  Despite decades of research, demonstration of all-optical detection and
control of free electron spins in silicon remains elusive. Here, we directly
probe the electron spin properties in bulk silicon by measuring the
polarization of luminescence following circularly polarized light excitation.
The experiments performed for both direct and indirect gap excitation allow not
only an experimental determination of the optical selection rules in silicon
for the different phononassisted transitions but they also lead to the
measurement of the spin relaxation of electrons in conditions which are not
accessible using transport techniques. We also measure the spin properties of
free excitons in bulk silicon, a very little explored field.
