Research On The Application Of Quantum Dots In LED Packaging

LED lighting devices has the advantages of energy saving,environmental protection,low cost and so on,and has occupied a leading position in today's lighting field.LED packaging,as a key link in the process of LED preparation,mainly uses traditional fluorescent materials as down-conversion materials.However,these fluorescent materials still have some shortcomings in the process of application,such as short fluorescence lifetime,low fluorescence quantum efficiency and wide fluorescence emission spectrum.In contrast,colloidal semiconductor quantum dots(QD)have the advantages of high luminous efficiency,extremely narrow photoluminescence band with full width of half-maximum(FWHM),high spectral color purity,wide coverage of excitation spectrum and other advantages.Using quantum dots to replace the traditional fluorescent material as a new type of narrow-band conversion materials used in the LED packaging,not only can achieve the emission wavelength control in the whole visible spectrum region,but also achieve high color saturation due to its extremely narrow FWHM and reduce the loss of additional luminescence efficiency caused by far-red and long-red components.In this paper,CdSe quantum dots with excellent optical properties were used as down-conversion materials,and the reliable CdSe/ZnS core/shell quantum dots and new CdS/CdSe/CdS quantum well quantum dots were successfully prepared by LSS hydrothermal method.The related characteristics of the synthesized samples were discussed and analyzed by through some commonly used test methods in the experiment.At the same time,CdS/CdSe/CdS quantum dots were successfully applied to LED packaging by Remote encapsulation technology,which prepared plant lighting LED devices and improved the color rendering and spectral efficiency of white LED.The main work and research results are as follows:1.Synthesis of CdSe/ZnS Core-Shell QDThe CdSe quantum dots were successfully prepared by LSS hydrothermal method at 150? for 9 hours.Using CdSe quantum dots as "seeds",ZnS shells were coated on the surface of CdSe nuclei.Furthermore,the mechanism of nucleation and growth of QDs was explored by changing the mole ratio of Cd:Se in the precursors.The results showed that CdSe/ZnS quantum dots with core/shell structure have good dispersibility,and their particle size is concentrated at 6.5�1.8nm.Compared with bare CdSe quantum dots,the fluorescence intensity of CdSe/ZnS core/shell quantum dots is significantly improved,and the lowest FWHM can reach 48 nm,and the emission peak is regulated in the visible light range.2.Synthesis of CdS/CdSe/CdS quantum well quantum dotsThe CdS/CdSe/CdS quantum well quantum dots with high fluorescence efficiency were successfully prepared by adding a narrow band gap(1.75 e V)CdSe well to the middle of the core and shell layer of wide-band gap(2.7e V)CdS.And the effects of temperature,time and molar concentration on the fluorescence spectra of CdS/CdSe/CdS quantum dots were studied.The results show that the CdS/CdSe/CdS quantum dots have good dispersive properties without agglomeration.The particle size distribution is 8.3�1.5nm,and the narrowest FWHM is up to 44 nm.Moreover,the fluorescence spectra of CdS/CdSe/CdS quantum dots are affected by the thickness of CdSe in the middle layer and slightly modulated by the thickness of the outermost CdS shell.3.Encapsulation of quantum dot LED The CdS/CdSe/CdS quantum well quantum dots are encapsulated into LED using Remote encapsulation technology.The results show that the quantum dot phosphors without Si O2 or organic polymer coating can be successfully encapsulated into LEDs by mixing them with silica gel.It can improve the color rendering of white LED and reduce the spectral efficiency loss compared with the traditional red phosphor.