Quantum Size Confinement Research Articles

Optical constants of multilayered colloidal ZnSe nanoparticles

The purpose of this study was to prepare multilayered films of colloidal ZnSe nanoparticles (NPs) and investigate their optical constants. Thin films comprising multilayered ZnSe–NPs were prepared on a SiO2 substrate using the layer-by-layer (LbL) method. The samples were studied using spectroscopic ellipsometry in the range of 0.75–3.20 eV. The film thickness increased linearly with the number of layers of colloidal NPs, and the prepared films were optically homogeneous. Furthermore, the refractive index of the ZnSe–NP films varied depending on the NP size owing to the quantum-confinement size effect. Multilayered ZnSe–NP films deposited using the LbL method are particularly useful as optical thin films because they can help control the film thickness and refractive index. It is expected that thin films with various refractive indices and corresponding dispersions can be produced using other semiconductor NPs and combinations thereof.

Magnetic field and anisotropic parabolic potential effects on ground state binding energy of impurity magnetopolaron in asymmetrical semi-exponential quantum wells

We performed the ground state binding energy (GSBE) and vibrational frequency (VF) of strong-coupling impurity magnetopolaron (SCIM) in asymmetrical semi-exponential quantum wells (ASEQWs) containing a hydrogen-like impurity in the center exposed to a uniform magnetic field through Lee-Low-Pines unitary transformation and linear combination operation method based on effective mass approximation. The results were expressed as functions of GSBE and VF for different magnetic field cyclotron frequency (MFCF) and Coulombic impurity potential (CIP) strength, the positive criteria of ASEQWs along the growth direction of QW and effectual confinement lengths of APCP along the coordinates were analyzed. Our findings revealed that the VF and GSBE were enhanced by increasing magnetic field cyclotron frequency and the parameter of asymmetrical semi-exponential confinement potential (ASECP), which was increased by reducing APCP effectual confinement length along the directions of coordinates. The above observations could be because of quantum size confinement effects.

Physical Origin of Dual-Emission of Au-Ag Bimetallic Nanoclusters.

On the origin of photoluminescence of noble metal NCs, there are always hot debates: metal-centered quantum-size confinement effect VS ligand-centered surface state mechanism. Herein, we provided solid evidence that structural water molecules (SWs) confined in the nanocavity formed by surface-protective-ligand packing on the metal NCs are the real luminescent emitters of Au-Ag bimetal NCs. The Ag cation mediated Au-Ag bimetal NCs exhibit the unique pH-dependent dual-emission characteristic with larger Stokes shift up to 200 nm, which could be used as potential ratiometric nanosensors for pH detection. Our results provide a completely new insight on the understanding of the origin of photoluminescence of metal NCs, which elucidates the abnormal PL emission phenomena, including solvent effect, pH-dependent behavior, surface ligand effect, multiple emitter centers, and large-Stoke’s shift.

