First-principles study of cadmium vacancy in CdWO_4 crystal

摘要

The structural relaxation, electronic structures and optical properties of CdWO_4 crystal containing cadmium vacancy (CWO:V_(Cd)) are studied by the CASTEP code. The cadmium vacancy (V_(Cd)) would trap two holes to maintain the local electrical neutrality. The calculated structural relaxation and electronic density of states reveals that the existent form of the hole in CWO:V_(Cd) should be oxygen molecular ion (O_2 ~(3-)). Therefore an associated color center [O_2 ~(3-)-V_(Cd)-O_2 ~(3-)] named as V_F center would form in the crystal. The calculated optical absorption spectrum for CWO:Vcd indicates that this V_F center would cause an absorption band peaking at about 650 nm with a shoulder at around 400 nm, which is in agreement with the experimental optical absorptions of the blue-grey colored CWO crystal.