Deep Blue And Ultraviolet Light-Emitting Diodes Based On Carbon Dots Synthesized By Solvothermal Method And Extraction From Plants

In recent years,colloidal quantum dots(QDs)semiconductors show their great potential in the fields of lighting,detection and display,.Since the first report of colloidal quantum dots in 1983,this extremely small material has been regarded as one of the most promising materials in the optoelectronic field in the coming decades.Since it can emit light from ultraviolet region to the infrared region and its high color purity and high brightness,quantum dot can be widely used in lighting,engineering detection,biological detection and large-size display.The traditional quantum dots include cadmium sulfide quantum dots and lead sulfide quantum dots.The fluorescence peaks of this type of quantum dots can cover from deep blue to infrared light,with high color purity,high luminance with simple synthesis so it can be widely applicated.In addition,the perovskite quantum dots that have emerged in recent years have also attracted the attention of the research team due to their excellent optoelectronic properties.Not only in the field of solar cells,perovskite quantum dots also show great potential in light-emitting area.Its wide luminous peak coverage and high luminance make it a hot spot in the current research field.However,most of the above-mentioned quantum dot materials are based on heavy metal such as lead and cadmium,which are highly toxic,and may cause bad effects on the human-beings and the natural environment.The European Union has also issued regulations to restrict the production and application of this quantum dot materials.In 2004,carbon quantum dots,a kind of carbon-based nanomaterials with excellent optical properties,were first reported in research,which have gradually raised attention since then.The carbon-based nanomaterials show greater potential than that of lead or cadmium-based Ⅱ-Ⅵ quantum dots and perovskite quantum dots.Carbon quantum dots with high color purity and spectral tunability gradually become very promising optical material in the new generation.Based on previous reports,carbon quantum dots are mainly synthesized by chemical methods such as combustion method and hydrothermal method.In these chemical synthetic methods,the use of chloride organic solvents is inevitable.Although carbon quantum dots have been widely studied and used in light-emitting diodes,their emission peak wavelength appears mostly longer than 450 nm.Thus,deep blue light and ultraviolet light,which are of great significance in biomedical and engineering detection fields,have not been reported in research yet.Therefore,we decided to conduct further research on deep blue and ultraviolet light-emitting devices based on carbon quantum dots and the non-toxic synthetic method of carbon quantum dots.In our work,we first fabricate deep blue organic light-emitting diode based on carbon quantum dots synthesized by hydrothermal method.We select the suitable materials for each layer and optimize the device structure.Finally,a deep blue lightemitting diode with the best photoelectric performance is obtained.The luminescence peak of the device is located at 428 nm.The maximum luminance can reach 159 cd/m~2 and the maximum external quantum efficiency is 0.88%.In order to improve the safety of this kind of material,we try a pure physical method to extract carbon dots from the seed’s inner skin of torreya grandis by centrifugation.The emission peak of light-emitting diodes based on the extracted light-emitting carbon dots appears at 438 nm with the full width at half maximum(FWHM)of 45 nm.The Commission International de I’Eclairage(CIE)color coordinate is located at(0.177,0.075).In addition,we try to fabricate ultraviolet light emitting diodes based on carbon dots synthesized by hydrothermal method.In this way,we hope to further expand the application prospect of carbon quantum dot in the fields of medicine and detection.The EL peak of the device is tested to be at 390 nm.By adjusting the concentration of the carbon quantum dot,we strive to fabricate the devices with the best photoelectric properties,but the luminance,current efficiency and external quantum efficiency of these devices are still too low to meet the requirement of daily applications.Therefore,we hope to use this work as an inspiration and provide guidance for the coming development of carbon quantum dots in the field of ultraviolet luminescence.