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Artykuły w czasopismach na temat "LED - Semiconductor Nanocrystals"
1
Erdem, Talha, i Hilmi Volkan Demir. "Color-Enrichment Semiconductor Nanocrystals for Biorhythm-Friendly Backlighting". Zeitschrift für Physikalische Chemie 232, nr 9-11 (28.08.2018): 1457–68. http://dx.doi.org/10.1515/zpch-2018-1134.
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Abstract Nanocrystals (NCs) offer great opportunities for developing novel light-emitting devices possessing superior properties such as high quality indoor lighting, efficient outdoor lighting, and display backlighting with increased color definition. The narrow-band emission spectra of these materials also offer opportunities to protect the human daily biological rhythm against the adverse effects of display backlighting. For this purpose, here we address this problem using color converting NCs and analyzed the effect of the NC integrated color converting light-emitting diode (NC LED) backlight spectra on the human circadian rhythm. We employed the three existing models including the circadian light, the melanopic sensitivity function, and the circadian effect factor by simultaneously satisfying the National Television Standards Committee (NTSC) requirements. The results show that NC LED backlighting exhibits (i) 33% less disruption on the circadian cycle if the same color gamut of the commercially available YAG:Ce LED is targeted and (ii) 34% wider color gamut while causing 4.1% weaker disruption on the circadian rhythm compared to YAG:Ce LED backlight if the NTSC color gamut is fully reproduced. Furthermore, we found out that blue and green emission peaks have to be located at 465 with 30 nm bandwidth and at 535 nm with 20 nm bandwidth, respectively, for a circadian rhythm friendly design while the red component offers flexibility around the peak emission wavelength at 636 nm as opposed to the requirements of quality indoor lighting. These design considerations introduced as a new design perspective for the displays of future will help avoiding the disruption of the human circadian rhythm.
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Lin, Chien-Chung, Hao-Chung Kuo, Guan-Ying Lee, Han-Yu Chao i Shao-Yi Weng. "77‐1: Invited Paper: The Colloidal Quantum Dot Based Color Conversion Layer for Micro LED Arrays". SID Symposium Digest of Technical Papers 54, nr 1 (czerwiec 2023): 1087–90. http://dx.doi.org/10.1002/sdtp.16760.
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The advances of micro LEDs and colloidal quantum dots have provided a great platform for the next generation of micro displays. Although the illuminating efficiency of colloidal quantum dots is close to 100%, the patterning of these nanocrystals is still important and need to be developed. We use semiconductor grade fabrication to obtain small pixels smaller than 10 micrometers and a large scale formation of array. The photonic characterization reveals the conversion efficiency is 20% and the excitation wavelength dependent behavior is also probed. A 1300‐hour of vacuum storage test showed this type of color conversion layer is stable and the emission wavelength and linewidth are almost unchanged.
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Cortés-Villena, Alejandro, i Raquel E. Galian. "Present and Perspectives of Photoactive Porous Composites Based on Semiconductor Nanocrystals and Metal-Organic Frameworks". Molecules 26, nr 18 (16.09.2021): 5620. http://dx.doi.org/10.3390/molecules26185620.
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This review focuses on the recent developments in synthesis, properties, and applications of a relatively new family of photoactive porous composites, integrated by metal halide perovskite (MHP) nanocrystals and metal-organic frameworks (MOFs). The synergy between the two systems has led to materials (MHP@MOF composites) with new functionalities along with improved properties and phase stability, thus broadening their applications in multiple areas of research such as sensing, light-harvesting solar cells, light-emitting device technology, encryption, and photocatalysis. The state of the art, recent progress, and most promising routes for future research on these photoactive porous composites are presented in the end.
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Keshari, Ashish K., i Avinash C. Pandey. "Size and Distribution: A Comparison of XRD, SAXS and SANS Study of II–VI Semiconductor Nanocrystals". Journal of Nanoscience and Nanotechnology 8, nr 3 (1.03.2008): 1221–27. http://dx.doi.org/10.1166/jnn.2008.370.
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The uniqueness of size dependent functional properties of II–VI semiconductor nanocrystals have led to the development of various techniques for determination of shape, size and distributions, although the accurate measurements of the particle sizes has always been a fundamental task in nanoscience and even become more crucial with the discovery of quantum confinement effect. Acomparison of the well established techniques X-ray diffraction (XRD), small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS) with an emphasis on size and distribution of the prepared samples are reported in order to elaborate more precise techniques for the analysis of particles sizes. Modified Scherrer formula for spherical particles has been used to calculate the particle sizes from XRD spectra. Analysis of SAXS data has been reported using Guinier model. Small angle neutron scattering measurements has been performed for ZnO nanocrystals and the scattering data obtained is simulated for polydisperse sphere. The bare ZnO, ZnS and CdS and doped with Mn2+ systems are taken within the framework of our discussion. These materials were synthesized by chemical precipitation route and found to have size distribution from 2 to 6 nm for spherical particles. Sizes determined from various techniques are in good agreement with each other however small angle scattering technique is more reliable than XRD to determine the sizes of the nanoparticles.
