Fabrication And Optical Properties Of White Light-emitting Zinc Oxide Doped With Rare Earth Ions

In the modern optical technology, rare earth ions which act as luminescent center play an important role in solid luminous materials. They can be rich in sharp fluorescence emission, covering almost visible to the ultraviolet region. They also have a great influence on the microstructure, electrical properties, magneto-optical nature of crystal material after being doped into the crystal. As a result, the preparation and their photophysical properties of semiconductor nano-crystals doped with rare earth ions have attracted much attention in recent years. As a new type of optical material, ZnO whose band gap at room temperature is 3.37eV own a high exciton binding energy(60 meV), much larger than GaN(25meV). It also has a strong absorption in the ultraviolet region and gradually acts as matrix in the rare earth ions doped luminescent material, these materials are candidates for traditional semiconductor light emitting diodes and many enable new technologies for highly distinguishable emissive flat panel displays. It may also be used to improve many electro optical applications that rely on the direct generation of either narrow or broad spectra.In this work, three Systems of single crystalline ZnO:Eu3+, ZnO:Eu3+/Tb3+ and ZnO:Eu3+/Dy3+ have been synthesized and efficient doping was realized. Their structures and luminescent properties were studied, efficient energy transfer from ZnO host to RE3+ were studied and energy transfer dynamics from Tb3+ ions to Eu+ ions and Eu3+ to Dy3+ were investigated. The main works are summed up as follow:First, single crystalline Europium ions doped ZnO have been synthesized by using a simple co-precipitation method. XRD spectra showed that europium ions may have been entered zinc oxide crystals. SEM shows that Eu3+ doped ZnO grains are smaller than undoped ZnO grains. TEM shows that most of the Eu3+ situated in ZnO lattice. The results of XPS demonstrate that most of the Eu3+situated in ZnO lattice, Sodium ions play a role as charge compensate when Eu3+ ions are doped into ZnO lattice. SEM indicates the substitution of Eu3+ for Zn2+ is dominant in the doping process. High efficient energy transfer from the ZnO host to Eu3+ ions was achieved, and a very sharp and intense red emission without defect background under ultraviolet or near-ultraviolet excitation was observed in the Eu-doped ZnO nanocrystals. This study opens up the possibility of fabricating new light-conversion materials with high color purity, high stability, and high luminescence efficiency, which have potential applications in advanced displays and LED backlights.Second, Single crystalline Europium and Terbium-codoped ZnO nanocrystals have been synthesized by using a simple co-precipitation method. Successful doping is realized so that strong green and red luminescence can be efficiently excited by UV and NUV light, demonstrating an efficient energy transfer from ZnO host to rare earth ions. Energy transfer from Tb3+ ions to Eu3+ ions in ZnO nanocrystals is also observed by analyzing luminescence spectra and the decay curves for the first time. In particular, it is found that red luminescence is greatly enhanced and green luminescence is remarkably quenched at low temperature, implying a resonant nonradiative energy transfer from Tb3+ ions to Eu3+ ions. CIE chromaticity coordinates of Eu3+/Tb3+ -codoped ZnO Under 385 nm excitation are very close to the standard equal energy white light illuminate. The results indicate Eu3+/Tb3+ -codoped ZnO nanocrystals are promising light-conversion materials and have potential in advanced displays and LED backlights.Three, single crystalline Europim and Dysprosium-codoped ZnO nanocrystals have been synthesized by using a simple co-precipitation method. Successful doping is realized so that strong blue, yellow and red luminescence can be efficiently excited by UV and NUV light, demonstrating an efficient energy transfer from ZnO host to rare earth ions. Energy transfer from Eu3+ ions to Dy3+ions in ZnO nanocrystals is also observed by analyzing luminescence spectra and the decay curves for the first time. By calculating the intensity ratio of electric dipole transition and magnetic dipole transition, it is found that asymmetric ratio of Eu3+ is significantly higher compared with that of Dy3+, electric dipole transition of Eu3+ is highly hypersensitive.