In the last two decades, semiconductor quantum dots-small colloidal nanoparticles-have garnered a great deal of scientific interest because of their unique properties. Among nanomaterials, CdTe holds special technological importance as the only known II-VI material that can form conventional p-n junctions. This makes CdTe very important for the dev

Cadmium telluride quantum dots (CdTe QDs) were prepared by chemical reaction and used to fabricate electroluminescence quantum dot hybrid junction device. QD-LED was fabricated using TPD: PMMA/CdTe/Alq3 device which synthesized by phase segregation method. The hybrid white light-emitting devices consist of three layers deposited successively on the ITO glass substrate; the first layer was of tetra-phenyl diaminobiphenyl (TPD) polymer mixed with polymethyl methacrylate (PMMA) polymers, while the second layer was 0.5¬†wt% of the (CdTe) QDs for hybrid device, whereas the third layer was tris (8-hydroxyquinoline) aluminum (Alq3). The organic light-emitting device (OLED) was considered by room temperature photoluminescence (PL) and electroluminescence (EL). Current-voltage (I-V) characteristics indicate that the output current is good compared to the few voltage (6¬†V) used which gives good results to generate white light. The electroluminescence (EL) spectrum of hybrid device shows a wide emission band covering the range 350,Äì700¬†nm. The emissions causing this white luminescence were identified depending on the chromaticity coordinates (CIE 1931): x¬†=¬†0.32, y¬†=¬†0.33. The correlated color temperature (CCT) was found to be about 5886¬†K.¬†Fabrication of EL devices from semiconductor material (CdTe QDs) between two layers, organic polymer (TPD) and organic molecules (Alq3), was effective in white light generation. The recombination processes and I-V characteristics give rise to the output current which is good compared to the few voltages used which give good results to generate light.

This paper gives an overview of molecular beam epitaxy (MBE) growth of and the optical properties of Cadmium Telluride (CdTe) quantum dots grown on Zinc Telluride (ZnTe) by self-assembly. It is shown that quantum dots in this material system can be obtained either by depositing CdTe at a high substrate temperature or by subjecting CdTe layer to a healing process, up to 70 seconds long before its capping or, eventually, by applying these two methods simultaneously. Moreover, it is found that one can also use the atomic layer epitaxy method to achieve the formation. From optical measurements performed on large quantum dot ensembles it is found that the quantum dot emission is much broader than that of quantum wells, and that it is observable up to much higher temperatures, which indicates strong exciton localization. The latter is also evidenced by an insensitivity of the decay time of the exciton recombination (^3O0 ps) to the temperature. From the presence of a second, very long decay time (^5 ns) and from disappearance of the sharp lines related to recombination in single dots, the acoustic phonon scattering of excitons is found to play an important role in these quantum dot structures. From a magnetic field dependence of the single dot emission energy, the exciton effective g-factor and spatial extension of the exciton wave function are deduced to be equal to -3 and 3 nanometers, respectively. Both the g-factor and the value of the diamagnetic shift are found to be independent of the energy of the quantum dot emission at Beta=Omicron Tau and of the in-plane symmetry of its potential. (11 figures, 35 refs.).

Captures the most up-to-date research in the field, written in an accessible style by the world's leading experts.

This book can be roughly divided into three parts: fundamental physico-chemical and physical principles of Nanoscience, chemistry and synthesis of nanoparticles, and techniques to study nanoparticles. The first chapter is concerned with the origin of the size dependence of the properties of nanomaterials, explaining it in terms of two fundamental nanoscale effects. This chapter also serves as a general introduction to the book, briefly addressing the definition and classification of nanomaterials and the techniques used to fabricate and study them. Chapter 2 lays out the theoretical framework within which to understand size effects on the properties of semiconductor nanocrystals, with particular emphasis on the quantum confinement effect. The optical properties of metal nanoparticles and metal nanostructures (periodic lattices) are discussed in Chapter 3. Chapter 4 is devoted to nanoporous materials, treating in detail their synthesis, structure and functional properties, as well as the physical properties of liquids confined in nanopores. The preparation methods, characterization techniques, and applications of supported nanoparticles are covered in Chapter 5. The sixth Chapter presents the essential physical-chemical concepts needed to understand the preparation of colloidal inorganic nanoparticles, and the remarkable degree of control that has been achieved over their composition, size, shape and surface. The last four Chapters are dedicated to a few selected characterization techniques that are very valuable tools to study nanoparticles. Chapter 7 concentrates on electron microscopy techniques, while Chapter 8 focuses on scanning probe microscopy and spectroscopy. Electron paramagnetic resonance (EPR) based spectroscopic techniques and their application to nanoparticles are explored in Chapter 9. Finally, Chapter 10 shows how solution Nuclear Magnetic Resonance (NMR) spectroscopic techniques can be used to unravel the surface chemistry of colloidal nanoparticles.

High-quality colloidal CdTe quantum wires having purposefully controlled diameters in the range of 5-11 nm are grown by the solution-liquid-solid (SLS) method, using Bi-nanoparticle catalysts, cadmium octadecylphosphonate and trioctylphosphine telluride as precursors, and a TOPO solvent. The wires adopt the wurtzite structure, and grow along the [002] direction (parallel to the c axis). The size dependence of the band gaps in the wires are determined from the absorption spectra, and compared to the experimental results for high-quality CdTe quantum dots. In contrast to the predictions of an effective-mass approximation, particle-in-a-box model, and previous experimental results from CdSe and InP dot-wire comparisons, the band gaps of CdTe dots and wires of like diameter are found to be experimentally indistinguishable. The present results are analyzed using density functional theory under the local-density approximation by implementing a charge-patching method. The higher-level theoretical analysis finds the general existence of a threshold diameter, above which dot and wire band gaps converge. The origin and magnitude of this threshold diameter is discussed.

Consisting of six chapters, written by experts in their field, this book charts the progress made in the use of quantum dots as the signaling component in optical sensors since their discovery in the early 1980s. In particular, it focuses on CdS-, CdSe-, and CdTe-type QDs due to their emission in the visible region of the electromagnetic spectrum. The book begins by detailing the range of methods currently used for the preparation and passivation of core/core–shell quantum dots and follows with a discussion on their electrochemical properties and potential toxicity. The book culminates by focusing on how electron and energy transfer mechanisms can be utilized to generate a range of quantum dot-based probes. This is the first text of its kind dedicated to quantum dot-based sensors and will appeal to those readers who have an interest in working with these versatile nanoparticles.