Silicon-Tin Alloyed Nanocrystals by Femtosecond Laser Plasma

Silicon’s (Si) indirect bandgap limits its absorption and possible applications, and therefore remarkable efforts are put into the possibility of fabricating a material compatible with the existing silicon technology that is also a direct bandgap material. Tin (Sn) alloying with silicon represents an exciting possibility to tune Si properties. In addition, at the quantum confinement size (<10 nm) when the material becomes a quantum dot, it becomes possible to control the electronic structure of a material by varying the size. Although the possibility to tailor the bandgap of elemental Si over a wide range has been demonstrated, it is very challenging to obtain stable alloyed SiSn quantum dots. In particular, alfa Sn has a crystal structure similar to Si with zero band gap: a diamond cubic crystal structure, and importantly affected by the crystal configuration and a possible change to a direct energy gap at sufficiently high Sn concentration. This therefore makes Sn a favorable element to create an alloy with a lower bandgap than Si. Exploiting these features would make alloyed SiSn NCs an important candidate for a broad range of applications such as next generation photovoltaic cells based on carrier multiplication, super high efficient photodetectors, fluorescent tags for biomedical applications etc. In this contribution we will discuss the synthesis paths and optoelectrical properties in the context of silicon, tin, and silicon/tin alloyed nanocrystals at high alloying concentrations. Our results show that plasma-based processes allow the synthesis of alfa tin alloyed SiSn QDs with unprecedented dimensions and alloying concentrations. We will present SiSn-QDs as the world’s highest alloys fabricated by confined plasma from femtosecond (fs) laser in liquid media with a high tin concentration of approximately 17% ever reported in literature to our knowledge. We have demonstrated for the first time the experimental and exact theoretical calculation determination of the thermal stability of the SiSn-NCs at those concentrations. We study their electronic properties by means of an approximate band structure suitable for finite-sized systems (quasi-band structure) derived from first-principles calculations. This work therefore advances the current state of the art, provides opportunities to compare and verify theoretical results and offer important directions for applications.

Silicon-Tin Alloyed Nanocrystals by Femtosecond Laser Plasma

Here we discuss the synthesis paths and optoelectronic properties in the context of alpha tin (α-Sn) phase and silicon/tin (SiSn) alloyed nanocrystals (NCs). We discuss the possibilities and benefits of stabilizing α-Sn in larger sized nanocrystals by alloying with silicon. We demonstrate that plasma-based processes allow the synthesis of stable elemental α-Sn NCs and also alloyed α-Sn based SiSn NCs with quantum confinement size and extraordinarily high Sn concentrations: i.e. SiSn NCs fabricated by confined plasma from femtosecond (fs) laser in liquid media with a high tin concentration of approximately 17%. We also discuss the experimental and exact theoretical calculation determination of the thermal stability of the α-Sn based nanocrystals.

Ultrasmall CsPbBr3 Quantum Dots with Bright and Wide Blue Emissions

Low‐dimensional metal halide perovskites have been widely regarded due to their unique crystal structure and photophysical properties. Herein, blue‐emission CsPbBr3 quantum dots (QDs) or nanocrystals (NCs) with extremely small crystal size (1–2 nm) but high photoluminescence quantum yield (PLQY, 72.4%) are synthesized with a new surface ligand, single (6‐amino‐6‐deoxy) beta cyclodextrin (6A‐βCD), which also acts as the confined‐growth template for such small QDs. Detailed photoluminescence spectrum and femtosecond transient absorption spectrum study proves that the blue emission with multiple peaks originates from both band‐edge radiation and exciton recombination. Furthermore, as a result of the small size, exciton localization in the form of self‐trapped excitons (STEs) and significant quantum size confinement effect are both important reasons for the efficient and wide blue emissions of these QDs. This work provides a new strategy not only to synthesize ultrasmall perovskite QDs but also to develop blue perovskite‐QD light‐emitting devices.

External electric and magnetic field effects on the polaron in a wurtzite nitride nanowire embedded in a nonpolar matrix

We examine the Frohlich polaron problem in wurtzite nitride cylindrical nanowire embedded in a nonpolar matrix within the framework of the Lee–Low–Pines variational approach. The effects of the external electric and magnetic fields and quantum-size confinement on polaron self-energy and effective mass due to electron interactions with both quasiconfined and interface optical phonons are investigated. The numerical results obtained for wurtzite GaN material are discussed in comparison with the zinc-blende structure cylindrical nanowires. The estimation of contributions of different phonon modes reveal that interface optical phonons are much more important in narrow wires. It is found that the electric field has a relatively pronounced influence on the polaron self-energy and effective mass, while the effect of the magnetic field is small. The obtained results will be of importance in further study of the phonon-assisted electro-optical properties in wurtzite semiconductor low-dimensional structures.

