ZnS中电子陷阱能级对光生电子弛豫过程的影响

采用微波吸收法,测量了在不同助熔剂条件及不同气氛下烧制的ZnS材料受到超短激光脉冲激发后的光电子衰减过程,并且测量了材料的热释光曲线。样品A采用过量的SrCl作为助熔剂,在1150℃下灼烧制备而成;其热释光曲线显示材料中有浅电子陷阱,电子陷阱密度小,光生电子衰减过程为双指数衰减过程,快过程寿命为45ns,慢过程寿命为312ns。样品B中加入了少量的NaCl作为助熔剂;热释光曲线显示有浅电子陷阱和深电子陷阱,且都有较高的密度,其光电子寿命为1615ns。在NH₄Br气氛中烧制样品C,热释光谱显示只有浅电子陷阱形成,光电子寿命为1413ns。结果表明材料的光电子寿命和浅电子陷阱密切相关,浅电子陷阱密度越大,光生电子寿命越长,深电子陷阱对光生电子瞬态过程影响很小。

Effect of Electron Traps in ZnS on the Decay Process of Photoelectrons

There are very few direct measurement techniques that can be used to establish the movement of carriers in powders and polycrystals.The microwave absorption dielectric spectrum detection technique is suitable for investigating dynamic processes undergone by photocarriers of semiconducting nanomaterials, powder luminescent materials, micropowder,nanocrystal materials and multicrystal membrane materials.Investigation of the kinetic decay process for free photoelectrons and shallow trapped electrons is helpful in achieving and understanding of the kinetic mechanism of luminescence and the energy level structure for luminescent material or other semiconducting crystal materials;also, it can provide a scientific basis for the improvement of the luminescence efficiency of semiconducting materials. The decay process of photoelectrons of ZnS powder materials after excitation with short pulse laser has been measured by microwave absorption method. The materials were prepared under different flux and protective gas. The thermoluminescence spectra of the materials has also been investigated. Sample A was sintered at 1 150℃ with excessive SrCl as flux. The thermoluminescence spectra showed that there were shallow-electron traps and the density of that was low. The decay processes of photoelectrons included two exponential decay processes and the lifetime of the fast process and the slow process were 45 ns and 312 ns respectively. Sample C was prepared with a small quantity of NaCl as flux. The thermoluminescence spectra of it showed that there are high density of shallow-electron traps and deep-electron traps in the materials. Its lifetime is 1 615 ns. The lifetime of Sample B which was sintered under NH₄Br protective gas is 1 413 ns and only shallow-electron traps was formed. It was proved that the lifetime of photoelectrons has close relation with the density of shallow-electron traps. The higher the density was, the longer the lifetime. But deep-electron traps have little effect on the instant process of photoelectrons.