The effects of temperature variation (between 5 and 296°K) and isotropic pressure variation (between 1 and 7.5 kgf/mm²) on the fine structure parameters b^q_k of Eu²⁺ in KCl and KI has been studied by electron paramagnetic resonance. The symmetry of the center is orthorhombic (C_2v) and only variations of b⁰₂, b²₂ and b²₄ are important.

A microscopic description of b^q_k is proposed, the temperature dependence is attributed partly to lattice dilatation and partly to two local modes which are revealed by vibronic structure of optical (f — d) transitions of Eu²⁺.