Band Gap Narrowing in Silane-Grafted ZnO Nanocrystals. A Comprehensive Study by Wide-Angle X-ray Total Scattering Methods

Zinc oxide (ZnO) is a largely investigated semiconducting nanomaterial for photocatalytic applications and is an excellent active layer candidate in photovoltaics. Among native defects, having a primary role in ZnO optoelectronic properties, the influence of nearly ubiquitous planar faults of wurtzite sequences in ultrasmall (≤5 nm) nanocrystals (NCs) remains poorly understood. Here, we present a thorough study of ZnO NCs prepared under morphological control of covalently grafted vinyltrimethoxysilane (VTMS) and exhibiting either narrowing or widening of the band gap upon NCs downsizing, depending on the NC growth rate. By using synchrotron X-ray total scattering data, atomistic models and the Debye Scattering Equation (DSE) method, complemented by spectroscopic (FTIR and UV–vis) investigations, we provide a comprehensive quantitative picture in which effects from planar defects are disentangled from those due to NC size, morphology, and lattice strain (here controlled by preferential binding of VTMS on the ZnO basal faces). When faults occur in high concentration (linear density up to 1.6 × 10⁶ cm–¹), NCs exhibit optical band gap narrowing (3.27 eV vs 3.37 eV in bulk ZnO), whereas gap widening (3.52 eV) is observed at a lower density (0.8 × 10⁶ cm–¹), at which quantum-size confinement effects prevail. Supported by photoluminescence and photodegradation experiments, surface defect passivation by VTMS, affecting visible emissions and photocatalytic properties of ZnO, is also discussed in relation to silane coating and fault-driven bandgap. This work sheds light on the complex interplay among planar defects, quantum size effect, and surface modifications in ultrasmall ZnO NCs and on the importance of advanced X-ray total scattering methods toward atomically precise control of defects in nanostructures.

Exploring Rapid Photocatalytic Degradation of Organic Pollutants with Porous CuO Nanosheets: Synthesis, Dye Removal, and Kinetic Studies at Room Temperature

In this work, we report the facile, environmentally friendly, room-temperature (RT) synthesis of porous CuO nanosheets and their application as a photocatalyst to degrade an organic pollutant/food dye using NaBH4 as the reducing agent in an aqueous medium. Ultrahigh-resolution field effect scanning electron microscopy images of CuO displayed a broken nanosheet-like (a length of ∼160 nm, a width of ∼65 nm) morphology, and the lattice strain was estimated to be ∼1.24 × 10–3 using the Williamson–Hall analysis of X-ray diffraction plots. Owing to the strong quantum size confinement effect, CuO nanosheets resulted in an optical energy band gap of ∼1.92 eV, measured using Tauc plots of the ultraviolet–visible (UV–vis) spectrum, resulting in excellent photocatalytic efficiency. The RT synthesized CuO catalyst showed a high Brunauer–Emmet–Teller surface area of 30.88 ± 0.2313 m2/g (a correlation coefficient of 0.99972) with an average Barrett–Joyner–Halenda pore size of ∼20.385 nm. The obtained porous CuO nanosheets exhibited a high crystallinity of 73.5% with a crystallite size of ∼12 nm and was applied as an efficient photocatalyst for degradation of the organic pollutant/food dye, Allura Red AC (AR) dye, as monitored by UV–vis spectrophotometric analysis and evidenced by a color change from red to colorless. From UV–vis spectra, CuO nanosheets exhibited an efficient and ultrafast photocatalytic degradation efficiency of ∼96.99% for the AR dye in an aqueous medium within 6 min at RT. According to the Langmuir–Hinshelwood model, photodegradation reaction kinetics followed a pseudo-first-order reaction with a rate constant of k = 0.524 min–1 and a half-life (t1/2) of 2.5 min for AR dye degradation in the aqueous medium. The CuO nanosheets showed an outstanding recycling ability for AR degradation and would be highly favorable and an efficient catalyst due to the synergistic effect of high adsorption capability and photodegradation of the food dye.

