  We present an inelastic neutron scattering study of the low energy
crystal-field excitations in the lightly doped cobalt perovskite
La_0.998Sr_0.002CoO_3. In contrast to the parent compound LaCoO_3 an inelastic
peak at energy transfer ~0.75 meV was found at temperatures below 30 K. This
excitation apparently corresponds to a transition between a ground state
orbital singlet and a higher excited orbital doublet, originating from a
high-spin triplet split by a small trigonal crystal field. Another inelastic
peak at an energy transfer ~0.6 meV was found at intermediate temperatures
starting from T > 30 K. This confirms the presence of a thermally induced
spin-state transition from the low-spin Co^3+ to a magnetic high-spin state in
the non-disturbed LaCoO_3 matrix. We suggest that hole doping of LaCoO_3 leads
to the creation of a magnetic polaron and hence to the low-to-high spin state
transition on the relevant Co sites.
