of PCBM (er = 4.0) compared to that of the polymer (er = 3.4), stabili...
566 citations
TL;DR: In this paper, a facile method for the synthesis of size and shape-controlled CuInS2 semiconductor nanocrystals was developed by thermolysis of a mixed solution of CuAc, In(Ac)3, and dodecanethiol in noncoordinating solvent 1-octadecene (ODE) at 240 °C.
Abstract: A facile method for the synthesis of size- and shape-controlled CuInS2 semiconductor nanocrystals was developed by thermolysis of a mixed solution of CuAc, In(Ac)3 (molar ratio of CuAc to In(Ac)3 = 1:1) and dodecanethiol in noncoordinating solvent 1-octadecene (ODE) at 240 °C. CuInS2 nanoparticles with size of 2 to ∼5 nm and nanorods with aspect ratio of 1 to ∼3 were obtained by adjusting the reaction parameters such as temperature and time. The as-prepared nanoparticles were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, selected area electron diffraction spectroscopy, inductively coupled plasma atomic emission spectroscopy, UV−vis absorption, and photoluminescence (PL) spectroscopy. The nanoparticle solutions exhibit tunable absorption and PL spectra with the absorption edge ranging from 550 to 750 nm and PL emission peaks from 600 to 750 nm, indicating a strong size-dependent quantum confinement effect. Optical measurements of the CuI...
515 citations
TL;DR: It is shown, based on measurements in high magnetic fields, that defects are the dominant source of light from Si nanocrystals, and it is shown that it is possible to control the origin of the photoluminescence in a single sample.
Abstract: Silicon dominates the electronics industry, but its poor optical properties mean that III–V compound semiconductors are preferred for photonics applications. Photoluminescence at visible wavelengths was observed from porous Si at room temperature in 1990, but the origin of these photons (do they arise from highly localized defect states or quantum confinement effects?) has been the subject of intense debate ever since. Attention has subsequently shifted from porous Si to Si nanocrystals, but the same fundamental question about the origin of the photoluminescence has remained. Here we show, based on measurements in high magnetic fields, that defects are the dominant source of light from Si nanocrystals. Moreover, we show that it is possible to control the origin of the photoluminescence in a single sample: passivation with hydrogen removes the defects, resulting in photoluminescence from quantum-confined states, but subsequent ultraviolet illumination reintroduces the defects, making them the origin of the light again.
480 citations
TL;DR: The synthesis of a size series of copper indium selenide quantum dots of various stoichiometries exhibiting photoluminescence from the red to near-infrared (NIR) is reported.
Abstract: We report the synthesis of a size series of copper indium selenide quantum dots (QDs) of various stoichiometries exhibiting photoluminescence (PL) from the red to near-infrared (NIR). The synthetic method is modular, and we have extended it to the synthesis of luminescent silver indium diselenide QDs. Previous reports on QDs luminescent in the NIR region have been primarily restricted to binary semiconductor systems, such as InAs, PbS, and CdTe. This work seeks to expand the availability of luminescent QD materials to ternary I−III−VI semiconductor systems.
425 citations
TL;DR: The crystal structure and photoluminescence properties of undoped and Ce3+-doped CaAlSiN3 as well as the application of white-light LEDs are reported in this article.
Abstract: The crystal structure and photoluminescence properties of undoped and Ce3+-doped CaAlSiN3 as well as the application of white-light LEDs are reported. CaAlSiN3 and CaAlSiN3:Ce3+ have been synthesized, starting from Ca3N2, AlN, Si3N4, and CeN or CeO2 with and without Li3N, by a solid state reaction at 1700 °C for 4 h under high purity nitrogen atmosphere. Instead of an ideal CaAlSiN3, a more appropriate formula is proposed to be CaAl1−4δ/3Si1+δN3 (δ ≈ 0.3−0.4) with an Al/Si ratio of about 1:2 on the basis of the bond valence sum calculations, in which Al/Si is disorderly occupied on the 8b site within Cmc21 space group. Ce3+ can be incorporated into the host lattice of CaAlSiN3, and the estimated maximum solubility of Ce3+ is about x = 0.02 (e.g., 2.0 mol % with respect to Ca) of Ca1−2xCexLixAlSiN3. CaAlSiN3:Ce3+ can be efficiently excited by blue light (450−480 nm) and yields yellow-orange emission with a broadband peaking in the range of 570−603 nm, originating from the 5d1 → 4f1 transition of Ce3+. With...