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Lin, Weyde M. M., Maksym Yarema, Mengxia Liu, Edward Sargent i Vanessa Wood. "Nanocrystal Quantum Dot Devices: How the Lead Sulfide (PbS) System Teaches Us the Importance of Surfaces". CHIMIA International Journal for Chemistry 75, nr 5 (28.05.2021): 398–413. http://dx.doi.org/10.2533/chimia.2021.398.
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Semiconducting thin films made from nanocrystals hold potential as composite hybrid materials with new functionalities. With nanocrystal syntheses, composition can be controlled at the sub-nanometer level, and, by tuning size, shape, and surface termination of the nanocrystals as well as their packing, it is possible to select the electronic, phononic, and photonic properties of the resulting thin films. While the ability to tune the properties of a semiconductor from the atomistic- to macro-scale using solution-based techniques presents unique opportunities, it also introduces challenges for process control and reproducibility. In this review, we use the example of well-studied lead sulfide (PbS) nanocrystals and describe the key advances in nanocrystal synthesis and thin-film fabrication that have enabled improvement in performance of photovoltaic devices. While research moves forward with novel nanocrystal materials, it is important to consider what decades of work on PbS nanocrystals has taught us and how we can apply these learnings to realize the full potential of nanocrystal solids as highly flexible materials systems for functional semiconductor thin-film devices. One key lesson is the importance of controlling and manipulating surfaces.
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Kulakci, M., U. Serincan i R. Turan. "Electroluminescence generated by a metal oxide semiconductor light emitting diode (MOS-LED) with Si nanocrystals embedded in SiO2layers by ion implantation". Semiconductor Science and Technology 21, nr 12 (25.09.2006): 1527–32. http://dx.doi.org/10.1088/0268-1242/21/12/004.
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Astankova, K. N., A. S. Kozhukhov, G. K. Krivyakin, Y. A. Zhivodkov, D. V. Sheglov i V. A. Volodin. "Interaction of low-fluence femtosecond laser pulses with a composite layer containing Ge nanoclusters: A novel type of nanofoam formation". Journal of Laser Applications 34, nr 2 (maj 2022): 022002. http://dx.doi.org/10.2351/7.0000620.
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In the present work, the low-fluence nonablating femtosecond laser irradiation (λ = 800 nm) of the GeO2 layer with Ge nanoclusters protected by SiO2 layers is studied by different types of microscopy (optical microscopy, atomic force microscopy, and scanning and transmittance electron microscopy) and Raman spectroscopy. After the laser modification, the multilayer thickness increased by 6%–29% depending on the laser fluence. It was found that the laser fluence of ∼40 mJ/cm2 was the optimal value for observing the swelling effect and was below the ablation threshold. Irradiation at this fluence led the Ge nanoclusters to decrease in size from 5–8 to ∼2 nm and crystallize, while the GeO2 matrix expanded due to the formation of GeO bubbles. The fabrication mechanism of the novel type of nanofoam consisting of a glassy matrix, cavities filled with gas, and semiconductor nanocrystals with reduced size dispersion is discussed. Presumably, this effect is associated with the selective absorption of IR (800 nm) laser radiation by Ge nanoclusters.
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Wang, Shiwei, Weiqiang Bo, Min Zhong, Cong Liu, Ying Li, Mingyuan Zhu, Yemin Hu i Hongmin Jin. "Effect of Cr Content on the Properties of Magnetic Field Processed Cr-Doped ZnO-Diluted Magnetic Semiconductors". Journal of Nanomaterials 2012 (2012): 1–7. http://dx.doi.org/10.1155/2012/501069.
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Cr-doped ZnO-diluted magnetic semiconductor (DMS) nanocrystals with various Cr contents were synthesized by hydrothermal method under high magnetic field. The result indicated that both the amount of Cr contents and high magnetic field significantly influenced crystal structure, morphology, and magnetic property of Cr-doped ZnO DMSs. When the Cr contents increased from 1 at% to 5 at%, the morphology of grains sequentially changed from flower-like to rod-like and then to the flake-like form. All the samples remained hexagonal wurtzite structure after Cr ions were doped into the ZnO crystal lattice. The Cr doping led to the increasing amount of defects and even enhanced the magnetic property of the matrix materials. All the Cr-doped ZnO DMSs obtained under high magnetic field exhibited obvious ferromagnetic behavior at room temperature. The results have also shown the successful substitution of the Cr3+ions for the Zn2+ions in the crystal lattice.
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Erdem, Talha, i Hilmi Volkan Demir. "Color science of nanocrystal quantum dots for lighting and displays". Nanophotonics 2, nr 1 (1.02.2013): 57–81. http://dx.doi.org/10.1515/nanoph-2012-0031.
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AbstractColloidal nanocrystals of semiconductor quantum dots (QDs) are gaining prominence among the optoelectronic materials in the photonics industry. Among their many applications, their use in artificial lighting and displays has attracted special attention thanks to their high efficiency and narrow emission band, enabling spectral purity and fine tunability. By employing QDs in color-conversion LEDs, it is possible to simultaneously accomplish successful color rendition of the illuminated objects together with a good spectral overlap between the emission spectrum of the device and the sensitivity of the human eye, in addition to a warm white color, in contrast to other conventional sources such as incandescent and fluorescent lamps, and phosphor-based LEDs, which cannot achieve all of these properties at the same time. In this review, we summarize the color science of QDs for lighting and displays, and present the recent developments in QD-integrated LEDs and display research. First, we start with a general introduction to color science, photometry, and radiometry. After presenting an overview of QDs, we continue with the spectral designs of QD-integrated white LEDs that have led to efficient lighting for indoor and outdoor applications. Subsequently, we discuss QD color-conversion LEDs and displays as proof-of-concept applications – a new paradigm in artificial lighting and displays. Finally, we conclude with a summary of research opportunities and challenges along with a future outlook.
