One-Step Synthesis of Sulfur Quantum Dots and Electroluminescent Properties
FENG Xiang-yu, JIANG Na, WANG Wei, LI Meng-qian, ZHAO Su-ling*, XU Zheng
Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronics Technology, Beijing Jiaotong University, Beijing 100044, China
Abstract：Sulfur quantum dots (SQDs), as a new kind of quantum dots without metal elements, not only have the advantages of environmental protection and non-toxicity but also the advantages of simple preparation, low cost, good quality solubility, and stable photoluminescence (PL) characteristics. Sulfur quantum dots have aroused great interest from researchers in the quantum dot field and have good application prospects in nanoelectronics, optics, catalytic chemistry, biomedicine, and sensors. Currently, the research on sulfur quantum dots mainly focuses on synthesising sulfur quantum dots and improving photoluminescence properties. Like carbon dots, these quantum dots can also display different light colors under the irradiation of ultraviolet lamps, but the green fluorescence properties need to be further improved. At present, the research on sulfur quantum dots mainly focuses on the synthesis of sulfur quantum dots and the improvement of photoluminescence properties. Like carbon dots, these quantum dots can also display different light colors under the irradiation of ultraviolet lamps, but the green fluorescence properties need to be further improved. At present, sulfur quantum dots are mainly prepared by the ultrasonic-assisted liquid-phase reaction. In this paper, long-chain thiol molecules of 1-dodecanethiol are used as a sulfur source, and blue elemental sulfur quantum dots are successfully synthesized in a short time (2 h) by one-step heating at a high temperature (240 ℃). The synthesized quantum dots are characterized by fluorescence spectrum (PL), absorption spectrum (Abs), Raman spectrum, infrared absorption spectrum, elemental analysis, and morphology analysis. It can be seen from the experiment that the absorption of sulfur quantum dots began gradually from 550 nm, which was mainly due to many surface defects of quantum dots. There is an obvious absorption edge at 450 nm, corresponding to band absorption; The absorption at 372 nm is attributed to the absorption caused by S2-8 in quantum dots. Under the excitation of 330 nm, the synthesized quantum dots show obvious blue light, with the main emission peak at 450 nm and the main half-peak width of about 50 nm. Then, different quantum dots were synthesized by changing the reaction temperature and time, respectively. It was found that with the increase in reaction temperature and reaction time, the synthesized sulfur quantum dots (SQDs) showed a change from blue to yellow-green when excited at 330 nm, and the main peak wavelengths of the fluorescence spectrum (PL) were at 400, 450 and 525 nm, respectively. The luminescence quantum yield (PLQY) of the synthesized sulfur quantum dots (SQDs) could be 1.48%. In addition, we used synthesized sulfur quantum dots (SQDs) to prepare electroluminescent devices for the first time, with the structure of ITO/PEDOT:PSS/PVK/S-QDs/B4PyMPM/LiF/Al. Then we tested the electroluminescent characteristics of the devices and successfully obtained the blue light emission of the sulfur quantum dots (SQDs) at 472 nm. By changing the thickness of the electron transport layer B4, the luminance of S-QLED devices can be changed, which has a specific guiding role in realizing the electroluminescence of sulfur quantum dots (SQDs).
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