Silver Chalcogenides Research Articles

Shortwave-Infrared Silver Chalcogenide Quantum Dots for Optoelectronic Devices.

Silver chalcogenide (Ag2X, X = S, Se, Te) semiconductor quantum dots (QDs) have been extensively studied owing to their short-wave infrared (SWIR, 900-2500 nm) excitation and emission along with lower solubility product constant and environmentally benign nature. However, their unsatisfactory photoluminescence quantum yields (PLQYs) make it difficult to obtain optoelectronic devices with high performances. To tackle this challenge, researchers have made great efforts to develop valid strategies to improve the PLQYs of SWIR Ag2X QDs by suppressing their nonradiative recombination of excitons. In this Perspective, we summarize the significant approaches of heteroatom doping and surface passivation to enhance the PLQYs of SWIR Ag2X QDs, and we conclude their application in high-efficiency optoelectronic devices. Finally, we examine the future trends and promising opportunities of Ag2X QDs with regard to their optical properties and optoelectronics. We believe that this Perspective will serve as a valuable reference for future advancement in the synthesis and application of SWIR Ag2X QDs.

Controlled growth of high-quality β-Ag2Se nanowires and their applications in near-infrared photodetection

This work reports the controlled growth of single-crystalline β-Ag2Se nanowires and their application in near-infrared photodetection. High-quality Ag2Se nanowires with an orthorhombic crystal structure are grown via the chemical vapor deposition method with a length up to 32.8 μm and a diameter down to 52.1 nm. By fine-tuning the growth parameters such as total tube inner pressure and precursor temperature, the length of Ag2Se nanowires can be precisely controlled. A dynamic growth model is also introduced to interpret the growth mechanism of Ag2Se nanowires. Two-terminal photodetectors based on single Ag2Se nanowire are fabricated and show competitive photodetection performance compared to that of other silver chalcogenide nanomaterial-based photodetectors. At room temperature, the fabricated Ag2Se nanowire-based photodetector exhibits a broadband response range of 400–1064 nm at a bias voltage of 2 V, while the peak photo-response performance is obtained in the near-infrared region. Under 830 nm light illumination, the maximum responsivity, specific detectivity, rise time and decay time are measured and calculated to be 99.6 mA/W and 4.01 × 106 Jones, 23.84 ms and 47.6 ms, respectively, demonstrating its potential in uncooled near-infrared photodetector applications.

Rational design and structural regulation of near-infrared silver chalcogenide quantum dots

Rational design and structural regulation of near-infrared silver chalcogenide quantum dots

Theoretical investigation of the silver chalcogenide molecules AgSe and AgTe electronic structure with dipole moment calculation

The spectroscopic constants (Re, Te, ωe, Be) are determined for 46 doublet and quartet low-lying states of the molecules AgTe and AgSe using CASSCF/MRCI (single and double excitations plus Davidson correction) calculations. The equilibrium bond length Re, and the vibrational frequency ωe of the ground state of both molecules have also been investigated using the density functional theory (DFT) incorporating eight different functionals along with different basis sets. The potential energy and permanent dipole moment curves of 23 states of each molecule have been investigated and depicted. This study represents the first theoretical investigation of the molecules AgSe and AgTe.

Hydrophilic Ag2Se quantum dots fluorescence enhancement by photoactivation using solar light

Silver chalcogenides showed potential for biomedicine due to their lower cytotoxicity, emission in the near-infrared region, and higher penetrability in biological tissues. However, the aqueous synthesis of these nanocrystals affords quantum dots (QDs) with lower quantum efficiency, when compared to the preparation in organic solvents. Thus, this work intended to enhance the fluorescence intensity of hydrophilic silver selenide (Ag2Se) QDs by irradiating them with visible light. Ag2Se QDs stabilized with mercaptossuccinic acid were prepared in water, achieving nanocrystals with an emission maximum of around 743 nm. These nanocrystals were irradiated with visible light for up to 60 min. Our results showed that 30 min of irradiation induced an emission enhancement of up to 800 %. Moreover, 60 min of irradiation afforded an improvement of more than 770 % together with a decrease in the full width at maximum wavelength. Thus, photoirradiation can be a simple and efficient strategy to improve silver chalcogenides’ quantum yields.

Enhancing the optical properties of hydrophilic Ag2Se NIR-II quantum dots by using chemometric approaches towards (bio)sensing applications

Silver chalcogenide quantum dots (QDs) are potential nanosensors for biological and environmental applications.