412 citations
TL;DR: In this article, the authors provide an overview of efforts to dope one of the most widely studied colloidal semiconductor nanocrystal systems, CdSe quantum dots, with a transition-metal dopant ion, Mn 2+, and describe the major new physical properties that have emerged following successful synthesis of this material.
Abstract: Recent advances in the chemistry of colloidal semiconductor nanocrystal doping have led to new materials showing fascinating physical properties of potential technological importance. This article provides an overview of efforts to dope one of the most widely studied colloidal semiconductor nanocrystal systems, CdSe quantum dots, with one of the most widely studied transition-metal dopant ions, Mn 2+ , and describes the major new physical properties that have emerged following successful synthesis of this material. These properties include spin-polarizable excitonic photoluminescence, magnetic circular dichroism, exciton storage, and excitonic magnetic polaron formation. A brief survey of parallel advances in the characterization of analogous self-assembled Mn 2+ -doped quantum dots grown by molecular beam epitaxy is also presented, and the physical properties of the colloidal quantum dots are shown to compare favorably with those of the self-assembled quantum dots. The rich variety of physical properties displayed by colloidal Mn 2+ -doped CdSe quantum dots highlights the attractiveness of this material for future fundamental and applied research.
TL;DR: The surface plasmon resonance (SPR) and photoemission properties of Ag nanoparticles are found to be sensitive tocitrate concentration and a blue shift in SPR and an enhancement in photoluminescence intensity are observed with increase in citrate concentration.
TL;DR: The observed transition from strong to weak quantum confinement in SnO2 QDs and ultrathin NWs is interpreted through the use of the Brus effective-mass approximation and the Nosaka finite-depth well model.
Abstract: SnO2 quantum dots (QDs) and ultrathin nanowires (NWs) with diameters of approximately 0.5-2.5 and approximately 1.5-4.5 nm, respectively, were controllably synthesized in a simple solution system. They are supposed to be ideal models for studying the continuous evolution of the quantum-confinement effect in SnO2 1D --> 0D systems. The observed transition from strong to weak quantum confinement in SnO2 QDs and ultrathin NWs is interpreted through the use of the Brus effective-mass approximation and the Nosaka finite-depth well model. Photoluminescence properties that were coinfluenced by size effects, defects (oxygen vacancies), and surface capping are discussed in detail. With the SnO2 QDs as building blocks, various 2D porous structures with ordered hexagonal, distorted hexagonal, and square patterns were prepared on silicon-wafer surfaces and exhibited optical features of 2D photonic crystals and enhanced gas sensitivity.
TL;DR: In this article, a series of Dπ-A-π-D type of near-infrared (NIR) fluorescent compounds based on benzobis(thiadiazole) and its selenium analogues were synthesized and fully characterized by 1H and 13C NMR, high-resolution mass spectrometry, and elemental analysis.
Abstract: A series of D-π-A-π-D type of near-infrared (NIR) fluorescent compounds based on benzobis(thiadiazole) and its selenium analogues were synthesized and fully characterized by 1H and 13C NMR, high-resolution mass spectrometry, and elemental analysis. The absorption, fluorescence, and electrochemical properties were also studied. Photoluminescence of these chromophores ranges from 900 to 1600 nm and their band gaps are between 1.19 and 0.56 eV. Replacing the sulfur by selenium can lead to a red shift for emission and reduce the band gaps further. Interestingly, compound 1 exhibits aggregation-induced emission enhancement effect in the solid state. All-organic light-emitting diodes based on M1 and M2 were made and exclusive NIR emissions above 1 μm with external quantum efficiency of 0.05% and maximum radiance of 60 mW Sr−1 m−2 were observed. The longest electroluminescence wavelength reaches 1115 nm.
TL;DR: Novel IR-to-vis upconverting nanoparticles of different rare earth metal dopants are presented, with a single excitation source of 980 nm, four different colors of nanocrystals can be spectrally separated under multiplexing conditions.
Abstract: Any labeling with multicolor markers can be affected by the autofluorescence of biological tissue due to the UV or blue light excitation sources, or the results are affected by fluorescence resonance energy transfer. In this work, we present novel IR-to-vis upconverting nanoparticles of different rare earth metal dopants. With a single excitation source of 980 nm, four different colors of nanocrystals can be spectrally separated under multiplexing conditions. The particles were phase transferred into polar solvents by means of silica encapsulation and were characterized by transmission electron microscopy, X-ray diffraction, and photoluminescence spectroscopy.