Sol-gel derived Al-doped ZnO nanoplates: Structural and optical properties

In the present work, undoped and Al-doped ZnO nanoplates have been prepared by sol–gel method and investigated their structural, morphological and optical properties. Structural analysis has been performed by powder X-ray diffraction (XRD) pattern. The XRD results exhibited that the synthesized nanostructures have hexagonal wurtzite phase of ZnO. Scanning electron microscopy (SEM) depicts the formation of nanoplates. The optical properties of the prepared samples have been studied using UV–visible (UV–vis) absorption and photoluminescence (PL) spectroscopy at 300 K. UV–vis absorption spectra revealed a large blue shift in absorption peak indicates quantum size confinement effect. Red-shifted absorbance peak is obtained for higher doping concentration of Al that may be attributed to change of the surfaces for nanoplates. PL spectra of undoped and Al-doped ZnO NPs have band edge luminescence in UV region and defects related optical emission such as violet emission at ~417 nm, blue emission at ~441 nm, blue–green emission at ~484 nm and green emission at ~524 nm in visible region. A significant enhancement of the PL intensity has been observed in 3 wt% Al-doped ZnO sample as compared to undoped ZnO which may be assigned to transformation of nanoclusters to nanoplates.

Relationship between the Photoluminescence Spectra and IR Spectroscopy of Mesoporous Silicon Samples during Long-Term Storage: The Effect of Immersion in an Aqueous Fe(NO&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt; Solutions

The article provides a comparative analysis of changes in the PL spectra and infrared spectroscopy (IR) with reference and immersion samples of mesoporous silicon during long-term storage in air at room temperature. Immersion was carried out in an aqueous solution of iron nitrate (Fe (NO3)3) with a concentration of 0.2 M and 0.5 M with three times: 5, 10 and 20 minutes. An analysis of the FIR data for etalon and immersion samples showed a number of features found during long-term storage of mesoporous silicon: (1) a sharp decrease in the density of hydride bonds; (2) the polynomial nature of the growth of O3-SiH and Si-OH bonds saturating dangling bonds; and (3) the polynomial growth of silicon dioxide with the formation of oxygen defects. It was found that after immersion in a solution of 0.5 M Fe (NO3)3 for 10 minutes, a more intense increase in the PL in mesoporous silicon is observed while maintaining its nanostructure after 200 days of storage compared with the etalon sample, for which a weak quantum size confinement (QSC) is observed. The main mechanism of photoluminescence increase in mesoporous silicon during long-term storage is radiative recombination from oxygen defect levels, not from a QSC effect.

Relationship between the Photoluminescence Spectra and IR Spectroscopy of Mesoporous Silicon Samples during Long-Term Storage: The Effect of Immersion in an Aqueous LiBr Solutions

Studies are devoted to determining the effect of long-term storage (up to 200 days) of untreated and immersion-treated layers of mesoporous silicon in an aqueous lithium bromide solution obtained by anodizing with a current density of 10 mA/cm2 in electrolyte HF: CH3OH = 2: 1. It was found that an increase in the PL intensity and its saturation with a storage time of more than 100 days in all samples is observed. A detailed analysis of absorbance on bonds in m/por-Si showed that during storage, hydrogen bonds are destroyed, and the PL peak intensity is proportional to the increasing concentration of non-stoichiometric oxide, in which oxygen atoms forms radiative states. It was shown that in the treated samples, the PL intensity decreases with increasing immersion time, but the mechanism of photoluminescence through the quantum size confinement (QSC) effect in mesoporous silicon without and with immersion in an aqueous LiBr solution is not significant.

Flat Lenses Based on 2D Perovskite Nanosheets.

