Color temperature control of quantum dot white light emitting diodes by grafting organic fluorescent molecules

Kim, Namhun; Lee, Jong-Ho; An, Hyuncheol; Pang, Changhyun; Cho, Sung Min; Chae, Heeyeop

doi:10.1039/c4tc01780c

Cited by 11 publications

(14 citation statements)

References 25 publications

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“…Ligands stabilize the QD surface to reduce fragile dangling bonds and functionalize the QDs for various applications . Ligands can bind to the QD surface via a variety of chemical anchor groups, as shown in Figure .…”

Section: Enhancing the Stability Of Qdsmentioning

confidence: 99%

Stability of Quantum Dots, Quantum Dot Films, and Quantum Dot Light‐Emitting Diodes for Display Applications

et al. 2019

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Quantum dots (QDs) are being highlighted in display applications for their excellent optical properties, including tunable bandgaps, narrow emission bandwidth, and high efficiency. However, issues with their stability must be overcome to achieve the next level of development. QDs are utilized in display applications for their photoluminescence (PL) and electroluminescence. The PL characteristics of QDs are applied to display or lighting applications in the form of color‐conversion QD films, and the electroluminescence of QDs is utilized in quantum dot light‐emitting diodes (QLEDs). Studies on the stability of QDs and QD devices in display applications are reviewed herein. QDs can be degraded by oxygen, water, thermal heating, and UV exposure. Various approaches have been developed to protect QDs from degradation by controlling the composition of their shells and ligands. Phosphorescent QDs have been protected by bulky ligands, physical incorporation in polymer matrices, and covalent bonding with polymer matrices. The stability of electroluminescent QLEDs can be enhanced by using inorganic charge transport layers and by improving charge balance. As understanding of the degradation mechanisms of QDs increases and more stable QDs and display devices are developed, QDs are expected to play critical roles in advanced display applications.

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Section: Enhancing the Stability Of Qdsmentioning

confidence: 99%

Stability of Quantum Dots, Quantum Dot Films, and Quantum Dot Light‐Emitting Diodes for Display Applications

et al. 2019

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“…The fabrication of single unit biofriendly white-light emitting (WLE) materials is advantageous in comparison to multiunit systems. Typically, the multiunit systems suffer from drawbacks related to nonradiative energy transfer, high energy consumption, self-absorption, and an unwanted change in color chromaticity coordinates, which restrict their application potential. − ,− Additionally, the use of toxic nanomaterials in fabricating WLE devices has short- and long-term impacts on the environment. − ,− These call for the fabrication of single unit WLE sources, using nontoxic and cost-effective materials. In comparison to the literature on other reported strategies, complexation on the surface of a Qdot has emerged as a unique, simple, and cost-effective strategy for fabricating single unit WLE materials with superior optical features. − For example, the formation of luminescent inorganic complexes either with the doped or undoped metal chalcogenide Qdots or with Qdots present in a protein matrix along with nanoclusters or with core/shell Qdots led to the fabrication of a nanocomposite that emitted bright natural white light with close to perfect white-light chromaticity color coordinates (0.33, 0.33), high color-rendering index (CRI) (>80), and high correlated color temperature (CCT) closer to daylight (6000 K). − Notably, a photostable single unit WLE nanocomposite could be fabricated on the basis of the formation of two different luminescent inorganic complexes (blue-emitting Zn 2+ /Mn 2+ acetylsalicylate and green-emitting zinc quinolate complexes) on the surface of an orange-emitting Mn 2+ -doped ZnS Qdot (Figure A) .…”

Section: Introductionmentioning

confidence: 99%

Chemical Reactions Involving the Surface of Metal Chalcogenide Quantum Dots

et al. 2019

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This invited feature article focuses on the chemical reactions involving the surface ions of colloidal quantum dots (Qdots). Emphasis is placed on ion-exchange, redox, and complexation reactions. The pursuit of reactions involving primarily the cations on the surface results in changes in the optical properties of the Qdots and also may confer new properties owing to the newly formed surface species. For example, the cation-exchange reaction, leading to systematic removal of the cations present on the as-synthesized Qdots, enhances the photoluminescence quantum yield. On the other hand, redox reactions, involving the dopant cations in the Qdots, could not only modulate the photoluminescence quantum yield but also give rise to new emission not present in the as-synthesized Qdots. Importantly, the cations present on the surface could be made to react with external organic ligands to form inorganic complexes, thus providing a new species defined as the quantum dot complex (QDC). In the QDC, the properties of Qdots and the inorganic complex are not only present but also enhanced. Furthermore, by varying reaction conditions such as the concentrations of the species and using a mixture of ligands, the properties could be further tuned and multifunctionalization of the Qdot could be achieved. Thus, chemical, magnetic, and optical properties could be simultaneously conferred on the same Qdot. This has helped in externally controlled bioimaging, white light generation involving individual quantum dots, and highly sensitive molecular sensing. Understanding the species (i.e., the newly formed inorganic complex) on the surface of the Qdot and its chemical reactivity provide unique options for futuristic technological applications involving a combination of an inorganic complex and a Qdot.