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Coropceanu, Igor, Eric M. Janke, Joshua Portner, Danny Haubold, Trung Dac Nguyen, Avishek Das, Christian P. N. Tanner i in. "Self-assembly of nanocrystals into strongly electronically coupled all-inorganic supercrystals". Science 375, nr 6587 (25.03.2022): 1422–26. http://dx.doi.org/10.1126/science.abm6753.
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Colloidal nanocrystals of metals, semiconductors, and other functional materials can self-assemble into long-range ordered crystalline and quasicrystalline phases, but insulating organic surface ligands prevent the development of collective electronic states in ordered nanocrystal assemblies. We reversibly self-assembled colloidal nanocrystals of gold, platinum, nickel, lead sulfide, and lead selenide with conductive inorganic ligands into supercrystals exhibiting optical and electronic properties consistent with strong electronic coupling between the constituent nanocrystals. The phase behavior of charge-stabilized nanocrystals can be rationalized and navigated with phase diagrams computed for particles interacting through short-range attractive potentials. By finely tuning interparticle interactions, the assembly was directed either through one-step nucleation or nonclassical two-step nucleation pathways. In the latter case, the nucleation was preceded by the formation of two metastable colloidal fluids.
Rozprawy doktorskie na temat "LED - Semiconductor Nanocrystals"
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Khon, Elena. "Synthesis and Applications of Heterostructured Semiconductor Nanocrystals". Bowling Green State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1374512926.
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Warner, Jamie. "Colloidal lead sulphide nanocrystals for quantum technology applications /". [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18436.pdf.
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Moroz, Pavel. "A Novel Approach for the Fabrication of All-Inorganic Nanocrystal Solids: Semiconductor Matrix Encapsulated Nanocrystal Arrays". Bowling Green State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1435324105.
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Shiman, Dmitriy I., Vladimir Sayevich, Christian Meerbach, Pavel A. Nikishau, Irina V. Vasilenko, Nikolai Gaponik, Sergei V. Kostjuk i Vladimir Lesnyak. "Robust Polymer Matrix Based on Isobutylene (Co)polymers for Efficient Encapsulation of Colloidal Semiconductor Nanocrystals". American Chemical Association, 2019. https://tud.qucosa.de/id/qucosa%3A74322.
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We introduce new oxygen- and moisture-proof polymer matrixes based on polyisobutylene (PIB) and its block copolymer with styrene [poly(styrene-block-isobutylene-blockstyrene), PSt-b-PIB-b-PSt] for the encapsulation of colloidal semiconductor nanocrystals. In order to prepare transparent and processable composites, we developed a special procedure of nanocrystal surface engineering including ligand exchange of parental organic ligands to inorganic species followed by the attachment of specially designed short-chain PIB functionalized with an amino group. The latter provides excellent compatibility of the particles with the polymer matrixes. As colloidal nanocrystals, we chose CdSe nanoplatelets (NPLs) because they possess a large surface and thus are very sensitive to the environment, in particular in terms of their limited photostability. The encapsulation strategy is quite general and can be applied to a wide variety of semiconductor nanocrystals, as demonstrated on the example of PbS quantum dots. All obtained composites exhibited excellent photostability, being tested in a focus of a powerful white-light source, as well as exceptional chemical stability in a strongly acidic media. We compared these properties of the new composites with those of widely used polyacrylate-based materials, demonstrating the superiority of the former. The developed composites are of particular interest for application in optoelectronic devices, such as color-conversion light-emitting diodes, laser diodes, luminescent solar concentrators, etc.
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Premathilaka, Shashini M. "Synthesis and Optical Properties of Colloidal PbS Nanosheets". Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1561463157379607.
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Jiang, Zhoufeng Jiang. "Zero-dimensional and two-dimensional colloidal nanomaterials and their photophysics". Bowling Green State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1522964027555741.
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Adam, Marcus. "Embedding of QDs into Ionic Crystals:". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-191160.
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Colloidal semiconductor quantum dots (QDs) have gained substantial interest as adjustable, bright and spectrally tunable fluorophores in the past decades. Besides their in-depth analyses in the scientific community, first industrial applications as color conversion and color enrichment materials were implemented. However, stability and processability are essential for their successful use in these and further applications. Methods to embed QDs into oxides or polymers can only partially solve this challenge. Recently, our group introduced the embedding of QDs into ionic salts, which holds several advantages in comparison to polymer or oxide-based counterparts. Both gas permeability and environmental-related degradation processes are negligible, making these composites an almost perfect choice of material. To evaluate this new class of QD-salt mixed crystals, a thorough understanding of the formation procedure and the final composites is needed. The present work is focused on embedding both aqueous-based and oil-based metal-chalcogenide QDs into several ionic salts and the investigations of their optical and chemical properties upon incorporation into the mixed crystals. QDs with well-known, reproducible and high-quality synthetic protocols are chosen as emissive species. CdTe QDs were incorporated into NaCl as host matrix by using the straightforward "classical" method. The resulting mixed crystals of various shapes and beautiful colors preserve the strong luminescence of the incorporated QDs. Besides NaCl, also borax and other salts are used as host matrices.