Ultrathin flat lenses based on metasurfaces or metamaterials have shown great promise in recent years as essential components in nano-optical system, with capability of abrupt changes of light wavefronts. However, such structural designs require complex nanopatterns and a time-consuming nanofabrication process. In this regard, flat lenses are developed based on 2D perovskite nanosheets, using a cost-effective mask-free femtosecond direct laser writing system. The optical properties of the 2D perovskite are rationally adjusted through facile composition engineering as well as thickness-dependent quantum-size confinement. A diffraction theory model is derived to understand the focusing mechanism of the 2D perovskite nanosheets flat lenses. The as-fabricated lenses exploit the tunable material property variations to effectively manipulate not only the amplitude but also the phase of the incident light to focus into a 3D focal spot with a sub-wavelength resolution in the range of 0.5-0.9λ. The results pave the way toward low-cost and large-scale high-resolution imaging applications in the future.

Surface- and Strain-Mediated Reversible Phase Transformation in Quantum-Confined ZnO Nanowires.

The phase stability of ZnO in a quantum-confinement size regime (sub-2-nm) remains fiercely debated. Applying insitu (scanning) transmission electron microscopy, we present the atomistic view of the phase transitions from the original wurtzite structure to an intermediate body-centered tetragonal and h-MgO structure under tensile strain in quantum-confined ZnO nanowires. Strikingly, such structural transitions are reversible after releasing the stress. Further theoretical calculations mirror the transition pathway and provide basic insight into the overall landscape regarding surface- and strain-dependent phase transition behavior. Our results provide the critical piece to solve the puzzle in phase stability of ZnO, which may prove essential for advancing a variety of nanotechnologies, e.g., quantum-dot light-emitting devices.

Ligand induced anomalous emission shift of size-controlled CsPbBr3 nanocrystals

CsPbX3 perovskite nanocrystals (NCs) have attracted much attention from researchers because of their excellent photoelectric properties like high quantum yield, large absorption cross section, and simple preparation process. The addition of ligands in the synthesis process has a significant effect on the microstructure and photophysical properties of solution-processed NCs, which needs further extensive studies. In this Letter, the effects of ligand electronegativity on the size and photoluminescence (PL) properties of CsPbBr3 NCs were reported. One is typical oleic acid with weak electronegativity, and another is 2-acrylamide-2-methylpropionic sulfonic acid with strong electronegativity. The third is their typical mixture with a molar ratio of 1:1. With the increase in ligand electronegativity, the size of CsPbBr3 NCs increases significantly. However, in contrast to the traditional quantum size confinement effect, the PL peak exhibits an abnormal blue shift gradually and the ligand passivation effect on NC surface defects also becomes more significant. The physical mechanism of this anomalous PL shift phenomena of CsPbBr3 NCs was investigated using the time-resolved PL spectrum and transient absorption spectrum.

Stimulating Charge Transfer Over Quantum Dots via Ligand-Triggered Layer-by-Layer Assembly toward Multifarious Photoredox Organic Transformation

Semiconductor quantum dots (QDs) have garnered tremendous attention by virtue of their substantial light-harvesting and conversion efficiencies, large number of active sites, unique quantum size confinement, and multiple exciton generation effects. In this regard, recent years have witnessed their widespread applications in photocatalysis. Nonetheless, intrinsic disadvantages of QDs including unfavorable photostability, ultrafast charge recombination rate, and sluggish kinetic of charge carriers retard the construction of high-efficiency QDs-based photocatalysts for solar energy conversion. Thus far, in-depth investigation on the visible-light-driven photoredox organic transformation over QDs has not yet been exhaustively explored, and corresponding photocatalytic mechanisms remain elusive. In this work, selecting cadmium selenide (CdSe) as a quintessential category of semiconductor QDs, we demonstrated a facile, green, easily accessible, and rather efficient electrostatic self-assembly strategy to conspicuously boost the versatile photoredox performances of CdSe QDs toward selective organic transformation under visible light irradiation by intimately integrating with graphene (GR) via judicious surface charge tuning. In this scenario, intrinsically negatively charged CdSe QDs and surface-modified positively charged GRs were utilized as the building blocks for spontaneous electrostatic self-assembly buildup, which gives rise to well-defined CdSe QDs–GR ensembles. More intriguingly, ligands capped on the CdSe QDs surface enable the alternate layer-by-layer (LbL) assembly of CdSe QDs and GR forming three-dimensional spatially multilayered heterostructures. Furthermore, it was significant to unveil that such self-assembled CdSe QDs–GR nanocomposites exhibit remarkably enhanced and multifunctional photoredox performances toward selective oxidation of aromatic alcohols to corresponding aromatic aldehydes and selective reduction of nitroaromatics to amino compounds under visible light irradiation, which far exceeds the pristine CdSe QDs counterpart, which exhibits almost negligible photoactivities. This can be ascribed to the pivotal role of GR for conspicuously capturing and shuttling electrons from band-gap photoexcitation of CdSe QDs, intimate interfacial contact between the building blocks, and enlarged specific surface area stemming from seamless GR encapsulation and intercalation, along with the unique ligand-triggered LbL assembly integration mode between CdSe QDs and GR, hence synergistically reducing the recombination rate and prolonging the lifetime of charge carriers. Furthermore, photoredox mechanisms of the CdSe QDs–GR ensemble were elucidated. It is anticipated that our work would afford an efficacious avenue to finely modulate the charge transport over QDs for solar energy conversion.