Research Progress on the Preparation Method of NIR-II Silver Chalcogenide Quantum Dots and Its Application in Cancer Diagnosis and Treatment

Research Progress on the Preparation Method of NIR-II Silver Chalcogenide Quantum Dots and Its Application in Cancer Diagnosis and Treatment

Efficient hydrogen evolution from g-C3N4 under visible light by in situ loading Ag2Se nanoparticles as co-catalysts

The low charge separation and transfer of g-C3N4 hinders its industrial application in photocatalytic hydrogen evolution. Here, we design a novel co-catalyst strategy to integrate Ag2Se nanoparticles in situ on the surface of g-C3N4. The optimized photocatalyst, 15% Ag2Se/g-C3N4, demonstrates remarkable photocatalytic efficiency in the hydrogen evolution rate, reaching to 1102.8 μmol·g−1·h−1, 7 times higher than g-C3N4. To further elucidate the photocatalytic activity of 15% Ag2Se/g-C3N4, we present a possible mechanism based on various characterizations and density functional theory calculations. This research offers potential insights for the future development of silver chalcogenide composites in photocatalysis.

Construction of machine-learning interatomic potential under heat flux regularization and its application to power spectrum analysis for silver chalcogenides

We propose a data-driven approach for constructing machine-learning interatomic potentials (MLIPs) trained under a regularization with the aim of avoiding nonphysical heat flux that arises from the many-body effect of MLIPs and is sensitive to their initial weight parameters. Specifically, we introduce a regularization term for the heat flux into the cost function of MLIPs to be minimized. Since the treatment of heat flux using MLIPs with regularization can be decomposed into elemental contributions or conducted in frequency space, this approach is expected to be useful for investigating the origin of thermal conductivity obtained from the Green-Kubo formula. However, the strength of regularization needs to be appropriately set because it may reduce not only the nonphysical part but also the intrinsic heat flux one. To this end, we investigated the conditions for constructing MLIPs that can reproduce the power spectra of heat flux associated with the empirical interatomic potential of Ag2Se, which consists of pairwise functions and do not contain a nonphysical heat flux. The power spectrum is useful because it helps to verify the effect of regularization and also contains the information on thermal conductivity and phonon. The appropriate strength could be estimated from the variation of the magnitude of regularization term as well as root mean square errors for total potential energy, atomic force, and virial stress with respect to the strengths, without reference spectrum data. As an application example, we explored the differences in power spectra between superionic and nonsuperionic conducting phases based on the heat flux regularization to MLIPs trained with the first-principles calculation data of Ag2S. Furthermore, our results demonstrate that training with the regularization improves the robustness of MLIPs as well as the reduction of the nonphysical heat flux.

Peculiarities of the Effect of Silver Chalcogenides on the Glass-Formation Temperature of Chalcogenide Glasses with Ionic Conduction

Peculiarities of the Effect of Silver Chalcogenides on the Glass-Formation Temperature of Chalcogenide Glasses with Ionic Conduction

Flexible Ag-S-Te System with Promising Room-Temperature Thermoelectric Performance.

Silver chalcogenides demonstrate great potential as flexible thermoelectric materials due to their excellent ductility and tunable electrical and thermal transport properties. In this work, we report that the amorphous/crystalline phase ratio and thermoelectric properties of the Ag2SxTe1-x (x = 0.55-0.75) samples can be modified by altering the S content. The room-temperature power factor of the Ag2S0.55Te0.45 sample is 4.9 μW cm-1 K-2, and a higher power factor can be achieved by decreasing the carrier concentration as predicted by the single parabolic band model. The addition of a small amount of excessive Te into Ag2S0.55Te0.45 (Ag2S0.55Te0.45+y) not only enhances the power factor by decreasing the carrier concentration but also reduces the total thermal conductivity due to decreased electronic thermal conductivity. Owing to the effectively optimized carrier concentration, the thermoelectric power factor and dimensionless figure of merit zT of the sample with y = 0.007 reaches, respectively, 6.2 μW cm-1 K-2 and 0.39, while the excellent plastic deformability is well maintained, demonstrating its promising potential as a flexible thermoelectric material at room temperature.

Ligand-induced surface reconstruction in Ag2S colloidal quantum dots for highly luminescent infrared fluorescence

Silver sulfide (Ag2S) colloidal quantum dots (CQDs) have attracted attention as potential bio-imaging materials owing to their narrow bandgap and biocompatibility; however, their low photoluminescence quantum yield (PLQY) has limited their applications. Here we introduce ligand-induced surface reconstruction strategy to dramatically improve the PLQY of Ag2S CQDs. We found that the low PLQY of Ag2S CQDs is due to the undesirable formation of a metallic Ag core during the CQD synthesis. By introducing alkyl thiols as oxidizing agents, the metallic Ag core is reoxidized that Ag vacancies in CQDs are refilled. This induces a reduced metallic Ag core and Ag-rich stoichiometry in the CQDs. The CQDs after the surface reconstruction show a 150× enhancement of photoluminescence at 1230 nm, with an absolute PLQY of 9%. This research suggests that simple ligand treatments can help improve the surface and optical properties of silver chalcogenide CQDs, including Ag2S CQDs, which may allow development of advanced optoelectronic devices.

