Synthesis of short-chain passivated carbon quantum dots as the light emitting layer towards electroluminescence

Ding, Yuanfei; Zhang, Feng; Xu, Jiacong; Miao, Yanqin; Yang, Yongzhen; Xu, Bingshe

doi:10.1039/c7ra02421e

Cited by 87 publications

(60 citation statements)

References 48 publications

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“…Hydrophylic CDs are much more common, and usually display very polyfunctional and disordered surface structures, characterized by an abundance of small polar groups, such as Hydroxyl, Carboxyl, Carboxylate, Amine, and Amide. Besides "standard" polar groups, some authors passivated the surface with more complex molecules, as polyethylene glycol (PEG), or polyethyleneimine (a long chain molecule which contains primary, secondary and tertiary amine groups), still obtaining highly fluorescent CDs [29,35,99,105]. The high water solubility (typically several g/L) of most CDs is a characteristic, which is very useful for many applications.…”

Section: The Structure Of Cdsmentioning

confidence: 99%

Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response

2018

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Carbon dots (CDs) are an emerging family of nanosystems displaying a range of fascinating properties. Broadly speaking, they can be described as small, surface-functionalized carbonaceous nanoparticles characterized by an intense and tunable fluorescence, a marked sensitivity to the environment and a range of interesting photochemical properties. CDs are currently the subject of very intense research, motivated by their possible applications in many fields, including bioimaging, solar energy harvesting, nanosensing, light-emitting devices and photocatalyis. This review covers the latest advancements in the field of CDs, with a focus on the fundamental understanding of their key photophysical behaviour, which is still very debated. The photoluminescence mechanism, the origin of their peculiar fluorescence tunability, and their photo-chemical interactions with coupled systems are discussed in light of the latest developments in the field, such as the most recent results obtained by femtosecond time-resolved experiments, which have led to important steps forward in the fundamental understanding of CDs. The optical response of CDs appears to stem from a very complex interplay between the electronic states related to the core structure and those introduced by surface functionalization. In addition, the structure of CD energy levels and the electronic dynamics triggered by photo-excitation finely depend on the microscopic structure of any specific sub-type of CD. On the other hand, this remarkable variability makes CDs extremely versatile, a key benefit in view of their very wide range of applications.

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Section: The Structure Of Cdsmentioning

confidence: 99%

Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response

2018

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“…Low roughness is favorable for the fabrication of high performance CD‐LEDs. The average roughness ( R a ) and root mean square roughness of the PVK:CD (30 wt%) film are 0.95 and 1.26 nm, respectively, which are lower than the values of other CD‐based emitting layer films …”

Section: Performances Of Blue Cd‐leds With Different Doping Concentramentioning

confidence: 79%

“…To our knowledge, this is the highest value compared with ever reported monochromic CD‐LEDs ( Table 2 ). These results also suggest that oleophylic CDs are beneficial to achieving higher brightness and purer EL emission of doped CD‐LEDs than hydrophilic CDs . However, the turn‐on voltage of the CD‐LED is 8.5 V, which is higher than that of other CD‐LEDs .…”

Section: Performances Of Blue Cd‐leds With Different Doping Concentramentioning

confidence: 86%

“… These results also suggest that oleophylic CDs are beneficial to achieving higher brightness and purer EL emission of doped CD‐LEDs than hydrophilic CDs . However, the turn‐on voltage of the CD‐LED is 8.5 V, which is higher than that of other CD‐LEDs . This may be related to the unideal transporting performance of CD‐doped emitting layer caused by long chain passivating ligands on the oleophylic CDs' surface .…”

Section: Performances Of Blue Cd‐leds With Different Doping Concentramentioning

confidence: 89%

“…However, the heavy metal elements in QDs are harmful to humans and environment, which limits their wide application in full‐color displays . In this situation, carbon dots (CDs), with excellent optical properties (tunable color emission, strong resistance to photobleaching, high fluorescence quantum yield (QY)), environmental‐friendliness, and wide availability and low cost of raw materials, are expected to replace traditional QDs for full‐color displays . In 2013, oleophylic CDs with QY of 60% were synthesized and the blue CD‐based light‐emitting diode (CD‐LED) (nondoped) with the maximum brightness of 24 cd m −2 was fabricated by using the oleophylic CDs as emitting layer .…”

Section: Performances Of Blue Cd‐leds With Different Doping Concentramentioning

confidence: 99%

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Ultrahigh Brightness Carbon Dot–Based Blue Electroluminescent LEDs by Host–Guest Energy Transfer Emission Mechanism

