MSO4:Eu2+(M =Mg,Ca, Sr,Ba)的等电子陷阱与热释光特性

在硫酸盐掺入稀土元素的研究中, 得到了几种掺入Eu²⁺的碱土金属硫酸盐磷光体MSO₄:Eu²⁺ (M =Mg, Ca, Sr, Ba), 这组磷光体具有与掺入三价稀土离子(Tm³⁺, Dy³⁺, Eu³⁺)的碱土金属硫酸盐截然不同的热释光特性, 热释光三维发光谱中只呈现一个热释光峰, 对γ和βup辐射的热释光剂量响应为线性-亚线性响应. 结果清楚地显现出Eu²⁺对碱土金属阳离子的等价取代而形成的等电子陷阱对这些磷光体的热释光特性起了关键性的作用, Eu²⁺等电子陷阱与基质中的本征缺陷SO₄^2-形成的缺陷复合体作为热释光多阶段过程的基本作用单元, 基本上产生一次作用热释光事件. SrSO₄:Eu²⁺是一种典型的等电子陷阱发光的磷光体, 它具有相当高的热释光和光释光发光效率.

Isoelectronic traps and thermoluminescence characteristics in MSO4:Eu2+ (M =Mg,Ca, Sr,Ba)

A series of alkaline earth sulphate phosphors MSO₄:Eu²⁺ (M =Mg, Ca, Sr, Ba) is obtained in doping experiments. It is discovered that these phosphors doped with Eu²⁺ ions have the thermoluminescence (TL) characteristics which are quite different from those in the alkaline earth sulphate phosphors doped with trivalent rare earth ions RE³⁺ (RE= Dy, Tm, Eu). It is also observed that there is only one glow peak in the three-dimensional emission spectrum and the radiation dose response of the glow peak is linear-sublinear in the series of phosphors MSO₄:Eu²⁺ (M =Mg, Ca, Sr, Ba). However, quite a lot of experimental results show that there are several glow peaks in the three-dimensional emission spectrum, and the TL radiation dose responses are linear-supralinear in the series of phosphors MSO₄:RE³⁺ (M =Mg, Ca, Sr, Ba and RE= Dy, Tm, Eu). The reason lies in the structures of defect complexes which are formed in the course of preparation of these phosphors and include intrinsic imperfects and dopants. These defect complexes can be regarded as basic elements in the TL multi-stage process. In the series of phosphors MSO₄:Eu²⁺ (M =Mg, Ca, Sr, Ba), the isoelectronic traps produced by doping Eu²⁺ ions which have the same valences as superseded alkaline earth ions are very localized traps to form the defect complexes (Eu²⁺ isoelectronic trap-SO₄^2-) that are basic elements in the TL multi-stage process, in which there are one-hit TL events basically. However, in the MSO₄:RE³⁺ (M =Mg, Ca, Sr, Ba) phosphors, the defect complexes (RE³⁺-SO₄^2--cation vacancy V_M) are basic elements in the TL multi-stage process, in which there are two-hit TL events basically. It is clear that the Eu²⁺ isoelectronic trap phosphors play key roles in TL Characteristics in MSO₄:Eu²⁺ (M = Mg, Ca, Sr, Ba). In addition, it has been observed that the wave length at the single TL peak in each of the three-dimensional emission spectra of the series of phosphors MSO₄:Eu²⁺ (M =Mg, Ca, Sr, Ba) is related to the substrate of each of these phosphors, such as the wave lengths at the TL peaks are 440, 385, 375 and 375 nm for MgSO₄:Eu²⁺, CaSO₄:Eu²⁺, SrSO₄:Eu²⁺, and BaSO₄:Eu²⁺ respectively. The experimental results display the characteristics of Eu²⁺ isoelectronic traps formed by substituting alkaline earth ions which have different cationic radii and electronegativities. The SrSO₄:Eu²⁺ phosphor can be called typical isoelectronic trap phosphor which has the higher TL and optical stimulated luminescence efficiency.