燃烧法合成Ln_2O_2S∶RE^(3+)(Ln=Gd,La;RE=Eu,Tb)X射线荧光粉及发光性能

Combustion Synthesis and Luminescence Characteristic of Ln_2O_2S∶RE^(3+) (Ln= Gd,La; RE=Eu,Tb) X-ray Phosphors

采用燃烧合成法,以稀土硝酸盐和二硫代乙二酰胺为反应物,通过控制两者的摩尔比例,在点燃温度为300 ~350℃时,制备了掺杂不同浓度稀土激活剂离子的硫氧化物X射线荧光粉。分别以X射线衍射(XRD)、扫描电子显微镜(SEM)、光致发光(PL)光谱及X射线激发的发光(XEL)光谱对样品进行了表征。XRD分析表明,当热处理温度低于500℃时,可得到单一相的硫氧化物X射线荧光粉,这就避免了高温烧结的缺点;而当烧结温度较高时,开始有硫酸氧化物出现。从SEM图像中可以看到荧光粉粉末具有疏松和多孔连续的三维的网络块状结构,但其初级粒子尺寸较小,均小于50nm,这在一定程度上,可以提高成像系统的空间分辨率。PL光谱分析表明,所制备的荧光粉样品分别呈现出Eu3+,Tb3+离子的特征发射。XEL光谱结果表明,尽管它与光致发光的激发原理不一样,但同样呈现出Eu3+,Tb3+离子的特征发射;这些样品本身对X射线的吸收系数及掺杂浓度不一样,因此它们的光发射效率也有所差别。

Combustion synthesis technology overcame the disadvantages of high temperature solid-state reaction, and resolved the serious pollution of sulfur for the environment, what's more, phosphor powders of the small particle size were achieved, which could enhance the resolution of imaging system to some extent. X-ray phosphor powders of Ln 2O 2S∶RE 3+ (where Ln=La,Gd; RE=Eu,Tb)were prepared by combustion reactions. In detail, different kinds of rare earth nitrates were weighed and mixed in stoichiometric amounts, where the doses of the dopant were 0.15%, 0.35% and 0.5% in mol fraction, respectively. The nitrates were molten during drying in an oven at 100 ℃, and during the cooling of these mixed nitrates reactants, appropriate amounts of organic fuel, such as dithio- oxamide were added, mixed and ground along with the nitrates, where molar ratio of dithiooxamide to the rare earth nitrates was 2. The mixtures were heated in an air tube furnace with the ignition temperature of 300~350 ℃. To evaluate the effects of heat treatment, the combustion-prepared powders were also heated to 500~700 ℃ in air. The samples were characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), photoluminescence(PL) and X-ray excited luminescence (XEL). XRD results showed the oxide sulfide phases only when the sintering temperatures were lower than 500 ℃, which avoided the defect of high sintering temperature. SEM results showed a loose, porous agglomeration and a continuous three-dimensional network, and the primary particlesize is not more than 50 nm. PL spectra showed the characteristic emission of rare earth activation ions, respectively. To our satisfaction, the PL intensities were nearly the same as some commercial X-ray phosphors. XEL spectra showed the same characteristic emission, although their luminescence principals were different each other. In addition, the absorption coefficients and the dopant concentration doped of these samples weren't the same for X-ray excitation, therefore, their light emission efficiencies were also different.