scholarly journals Degradation Dynamics of Quantum Dots in White LED Applications

2021 ◽  
Author(s):  
Hsiao-Chien Chen ◽  
Cher Ming Tan ◽  
Abdul Shabir ◽  
Preetpal Singh ◽  
Kai Wang
Keyword(s):  
Quantum Dots ◽  
Light Intensity ◽  
White Light ◽  
Density Functional ◽  
Wavelength Shift ◽  
Initial State ◽  
Functional Theory ◽  
Practical Applications ◽  
Three Stages ◽  
Cds Qds

Abstract Quantum dots (QDs) are being investigated in a hybrid white light LED structure which inculcates phosphor in the package with blue LED chip as light source. Upon prolong operation, degradation of CdS QDs is observed which can limit its practical applications. The degradation includes intensity reduction as well as emitted wavelength shift of the white light. Three stages of degradation are observed, namely an enhancement state where light intensity is observed to increase, followed by a rapid degradation stage where light intensity decreases rapidly, and finally a slower degradation state where light intensity degradation rate slows down and continue till end of test.In this work, the degradation of CdS QDs is analyzed using various material analysis tools. Density functional theory (DFT) calculation is performed to confirm the spectroscopy results. It is found that the time evolving degradation of QDs begins from the oxidation of sulfur vacancy of CdS QDs by nearby oxygen atoms due to the imperfection of the protective coating around the QDs in combination of the presence of blue light, and this oxidation renders a transformation of CdS into CdO at the initial state. The final stage is the formation of CdSO4 via some intermediate processes.

scholarly journals Degradation dynamics of quantum dots in white LED applications

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hsiao-Chien Chen ◽  
Abdul Shabir ◽  
Cher Ming Tan ◽  
Preetpal Singh ◽  
Jia-Hung Lin
Keyword(s):  
Quantum Dots ◽  
Light Intensity ◽  
White Light ◽  
Density Functional ◽  
Light Emission ◽  
Green Light ◽  
Blue Shift ◽  
Practical Applications ◽  
Initial Stage ◽  
Green Light Emission

AbstractQuantum Dots (QDs) are being investigated in a hybrid white light LED structure which inculcates phosphor in the package with a blue LED chip as the light source recently. In this work, Zn doped CdS QD with ZnS shell together with green light emission phosphor is used. Upon prolonged operation, degradation of the LEDs due to the degradation of QDs is observed, which can limit its practical applications. The degradation includes intensity reduction as well as blue shift of the emitted wavelength from the white light. Three stages of degradation are observed, namely an enhancement state where light intensity is found to increase, followed by a rapid degradation stage where light intensity decreases rapidly, and finally a slower degradation stage where the degradation rate of light intensity slows down and continues till the end of the test. Through various detail material analysis, with confirmation from the density functional theory (DFT) calculations, we find that the degradation of the LEDs is due to the time evolving degradation of CdS core structure, beginning from the oxidation of sulfur vacancy of CdS QDs by the nearby oxygen atoms as a result of imperfection of the ZnS protective coating around the QDs in the presence of blue light. This oxidation renders a transformation of CdS into CdO at the initial stage. The final stage is the formation of CdSO4 via some intermediate processes.

Cyclodextrins Stabilize TOPO-(CdSe)ZnS Quantum Dots In Water

2004 ◽  
Vol 823 ◽  
Author(s):  
Jun Feng ◽  
Yong-Hyun Kim ◽  
S. B. Zhang ◽  
Shi-You Ding ◽  
Melvin P. Tucker ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Quantum Dots ◽  
First Principles ◽  
Density Functional ◽  
Water Soluble ◽  
Hydroxyl Group ◽  
Functional Theory ◽  
Chemical Action ◽  
Coordinate Bond ◽  
Device Applications

AbstractChemical action between cyclodextrins (CDs) and TOPO-(CdSe)ZnS quantum dots (QDs) generates a water-soluble solution of CD-QDs. Hydrophobic TOPO molecules on surface of the QDs are compatible to thread through the pockets of CDs and make the hydroxyl group on end of CDs to approach the ZnS surface, and then cause the interaction between ZnS and the hydroxyls. In this paper, Photoluminescence of the γ-CD-QD solution appeared about 15 nm of red movement compared with that of the QDs in hexane; 58% replacement of the crystal coordinate bond of Zn-S with that of Zn-O in the ZnS shell was demonstrated by using first-principles density functional theory and the red shift of the photoluminescence of CD-QDs; and –0.11eV of the energy gain of the exchange model was calculated by using an effective mass (EM) model. CD-QDs will provide water-soluble QDs with conjugational group for biology and molecule-device applications.

scholarly journals Adjusting the band structure and defects of ZnO quantum dots via tin doping

RSC Advances ◽  
2017 ◽  
Vol 7 (19) ◽  
pp. 11345-11354 ◽  
Author(s):  
Weimin Yang ◽  
Bing Zhang ◽  
Qitu Zhang ◽  
Lixi Wang ◽  
Bo Song ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Quantum Dots ◽  
Band Structure ◽  
Density Functional ◽  
Band Structures ◽  
Functional Theory ◽  
Doped Zno ◽  
Zno Quantum Dots

The structures and band structures of Sn doped ZnO were investigated by density functional theory as well as experiment.

Influences of Fe Doping on the Electronic Structure of Mg(0001) Surface and Hydrogenation Mechanism in Fe-Doped Mg(0001) Surface

2013 ◽  
Vol 873 ◽  
pp. 114-120 ◽  
Author(s):  
Zhi Wen Wang ◽  
Xin Jun Guo ◽  
Hong Xia Zhang ◽  
Li Li
Keyword(s):  
Density Functional ◽  
Hydrogen Molecule ◽  
Functional Theory ◽  
Practical Applications ◽  
Atom Diffusion ◽  
Charge Density Difference ◽  
The Density Functional Theory ◽  
Diffusion Paths ◽  
The Stability ◽  
Dissociation Path

First-principles calculations within the density functional theory (DFT) have been carried out to study the interaction of hydrogen molecule with Fe-doped Mg (0001) surfaces. First we have calculated the stability of the Fe atom on the Mg surface, On the basis of the energetic criteria, Fe atom prefer to substitute one of the Mg atoms from the second layer. In the second step, we have studied the interaction between hydrogen molecule and the Fe-doped Mg (0001) surface. The results show that for Fe atoms doped Mg (0001) surface in the second layer, enhances the chemisorption interaction between H2molecule and Fe atom, but also benefits H atom diffusion into Mg bulk with relatively more diffusion paths compared with that of clean Mg surface. Charge density difference plots provided some ideas about why certain alloying elements on the surface reduce the energy barrier of H2molecule dissociation on Fe-doped Mg (0001) surface. We can see that Fe as catalyst for the hydrogenation/dehydrogenation of Mg alloy samples and provide more dissociation path for H2molecule and diffusion paths for H atom, The present results not only beneficial for clarify the experimentally observed fast hydrogenation kinetics for Fe-capped Mg materials but also help to design new types of hydrogen storage materials for practical applications in the auto industry.

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