  The spin dynamics of electron doped Mott insulators on a triangular lattice
is studied based on the $t-J$ model. It is found that the particularly
universal behaviors of integrated dynamical spin structure factor seen in the
doped Mott insulators on a square lattice, are absent in the doped Mott
insulators on a triangular lattice, indicating the presence of the normal state
gap. As a result, the spin-lattice relaxation rate 1/$T_{1}$ divided by $T$
reduces with decreasing temperatures in the temperature region above
0.2$J$$\approx$50K, then follows a Curie-Weiss-like behavior at the temperature
less than 50K, in qualitative agreement with experimental observations.
