氟镁钡晶体的本征缺陷及掺杂机理的研究

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摘要

BaMgF4晶体化合物是一种极有应用价值的材料，其特点是容易生长出较大尺

寸且光学性质良好的单晶。BaMgF4晶体具有良好的压电性和铁电性，室温下具有

顺磁性，低温下可转换成反铁磁性，并且是多种稀土离子及过渡离子激活磷光体

的良好基质。近年来关于 BaMgF4晶体作为基质的性质研究，着重点在磷光体上，

而对于基质本身的研究却寥寥无几。纵然 BaMgF4是一种宽禁带的晶体，禁带宽度

达10.33eV，比 BaLiF3晶体的禁带宽度还要大，但是在晶体生长过程或者外界存

放中，不可避免的会产生跟禁带相关的缺陷。而针对于晶体作为基质的整个物性

研究，还存留在实验研究方面，从理论方面的研究及分析则可以让我们重新审视

这些实验结果，为结果的分析及应用提供更加可靠可信的理论依据。

本文借助计算机模拟技术，针对 BaMgF4晶体的 F型色心和掺杂 Ce3+离子和

Sm2+的电子态密度和光学性质进行研究。内容主要由五部分组成:BaMgF4晶体的研

究背景介绍(第一章)；计算机模拟计算的理论基础(第二章)；完整 BaMgF4晶体的

晶体结构及用 CASTEP 软件对其晶体物理性质的模拟计算(第三章)；用 DV-Xα软

件对 BaMgF4晶体中 F型色心的模拟计算(第四章)；用 DV-Xα软件对 BaMgF4晶体

掺杂稀土离子的模拟计算(第五章)。

第一章，绪论，主要阐述了 BaMgF4晶体研究背景，最新研究进展和本文将要

进行的研究内容。

第二章，简述密度泛函理论，并对 DV-Xα和CASTEP 计算软件作简单介绍。

第三章，介绍晶体结构，借用 CASTEP 软件模拟计算完整晶体的电子结构和

光学性质。结果表明 BaMgF4晶体沿三个晶轴方向的偏振吸收峰位置很接近，光学

性质相似，但吸收的强度明显不同，表明存在着各向异性。完整的 BaMgF4晶体在

可见光区没有吸收，即晶体呈透明状，但在 60~80nm 处存在很强的吸收。

第四章，用 DV-Xα软件进行模拟计算，拟合 BaMgF4晶体离子间的势参数， 1)

研究完整 BaMgF4晶体及 F心的电子结构和物理性质，结果表明，F心会在 BaMgF4

晶体中引起 236-274nm 的吸收，与实验值 247nm 段的吸收相吻合。并且计算结果

表明采用 Castep 和DV-Xα所得的完整晶体的电子密度分布相同，为理论计算的正

确性提供证据。

第五章，用 DV-Xα软件分别模拟拟合 BaMgF4:Ce3+和BaMgF4:Sm2+晶体离子间

的势参数，研究 BaMgF4:Ce3+的光谱结构和 BaMgF4:Sm2+的光谱结构。结果表明，

Ce3+离子的 f-d 跃迁共产生四个跃迁项，而 Sm2+离子的 f-f 跃迁谱线包括 5D0-7F0，

5D0-7F2，5D1-7F3，5D1-7F4电偶极跃迁和 5D0-7F1磁偶极跃迁五个跃迁项。BaMgF4

晶体在此只起到基质材料的作用。并且在 BaMgF4:Sm 晶体中，由于 Sm3+的离子半

径和 Ba2+离子相差甚远较之 Sm2+离子，故只存在 Sm2+离子，并且取代的是 Ba2+

离子格位。

关键词:BaMgF4晶体 F型色心 Ce3+:BaMgF4Sm2+:BaMgF4电子结构

光学性质

ABSTRACT

BaMgF4crystal is known as the wide-gap fluorides with the ultrafast (~1ns) core

valence emission in the 190-220 nm region, which is a very suitable host for transition

metal and rare earth ion impurities and has promising properties for solid state laser

applications. A fast Ce3+-associated photo- and X- ray luminescence was found in Ce:

BaMgF4. The crystal is of interest for the development of radiation detectors.

