Thermal‐electric alignment and stark effect of Z1 centers in KCl

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Abstract
The experimental results of detailed electro‐optical studies on Z1 centers in KCl doped with Ca, Sr, and Ba are reported. For randomly oriented Z1 center systems an isotropic quadratic Stark effect is measured, with a spectral dependence (close to a third derivative of the Z1 absorption) markedly different from that of F centers. The equality of the Z1 center orientations can be disturbed by the application of de fields (about 104 Vcm−1) above 120°K, leading to the development of a linear Stark effect. The spectral dependence and characteristic anisotropy of this linear Stark effect are determined. Quantitative pulse annealing experiments under applied de field show that the Z1 centers reorient with an activation energy of ≈0.4 eV. This process is attributed to jumps of the cation vacancy among equivalent lattice sites within the Z1 complex and will be discussed on the basis of a vacancy‐centered model proposed earlier [1].