Mercaptopropionic acid stabilized CdTe QDs can easily be co-crystallized with NaCl, while thioglycolic acid as stabilizing agent results in only weakly emitting powder-like mixed crystals. This challenge was overcome by adjusting the pH, the amount of free stabilizer and the type of salt used, demonstrating the reproducible incorporation of highest-quality CdTe QDs capped with thioglycolic acid into NaCl and KCl salt crystals. A disadvantage of the "classical" mixed crystallization procedure was its long duration which prevents a straightforward transfer of the protocol to less stable QD colloids, e.g., initially oil-based, ligand exchanged QDs. To address this challenge, the "Liquid-liquid-diffusion-assisted-crystallization" (LLDC) method is introduced. By applying the LLDC, a substantially accelerated ionic crystallization of the QDs is shown, reducing the crystallization time needed by one order of magnitude. This fast process opens the field of incorporating ligand-exchanged Cd-free QDs into NaCl matrices. To overcome the need for a ligand exchange, the LLDC can also be extended towards a two-step approach. In this modified version, the seed-mediated LLDC provides for the first time the ability to incorporate oil-based QDs directly into ionic matrices without a prior phase transfer.
The ionic salts appear to be very tight matrices, ensuring the protection of the QDs from the environment. As one of the main results, these matrices provide extraordinary high photo- and chemical stability. It is further demonstrated with absolute measurements of photoluminescence quantum yields (PL-QYs), that the PL-QYs of aqueous CdTe QDs can be considerably increased upon incorporation into a salt matrix by applying the "classical" crystallization procedure. The achievable PL enhancement factors depend strongly on the PL-QYs of the parent QDs and can be described by the change of the dielectric surrounding as well as the passivation of the QD surface. Studies on CdSe/ZnS in NaCl and CdTe in borax showed a crystal-induced PL-QY increase below the values expected for the respective change of the refractive index, supporting the derived hypothesis of surface defect curing by a CdClx formation as one main factor for PL-QY enhancement.
The mixed crystals developed in this work show a high suitability as color conversion materials regarding both their stability and spectral tunability. First proof-of-concept devices provide promising results. However, a combination of the highest figures of merit at the same time is intended. This ambitious goal is reached by implementing a model-experimental feedback approach which ensures the desired high optical performance of the used emitters throughout all intermediate steps. Based on the approach, a white LED combining an incandescent-like warm white with an exceptional high color rendering index and a luminous efficacy of radiation is prepared. It is the first time that a combination of this highly related figures of merit could be reached using QD-based color converters. Furthermore, the idea of embedding QDs into ionic matrices gained considerable interest in the scientific community, resulting in various publications of other research groups based on the results presented here.
In summary, the present work provides a profound understanding how this new class of QD-salt mixed crystal composites can be efficiently prepared. Applying the different crystallization methods and by changing the matrix material, mixed crystals emitting from blue to the near infrared region of the electromagnetic spectrum can be fabricated using both Cd-containing and Cd-free QDs. The resulting composites show extraordinary optical properties, combining the QDs spectral tunability with the rigid and tight ionic matrix of the salt. Finally, their utilization as a color conversion material resulted in a high-quality white LED that, for the first time, combines an incandescent-like hue with outstanding optical efficacy and color rendering properties. Besides that, the mixed crystals offer huge potential in other high-quality applications which apply photonic and optoelectronic components.
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Hatami, Soheil, Christian Würth, Martin Kaiser, Susanne Leubner, Stefanie Gabriel, Lydia Bahrig, Vladimir Lesnyak i in. "Absolute photoluminescence quantum yields of IR26 and IR-emissive Cd₁₋ₓHgₓTe and PbS quantum dots: method- and material-inherent challenges". Royal Society of Chemistry, 2015. https://tud.qucosa.de/id/qucosa%3A36307.
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Bright emitters with photoluminescence in the spectral region of 800–1600 nm are increasingly important as optical reporters for molecular imaging, sensing, and telecommunication and as active components in electrooptical and photovoltaic devices. Their rational design is directly linked to suitable methods for the characterization of their signal-relevant properties, especially their photoluminescence quantum yield (Φf ). Aiming at the development of bright semiconductor nanocrystals with emission >1000 nm, we designed a new NIR/IR integrating sphere setup for the wavelength region of 600–1600 nm. We assessed the performance of this setup by acquiring the corrected emission spectra and Φf of the organic dyes |trybe, IR140, and IR26 and several infrared (IR)-emissive Cd₁₋ₓHgₓTe and PbS semiconductor nanocrystals and comparing them to data obtained with two independently calibrated fluorescence instruments absolutely or relative to previously evaluated reference dyes. Our results highlight special challenges of photoluminescence studies in the IR ranging from solvent absorption to the lack of spectral and intensity standards together with quantum dot-specific challenges like photobrightening and photodarkening and the size-dependent air stability and photostability of differently sized oleate-capped PbS colloids. These effects can be representative of lead chalcogenides. Moreover, we redetermined the Φf of IR26, the most frequently used IR reference dye, to 1.1 × 10⁻³ in 1,2-dichloroethane DCE with a thorough sample reabsorption and solvent absorption correction. Our results indicate the need for a critical reevaluation of Φf values of IR-emissive nanomaterials and offer guidelines for improved Φf measurements.
