Ternary Alloyed Quantum Dots Research Articles

Ternary alloyed HgCdTe nanocrystals for short-wave and mid-wave infrared region optoelectronic applications

Semiconductor quantum dots (QDs) are emerging as the forefront alternative for the conventional imaging technology, particularly in infrared region from near infrared (0.75–1.4 μm) to long-wave infrared (8–14 μm) region. A handful of materials are explored for mid infrared imaging QDs and they are all invariably binary semiconductor compounds. Ternary alloyed quantum dots in many previous cases have shown properties that are unique and better than parent binary compounds. In this work, we have synthesized ternary alloyed HgCdTe quantum dots and studied their photophysical properties. Previously studied ternary alloyed HgCdTe CQDs absorb and emit in regions limited upto near-infrared region. We have tuned the excitonic absorption of HgCdTe QDs in the range of 2.2–5 μm, where addition of cadmium clearly showed blueshift in excitonic peak as compared to that of HgTe QDs. Structural properties are studied by TEM, XRD & XPS techniques. Electrical behaviour is studied by measuring I-V, I-V-T curves. Photodetectors are fabricated in photoconductive geometry showing promising photo-response under visible (532 nm) and NIR (810 nm, 1550 nm) excitation. Responsivity of the devices is in the order of 1 mA W−1 at 1 V bias and show good linearity over irradiance range of 0.025 and 2.5 W cm−2. These results pave the way for development of next generation cost-effective short-wave and mid-wave infrared region optoelectronic devices based on narrow bandgap HgCdTe nanocrystals.

Colloidal Chemistry in Molten Salts: Synthesis of Luminescent In1- xGa xP and In1- xGa xAs Quantum Dots.

Control of composition, stoichiometry, and defects in colloidal quantum dots (QDs) of III-V semiconductors has proven to be difficult due to their covalent character. Whereas the synthesis of colloidal indium pnictides such as InP, InAs, and InSb has made significant progress, gallium-containing colloidal III-V QDs still remain largely elusive. Gallium pnictides represent an important class of semiconductors due to their excellent optoelectronic properties in the bulk; however, the difficulty with the synthesis of gallium-containing colloidal III-V QDs has largely prohibited their exploration as solution-processed semiconductors. Here we introduce molten inorganic salts as high-temperature solvents for the synthesis and manipulation of III-V QDs. We demonstrate cation exchange reactions on presynthesized InP and InAs QDs to form In1- xGa xP and In1- xGa xAs QDs at temperatures above 380 °C. This approach produces novel ternary alloy QDs with controllable compositions that show size- and composition-dependent absorption and emission features. Emission quantum yields of up to ∼50% can be obtained for In1- xGa xP/ZnS core-shell QDs. A comparison of the optical properties of InP/ZnS core-shells with In1- xGa xP/ZnS core-shells reveals that Ga incorporation leads to significant improvement in the optical properties of III-V/II-VI core-shell emitters which is of great importance for quantum dot-based lighting and display applications. This work also demonstrates the potential of molten inorganic salts as versatile solvents for the synthesis and processing of colloidal nanomaterials at temperatures inaccessible for traditional solvents.

STRUCTURAL AND OPTICAL PROPERTIES IN NEAR INFRARED OF CdTeSe COLOIDAL QUANTUM DOTS FOR POTENTIAL APPLICATION IN SOLAR CELLS

Abstract: This report presents the results on the optical properties of CdTeSe ternary alloyed quantum dots (QDs) fabricated by colloidal chemical method. We have used the micro-Raman spectra as a tool to determine the formation of CdTeSe alloy phase, the composition ratio of Te:Se when fabricated at different temperatures from 180 oC to 280 oC. The intensity ratio of two vibration lines at 159 cm-1 and 188 cm-1 allows the determination of Te:Se composition ratio available in QD samples. The Raman spectra of CdTexSe1-x when x changes between 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1, fabricated at 260 oC, shows clearly the change in intensity of the optical vibration lines. The absorption and emission spectra of CdTeSe QDs show that the absorption edge of these QDs shifts up to 880 nm and up to ~ 860 nm for the emission. Detailed studies on size, structural, vibration and optical characteristics of ternary alloyed QDs are also discussed. The absorption region of fabricated CdTeSe QDs are completely suitable for usage in solar cells.

Synthesis, Structural and Optical Characterization of CdTeSe/ZnSe and CdTeSe/ZnTe Core/Shell Ternary Quantum Dots for Potential Application in Solar Cells

This work presents the results on the fabrication, structural and optical properties of CdTeSe/ZnTe and CdTeSe/ZnSe n monolayers (ML) (with n = 0,1,2,4 and 6 being the nominal shell monolayer thickness) ternary alloyed core/shell quantum dots (QDs). Transmission electron microscopy has been used to observe the shape and size of the QDs. These QDs crystallize at the zinc-blende phase. Raman scattering has been used to characterize the CdTeSe QDs’ alloy composition in the fabrication and coating processes. The Raman spectrum of CdTeSe QDs, in the frequency range from 100 cm−1 to 300 cm−1, is a composite band with two peaks at 160 cm−1 and 192 cm−1. When the thickness of the ZnTe shell is 4 ML, the peak of the Raman spectrum only appears at 160 cm−1. For the ZnSe 4 ML shell, the peak only appears at ∼200 cm−1. This shows that the nature of the CdTeSe QDs is either CdTe-rich or CdSe-rich depending on the shell of each sample. The shell thickness of 2 ML does not change the ternary core QDs’ crystalline phase. The absorption and photoluminescence spectra show that the absorption and emission bands can be shifted to 900 nm, depending on each ternary alloyed QD core/shell sample. This near-infrared spectrum region is suitable␣for applications in solar cells.