TL;DR: A technique so that both transmission electron microscopy and microphotoluminescence can be performed on the same semiconductor nanowire over a large range of optical power, thus allowing us to directly correlate structural and optical properties of rotationally twinned zinc blende InP nanowires.
Abstract: We have developed a technique so that both transmission electron microscopy and microphotoluminescence can be performed on the same semiconductor nanowire over a large range of optical power, thus allowing us to directly correlate structural and optical properties of rotationally twinned zinc blende InP nanowires. We have constructed the energy band diagram of the resulting multiquantum well heterostructure and have performed detailed quantum mechanical calculations of the electron and hole wave functions. The excitation power dependent blue-shift of the photoluminescence can be explained in terms of the predicted staggered band alignment of the rotationally twinned zinc blende/wurzite InP heterostructure and of the concomitant diagonal transitions between localized electron and hole states responsible for radiative recombination. The ability of rotational twinning to introduce a heterostructure in a chemically homogeneous nanowire material and alter in a major way its optical properties opens new possibilities for band-structure engineering.
TL;DR: In this paper, a ligand exchange was used to tune optical and photoluminescence properties of one of the most stable quantum clusters of gold, Au25SG18 (SG-glutathione thiolate), functionalized by the exchange of −SG with functionalized -SG and with an altogether different ligand, namely, 3-mercapto-2-butanol (MB).
Abstract: Ligand exchange offers an effective way to modify the properties of the recently prepared quantum clusters of gold. To tune optical and photoluminescence properties of one of the most stable quantum clusters of gold, Au25SG18 (SG-glutathione thiolate), we functionalized it by the exchange of −SG with functionalized -SG and with an altogether different ligand, namely, 3-mercapto-2-butanol (MB). The products were characterized by various techniques such as optical absorption (UV−vis), Fourier-transform infrared (FT-IR), nuclear magnetic resonance (NMR), X-ray photoelectron (XPS), and luminescence spectroscopies, mass spectrometry, and thermogravimetry (TG). Analyses of the TG data helped to establish the molecular composition of the products. Ligand exchange reaction was monitored by NMR spectroscopy, and it was found that the exchange reaction follows a first order kinetics. The XPS study showed that after the exchange reaction there was no change in the chemical nature of the metal core and binding energy...
TL;DR: Small carbon nanoparticles doped with inorganic salts serve as a highly promising new platform for brightly photoluminescent dots that are competitive to the commercially available CdSe/ZnS QDs in luminescence brightness.
Abstract: There have been rapid advances in the development and applications of semiconductor quantum dots (QDs) represented by CdSe/ZnS. However, a serious limitation of these QDs is the necessary use of toxic heavy metals. It is reported here that small carbon nanoparticles doped with inorganic salts serve as a highly promising new platform for brightly photoluminescent dots. The photoluminescent carbon dots with the carbon core doped with ZnO (CZnO-Dots) or ZnS (CZnS-Dots) in aqueous solutions are competitive to the commercially available CdSe/ZnS QDs in luminescence brightness.
TL;DR: In this paper, the photovoltaic efficiency via exposure of organic poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) devices to solvent vapor at room temperature is reported.
Abstract: Improvement of the photovoltaic efficiency via exposure of organic poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) devices to solvent vapor at room temperature is reported. In situ photoluminescence (PL) and Raman spectroscopy, in conjunction with ex situ optical absorption and atomic force microscopy, have been used to provide insight into the nanoscale morphological changes occurring during solvent vapor annealing. We found that in 1 : 1 composites of P3HT : PCBM, suppression of PL, narrowing in line-width of the 1442 cm−1 P3HT Raman peak, and strong modifications in the optical absorption spectra were observed during solvent vapor annealing, while minimal changes occurred in pure P3HT films. We attribute these spectral modifications to de-mixing of PCBM and subsequent stacking of P3HT in coplanar conjugated segments, similar to what is observed during thermal annealing.
TL;DR: A series of Cu-doped ZnIn2S4 photocatalysts has been synthesized by a facile hydrothermal method, with the copper concentration varying from 0 wt% to 2.0 wt%.