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Abel, Keith Alexander. "Synthesis and characterization of colloidal lead chalcogenide quantum dots and progress towards single photons on-demand". Thesis, 2011. http://hdl.handle.net/1828/3481.
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Nanometer-sized semiconductor crystals, termed ‘quantum dots’, are of fundamental interest because of their size-tunable properties. Three-dimensional quantum confinement of charge carriers by the small crystal size results in discrete atomic-like electronic states. This dissertation describes the synthesis and in-depth characterization of lead chalcogenide colloidal quantum dots for forthcoming applications as near-infrared single photon emitters. An efficient single photon source that operates at telecommunication wavelengths (between 1.3 and 1.6 µm) is a basic requirement for many photonic quantum technologies, such as quantum computing and quantum cryptography.
Chapters 1 and 2 of this work provide an introduction to colloidal quantum dots and their use as single photon emitters. It includes a description of photonic crystal microcavities and their ability to enhance the spontaneous emission rate of quantum dots. The synthesis and basic characterization of PbSe and PbS quantum dots is then discussed in chapter 3. In particular, a new synthetic method for the preparation of highly photoluminescent PbS quantum dots is presented. PbSe/CdSe core/shell quantum dots prepared by a cation exchange reaction are also described and a significant improvement in photo-stability is shown. Chapter 3 concludes with a description of three different surface modification techniques. PbSe core and PbSe/CdSe core/shell materials are investigated further in chapter 4 by advanced characterization techniques that include high-angle annular dark field (HAADF) imaging, energy-filtered transmission electron microscopy (EF-TEM) imaging, energy-dependent X-ray photo-electron spectroscopy (XPS), small angle X-ray scattering (SAXS), and small angle neutron scattering (SANS). The information obtained from these techniques is combined to form a structural model of the PbSe core and PbSe/CdSe core/shell quantum dots with greater complexity than previously reported. In chapter 5, the temperature-dependent photoluminescence from PbSe and PbSe/CdSe core/shell quantum dots is discussed and a thermal model is presented that accounts for the large (non-trivial) temperature dependence of the Stokes shift and photoluminescence lineshape over the entire temperature range (4.5 to 295 K). Chapter 6 examines two scalable methods to integrate the colloidal quantum dots into silicon two-dimensional photonic crystal slab microcavities (a requirement for efficient single photon emission). Finally, conclusions and possible future work are discussed in chapter 7.Graduate
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Adam, Marcus. "Embedding of QDs into Ionic Crystals:: Methods, Characterization and Applications". Doctoral thesis, 2015. https://tud.qucosa.de/id/qucosa%3A29121.
Pełny tekst źródłaStreszczenie:
Colloidal semiconductor quantum dots (QDs) have gained substantial interest as adjustable, bright and spectrally tunable fluorophores in the past decades. Besides their in-depth analyses in the scientific community, first industrial applications as color conversion and color enrichment materials were implemented. However, stability and processability are essential for their successful use in these and further applications. Methods to embed QDs into oxides or polymers can only partially solve this challenge. Recently, our group introduced the embedding of QDs into ionic salts, which holds several advantages in comparison to polymer or oxide-based counterparts. Both gas permeability and environmental-related degradation processes are negligible, making these composites an almost perfect choice of material. To evaluate this new class of QD-salt mixed crystals, a thorough understanding of the formation procedure and the final composites is needed. The present work is focused on embedding both aqueous-based and oil-based metal-chalcogenide QDs into several ionic salts and the investigations of their optical and chemical properties upon incorporation into the mixed crystals. QDs with well-known, reproducible and high-quality synthetic protocols are chosen as emissive species. CdTe QDs were incorporated into NaCl as host matrix by using the straightforward "classical" method. The resulting mixed crystals of various shapes and beautiful colors preserve the strong luminescence of the incorporated QDs. Besides NaCl, also borax and other salts are used as host matrices.
Mercaptopropionic acid stabilized CdTe QDs can easily be co-crystallized with NaCl, while thioglycolic acid as stabilizing agent results in only weakly emitting powder-like mixed crystals. This challenge was overcome by adjusting the pH, the amount of free stabilizer and the type of salt used, demonstrating the reproducible incorporation of highest-quality CdTe QDs capped with thioglycolic acid into NaCl and KCl salt crystals. A disadvantage of the "classical" mixed crystallization procedure was its long duration which prevents a straightforward transfer of the protocol to less stable QD colloids, e.g., initially oil-based, ligand exchanged QDs. To address this challenge, the "Liquid-liquid-diffusion-assisted-crystallization" (LLDC) method is introduced. By applying the LLDC, a substantially accelerated ionic crystallization of the QDs is shown, reducing the crystallization time needed by one order of magnitude. This fast process opens the field of incorporating ligand-exchanged Cd-free QDs into NaCl matrices. To overcome the need for a ligand exchange, the LLDC can also be extended towards a two-step approach. In this modified version, the seed-mediated LLDC provides for the first time the ability to incorporate oil-based QDs directly into ionic matrices without a prior phase transfer.
