水热法制备MgWO_4及其发光性质

Hydrothermal Synthesis of MgWO_4 and Its Luminescence

以硝酸镁、钨酸钠为原料,氢氧化钠和硝酸作为pH调节剂,在180～230℃水热条件制备纯相的MgWO4。探讨了水热反应温度对MgWO4纯相形成以及煅烧温度对其晶型、发光性质的影响。分别用粉末X射线衍射、荧光光谱、扫描电子显微镜和综合热分析等手段对样品进行表征。结果表明,水热法可以直接制得不含结晶水MgWO4晶体,属于四方晶系,形貌呈片状,厚度约为几个纳米。样品热重分析和高温煅烧的结果表明,水热法所得MgWO4晶体在850℃附近出现晶型转化,由四方晶系转变为单斜晶系,并导致发光性质的明显变化。SEM显示煅烧前的样品形貌为片状,不同温度煅烧后由片状逐渐向棒状转变。

MgWO4 is a self-activated luminescent material, chemical and luminous properties are stable. It has high quantum efficiency and has been used as lamp phosphor for a long-term. MgWO4 is usually prepared by solid-phase method using high purity MgO or MgCO3 mixture with WO3, then sintered at about 1 200℃ for several hours. Solid-phase approach leads to unhomogeneous distribution of sample size, the particles easily , and the particle size is difficult to control, but hydrothermal method can overcome these shortcomings. In recent years, hydrothermal method has been used to synthesis some kinds of tungstate samples, such as BaWO4, NaLa（ WO4 ） 2, PbWO4 and so on, but to synthesis MgWO4, it has not been reported. Amberg and John. R synthesized pure MgWO4 · H2O and MgWO4 · 2H2O by mild hydrothermal method, but without studying on their luminescent properties. This article reports about using hydrothermal method to synthesis MgWO4 crystal without crystalline H2O. A pure phase MgWO4 was synthesized by hydrothermal method from Mg（ NO3 ）2 and Na2WO4 solutions. The effects of hydrothermal temperatures on lattice phase, sintering temperatures on the morphology, structure and fluorescence intensity of MgWO4 powder were investigated. Samples were characterized by X-ray diffraction （XRD）, fluorescence spectrometer, scanning electron microscope （SEM） and TG-DSC. The results showed that MgWO4 without crystalline H2O molecule can be synthesized at 180 -230℃ hydrothermal temperatures. The as-prepared sample has a tetragonal structure and transfer to monocline structure when sintered at 850 ℃ or higher temperature. Fluorescence spectra showed that MgWO4 has a broad emission band peaked at 480 nm. The emission intensity becomes stronger as the sintering temperature increases from 750 ℃ to 1 050 ℃. SEM images showed that the size of MgWO4 particles increases with the sintering temperature.