Abstract: A series of Cu-doped ZnIn2S4 photocatalysts has been synthesized by a facile hydrothermal method, with the copper concentration varying from 0 wt% to 2.0 wt%. The physical and photophysical properties of these Cu-doped ZnIn2S4 photocatalysts were characterized by X-ray diffraction (XRD), photoluminescence spectroscopy (PL), scanning electron microscopy (SEM), and UV−visible diffuse reflectance spectroscopy (UV−vis). The diffuse reflectance and photoluminescence spectra of Cu-doped ZnIn2S4 shifted monotonically to longer wavelengths as the copper concentration increased from 0 wt% to 2.0 wt%, indicating that the optical properties of these photocatalysts greatly depended on the amount of Cu doped. Meanwhile, the layered structure of ZnIn2S4 would be destructed gradually by Cu doping. The photoactivity of ZnIn2S4 was enhanced when Cu2+ was doped into the crystal structure. The highest photocatalytic activity was observed on Cu (0.5 wt%)–doped ZnIn2S4, with the rate of hydrogen evolution to be 151.5 μmol/h u...
TL;DR: The emergence of a fast luminescence decay component under strong optical excitation indicates that Auger processes are partially responsible for inhibiting two-photon generation and suggests that carbon nanotubes could be used as a source of single photons for applications in quantum cryptography.
Abstract: We report the first observation of photon antibunching in the photoluminescence from single carbon nanotubes. The emergence of a fast luminescence decay component under strong optical excitation indicates that Auger processes are partially responsible for inhibiting two-photon generation. Additionally, the presence of exciton localization at low temperatures ensures that nanotubes emit photons predominantly one by one. The fact that multiphoton emission probability can be smaller than 5% suggests that carbon nanotubes could be used as a source of single photons for applications in quantum cryptography.
TL;DR: In this paper, the optical properties of K 2 SiF 6 were reported and the luminescence centers of sharp red emission at ∼630 nm were ascribed to the Mn 4+ ions in the octahedral site.
Abstract: The aim of this paper is to report the optical properties of K 2 SiF 6 :Mn 4+ phosphor prepared by wet chemical etching of Si wafers in a HF/KMnO 4 mixed solution. The luminescence centers of sharp red emission at ∼630 nm are ascribed to the Mn 4+ ions in the octahedral site of K 2 SiF 6 gained by the activation of local vibration modes ( 4 A 2 → 2 E). All the expected electronic and vibronic origins of the 2 E → 4 A 2 , 4 A 2 → 4 T 2 , and 4 A 2 → 4 T 1 transitions of the Mn 4+ ions are identified and depicted in the TanabeSugano diagram of a 3d 3 transition-metal system. The temperature-dependent photoluminescence properties suggest that the anti-Stokes/Stokes intensity ratio can be explained by the Maxwell-Boltzmann factor but only at low temperatures and low-excitation power intensities.
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01 Jan 2008
TL;DR: In this paper, the growth mechanism, shape and composition control of semiconductor nanocrystals were discussed. But the authors focused on the synthesis of semiconductors in organic solvents and not on their application in biomedicine.
Abstract: -Growth mechanism, shape and composition control of semiconductor nanocrystals.-Synthesis of semiconductor nanocrystals in organic solvents.-Aqueous synthesis of semiconductor nanocrystals. Multishell semiconductor nanocrystals.-Self-assembly of semiconductor nanocrystals into ordered superstructures. -Semiconductor nanocrystal-polymer composites.-Layer-by-layer assembly with semiconductor nanoparticles and nanowires.-Exciton-phonon interaction in semiconductor nanocrystals.-Anti-Stokes photoluminescence in semiconductor nanocrystal quantum dots.-Exciton dynamics and energy transfer processes in semiconductor nanocrystals. -Flourescence spectroscopy of single CdSe nanocrystals.-Applications of quantum dots in biomedicine.
TL;DR: In this paper, Tb3+ and Yb3 + codoped transparent oxyfluoride glass ceramics containing CaF2 nanocrystals were synthesized, and the formation of CaF 2 nanocrystal in the glass Ceramics was confirmed by x-ray diffraction and high resolution transmission electron microscopy.
Abstract: Tb3+–Yb3+ codoped transparent oxyfluoride glass ceramics containing CaF2 nanocrystals were synthesized. The formation of CaF2 nanocrystals in the glass ceramics was confirmed by x-ray diffraction and high resolution transmission electron microscopy. The incorporation of Tb3+ and Yb3+ into CaF2 nanocrystal lattice was confirmed by energy dispersive spectroscopy. Infrared quantum cutting involving Yb3+ 950–1100nm (F5∕22→F7∕22) emission was achieved upon the excitation of D45 energy level of Tb3+ at 484nm. The photoluminescence properties have been studied for these glass ceramics. Yb3+ concentration dependent quantum efficiency was calculated, and the maximum efficiency approaches 155% before reaching concentration quenching threshold.
