Mechanoluminescence and thermoluminescence of BaFCl:Sm 2+ and BaFBr:Sm 2+ crystals

The alkaline-earth fluorohalide crystals MFX, where M=Ca, Sr, Ba, Pb and X=Cl, Br, I, form an important class of materials crystallizing in the PbFCl-type tetragonal structure which is also called the matlockite structure. These compounds have long been of interest because of the various defect species which can be detected by spin resonance and associated techniques. The crystals were prepared by slow cooling of the melt of a stoichiometric mixture of BaF ₂ and the corresponding chloride or bromide under 0.2 bar of ultrapure argon (5N5), often slightly fluorinated. We have studied the mechanoluminescence (ML) of BaFBr:Sm ²⁺ and BaFCl:Sm ²⁺ crystals. It is seen that after the impact of a moving piston, initially the ML intensity increases with time, attains a maximum value and then it decreases with time up to a particular minimum value, and then it increases again, attaining a peak value and finally disappears. The first peak lies in the deformation region and the second peak lies in the post-deformation region. The ML intensity of the BaFCl:Sm ²⁺ crystal is much higher than the ML intensity of the BaFBr:Sm ²⁺ crystal. For different impact velocities, the ML intensity increases with velocity; and the total ML intensity attains a saturation value for higher impact velocities. The total ML intensity increases with the increase in the applied load. It is suggested that the moving dislocation produced during deformation of crystals captures holes from hole-trapped centers (like H centers), and the subsequent radiative recombination of the dislocation holes with electron gives rise to ML. Thermoluminescence (TL) of BaFBr:Sm ²⁺ and BaFCl:Sm ²⁺ crystals was studied after exposure to ultraviolet rays with the help of a TLD reader. The peak of TL for the BaFBr:Sm ²⁺ crystal is found at ～247°C and for BaFCl:Sm ²⁺ crystals at 283°C. The TL intensity initially increases with increase in the UV radiation and then it attains saturation for higher values of UV exposure. The absorption spectrum was recorded with the help of a UV–visible spectrophotometer (Shimadzu). The band found at 275 nm was attributed to H centers.     

X射线诱导BaFCl:Eu2+光激励发光过程的新观察

本文研究了ＢａＦＣｌ：Ｅｕ＾２＾＋光激励发光（ＰＳＬ）对Ｘ射线剂量的响应关系，光激励发光的衰减规律，以及色心的形成与转型。除了简单的Ｆ心之外，我们还发现了Ｆ心的缔合中心，它们的吸收带位于７００－９５０ｎｍ。连续光激励Ｆ心时，光激励发光呈指数型衰减，而光激励发光（ＴＳＬ）也显现类似的衰减规律。光激励Ｆ缔合中心时，伴随着光激励发光还可能有一些无辐射跃迁过程的产生，例如色心的分解，转型和解离电子的再捕获     

紫外线对BaFCl:Eu光激励发光的增强效应

对X射线辐照后的BaFCl:Eu样品,通过研究紫外线辐照对光激励发光的影响,发现在一定条件下紫外线对光激励发光有增强的作用,并且根据光谱研究提出了光激励发光的过程为Eu²⁺和陷阱争夺激发态电子的观点,从机理上对这一现象进行了解释.     

无机材料BaFCl0.5Br0.5：Sm^2＋光子选通光谱烧孔

本文报道了无机材料的BaFCl_(0.5)Br_(0.5):Sm~(2+)的光子选通光谱烧孔.文中叙述了光子选通光谱烧孔的机制.在低温4.2K下进行多孔烧孔和探测.测量了孔的选通性和稳定性.实现了孔的可擦除和重复烧孔.测量结果表明,处于4.2K的BaFCl_(0.5)Br_(0.5):Sm~(2+)样品,在一个非均匀加宽轮廓内可实现1×10~3个以上数目的永久性光谱烧孔.     

Study on the PSL mechanism in BaFCl:Eu<Superscript>2+</Superscript> phosphors

In this paper, the ESR and photoluminescence (PL) of BaFCl and BaFCl:Eu²⁺ radiated or un-radiated by X-ray were observed. The single electron in the color center could be produced in BaFCl without Eu²⁺. A series of traps of different energy level in BaFCl lattice were formed, and some shallow traps of them could be bleached by Vis-light, and the other deep traps could not. The bleaching effects on ESR and photostimulated luminescence (PSL) were investigated. An F-H-Eu²⁺ complex (F color center, H color center and Eu²⁺ complex) in the lattice of BaFCl:Eu²⁺ was suggested when the phosphor was X-ray irradiated. The Eu²⁺ located in the complex has only contribution to the ESR signal, but has no contribution to PL spectrum. The excitation of both F-center and located Eu²⁺ could decompose the complex to induce bleaching. The 440 nm light could excite the F-centers and the 220 nm and 270 nm could excite the located Eu²⁺, and the excitation disturbed the F-H-Eu²⁺ complex and caused a decrease of the PSL.