A Facile Preparative Route of Nanoscale Perovskites over Mesoporous Metal Oxide Films and Their Applications to Photosensitizers and Light Emitters

AbstractBy two‐step sequential Pb2+ adsorption and reaction with methylammonium‐iodide (MAI) or ‐bromide (MABr) at a low concentration level of 0.06–0.10 m over mesoporous TiO2 or ZrO2 film, a well‐defined nanoscale CH3NH3PbI3 (MAPbI3) photosensitizer or CH3NH3PbBr3 (MAPbBr3) light emitter could be prepared in situ, respectively in a reproducible and atom‐economical way. The as‐prepared nanoscale perovskites are compared with their thin film counterparts in terms of light absorption/emission, crystallinity, surface morphology, and energy‐conversion efficiency. The nanoscale perovskite‐decorated films display more transparency than the bulky film due to the much lower amount deposited, while blueshifted and overwhelmingly brighter photoluminescence is observed in the “nano” relative to the “bulk” due to quantum size confinement. Transmission electron microscopy images also clearly show that a few nanometer‐sized perovskite dots are deposited homogeneously over the surface of TiO2‐ or ZrO2‐particulate film in the course of the current preparative route. When the nano‐MAPbI3 is tested as a photosensitizer in a solid‐state dye‐sensitized solar cell configuration with a very thin (≈650 nm) TiO2 mesoporous film, it has a promising initial power conversion efficiency of 6.23%, which outperformed the result of 2.28% from a typical organic molecular dye coded as MK‐2.

Atmospheric Plasma Synthesized and Surface Engineered Silicon and Graphene Nanocrystals in Energy Applications

