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The Influence of “Rotational” Lattice Deformation States on the F Center Emission
Author(s) -
Ascarell G.
Publication year - 1974
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220630135
Subject(s) - excited state , atomic physics , stark effect , ionic bonding , population , polarization (electrochemistry) , ion , radiative transfer , electric field , physics , chemistry , condensed matter physics , quantum mechanics , demography , sociology
Recent ENDOR measurements of the relaxed excited state of the F center indicate that this state is p like. Previous theories of the temperature dependence of the radiative lifetime of the F center and of the Stark effect in emission are based on the assumption that the excited state is s like with an admixture of the p like states produced by the interaction with Γ 4 −modes. The present model supposes instead an extended p like excited state and a large lattice relaxation of Γ 3 +symmetry. The electronic state and the associated lattice are described by an appropriate vibronic state. It is assumed that a series of rigid rotator “rotational” states can be associated with each of the forementioned vibronic states. These “rotational” states are interpreted as describing the rotation of the center of mass of the nearest neighbour ions around the geometrical center of the vacancy. The Stark effect can be explained as having both an electronic and an ionic component. The latter is very much enhanced by the local electric field produced by the change of the electronic charge distribution resulting from the applied field. The ionic contribution to the Stark effect is larger than the electronic one. The changes of lifetime produced by the applied field do not depend on the direction of polarization of the emitted light in agreement with the experimental result. The major difficulty of the model is that it predicts no polarization of the emission. This is contrary to the experimental result. To explain the observed effect a selective population of some of the p i states must be assumed during lattice relaxation in a crystal subject to an external electric field.