  We show that effectively cold metastable states in one-dimensional
photo-doped Mott insulators described by the extended Hubbard model exhibit
spin, charge and $\eta$-spin separation. Namely, their wave functions in the
large on-site Coulomb interaction limit can be expressed as $|\Psi\rangle
=|\Psi_{\rm charge}\rangle|\Psi_{\rm spin}\rangle |\Psi_{\rm
\eta-spin}\rangle$, which is analogous to the Ogata-Shiba states of the doped
Hubbard model in equilibrium. Here $\eta$-spin represents the type of the
photo-generated pseudeparticles (doublon or holon). $|\Psi_{\rm charge}\rangle$
is determined by spinless free fermions, $|\Psi_{\rm spin}\rangle$ by the
isotropic Heisenberg model in the squeezed spin space, and $|\Psi_{\rm
\eta-spin}\rangle$ by the XXZ model in the squeezed $\eta$-spin space. In
particular, the metastable $\eta$-pairing and charge-density-wave (CDW) states
correspond to the gapless and gapful states of the XXZ model. The specific form
of the wave function allows us to accurately determine the exponents of
correlation functions. The form also suggests that the central charge of the
$\eta$-pairing state is 3 and that of the CDW phase is 2, which we numerically
confirm. Our study provides analytic and intuitive insights into the
correlations between active degrees of freedom in photo-doped strongly
correlated systems.