Silver chalcogenide loaded V2CTx MXene-molecularly imprinted polymer-based novel ratiometric sensor for the early predictive cancer marker: L-Fucose

Fucosylated-haptoglobin (Hpt) and urinary free L-fucose (FU) are primary markers in the progression of tumor and metastasis-related to cancer of the liver (Hepatocellular carcinoma), pancreatic, prostate, colon and oral cancer. The p-aminobenzoic acid (PABA)-FU containing molecularly imprinted polymer (MIP) cavities were accessed to detect FU molecules with signal amplifying layer of novel silver selenide (Ag2Se) doped vanadium carbide (V2CTx) MXene. The selection of suitable monomers through theoretical calculations and optimization of factors involved in the fabrication of a MIP-based sensor via Taguchi orthogonal array (5 × 5) was abundant in improvising the sensor performance. Ratiometry of the oxidation response of FU (IFU) and Ag2Se@V2CTx (IM) played a vital role in eliminating the interference of serum proteins which includes Hpt (undigested), thus sample pretreatment is not required. The extraordinary selectivity with remarkable LOD (1.85 μM) was achieved for FU detection in 100 mM PBS (pH = 6.0) and structurally mimicking interferents failed to show an impactful response against the sensor. Urinary-free FU (spiked) and serum FU (unspiked and spiked) were analyzed in which the LOD of urinary-free FU was as low as 2.22 μM. In addition, normal human serum showed 440.2 μM of FU and the %recovery of FU-spiked samples was between 98.0 and 101.5%.

A brighter era for silver chalcogenide semiconductor nanocrystals

Silver chalcogenide semiconductor nanocrystals (Ag2E SNCs) have become a household name in the biomedical field, where they are used as contrast agents in bioimaging, photothermal therapy agents, and luminescent nanothermometers. The prominent position they have come to occupy in this field stems from a unique combination of features, above all near-infrared excitation and emission alongside low cytotoxicity. However, the first reports on Ag2E SNCs showed that a great limitation of these luminescent nanomaterials resided in their low photoluminescence quantum yield, which results in reduced brightness: a crippling feature in bioimaging and biosensing. In this article, we provide an overview of the strategies developed to overcome this hurdle. These strategies aim to remedy the presence of defects in the SNC core and/or surface, the presence of metallic silver, and off-stoichiometric composition. These features stem from the high mobility and redox potential of Ag+ ions, alongside the difficulty in controlling the nucleation and growth rate of Ag2E SNCs. The effectiveness of each approach is discussed. Lastly, a perspective on future research efforts to make Ag2E SNCs even brighter – and thus more effective in biomedical applications – is provided, with the hope of inspiring further investigation on these nanomaterials with a rich, complex set of physicochemical and spectroscopic properties.

Study of the defect chemistry in Ag2Q (Q = S, Se, Te) by first-principles calculations

Ag2Q-based (Q = S, Se, Te) silver chalcogenides show great potential in thermoelectrics due to their suitable band gaps, high electron mobilities, and even remarkable ductility. Particularly, Ag2S and Ag2S/Se/Te solid solutions have been reported with both good ductility and thermoelectric performance, which are extremely suitable for the application in flexible wearables. However, the underlying mechanism of the native n-type conduction and p-type undopability for Ag2Q remains elusive. Herein, we use first-principles calculations based on density functional theory combined with GW correction to investigate the defect chemistry in Ag2Q. It is found that the site potential and Voronoi volume deviations resulting from Ag interstitials are noticeably smaller than those caused by Ag vacancies, which makes Ag interstitials with low formation energy more desirable during preparation, contributing to the native n-type conduction. The small and even negative dopability windows, on the other hand, account for the p-type undopability of Ag2Q. The calculated carrier concentrations of pristine Ag2Q are well consistent with the experimental observations, validating the reliability of our defect calculations. This work provides valuable guidance for first-principles calculation of defect chemistry in other narrow-gap semiconductors.