The ionic salts appear to be very tight matrices, ensuring the protection of the QDs from the environment. As one of the main results, these matrices provide extraordinary high photo- and chemical stability. It is further demonstrated with absolute measurements of photoluminescence quantum yields (PL-QYs), that the PL-QYs of aqueous CdTe QDs can be considerably increased upon incorporation into a salt matrix by applying the "classical" crystallization procedure. The achievable PL enhancement factors depend strongly on the PL-QYs of the parent QDs and can be described by the change of the dielectric surrounding as well as the passivation of the QD surface. Studies on CdSe/ZnS in NaCl and CdTe in borax showed a crystal-induced PL-QY increase below the values expected for the respective change of the refractive index, supporting the derived hypothesis of surface defect curing by a CdClx formation as one main factor for PL-QY enhancement.
The mixed crystals developed in this work show a high suitability as color conversion materials regarding both their stability and spectral tunability. First proof-of-concept devices provide promising results. However, a combination of the highest figures of merit at the same time is intended. This ambitious goal is reached by implementing a model-experimental feedback approach which ensures the desired high optical performance of the used emitters throughout all intermediate steps. Based on the approach, a white LED combining an incandescent-like warm white with an exceptional high color rendering index and a luminous efficacy of radiation is prepared. It is the first time that a combination of this highly related figures of merit could be reached using QD-based color converters. Furthermore, the idea of embedding QDs into ionic matrices gained considerable interest in the scientific community, resulting in various publications of other research groups based on the results presented here.
In summary, the present work provides a profound understanding how this new class of QD-salt mixed crystal composites can be efficiently prepared. Applying the different crystallization methods and by changing the matrix material, mixed crystals emitting from blue to the near infrared region of the electromagnetic spectrum can be fabricated using both Cd-containing and Cd-free QDs. The resulting composites show extraordinary optical properties, combining the QDs spectral tunability with the rigid and tight ionic matrix of the salt. Finally, their utilization as a color conversion material resulted in a high-quality white LED that, for the first time, combines an incandescent-like hue with outstanding optical efficacy and color rendering properties. Besides that, the mixed crystals offer huge potential in other high-quality applications which apply photonic and optoelectronic components.
Książki na temat "LED - Semiconductor Nanocrystals"
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Erdem, Talha, i Hilmi Volkan Demir. Color Science and Photometry for Lighting with LEDs and Semiconductor Nanocrystals. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-13-5886-9.
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Demir, Hilmi Volkan, i Talha Erdem. Color Science and Photometry for Lighting with LEDs and Semiconductor Nanocrystals. Springer, 2019.
Znajdź pełny tekst źródłaCzęści książek na temat "LED - Semiconductor Nanocrystals"
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Singh, Jyoti, Niteen P. Borane i Rajamouli Boddula. "Milestone Developments and New Perspectives of Nano/Nanocrystal Light Emitting Diodes". W Light-Emitting Diodes - New Perspectives [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.108907.
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Light emitting diode (LED) is a one type of p/n junction semiconductor device which is used in less energy consumption for numerous lighting functions. Because of their high performance and long existence, their eye-catching application is getting increasing numbers in recent times. LEDs are nowadays defined as using the “ultimate light bulb”. In a previous couple of years, its efficiency has been multiplied through converting it to nano size. This new light-emitting has a nano-pixel structure and it affords high-resolution performance and the geometry of the pixel is cylindrical or conical form. Due to the fact that the previous few years, a few impurity-doped nanocrystal LEDs are varying a good deal in trend. Its performance is very excessive and consumes a smaller amount of voltage. Its monochromatic behavior and indicator excellent are shown publicly demanded in the market and in this work, it’s covered evaluations of the fundamental’s standards of LEDs and the specific mixed metallic and nanocrystal shape of emitters. In addition, it covers the upcoming challenges that the current trend is working to resolve to get efficient materials to fulfill the future energy crisis.
Streszczenia konferencji na temat "LED - Semiconductor Nanocrystals"
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Gutsul, T., A. Nicorici i A. Todosiciuc. "Solvothermal synthesis of lead telluride micro- and nanocrystals". W 2011 International Semiconductor Conference (CAS 2011). IEEE, 2011. http://dx.doi.org/10.1109/smicnd.2011.6095785.
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Martínez-Pastor, Juan P. "Applications in nanophotonics of lead halide perovskite nanocrystals". W Applied Light-Matter Interactions in Perovskite Semiconductors 2021. València: Fundació Scito, 2021. http://dx.doi.org/10.29363/nanoge.almips.2021.020.
