A Bright and Stable Violet Carbon Dot Light‐Emitting Diode

Abstract

Violet light‐emitting diodes (LEDs) with emission at 400 nm are very important for solid‐state lighting, high‐density information storage, display technology, and biology medical treatment. Wide band‐gap semiconductors and/or the semiconductor quantum dots (QDs), typically based on heavy metals such as cadmium and lead, are promising candidates for the violet LEDs, but so far these have had external quantum efficiencies (EQEs) lower than 0.31% (luminance 147.6 cd cm−2; 410 nm). Herein, violet light‐emitting materials and the violet LED devices based on carbon dots (CDots) are presented. The CDots have absolute photoluminescence quantum yield of 23.9% and produce two‐narrow‐peak emission at 382 and 401 nm with narrow full‐width at half‐maximum about 30 nm, respectively. The violet LEDs based on these CDots display high performance with a maximum luminance of 163 cd m−2 (electroluminescence peak located at 408 nm; Commission International de I'Eclairage color coordinate (0.180, 0.121)) and high EQE of 0.831%, exceeding that of previously reported semiconductor QDs‐based violet LEDs. Moreover, these CDots‐based violet LEDs have a high current efficiency of 0.62 cd A−1, a long lifetime (T50, 50 h), as well as a low turn‐on voltage of 3.7 V.

Ultra‐Bright and Stable Pure Blue Light‐Emitting Diode from O, N Co‐Doped Carbon Dots

“…Fourier transform infrared (FTIR) spectrum of CDs is shown in Figure 1b, in which, a series of peaks located at 3455, 3245, 2921, 1632, 1381, and 1120 cm –1 were attributed to stretching vibration of O─H, stretching vibration of N─H, stretching vibration of C─H, stretching vibration of C═C/C═O/C═N, bending vibration of C─C/C─N and bending vibration of C─O, severally. [ 23,24 ] The FTIR spectra of CDs in the present and 5 years ago were drawn in Figure S2a–c, Supporting Information, suggesting the structural stability of CDs during 5‐year storage. X‐ray photoelectron spectroscopy (XPS) survey spectrum (Figure S1e, Supporting Information) confirmed that CDs only contain carbon, nitrogen, and oxygen elements.…”

“…And the emissive peak located at 444 nm when the temperature was frozen to 5 K. The position of emission peak red‐shifted by 3 nm for all the process of temperature increment from 5 to 293 K. It could be explained by enhancing the possibility of carrier coupling because of the increment of temperature with the improvement of the distortions and structural vibrations. [ 23,29 ]…”

“…[ 13–22 ] These pure blue light‐emitting diodes involved the traditional QDs (QLEDs) containing heavy metal elements, such as gallium nitride, gallium arsenide, and cadmium sulfide, which are harmful to mankind and the daily environment. [ 23,24 ] It is a great challenge to develop the cost‐effective, environmental‐friendly, low toxic, and highly efficient luminescent materials, as well as, their pure blue LEDs.…”

Highly stable and bright blue light-emitting diodes based on carbon dots with a chemically inert surface

“…The flexural vibration of C-C/C-N and C-O are observed at 1382 and 1238 cm -1 . [31][32]40] Ultraviolet and visible spectrophotometry (UV-vis) is usually used to research into the optical absorption properties of materials. In the Figure 1c, the strong absorption peak situated at 204 nm indicates that π-π* transition of conjugated aromatic C=C bond.…”

Carbon‐Dot‐Based White‐Light‐Emitting Diodes with Adjustable Correlated Color Temperature Guided by Machine Learning

“…Also, CDs have opened up an avenue in community of light‐emitting diodes (LEDs) resulting from their inherent optical advantages, such as emission wavelength tunability, high photoluminescence quantum yield (PLQY), good solubility in different solvents and low photobleaching [25–34] . Up to now, by using diverse synthetic methods and various precursors, CDs have been fabricated with photoluminescence (PL) emission from red to violet [35] . Very recently, the development of this field is rapid, the PLQY of some CDs is up to 90 %, and the full width at half maxima (FWHM) of their PL spectrum are narrow to about 20 nm, [36–39] which are basically close to the requirements of display devices.…”