The Research Of Preparation And Optoelectronic Characteristices Of ZnO Nanomaterials With Rare Earth Doped

Zinc oxide （ZnO） is a third-generation optoelectronic semiconductor material with wide direct bandgap of 3.37 eV and exciton binding energy of 60 meV at room temperature （RT）, which suggests that ZnO have great potential in electroluminescent applications （light-emitting diodes, LEDs）. ZnO with quantum dot （QD） size may exhibit new optoelectronic properties when rare earth （RE） ions are doped because RE ions have rich energy levels and unique f-f and f-d orbital transition which could enrich the light-emitting properties of ZnO material, so that one may obtain red, green or blue emission by RE doping. Research of RE doped ZnO QD is of great significance because this may be an effective approach to achieve red, green, blue and even white LED devices.ZnO are prepared by sol-gel method in this thesis. We have prepared four systems denoted as follows:ZnO QD, ZnO QD:La³⁺, ZnO QD:Eu³⁺ and ZnO QD:Tb³⁺. Impact factors of the film quality, photoluminescent （PL） properties, electroluminescent （EL） performance under preparation process in various experimental conditions and current-voltage （I-V） characteristics under different experimental parameters have been studied systematically. We achieved stable electroluminescence from RE-doped ZnO QD light-emitting devices. The main contents are as follows:（1） ZnO QD is prepared by by sol-gel method. The best experimental conditions of film quality and PL performance in preparing ZnO QD film have been found. The ZnO QD thin films are made into light-emitting devices. I-V tests show that the ZnO QD devices exhibit rectifying characteristic. When forward bias is applied, the devices realize the green light emission and stay stable without much heat. EL spectra shows that the luminescence intensity of devices has increased with increasing input voltage.（2） ZnO QD:La³⁺sol are prepared by sol-gel method. Growth temperature and doping concentration are controlled in the experiment. RE ions have been doped into ZnO QD effectively and distribute uniformly in the film. The size of ZnO grain turned bigger after La³⁺is doped. With the increase of temperature, the size of grain has tendency to increase. ZnO QD: La³⁺thin films are packaged into devices with the optimal doping concentration and temperature. under sufficient current injection the ZnO QD:La³⁺thin film device show stable green light emission. EL spectra under different input current have been detected, which show that the device of luminous intensity increase with the increase of input current.（3） ZnO QD:Eu³⁺ and ZnO QD:Tb³⁺ thin films are prepared by sol-gel and spin-coating method. Light-emitting devices are fabricated based on the optimal experiment conditions above. Experimental results illustrate that the Eu³⁺and Tb³⁺ evenly mix into the ZnO QD thin films and the crystallization of the films is improved by reducing the grain size base on the experimental method and parameters. From the PL spectra, it can be seen that UV peak displays blue shift, but in the visible region, red shift occurs. I-V characteristic shows that the RE doped thin film device has rectifying behaviors too. The doped device can realize stable yellow green light emission under different constant current. Luminescence peaks corresponding to RE ions have been observed in EL which shows that the Eu³⁺and Tb³⁺act as a center of the light emission in ZnO QD.Finally, each film samples are annealed for further investigation. PL results show that both visible and UV light emission decreased in the ZnO QD and ZnO QD:RE thin films after annealing. Devices had been tested under various constant current but cannot achieve any light emission.