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Marso, M., M. Mikulics, H. Luth, Z. Sofer, P. Kordos i H. Hardtdegen. "Hybrid optoelectronics based on a nanocrystal/III-N nano-LED platform". W 2016 11th International Conference on Advanced Semiconductor Devices & Microsystems (ASDAM). IEEE, 2016. http://dx.doi.org/10.1109/asdam.2016.7805899.
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Colvin, V. L., J. J. Shiang, W. Hoheisel, C. Johnsona, R. W. Schoenlein, D. M. Mittleman, S. J. Rosenthal, C. V. Shank i A. P. Alivisatos. "Time Evolution of Excited States in CdSe Nanocrystals". W International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/up.1994.tuc.5.
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Early theoretical work predicted that quantum dots would exhibit discrete, well separated optical excitations, with narrow linewidths, and uncommonly large excited state polarizabilities1. This unusual combination could result in some unusual nonlinear properties. Ever since there has been steady progress in the preparation and characterization of nanometer size semiconductor nanocrystals, with CdSe still remaining the prototypical direct band gap material2. During the past two years we have undertaken a systematic study of the size dependent photophysics in these materials. Colloidally prepared II-VI nanocrystals embedded in polymers and cooled to low T lend themselves readily to the application of many time and frequency resolved optical characterization techniques3. These include absorption, fluorescence, electric field modulation of the absorption and fluorescence, three pulse photon echoes, and resonance Raman scattering.
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Willsey, Aliza M., Kassidy Fields, Thomas S. Welles, Hanjie Lin, Weiwei Zheng i Jeongmin Ahn. "Investigation of Emission Reduction and Power Generation on Electrochemical Catalytic Membranes With the Addition of Perovskite Nanocrystals". W ASME 2022 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/imece2022-95571.
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Abstract With the depletion of fossil fuel resources, as well as increasing global temperatures, the interest in sustainable energy is on the rise. Currently, cars are a significant source of harmful emissions due to the use of internal combustion engines. Incomplete combustion byproducts are extremely harmful to the environment and the population, with links to acid rain, smog, and respiratory issues. While green energy solutions, such as electric vehicles, are being developed, the treatment of exhaust can also be an effective way to reduce the release of emissions into the atmosphere. It has been shown that a solid oxide fuel cell (SOFC) is able to break down emissions, even exceeding the capability of typical exhaust treatment methods. An investigation into the usage of an SOFC as an exhaust treatment material has found that the amplification of a signal generated across the cell has an even greater effect on emission reduction. Here, the addition of cesium lead bromide (CsPbBr3) nanocrystals to the fuel cell is being investigated. The SOFC is tested as an exhaust treatment solution and as a power generation device in comparison to a typical SOFC without added CsPbBr3 nanocrystals. CsPbBr3 is a perovskite semiconductor, so it is expected to have an effect on the reactivity of the fuel cell. Investigating the effects of adding nanocrystals into a SOFC will lead to advancements in exhaust treatment systems as well as power generation systems. The work here will show a direct relationship between the quantity of nanocrystals contained in the SOFC to the emission reduction and power generation abilities of the SOFC.
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Rizzo, Aurora, Marco Mazzeo i Giuseppe Gigli. "Multilayer hybrid LEDs based on colloidal inorganic semiconductors nanocrystal and PIN technology". W Photonics Europe, redaktorzy Paul L. Heremans, Michele Muccini i Eric A. Meulenkamp. SPIE, 2008. http://dx.doi.org/10.1117/12.780484.
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Chen, Kok Hao, i Jong Hyun Choi. "DNA Oligonucleotide-Templated Nanocrystals: Synthesis and Novel Label-Free Protein Detection". W ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11958.
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Semiconductor and magnetic nanoparticles hold unique optical and magnetic properties, and great promise for bio-imaging and therapeutic applications. As part of their stable synthesis, the nanocrystal surfaces are usually capped by long chain organic moieties such as trioctylphosphine oxide. This capping serves two purposes: it saturates dangling bonds at the exposed crystalline lattice, and it prevents irreversible aggregation by stabilizing the colloid through entropic repulsion. These nanocrystals can be rendered water-soluble by either ligand exchange or overcoating, which hampers their widespread use in biological imaging and biomedical therapeutics. Here, we report a novel scheme of synthesizing fluorescent PbS and magnetic Fe3O4 nanoparticles using DNA oligonucleotides. Our method of PbS synthesis includes addition of Na2S to the mixture solution of DNA sequence and Pb acetate (at a fixed molar ratio of DNA/S2−/Pb2+ of 1:2:4) in a standard TAE buffer at room temperature in the open air. In the case of Fe3O4 particle synthesis, ferric and ferrous chloride were mixed with DNA in DI water at a molar ratio of DNA/Fe2+/Fe3+ = 1:4:8 and the particles were formed via reductive precipitation, induced by increasing pH to ∼11 with addition of ammonium hydroxide. These nanocrystals are highly stable and water-soluble immediately after the synthesis, due to DNA termination. We examined the surface chemistry between oligonucleotides and nanocrystals using FTIR spectroscopy, and found that the different chemical moieties of nucleobases passivate the particle surface. Strong coordination of primary amine and carbonyl groups provides the chemical and colloidal stabilities, leading to high particle yields (Figure 1). The resulting PbS nanocrystals have a distribution of 3–6 nm in