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