Isotope structure in optical spectra of LiYF_{4}:Ho^{3+}

We report the first observation of isotope shifts in optical spectra of an impurity in a solid associated with isotopes in the impurity surrounding. Static and dynamic couplings of impurity electronic states with the crystal lattice are discussed as a possible cause of the observed isotope structure in optical spectra of ${\mathrm{LiYF}}_4$:Ho