Photostriction of CdF$\text{}_{2}$:In Crystals

Lattice relaxation accompanying phototransformation of In bistable centers from the ground, deep state to the shallow state in CdF$\text{}_{2}$ crystal has been measured with the use of scanning tunnelling microscope. It is shown that relatively small macroscopic changes of the crystal length in the order of 1.8×10$\text{}^{-6}$ accompany the phototransformation of In ions. Lattice expansion upon the influence of population of shallow donor levels in CdF$\text{}_{2}$ explains the observed small changes of lattice constant during the process.