The Up-conversion Luminescence Of Rare Earth Doped ZnO Powders

In recent years, rare earth (RE) doped up-conversion optical materials have been extensively studied owing to their potential applications in infrared detection, 3D display, undersea communication, biology label and so on. The choice of host material is an important factor in the research of up-conversion materials. Up to now, chemical stability, mechanic characteristic and thermal stability of the host materials with good luminescence characteristics still have some problems to be solved. Therefore it becomes the hotspot to find the host materials with low phonon energy, high conversion efficiency, good physical and chemical performance in the up-conversion research. As an important photoelectric and piezoelectric compound semiconductor, with a direct wide bandgap, ZnO has a potential application in up-conversion fields because of its excellent physical and chemical stability and lower phonon energy (437cm-1). Based on this background, in this dissertation, we fabricated several rare earth co-doped ZnO materials through high temperature oxidation method and chemical combustion method. According to the results of Raman, X-ray diffraction (XRD), scanning electron microscopy (SEM), we investigated the influence of the doping rare earth ions, the compositions and microstructures on the up-converted luminescence of the prepared samples. The main results obtained are described as follows:1. RE³⁺ ions co-doped ZnO powders were prepared by the high temperature oxidation method and chemical combustion method, respectively. Spectroscopic measurements, such as XRD, SEM and Raman, prove that the RE³⁺ ions have been doped into the lattice positions of ZnO.2. Under the excitation of 980 nm diode laser, a strong red up-conversion emission was observed in both Er³⁺/Yb³⁺ co-doped ZnO powders that fabricated through two different methods. The red up-converted luminescence intensity of samples prepared by chemical combustion method occupies 94.1% of the total intensity. Compared to the samples prepared by high temperature oxidation method, its color purity was greatly improved.3. Under the excitation of 980 nm diode laser, green and blue up-conversion emissions centered at 552 and 477 nm, respectively, were observed in Ho³⁺/Yb³⁺ and Tm³⁺/Yb³⁺ co-doped ZnO powders that prepared by chemical combustion. The luminescence intensity has been enhanced with the increase of the mol ratio Yb³⁺/RE³⁺ (RE³⁺ = Ho³⁺ ion or Tm³⁺ ion).4. Under 488 nm Ar+ laser excitation, a violet up-conversion luminescence was obtained, and it was achieved through the forward and back energy transfer between Er³⁺ and Yb³⁺ ions.Our results show that ZnO as a host material will have the potential applications in the up-conversion red phosphors and ultraviolet laser materials.