  We apply polarization resolved photoluminescence spectroscopy to measure the
spin polarization of a two dimensional electron gas in perpendicular magnetic
field. In the vicinity of filling factor nu=5/2, we observe a sharp
discontinuity in the energy of the zero Landau level emission line. We find
that the splitting between the two circular polarizations exhibits a sharp drop
at nu=5/2 and is equal to the bare Zeeman energy, which resembles the behavior
at even filling factors. We show that this behavior is consistent with filling
factor nu=5/2 being unpolarized.
