The temperature drops of the photon echo intensity at the resonance tr
ansition P-3(0) - H-3(4) and 1D2 - H-3(4) of the Pr3+ ion are for the
first time studied in the low symmetry impurity crystal Y2SiO5:Pr3+ in
the temperature region 4.2 to 20 K. It is shown that the results obta
ined cannot be interpreted on the basis of known mechanisms of optic t
ransition dephasing in impurity atoms.