Study On The Improvement Of The Photoluminescence Property Of Eu Doped YBO₃Phosphor

Eu³⁺doped YBO₃has been widely used as a red phosphor for PDP, HDTV, projection TVand other flat panel display devices because of its stability, relatively low cost and excellentluminescent properties. However, there are still many problems in practice. CommercialYBO₃:Eu³⁺phosphor produced by solid-state method requires a subsequent shattering process toobtain smaller particles. The consequent uniform and the increased defects cause negative effectson its light-emitting efficiency. Meanwhile, the color purity of YBO₃:Eu³⁺phosphor can’t satisfyvarious kinds of display devices since its orange emission centered at594nm is the highestemission. It is a great challenge to improve the luminescence property of existing YBO₃:Eu³⁺phosphor to meet the development of the large-screen high-resolution color displays, computerterminals and other top-of-the-line displays.In this thesis, hydrothermal method was applied to synthesize YBO₃:Eu³⁺phosphor.Hexagonal YBO₃:Eu³⁺phosphor was prepared with excellent crystallinity. Ion doping techniquewas applied to improve its photoluminescence property. In the preparation process, adding ofsingle Li+ion dramatically increased the emission intensity of the YBO₃:Eu³⁺phosphor. Itachieves the highest when1%Li+ion was added, being enhanced about20%. In such condition,the obtained YBO₃:Eu³⁺phosphor was well-shaped spherical balls dispersing within a narrowrange of size distribution around15μm. Adding of5%Li+ion improves the YBO₃:Eu³⁺phosphor to reach the second highest emission intensity, being enhanced about10%. Uniformspherical balls were also obtained in this condition, while the diameter of the balls is around5μm. All the balls are aggregated by sub-crystallines of sheets.Then, adding of both Li+ion and alkaline earth metal ions was studied on their influence onthe photoluminescence property of YBO₃:Eu³⁺phosphor. The emission intensity was enhancedabout twice as much when1%Li+ion and5%alkaline earth metal ion were addedsimultaneously. The obtained YBO₃:Eu³⁺phosphor was also uniform balls in diameter of about10μm. however, the sub-crystallines aggregated so tightly that made the balls more like clewswithout obvious sheets inside. Increased hydrothermal temperature enhanced the luminescenceproperty of YBO₃:Eu³⁺phosphor. While prolonged hydrothermal reaction time caused negativeinfluence probably due to the quenching of the lattice defects during thedissolution-recrystallization process, which are reported as supporters for energy transform. XPS analysis results implied that neither Li+ion nor alkaline earth metal ion existed in theobtained YBO₃:Eu³⁺phosphor. Only trace amount of the alkaline earth metal ion can be tested atthe early stage of the hydrothermal reaction when just amorphous solid product was formed. Itcan be concluded that neither Li+ion nor alkaline earth metal ion participate in the crystallizationprocess of YBO₃:Eu³⁺crystal. Their roles in the hydrothermal reaction were more likely to act asmedia to interpret the crystallization of YBO₃:Eu³⁺in general route. The consequentachievement of the uniform and regular spherical morphology and narrow distribution of particlesize contributed to the improvement of the photoluminescence property of YBO₃:Eu³⁺.Organism is always a preferred choice to tune the shape of inorganic materials. In this work,malonic acid was chosen to modify the morphology of YBO₃:Eu³⁺phosphor. Persimmon cakeshaped YBO₃:Eu³⁺phosphor was prepared by controlling the pH value in9.0⁹.5precisely.Perfect spherical shape aggregated by nano-sheets can be obtained after the adding of ethanol. Asubsequent annealing process was carried out to remove the impurities caused by organism. As aresult, the emission intensity of YBO₃:Eu³⁺was enhanced about10%.Structure design of YBO₃:Eu³⁺phosphor was explored in the last chapter. Carbon balls indiameter of about100nm were first synthesized as a hard template by a low-temperaturehydrothermal reaction. Then, YBO₃:Eu³⁺sol-gel was coated on the surface of the carbon ballslayer by layer. After an elaborately designed annealing process, core-shell structured and hollowstructured YBO₃:Eu³⁺phosphor can be synthesized, respectively. Thickness of the layer wasabout several tens of nanometers. Such YBO₃:Eu³⁺performed weak emission intensity. Thehollow structure was not that perfect mainly due to the form of2D nano-sheets. Such synthesisroute is still rough and need further research.In summary, photoluminescence property of YBO₃:Eu³⁺phosphor synthesized byhydrothermal method was studied in this thesis by ion doping and morphology tailor. Greatimprovement was achieved when the YBO₃:Eu³⁺phosphor was in uniform spherical shape withnarrow size distribution. Core-shell structured and hollow structured YBO₃:Eu³⁺phosphor wasexplored searching for a possible route to save the cost and improve the utilization.