Scintillation availability is substantially determined by the transparency losses due to

the radiation coloration.

From this point of view, the problem of the radiation resistance of the crystals is

relevant. In the previous articles, the radiating sensitivity of BaMgF4crystals from the

point of view of the structural defect presence had been mentioned, and the transition

energy was calculated by a semi-empirical Mollwo-Ivey equation [1]. The absorption

band triplet with maxima at 236, 257 and 274 nm should be corresponding to the

F-centre in different positions due to a low symmetry of this crystal structure [2]. Due to

lack of direct experimental evidence or theoretical calculations, the origins of 236, 257

and 274 nm absorption bands are not clearly up to now.

Therefore, it is very important to study the defects in BaMgF4crystal in order to

improve its optical properties. Although there are many experimental studies on the

optical spectra of BaMgF4crystal doped with rear lions.

The thesis mainly consists of six sections: The first part is the introduction. The

second part introduces the basic calculation theory and related computer programs. The

third part is the instructor of the BaMgF4crystaland simulation of the perfect BaMgF4

crystal. The fourth part simulates the intrinsic defects in BaMgF4crystal. The fifth part

discusses the electronic structures and physical properties of BaMgF4crystal doping

with Ce3+ and Sm2+, respectively.

1) Introduction includes the introduction of the basic physical properties of BaMgF4

crystal, the research background and situation of BaMgF4crystal at home and

abroad, the purpose and the main works of this thesis.

2) Theoretical basis, introduces the Density Function Theory combined with plane

wave and pseudo-potential method, and the two codes adopted in the thesis,

CASTEP and DV-Xα.

3) Calculation of the structural properties, electronic structures and optical properties

of the perfect BaMgF4crystal by CASTEP. The calculated spectra of the BaMgF4

crystal exhibit two absorption bands located at 14.2~14.475eV and 21.48-21.767eV.

The minimal absorption edge is 10.337eV, which is so close to the intrinsic

absorption edge 10.333eV (125nm).

4) Calculation of the electronic structures and optical properties of the BaMgF4

containing F type color center by DV-Xα. It is concluded from the calculated results

that the energy levels of F color center located in the forbidden band of the crystal.

The optical transition energy from the ground state to excited state for F color center

is 5.12eV, which corresponds to the 242nm absorption bands. This calculated results

are well consisted with the experimental results. The absorption bands resulted from

the F color center in the BaMgF4crystal are located around the 236-274nm.

5) Calculation of the electronic structures and optical properties of the BaMgF4doping

with Ce3+ and Sm2+ by DV-Xα in separately.

6) Conclusion of the thesis.

Key Words:BaMgF4crystal,F color center,Ce3+:BaMgF4,Sm2+:BaMgF4,

Electronic structures,Optical properties.

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摘要：

摘要BaMgF4晶体化合物是一种极有应用价值的材料，其特点是容易生长出较大尺寸且光学性质良好的单晶。BaMgF4晶体具有良好的压电性和铁电性，室温下具有顺磁性，低温下可转换成反铁磁性，并且是多种稀土离子及过渡离子激活磷光体的良好基质。近年来关于BaMgF4晶体作为基质的性质研究，着重点在磷光体上，而对于基质本身的研究却寥寥无几。纵然BaMgF4是一种宽禁带的晶体，禁带宽度达10.33eV，比BaLiF3晶体的禁带宽度还要大，但是在晶体生长过程或者外界存放中，不可避免的会产生跟禁带相关的缺陷。而针对于晶体作为基质的整个物性研究，还存留在实验研究方面，从理论方面的研究及分析则可以让我们重新审视这些...

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