BaFBr∶Eu^(2+)的发光及电特性研究

Luminescence and Electrical Properties of BaFBr∶Eu^(2+)

采用高温固相反应方法制备的BaFBr∶Eu2+粉末样品,未经X射线、真空紫外或紫外光辐照,用波长大于400nm的光激发样品,可观测到Eu2+的390nm发光。样品的电子自旋共振(ESR)谱证实在BaFBr∶Eu2+粉末样品的制备过程中,会产生大量的晶格缺陷,分别为电子和空穴陷阱,它们在光激励发光过程中充当不可缺少的角色。本工作将BaFBr∶Eu2+粉末制成压片,在其一侧制作两个电极,以研究电阻 电压关系、剩余电压随时间的变化以及与电极材料的关系等电学特性。电特性研究结果也表明,样品中有电子和空穴陷阱两类缺陷,BaFBr∶Eu2+的发光,源自激发能通过这两类缺陷向Eu2+的能量传递。

BaFBr∶Eu2+ is a kind of photostimulated luminescence (PSL) material with a wide energyband bigger than 8eV. For BaFBr∶Eu2+ powder samples, without preirradiation of Xray, VUV or UVlight, the radiative transition of Eu2+ ion peaked at about 390nm can be observed, even if the excitation wavelength is longer than 400nm. The electron spin resonance (ESR) spectrum reveals that there are both electron and holetype traps in powder samples, which play an important role in the PSL process of BaFBr∶Eu2+. The slice of BaFBr∶Eu2+ powder was fabricated under pressure. Two electrodes were evaporated or glued on the surface of slices, so that we can study the electrical properties of BaFBr∶Eu2+, such as the relationship between resistance and voltage, variation of remainder voltage with time and effect of electrode material on it. When a direct current voltage is applied between two electrodes on slices, we have found that at the interface between BaFBr slice surface and electrodes, there exists charge carrier accumulating as a result of the potential barriers, and when the applied voltage was canceled, we can also detect the remainder voltage due to the residual carrier at the interface. The remainder voltage will be decreased with time. When the applied voltage between two electrodes of samples was changed, from higher value to lower one or in inverse direction, the IV curves, therefore the relationship between resistance and voltage, are different. For different materials of electrode, such as Ag or Cu, if applied voltages are low, the remainder voltage is almost a constant which is only related to the material of electrodes, but, when the applied voltage is high enough, the remainder voltage will decrease with the increase of applied voltage. We believe that this phenomenon might result from the penetration of charge carriers through potential barriers under high applied voltages. The investigation results of electrical properties of BaFBr∶Eu2+ show that there exist both electron and hole traps in BaFBr∶Eu2+. The trapped electrons and holes are first escaped to conduction band or valence band, and then transported, respectively, to excited or fundamental levels of Eu2+ ion. As a result, the Eu2+ will be excited and its radiative recombination can be observed.