Research On The Preparation And Bandwidth Characteristics Of White LED Based On Quantum Dots

The research work of this thesis is mainly supported by the National Science Fund for Distinguished Young Scholars “Preparation of semiconductor nanomaterials and the quantum dot optoelectronic devices”,the project number is 61225018 and the National Natural Science Foundation of China “Research on preparation High Efficiency LED of Inorganic Perovskite Quantum Dots”,the project number is 61675086.Visible light communication(VLC)is a wireless optical communication technology that has developed with the development of white light emitting diodes(LED)lighting technology.White LED with low power consumption,long lifetime,small size,et al.,can replace the fluorescent lamps,incandescent lamps and other traditional lighting sources,as the next generation of solid light source.Compared with the traditional lighting source,white LED has a short response time,easy to high-speed modulation characteristics,it can be designed based on white LED indoor visible wireless communication systems and networks to achieve the dual functions of lighting and communication.At present,most of the visible light communication was in the experimental stage.Although the overall system has been achieved,there are still many problems to be resolved.Among them,how to prepare high efficiency,high bandwidth white LED devices is a key problem in visible light communication.In this paper,we made detailed study and discussion on this problem.The high luminous efficiency and wide bandwidth,lighting communication dual-use white LED was fabricated by the use of short fluorescence lifetime colloidal quantum dots(QDs).We focuse on solving the problem about the colloidal quantum dot phosphor and excitation chip combination device.The detailed research contents of this paper are shown as follow:(1)The preparation and characterization of Cd Se/Zn S quantum dots,Ag In S2/Zn S quantum dots,Cs Pb X3(X = Cl,Br,I)perovskite quantum dots and polymer dots were studied and prepared.We used the four nanomaterials to fabricate white light LED,respectively.The optical properties and stability of the devices were analyzed.And the white LEDs based on PDs with short relaxation life were discussed in detail.By adjusting the ratio of green and red PDs,a group of high color rendering index(CRI),color temperature adjustable white LEDs were fabricated.(2)The theoretical model was established to analyze the factors that influences the modulation bandwidth of the white LED and the relationship between the modulation bandwidth and the fluorescence lifetime.The theoretical modulation bandwidths were fitted with the change of the fluorescence lifetime and the luminous flux,respectively.The influencing on the composite components mechanism of the blue Ga N chip and the coupling emission between quantum dot fluorescent powder were analyzed and the main factors that confine the modulation bandwidth were also realized.The effective matching of the quantum dot fluorescent material with the excitation source is achieved.(3)We designed the test circuit of white LED devices' modulation bandwidth,including the transmitter circuit and the receiver circuit.The transmitter circuit used the high-speed photodiode to convert the optical signal into electrical signal,amplified the signal through the operational amplifier,adjusts the input signal frequency,and finally we obtained the actual modulation bandwidth of the LED.(4)Cd Se/Zn S quantum dots,Zn Cu In S/Zn S quantum dots,polymer dots and Cs Pb X3(X = Cl,Br,I)perovskite quantum dots and rare earth YAG: Ce phosphor materials were selected for different fluorescence lifetime.The white LED devices were prepared according to the theoretical model.The control variables were used to adjust the variables in the model one by one,and the actual bandwidths were tested and characterized.Finally,the theoretical calculation results were compared with the experimental results,and we analyzed the factors that limit the white LED bandwidth.The innovation of this paper is that the quantum dots are used as the fluorescent white fluorescent LED prepared in the visible light communication.And we firstly establish the theoretical model to analyze the factors that affect the bandwidth.Taking into account the requirements of high color rendering and high luminous efficiency,the bandwidth limitations of traditional phosphor materials have been broken.