diameter, while a broader size distribution is observed with Fe3O4 nanoparticles as shown in Figure 1b and c, respectively. A similar observation was reported with the pH change-induced Fe3O4 particles of a bimodal size distribution where superparamagnetic and ferrimagnetic magnetites co-exist. In spite of the differences, FTIR measurements suggest that the chemical nature of the oligonucleotide stabilization in this case is identical to the PbS system. As a particular application, we demonstrate that aptamer-capped PbS QD can detect a target protein based on selective charge transfer, since the oligonucleotide-templated synthesis can also serve the additional purpose of providing selective binding to a molecular target. Here, we use thrombin and a thrombin-binding aptamer as a model system. These QD have diameters of 3∼6 nm and fluoresce around 1050 nm. We find that a DNA aptamer can passivate near IR fluorescent PbS nanocrystals, rendering them water-soluble and stable against aggregation, and retain the secondary conformation needed to selectively bind to its target, thrombin, as shown in Figure 2. Importantly, we find that when the aptamer-functionalized nanoparticles binds to its target (only the target), there is a highly systematic and selective quenching of the PL, even in high concentrations of interfering proteins as shown in Figure 3a and b. Thrombin is detected within one minute with a detection limit of ∼1 nM. This PL quenching is attributed to charge transfer from functional groups on the protein to the nanocrystals. A charge transfer can suppress optical transition mechanisms as we observe a significant decrease in QD absorption with target addition (Figure 3c). Here, we rule out other possibilities including Forster resonance energy transfer (FRET) and particle aggregation, because thrombin absorb only in the UV, and we did not observe any significant change in the diffusion coefficient of the particles with the target analyte, respectively. The charge transfer-induced photobleaching of QD and carbon nanotubes was observed with amine groups, Ru-based complexes, and azobenzene compounds. This selective detection of an unlabeled protein is distinct from previously reported schemes utilizing electrochemistry, absorption, and FRET. In this scheme, the target detection by a unique, direct PL transduction is observed even in the presence of high background concentrations of interfering negatively or positively charged proteins. This mechanism is the first to selectively modulate the QD PL directly, enabling new types of label free assays and detection schemes. This direct optical transduction is possible due to oligonucleotidetemplated surface passivation and molecular recognition. This chemistry may lead to more nanoparticle-based optical and magnetic probes that can be activated in a highly chemoselective manner.
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Yan, Caiman, Hanguang Lu, Zongtao Li, Jiexin Li, Jiasheng Li, Yong Tang i Binhai Yu. "The contrast ratio improvement of perovskite nanocrystals LEDs devices based on carbon nanotubes". W 2019 16th China International Forum on Solid State Lighting & 2019 International Forum on Wide Bandgap Semiconductors China (SSLChina: IFWS). IEEE, 2019. http://dx.doi.org/10.1109/sslchinaifws49075.2019.9019797.
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Kim, Myeongsub, i Minami Yoda. "Using Quantum Dots for Liquid-Phase Thermometry at Near-Infrared Wavelengths in Silicon Devices". W 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22885.
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The need for new thermal management technologies to cool electronic components with their ever-increasing density and power requirements has renewed interest in techniques for measuring liquid-phase coolant temperatures, especially nonintrusive techniques with micron-scale spatial resolution. A variety of optical liquid-phase thermometry techniques exploit the changes in the emission characteristics of fluorescent, phosphorescent or luminescent tracers suspended in a liquid-phase coolant. Such techniques are nonintrusive and have micron-scale spatial resolution, but they also require optical access to both excite and image the emissions. Silicon (Si), the leading material for electronic devices, is opaque at visible wavelengths, but is partially transparent in the near-infrared (IR). To date, the only tracers that emit at near-IR wavelengths with reasonable quantum yield are IR quantum dots (IRQD), colloidal nanocrystals of semiconductor materials such as lead sulfide (PbS). Previous work has shown that the intensity of emissions at 1.55 μm from PbS IRQD suspended in toluene are temperature-sensitive, decreasing by as much as 15% as the temperature increased from 20 °C to 60 °C. The accuracy of temperature measurements using PbS IRQD was estimated to be about 5 °C, based on 95% confidence intervals, where the major limit on the accuracy of the technique was the poor photostability of this material [1]. Recently, a new method for creating a cadmium sulfide (CdS) overcoat layer on PbS “cores” has been developed [2]. The experimental results presented here on the temperature sensitivity of these PbS/CdS core-shell infrared quantum dots with an emission peak around 1.35 μm and a diameter of 5.7 nm (with a core diameter of 4 nm) suggest that these new core-shell structures are more temperature-sensitive than the PbS cores. These core-shell quantum dots, when suspended in toluene, were found to have a 0.5% decrease in emission power per °C increase in temperature at suspension temperatures ranging from 20 °C to 60 °C. The uncertainty in the liquid-phase temperatures derived from these emissions was estimated to be less than 0.3 °C based on the standard deviation. Furthermore, the PbS/CdS quantum dots were highly photostable, with a consistent response more than 100 days after suspension. These results imply that that these new IRQD can be used to measure liquid-phase coolant temperatures without disturbing the flow of coolant at an accuracy comparable to commercially available thermocouples in monolithic Si devices.