荧光体CaSO_4∶Eu的近紫外发光性质

AUV Emission Properties of Phosphor CaSO_4 ∶Eu

CaSO4∶Eu是一种人们早已较为熟知的发光材料,由于其优异的热释发光特性而被广泛应用于辐射剂量学方面。近年来由于崭新的光致发光液晶显示模式的出现,人们又对其近紫外发射特性产生了极大兴趣。考察了CaSO4∶Eu的发光特性和材料的各种制备方法,以及制备条件对发光性能的影响,特别是对其近紫外发射性能的影响。实验表明,对于还原彻底、结晶良好的样品,激活剂Eu几乎全部以二价铕离子的形式存在,是一种很好的近紫外发射材料。该材料能被低压汞蒸气放电辐射有效激发,其发射带的峰值在386 nm附近,随Eu的掺杂浓度不同而略有差异,半峰全宽约为16 nm,基本满足了近紫外发射的要求,可应用于光致发光液晶显示器件的背照明光源中。

The phosphor CaSO4： Eu is a interesting material because of its very high sensitivity to ionizing radiations, negligible fading rate and high chemical stability. It has been used in the thermolumineseent（TL） dosimetry of γ-ray, β-ray, X-ray, neutrons and high-energy cosmic rays. In CaSO4： Eu the chemical valence of the incorporated Eu ions can be ＋ 3 and/or ＋ 2 valence depending on the preparing methods. Most of the published papers about this phosphor were concerned with the thermoluminescent characteristics. Recently its photoluminescent properties attract more and more attentions. In this work the main attention was paid to its near ultra-violet （AUV） emission of the Eu2^＋ ions in the phosphor CaSO4： Eu. The luminescence spectra of the CaSO4： Eu samples prepared with different methods were measured at room temperature in order to examine the effects of the preparing method on their luminescent properties. Experiments showed that the Ca and Eu sulphate co-deposition method is a better one for the AUV emission of the Eu2 ^＋ ions in these phosphors. In the concrete, a proportional amount of pure CaCl2 and EuCl3 was solved in deionized water and the co-precipitate was obtained by adding some sulfuric acid to the mixed aqueous solution. After washing by deionized water and drying the co-precipitate was fired at 650 - 750 ℃ for one hour under a weak reducing atmosphere. In the phosphors CaSO4： Eu prepared with this method the Eu^2＋ ions are predominant over the Eu^3＋ ions. In the phosphor the emission comes from the 5d-4f transition of the Eu2＋ ions. Its emission peak is at about 386 - 390 nm and its FWHM is about 16 nm. The UV excitation spectrum is composed of two bands peaking at about274 nm and 323 nm, respectively. They are attributed to the absorption of the 5f-4d transitions of the Eu^2＋ ions. When the content x is between 0. 003 and 0. 024 the phosphor gives a stronger AUV emission, the strongest emission occurs when the x is at about 0.02. The increase of the concentration of the incorporated Eu^2＋ ions makes the emission band shift slightly to the longer wavelength. The results showed that CaSO4： Eu^2＋ is a good candidate as the phosphors used in the backlight source of PLLCD.