TL;DR: In this article, the aromatic ligand capped CdSe quantum dots are prepared through ligand exchange with trioctylphosphine oxide (TOPO) capped quantum dots.
Abstract: CdSe quantum dots have been encapped with aromatic ligands: α-toluenethiol, thiophenol, and p-hydroxythiophenol to enhance the photoluminescence (PL) quenching and photoelectric properties of the quantum dots. The aromatic ligand capped CdSe quantum dots are prepared through ligand exchange with trioctylphosphine oxide (TOPO) capped CdSe quantum dots. The XPS surface chemistry analysis and elemental analysis has confirmed the success of ligand exchange from TOPO to aromatic ligands. Both XRD and HRTEM-SAED studies indicate the crystalline structure of CdSe quantum dots not only remains but is also improved by the ligand exchange of TOPO with thiol molecules. Time resolved PL decay measurements indicate thiophenol and p-hydroxythiophenol ligands effectively quench the emission and have much shorter PL lifetimes than that of TOPO and that of α-toluenethiol. Thus, both thiophenol and p-hydroxythiophenol can act as an effective acceptor for photogenerated holes through aromatic π-electrons. Thiophenol also exhibits good charge transport behavior showing a 10-fold increase in short circuit current density (Isc) as compared with TOPO in the photocurrent study of fabricated photovoltaic devices.
TL;DR: Exposure to thiols is found to improve EQE from 5 to 22% and, combined with the improvement in V(oc), improve power conversion efficiency to 2.6% under 76 mW/cm(2) at 1 microm wavelength, consistent with recent reports in photoconductive PbS CQD photodetectors that thiol exposure substantially removes deep electron traps.
Abstract: The use of thiol-terminated ligands has recently been reported to enhance 10-fold the power conversion efficiency (PCE) of colloidal quantum dot (CQD) photovoltaic (PV) devices. We find herein that, in a representative amine-capped PbS colloidal quantum dot materials system, improved mobility following thiol treatment accounts for only a 1.4-fold increase in PCE. We then proceed to investigate the origins of the remainder of the quadrupling in PCE following thiol treatment. We find through measurements of photoluminescence quantum efficiency that exposure to thiols dramatically enhances photoluminescence in colloidal quantum dot films. The same molecules increase open-circuit voltage (Voc) from 0.28 to 0.43 V. Combined, these findings suggest that mid-gap states, which serve as recombination centers (lowering external quantum efficiency (EQE)) and metal−semiconductor junction interface states (lowering Voc), are substantially passivated using thiols. Through exposure to thiols, we improve EQE from 5 to 22...
TL;DR: In this article, the authors showed that the recombination of photogenerated charge carrier between the hybrid orbital of Bi6s and O2p (VB) to the empty W5d orbital is inhibited greatly in composite semiconductors.
TL;DR: In this article, the zinc oxide (ZnO) thin films obtained by the atomic layer deposition (ALD) method using diethyl zinc and water precursors, which allowed them to lower deposition temperature to below 200°C.
Abstract: We report on the zinc oxide (ZnO) thin films obtained by the atomic layer deposition (ALD) method using diethyl zinc and water precursors, which allowed us to lower deposition temperature to below 200 °C. The so-obtained “as grown” ZnO layers are polycrystalline and show excitonic photoluminescence (PL) at room temperature, even if the deposition temperature was lowered down to 100 °C. Defect-related PL bands are of low intensity and are absent for layers grown at 140−200 °C. This is evidence that extremely low temperature growth by ALD can result in high quality ZnO thin films with inefficient nonradiative decay channels and with thermodynamically blocked self-compensation processes.
TL;DR: In this paper, a combination of sol−gel process and electrospinning was used to combine one-dimensional YVO4:Ln and quasi-one-dimensional VO4-Ln nanofibers.
Abstract: One-dimensional YVO4:Ln and Y(V, P)O4:Ln nanofibers and quasi-one-dimensional YVO4:Ln microbelts (Ln = Eu3+, Sm3+, Dy3+) have been prepared by a combination method of sol−gel process and electrospinning. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG−DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), and time-resolved emission spectra as well as kinetic decays were used to characterize the resulting samples. Due to an efficient energy transfer from vanadate groups to dopants, YVO4:Ln phosphors showed their strong characteristic emission under ultraviolet excitation (280 nm) and low-voltage electron beam excitation (1−3 kV). The energy transfer process was further studied by the time-resolved emission spectra as well as kinetic decay curves of Eu3+ upon excitation into the VO4...