The role of OH ions in the stabilization of F colour centres in LiF |
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Authors: | VM Khulugurov VN Salomatov IM Kalogeras A Vassilikou-Dova I Christakis |
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Institution: | (1) Irkutsk State University, Institute of Applied Physics, 20 Gagarin Boulevard, 664003 Irkutsk, Russia, RU;(2) Irkutsk State Institute of Transport Engineers, 15 Tchernyshevsky Street, 664074 Irkutsk, Russia, RU;(3) University of Athens, Department of Physics, Solid State Physics Section, Panepistimiopolis, 157 84 Zografos, Greece, GR |
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Abstract: | Thermally Stimulated Depolarisation Current (TSDC) and optical methods are applied to a range of alkali-fluoride crystals
in order to establish a model for the stable F
2
+
- like colour centres in LiF:OH-. The experimental results for LiF:OH- suggest that the OH- defects are partially destroyed under ionising irradiation or during crystal growth. The low-temperature dielectric relaxation
signals in LiF:OH- and LiF:Mg2+,OH- are attributed to highly interacting hydroxide ions and products of their destruction located in extended lattice defects.
In LiF:OH-, in contrast to other alkali halides, the results advocate for a defect-structure model, which considers a neutral defect
(ND, probably O2 or H2) sited at the anion vacancy of the O2--V
a
+
dipole and which possibly is the “nucleus” for the F
2
+
centre. The proposed F
2
+
(ND, O-) model seems to better explain the dielectric results, compared to the older F
2
+
(O2-) and F
2
+
(O-) models. The estimate for the electric dipole moment derived from the experimental TSDC bands, gives a value for the F
2
+
- like centre in LiF:OH- between those of the F
2
+
(O-) and F
2
+
(O2-) defects, in good agreement with the proposed F
2
+
(ND,O-) model. The reduction of the activation energy barrier of the (re)orientation process of the Mg2+V
c
-
(OH-) complexes in LiF:Mg2+,OH-, and the low-temperature shift of their TSDC band, compared to the single Mg
2
+
V
c
-
peak in LiF:Mg2+, are tentatively ascribed to an increase in the crystal-lattice parameters owing to the presence of OH- and/or products of its destruction.
Received 31 August 2001 / Received in final form 30 March 2002 Published online 9 July 2002 |
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Keywords: | PACS 77 22 Ej Polarisation and depolarisation – 42 55 Rz Doped insulator lasers and other solid state lasers |
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