不同制备条件对Zn_2SiO_4∶Mn^(2+)粉末发光性能的影响

Effect of Preparation Condition on the Luminescent Properties of Zn_2SiO_4∶Mn^(2+) Phosphors

利用溶胶-凝胶法制备了Zn2SiO4∶Mn2+粉末,探讨了体系pH值、热处理温度、煅烧气氛对材料结构和发光性能的影响。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、光致发光(PL)谱等分析手段对Zn2SiO4∶Mn2+粉末的结构、颗粒大小、形貌、发光性能进行了表征。结果表明:溶胶的pH值影响制备的粉体的结晶性和颗粒大小,当溶胶pH值为4.34时,体系水解缩聚反应充分,所得荧光粉的光致发光强度最强;煅烧气氛显著影响荧光粉的发光强度,前驱体在N2(90%)+H2(10%)的还原气氛下煅烧得到的发光粉发光强度最强;最佳热处理温度为900℃。

Owing to its properties of high-luminescent efficiency, chemical stability and wet-resistence, Zn2SiO4 exhibits more excellent performance than the sulfides as luminescent host material. Zn2SiO4： Mn^2＋ （willemite） is an efficient phosphor for plasma display, cathodoluminescent and electroluminecent displays. Over the past few decades, researchers have studied intensely about factors influencing on the photoluminescent properties of Zn2SiO4： Mn^2＋ , such as calcining temperatures, concentration of Mn^2＋ , atmosphere of heat treatment, various preparation methods. However, the pH value of the Zn2SiO4： Mn^2＋ precursor sol also plays an important role in its luminescent properties. Herein, we investigate the effects of pH value of the precursor sol, heating atmosphere （oxidizing, neutral protecting and reducing） and calcining temperature on the photoluminescent intensitv of Zn2 SiO4 ： Mn^2＋ phosphor powder. Zn2SiO4： Mn^2＋ phosphors have been prepared via a sol-gel route. Different pH values of the sol resulted in different geling time and the sol with pH value lower than 3 could not be gelatinized. After pre-heating at 600 ℃, Zn2SiO4： Mn^2＋ precursors were calcined in different atmosphere （air, N2 and mixture of 10% H2 ＋ 90% N2 ） at heating temperature varing from 800 ℃ to 1 100 ℃. The structure of Zn2SiO4： Mn^2＋ has been characterized by X-ray diffraction （XRD）, which shows that all the phase of phosphors is with α-Zn2SiO4 phase. The phosphor prepared from the sol with pH of 4.34 has the best crystallinity. Scanning electron microscope （SEM） is used to measure the particle size of the Zn2SiO4： Mn^2＋ phosphors and the mean size of the phosphor obtained from the sol with pH value of 4.34 is about 100 nm, larger than the size of the phosphors obtained from sols with pH values of 5.32 and 6.53. The results of photoluminescent （PL） spectra indicate that the PL intensity of the phosphor increases with increasing the pH value of precursor sol, and the maximum was obtained when the pH value of precursor sol is 4, 34. Because the phosphor obtained from the sol with pH value of 4.34 has best crystallinity, and its particle size is larger, leading to smaller specific surface area. When the specific surface area is smaller, there are lower defects in the surface of particles and fewer nonradiative transitions appear. Additionally, the hydrolysis and polycondensation reactions of the precursor sol with pH value of 4.34 have been carried throughly and properl in the well dispersion of the Mn ions. The emission intensity of Zn2SiO4： Mn^2＋ phosphors calcined y, resulting in the mixture of nitrogen and hydrogen is stronger than those of the phosphors calcined in the other heating atmosphere. Reducing atmosphere could easily split Mn-Mn pair and produce large number of isolated Mn ions. With H2 existing in the heating atmosphere, more Zn ions incline to be volatilized and more Mn ions would substitute for Zn ions. Therefore, the PL intensity of Zn2SiO4： Mn^2＋ phosphors is the strongest when the pH value of the precursor sol is 4.34 and the phosphors are calcined in the mixture of N2 and H2 at 900 ℃.