Spectroscopic investigation of alloyed quantum dot-based FRET to cresyl violet dye.

Quantum dots (QDs), bright luminescent semiconductor nanoparticles, have found numerous applications ranging from optoelectronics to bioimaging. Here, we present a systematic investigation of fluorescence resonance energy transfer (FRET) from hydrophilic ternary alloyed quantum dots (CdSeS/ZnS) to cresyl violet dye with a view to explore the effect of composition of QD donors on FRET efficiency. Fluorescence emission of QD is controlled by varying the composition of QD without altering the particle size. The results show that quantum yield of the QDs increases with increase in the emission wavelength. The FRET parameters such as spectral overlap J(λ), Förster distance R0, intermolecular distance (r), rate of energy transfer k(T)(r), and transfer efficiency (E) are determined by employing both steady-state and time-resolved fluorescence spectroscopy. Additionally, dynamic quenching is noticed to occur in the present FRET system. Stern-Volmer (K(D)) and bimolecular quenching constants (k(q)) are determined from the Stern-Volmer plot. It is observed that the transfer efficiency follows a linear dependence on the spectral overlap and the quantum yield of the donor as predicted by the Förster theory upon changing the composition of the QD.

Mechanism to Detect Pesticide Residues in Tealeaves Based on CdZnSe/ZnS Ternary Alloy Quantum Dots

In this report, we present the optical properties of the biosensors fabricated from CdZnSe/ZnS quantum dots. The optical properties such as absorption and emission of the ternary quantum dots before and after coupling with the protein molecules like streptavidine (SA) and acetylcholinesterase enzymes (AChE), to form a biosensor structure, will be presented. In particular, the changes in luminescence intensity according to the pH value of the solution environment containing biosensor have been considered, before and after the presence of pesticides. The changes in luminescence intensity of the biosensor after the presence of pesticide over time from 2 seconds to 26 minutes were also surveyed. We have been carried out the tests to determine the trace amounts of commercial pesticides like Motox 5EC, containing 5% cypermethrin and Tungatin 10 EC, containing 10% abamectin, on the real samples of tealeaves. Some characteristics of the relationship between composition, structure, and special optical properties of ternary alloy quantum dots will also be presented. These studies open up the potential applications of ternary quantum dots for agricultural production.

Study on the fabrication of CdZnSe/ZnSeS ternary alloy quantum dots

In an effort to search for new compositions and structures of quantum dots with suppressed blinking photoluminescence (random switching between states of high (on) and low (off) emissivity under continuous photo-excitation) and to serve application purposes in biosensors and in optoelectronic devices, we have studied the fabrication of new CdZnSe/ZnSeS ternary alloy quantum dots (QD). In this work, we present new results on the fabrication of the alloy core/shell quantum dots having a shell thickness of about 1.52 nm and a varied shell composition in Se/S ratio. The influence of the growth temperature on the structural properties (crystalline phase and cell), size and elemental compositions of the core and core/shell QDs is presented. Analysis and in-depth comparison of the calculated ternary QDs' composition are performed based on the energy dispersive X-ray spectroscopy (EDS) data and the first exciton absorption peak position and size. Interpretation of the experimental results is also provided.

Quantum Dots: Blue Liquid Lasers from Solution of CdZnS/ZnS Ternary Alloy Quantum Dots with Quasi‐Continuous Pumping (Adv. Mater. 1/2015)

Quantum Dots: Blue Liquid Lasers from Solution of CdZnS/ZnS Ternary Alloy Quantum Dots with Quasi‐Continuous Pumping (Adv. Mater. 1/2015)

Blue liquid lasers from solution of CdZnS/ZnS ternary alloy quantum dots with quasi-continuous pumping.

A blue (ca. 440 nm) liquid laser with an ultra-low threshold through which quasi-continuous wave pumping is accessible is achieved by engineering unconventional ternary CdZnS/ZnS alloyed-core/shell QDs. Such an achievement is enabled by exploiting the novel gain media with minimal defects, suppressed Auger recombination, and large gain cross-section in combination with high-quality-factor whispering gallery mode resonators.

Sensitive Organophosphorus and Carbamate Pesticides Biosensor Based on Acetylcholinesterase and CdZnSe/ZnS Ternary Alloy Quantum Dots

This report presents the results of ternary alloy quantum dots (TQDs) manufacturing and its superior optical properties to fabricate the biosensor for pesticide detection. The explanation for the changes in PL intensity based on the change of electronic charges that alters the pH value of the surrounding environment, and the types of interaction on the surface of CdZnSe/ZnS TQDs were discussed. We show the decomposition process of the indicator (ATCh) with the catalysis from acetylcholinesterase enzyme (AChE) that inhibited by organophosphorus and carbamate pesticides including Trichlorfon (TF), Cypermethrin (CH), Abamectin (AT), and Carbosulfan (CS) with concentrations from 0.05 ppm to 10 ppm.

Size Distribution and Scaling Behavior of InAlAs/AlGaAs Quantum Dots Grown on GaAs by Molecular Beam Epitaxy

We studied the size distribution and scaling behavior of self-assembled InAlAs/AlGaAs quantum dots (QDs) grown on GaAs in the Stranski–Krastanow (SK) mode by molecular beam epitaxy (MBE) at 480 and 510 °C as a function of InAlAs coverage. A scaling function of the volume was found for the first time in ternary alloy QDs. The function was similar to that of InAs/GaAs QDs, which agreed with the scaling function for a two-dimensional submonolayer homoepitaxy simulation with a critical island size of i = 1. However, a characteristic of i = 0 was also found as a tail in a large volume.