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“…Meanwhile, white-emitting QLEDs also have been developed not only for display devices with a color filter but also for solid-state lighting devices. [7,8] White QLEDs have several advantages to solar radiation spectrum due to the spectral vacancies between each primary color. To realize sunlike emission in QLEDs, it is required to use more primary colors.…”

Section: Introductionmentioning

confidence: 99%

“…Meanwhile, white‐emitting QLEDs also have been developed not only for display devices with a color filter but also for solid‐state lighting devices. [ 7,8 ] White QLEDs have several advantages to implement white light‐emission, especially compared to white OLEDs; the white OLEDs require a complicated multilayer structure to form blue/yellow or blue/green/red emitting layers (EMLs). [ 9 ] Also, to change the emission peak wavelength for tuning the properties of white light, a new emitter molecule structure should be designed.…”

Section: Introductionmentioning

confidence: 99%

Sunlike White Quantum Dot Light‐Emitting Diodes with High Color Rendition Quality

Hong

Kim

Kwak

2020

Advanced Optical Materials

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implement white light-emission, especially compared to white OLEDs; the white OLEDs require a complicated multilayer structure to form blue/yellow or blue/ green/red emitting layers (EMLs). [9] Also, to change the emission peak wavelength for tuning the properties of white light, a new emitter molecule structure should be designed. On the contrary, white QLEDs can be simply fabricated with mixed colors of QDs in a single EML, [10-12] which makes their device structure and fabrication process as easy as monochromatic QLEDs. In addition, the spectral peak can be easily and precisely adjustable by changing the size of the QD core, enabling to tailor the characteristics of the white light, such as the color rendering index (CRI) and correlated color temperature (CCT). Owing to these advantages of QDs and QLEDs, a high color-quality lighting source based on white QLEDs can be achievable. Natural light from the sun is one of the best illuminants exhibiting a CRI of 100, meaning that any colors can be rendered over the entire visible spectral ranges (from red to violet). The sunlight also contains spectra essential for all organic creatures on earth. For instance, photosynthesis requires a variety of wavelengths depending on the types of chlorophylls. [13,14] The human circadian rhythm is also affected by the change of light intensity and color of the sunlight over time. [15-17] The lighting devices used in aquariums should contain short wavelengths of blue-violet colors to reproduce the natural underwater conditions as well as the other visible wavelengths to show the colors of creatures for visitors. In this wise, for a variety of purposes, it is undoubtedly demanded that artificial light sources show a "sunlike" emission spectrum as similar to the sunlight as possible. White OLEDs may have a high CRI of >85 but they are too costly due to the complicated fabrication process as mentioned above. Meanwhile, researches on white QLEDs have been increasing continuously since the first white QLED was demonstrated in 2004. [18-30] In particular, the Bulović group reported trichromatic QLEDs emitting white light solely from QDs by mixing red, green, and blue QDs in the EML in 2007. [18] The QD mixing method also has the advantages of simple processing and color tuning by changing the blending ratio between QDs. In 2014, the first tetrachromatic white QLED was demonstrated, showing the highest CRI of 93. [19] It was a meaningful result demonstrating a high CRI from white QLEDs consisting of narrow spectra of primary colors. Nevertheless, the spectrum is still dissimilar to the Although it is demanded for general lighting sources to have high color rendition qualities close to natural daylight, it is difficult to make sunlike artificial illuminants due to limited tunability of phosphors and complicated fabrication processes. On the contrary, white-emitting quantum dot (QD) light-emitting diodes (QLEDs) can be easily produced by mixing several colors of QDs in a single emitting layer (EML). In this work, sunlike white QLEDs showi...

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Color temperature control of quantum dot white light emitting diodes by grafting organic fluorescent molecules

Cited by 11 publications

References 25 publications

Stability of Quantum Dots, Quantum Dot Films, and Quantum Dot Light‐Emitting Diodes for Display Applications

Stability of Quantum Dots, Quantum Dot Films, and Quantum Dot Light‐Emitting Diodes for Display Applications

Chemical Reactions Involving the Surface of Metal Chalcogenide Quantum Dots

Sunlike White Quantum Dot Light‐Emitting Diodes with High Color Rendition Quality

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