A novel strategy to construct activatable silver chalcogenide quantum dots nanoprobe for NIR-Ⅱ fluorescence imaging of hypochlorous acid in vivo

It is necessary to develop sensitive and selective probes for real-time in vivo monitoring of hypochlorous acid (HClO) which plays a significant role in physiological and pathological processes. The second near-infrared (NIR-Ⅱ) luminescent silver chalcogenide quantum dots (QDs) have shown great potential in developing activatable nanoprobe for HClO in terms of their outstanding imaging performance in the living organism. However, the limited strategy for the construction of activatable nanoprobes severely restricts their widespread applications. Herein, we proposed a novel strategy for developing an activatable silver chalcogenide QDs nanoprobe for NIR-Ⅱ fluorescence imaging of HClO in vivo. The nanoprobe was fabricated by mixing an Au-precursor solution with Ag2Te@Ag2S QDs to allow cation exchange and release Ag ions and then reducing the released Ag ions on the QDs surface to form an Ag shell for quenching of the emission of QDs. The Ag shell of QDs was oxidized and etched in the presence of HClO, resulting in the disappearance of their quenching effect on QDs and the activation of the QDs emission. The developed nanoprobe enabled highly sensitive and selective determination of HClO and imaging of HClO in arthritis and peritonitis. This study provides a novel strategy for the construction of activatable nanoprobe based on QDs and a promising tool for NIR-Ⅱ imaging of HClO in vivo.

Engineering of Advanced Materials for High Magnetic Field Sensing: A Review

Advanced scientific and industrial equipment requires magnetic field sensors with decreased dimensions while keeping high sensitivity in a wide range of magnetic fields and temperatures. However, there is a lack of commercial sensors for measurements of high magnetic fields, from ∼1 T up to megagauss. Therefore, the search for advanced materials and the engineering of nanostructures exhibiting extraordinary properties or new phenomena for high magnetic field sensing applications is of great importance. The main focus of this review is the investigation of thin films, nanostructures and two-dimensional (2D) materials exhibiting non-saturating magnetoresistance up to high magnetic fields. Results of the review showed how tuning of the nanostructure and chemical composition of thin polycrystalline ferromagnetic oxide films (manganites) can result in a remarkable colossal magnetoresistance up to megagauss. Moreover, by introducing some structural disorder in different classes of materials, such as non-stoichiometric silver chalcogenides, narrow band gap semiconductors, and 2D materials such as graphene and transition metal dichalcogenides, the possibility to increase the linear magnetoresistive response range up to very strong magnetic fields (50 T and more) and over a large range of temperatures was demonstrated. Approaches for the tailoring of the magnetoresistive properties of these materials and nanostructures for high magnetic field sensor applications were discussed and future perspectives were outlined.

Anisotropic topological surface states in thin-film monoclinic Ag2Se

Silver chalcogenide systems have recently attracted significant attention due to their promising topological insulating properties. Here we conducted systematic low-temperature local scanning tunneling microscopy/spectroscopy and first-principles studies on the surface states of monoclinic Ag2Se thin films grown using molecular beam epitaxy. Through the use of quasi-particle interference patterns, we have observed evidence for topological surface states on the selenium-terminated surfaces with different types of defect densities. The results of ab initio calculations confirm the existence of nontrivial topological surface states in the monoclinic Ag2Se structure, for which such properties have not been previously reported. The energy dispersion determined using voltage-dependent standing wave patterns suggests that these topological states have an anisotropic Dirac cone structure. This discovery may lead to new applications for monoclinic Ag2Se in the rapidly growing fields of nanoelectronics and spintronics.

SILVER SULFIDES AND SELENIDES IN ORES FROM Au-Ag EPITHERMAL DEPOSITS OF THE OKHOTSK-CHUKOTKA VOLCANIC BELT

Mineral associations and compositions of sulfoselenides and other silver chalcogenides from epithermal deposits of the Okhotsk-Chukotka volcanic belt (North-East Russia) - Rogovik, Lunnoye, Julietta, Valunistoe, Corrida and Pepenveem have been studied. Different types of relationships between S-naumannite and Se-acanthite in the ores of the studied deposits have been established. It is shown that a general pattern in the sequence of formation of silver chalcogenides is the replacement of S-naumannite and Se-bearing minerals (Se-galena, Se-stephanite) of early parageneses by Se-acanthite or acanthite at later stages. Based on the results of thermodynamic calculations and data on the composition of the main productive mineral associations, the physicochemical parameters (T, ƒS2, ƒSe2, ƒO2, pH) of ore formation at these deposits were reconstructed.

Transformations of silver(i) chalcogenide clusters induced by halide ions as dopant components rather than surface active species

The distinctive transformation of a {Ag32} cluster was achieved by incorporating different halide ions, and the process induced high selectivity luminescence.