The Synthesis And Properties Of (Oxy) Nitride Materials

In recent years, light-emitting diode（LED） is the fastest developing illumination device since it has long lifetime and high effiency.The current domainant solution of LED is using blue or UV LED chip with appropriate phosphors. So the performance of LED tends to depend on the quality of phosphors.（Oxy） nitride phosphors have good chemical and physical stability and varied crystal structure. Due to the special nephelauxetic effect brought by O/N replacement, the luminescence of（oxy） nitride phosphors can be controlled by changing its crystal structure.This thesis focuses on the preparing method, crystal structure, luminescence property, doping effect and thermal stability of two kinds of（oxy） nitride phosphors: CeAl₁₁O₁₈ and Y₄Si₂O₇N₂. This thesis can be divided into five chapters. The first chapter introduces the background of（oxy） nitride phosphors research, luminescence mechanism, common preparing method and density functional theory（DFT）. Chapter 2 shows the experiment part including raw materials and equipment.Chapter 3 reports the CeAl₁₁O₁₈ base phosphor prepared by solid-state reaction process. Stoichiometric raw materials were put into BN crucibles and fired at a temperature of 1700 ℃ for 2h in flowing nitrogen gas. Si-N doped CeAl₁₁O₁₈ lost the OMe in pure CeAl₁₁O₁₈ leading to the decrease of photoluminescence intensity of blue emission. Meanwhile, the UV emission became higher. Si-N doped CeAl₁₁O₁₈ has better thermal stability. Besides, Eu-Li doped CeAl₁₁O₁₈ were firstly prepared. There is energy transition between Ce³⁺ and Eu²⁺, which results in higher photoluminescence intensity of blue emission.In chapter 4, Y₄Si₂O₇N₂: Eu²⁺ phosphor was prepared by a pretreatment method. The key process is that HI was poured into the beaker until Eu₂O₃ was completely dissolved. HI makes the Eu₂O₃ become EuI₃. During the process of heating and drying, the reducing property of I- reduces Eu³⁺ ions into Eu²⁺. Y₄Si₂O₇N₂: Eu²⁺ phosphor has a broad emission band in the range of 400–500 nm with good thermal stability. The existence of Eu²⁺ is verified by X-ray absorption near-edge structure（XANES） and photoluminescence. Furthermore, the effect of Zr doping on the luminescence properties of Y_3.98-yZr_ySi₂O₇N₂: 0.02Eu²⁺ phosphor was researched. It found that the Zr doping leads to an emission blueshift and improves the luminescence intensity when y<0.03 but the peak remains stable and the luminescence intensity decreases when y>0.03.Chapter 5 summarizes the whole paper and gives the expection.