We have attempted to induce the theoretically predicted anharmonic lattice modes called intrinsic localized modes in the NaI single crystal lattice by UV excitation of the impurity electronic states of Tl+ substitution centers. Comparison of low-temperature phonon density of states measured by inelastic neutron scattering with and without simultaneous UV illumination of the sample did not reveal significant difference. Results are discussed in the context of possible improvements of the proposed experiment.