Miao

Zheng

et al. 2018

Advanced Optical Materials

Self Cite

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green, yellow, orange, and red hydrophilic CDs were synthesized by Yuan et al., and multicolor CD-LEDs were fabricated by using these CDs separately as emitting layer, with the maximum luminance of 136, 93, 60, 65, 12 cd m −2 , respectively. [11] However, the research of CD-LEDs is still at the initial stage, and the brightness of monochromatic CD-LEDs is still far from reaching commercialization level. Therefore, it is a great challenge for applying CDs to full-color displays.Currently, CDs in solid state always suffer from obvious fluorescence quenching. [14,15] Consequently, the prepared CD-LEDs exhibit a low luminance owing to fluorescence quenching. [16] In 2017, Yuan et al. obtained white CD-LED by doping green hydrophilic CDs in poly(N-vinylcarbazole) (PVK) as the emitting layer. [11] The high brightness of 2050 cd m −2 indicates that the method of hostguest doping can significantly improve luminance of the device. However, because of an incomplete energy transfer from PVK to CDs, the electroluminescent (EL) spectra for the fabricated CD-LEDs always contain the strong blue emission from PVK, which is probably related to the limited doping concentration of hydrophilic CDs. PVK is only soluble in chlorobenzene or chloroform, which makes it difficult to tune hydrophilic CDs' concentration during a doping process, because the precipitation from the mixed solutions at a high doping concentration of hydrophilic CDs could significantly reduce the performance of doped devices. So, oleophylic CDs are needed to obtain high brightness and pure emission of doped CD-LEDs.In present study, oleophylic CDs with QY of 41% were obtained using anhydrous citric acid as a carbon precursor and hexadecylamine as a passivation agent by one-step microwave carbonization method. Then, the strategy of host-guest doping was adopted to fabricate blue CD-LEDs by using the oleophylic CDs (guest) doped in PVK (host) as the emitting layer, because the oleophylic CDs and PVK could be well cosoluble in chlorobenzene at any doping concentration. Thus, the fabricated CD-LED realizes pure blue emission that dominantly originates from the emission of CDs by the host-guest energy transfer mechanism. Consequently, the CD-LED achieves the ultrahigh brightness of 569.8 cd m −2 , with the Internationale de L'Eclairage (CIE) coordinates of (0.22, 0.27), which is the highest value for monochromic CD-LEDs ever reported. Our result shows that oleophylic CDs are conducive to fabricating CD-LEDs with both high brightness and pure emission. Ultrahigh brightness blue carbon dot-based light-emitting diodes (CD-LEDs)are fabricated by a host-guest doping method with poly(N-vinylcarbazole) (PVK) as the host to realize the high brightness and pure emission of CD-LEDs. Oleophylic CDs are synthesized as the dopant to obtain a wide range of doping concentration of CDs because oleophylic CDs and PVK can be well cosoluble in chlorobenzene at any doping concentration. Therefore, the CD-LEDs emitting pure blue light that dominantly originates from CDs' emission are real...

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Self‐Quenching‐Resistant Red Emissive Carbon Dots with High Stability for Warm White Light‐Emitting Diodes with a High Color Rendering Index

Zhang

Yang

Wan

et al. 2020

Advanced Optical Materials

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Due to the excellent characteristics of energy‐saving, environmentally friendly and long‐life, the solid‐state lighting based on white light‐emitting diodes (WLEDs) is an emerging technology to replace traditional lighting solutions. However, the lack of red component of the most established method for fabricating commercial WLEDs results in high correlated color temperature (CCT) and low color rendering index (CRI). Herein, red‐emitting carbon dots (R‐CDs) with self‐quenching‐resistant property are synthesized using melamine and dithiosalicylic acid as precursors. In addition, R‐CDs exhibit high thermal and photostability under high temperature and strong blue light irradiation. On the basis of the unique features of R‐CDs, a WLED is fabricated by combining a blue‐LED chip with commercial Ce3+:Y3Al5O12 and R‐CDs phosphors, which exhibits warm white light with a color coordinate of (0.41, 0.38), a high CRI of 92.7 and a CCT of 3827 K. Besides, the WLED exhibits good optical stability upon the increase of drive current from 20 to 100 mA. The results suggest R‐CDs can be used as a color converter to fabricate high‐quality warm WLEDs.

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Synthesis of short-chain passivated carbon quantum dots as the light emitting layer towards electroluminescence

Abstract: S-CQDs were chosen as a light emitting layer by virtue of their structure characteristics, optical properties and film-forming ability to obtain CQD-LEDs.

Cited by 87 publications

References 48 publications

Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response

Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response

Ultrahigh Brightness Carbon Dot–Based Blue Electroluminescent LEDs by Host–Guest Energy Transfer Emission Mechanism

Self‐Quenching‐Resistant Red Emissive Carbon Dots with High Stability for Warm White Light‐Emitting Diodes with a High Color Rendering Index

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