Environmental and abundant silicon (Si) and carbon (C) play primary roles in current photovoltaic technologies. Si- and C- nanomaterials exhibit unique properties exhibited used in many field of application (e.g. solar cells, biology, optoelectronics). For instance, Si due to indirect energy band gap is poor in absorption and photoluminescence emission properties which can be enhanced at quantum confinement size due to electronic state and energy band engineering at quantum confinement size. On the other hand C-nanostructures based on sp2 hybridization reflect high strength, high electrical conductivities and enhanced photoluminescence. In this contribution we demonstrate that confined atmospheric plasma interactions through liquid is suitable either for synthesis and or surface treatment of Si- and C- quantum nanomaterials. Two deferent plasma-liquid sources are applied for synthesis and surface engineering. Namely, femtosecond (fs) laser beam (100 fs) is used to generate a plasma in the liquid and an atmospheric pressure direct-current (dc) microplasma generated under ambient air condition and coupled to the colloid via a counter electrode. We show that graphene nanocrystals with sizes around 5 nm can be synthesized using both plasma sources. We show that the graphene nanocrystals with different room temperature photoluminescence properties covering spectral range from 400nm to 850 nm can be formed as a function of molecular precursors. Furthermore whereby incorporated into a solar cell an high open-circuit voltage of 1.8 V is achieved. On the other hand, we show that during the plasma processing the Si- nanocrystals can be successfully used to tune OH surface functionalization. We discuss how the microplasma processing allows us to gradually change the degree of OH coverage, enabling us, in turn, to gradually shift the emitted light in the photoluminescence spectra by up to 100 nm to longer wavelengths at room temperature. The first-principles calculations are consistent with the experimentally observed dependence of the photoluminescence wavelengths on the OH coverage and show that the photoluminescence redshift is determined by the charge transfer between the Si-NC and the functional groups, while on the other hand surface strain plays only a minor part. Moreover, such a functionalized Si- nanocrystals can better interact with host matrix or can be introduced within. We present study on organic-inorganic hybrid based on methylammonium iodo bismuthate (CH3NH3)3(Bi2I9) (MABI) thin films. Due to the large proportion of localized excitons coupled with delocalized excitons from intercluster energy transfer an anisotropic photoluminescence is observed. Nonlinear photoluminescence properties at excitation energy above twice band gap indicate a carrier multiplication due to the low dimensionality Bi2I9 clusters. We show that the MABI structure can also accommodate plasma surface engineered Si nanocrystals that enhance the excitons dissociation.

Controlled Synthesis, Formation Mechanism, and Applications of Colloidal Ag8SnS6 Nanoparticles and Ag8SnS6/Ag2S Heterostructured Nanocrystals

Semiconductor nanocrystals (SC NCs) have attracted scientists’ attention because of their size- and shape-dependent optical properties. Now, many scientists’ research is focused on the synthesis of the earth-abundant and environmentally compatible SC NCs and their applications for solar energy conversion. Herein, colloidal silver-based I–IV–VI SC NCs, Ag8SnS6 nanoparticles (NPs) were synthesized. Ag8SnS6 NPs showed a strong quantum size confinement effect from optical measurement. The photocurrent response measurement showed a typical n-type property for Ag8SnS6 NPs. It is very interesting that colloidal Ag8SnS6/Ag2S heterostructured nanocrystals (HSNCs), containing drop-shaped and little bowtie-shaped HSNCs, can also be synthesized via changing the adding process of precursors in the beginning of the experiment. The first formation of Ag NPs is very important to form Ag8SnS6/Ag2S HSNCs. A seeded growth mechanism was proposed to explain the formation of Ag8SnS6/Ag2S HSNCs. The polycrystalline structure in...

High-loaded and transparent LaxCe1-xF3 — polystyrene nanocomposite scintillators for radiation detection

For radiation detection, sensitivity, response time, and energy resolution are important. Scintillating nanoparticles, in principle, can have enhanced light output in comparison with their bulk materials due to quantum size confinement and increased overlap of electron and hole wave function. However, the aggregation and the loss of transparency at high loading into polymers are the challenging issues for practical applications. Here, for the first time, we report a new method to fabricate the blue-emitting nanocomposites with up to 30 wt% nanoparticle loading. First, the polymerizable surfactant coated La0.6Ce0.4F3 nanoparticles are synthesized, and then, they are loaded up to 30 wt% in a polystyrene matrix. The nanocomposites show an intense luminescence and a good transparency, performing much better than the commercial EJ-200 plastic scintillator. The gamma spectra acquired with the nanocomposite show a photopeak for the Co-57 isotope. The gamma spectra of Cs-137 show a full energy peak at around 622 keV, due to the escape of La and Ce Kα X-rays. The observation of the photopeaks is attributed to the enhanced photoelectric effect as a result of increased effective atomic number (Zeff). All these indicate that the high loaded nanocomposites are promising for radiation detection and nuclear material surveillance for homeland security.