Synthesis And Up-conversion Luminescent Properties Of Rare-Earth Doped Zinc Oxide Phosphor

Up-conversion luminescence (UPL) is a physical process where one high energy photon is emitted after absorbing two or more low energy photons. Due to this characteristic, UPL materials show extensively applications in short-wave laser, three-dimensional display, IR radialization detection, laser anti-counterfeiting brand, biology fluorescent label and so on. Traditional UPL material hosts are fluorides and rare-earth oxides. For years, many researches have been performed on the preparation and different characteristics of zinc oxide, and lots of new results have been obtained. However, there are few researches on preparation technologies and upconversion luminescence of rare earth doped zinc oxide. For UPL materials, the phonon energy is considered as one of the most important factors, viz host materials with low phonon energy has high UPL efficiency. The phonon energy of znic oxide is about 437cm^-1. So zinc oxide with quite low phonon energy, high chemistry stability and eco-friendly property is expected to be a excellent host material.In this study, rare earth doped zinc oxide phosphors were synthesized by solid state method, combustion method, precipitation method and hydrothermal method, Basic technical parameters were confirmed by experiments, and mechanism of UPL was systemly discussed. The phase, micro-structure and luminescent properties of samples were characterized by X-ray diffraction analysis, scanning electron microscope transmission electron microscope and spectroscopic analysis.The phosphors with high red light purity were prepared by solid state method. The up-conversion spectrum showed green and red emissions bands under 980nm LD excitation. The intensity of red emission was far higher than that of the green emission due to the cross-relaxation process (⁴F_7/2+⁴I_11/2â†'⁴F_9/2+⁴F_9/2), which restrained the electron population of green emission energy level, enhanced the efficiency of red light emission remarkably, and brought about high fluorescent branding ratio of red to green. The morphology and UPL properties of ZnO:Yb³⁺,Er³⁺ prepared by combustion, precipation and hydrothermal methods were studied The results indicated that the morphologies were amorphous, sphericity and pillar, respectively; The green light emission dominates in the up-conversion spectrum whch was different from spectrum by solid state method. The difference of preparation technologies and particle size are the main reason to result in the different properties of UPL.