  It is usually assumed that when performing a photoluminescence experiment on
a microcavity containing an inhomogeneously broadened quantum dots ensemble,
the cavity mode appears as a positive peak with a linewidth that reflects the
mode quality factor Q. We show in this article that this conclusion is in
general not true, and that the measured mode linewidth depends strongly on the
excitation power for microcavities having large Purcell factors. We analyze
theoretically this effect in the case of the micropillar cavity and we show
that the same microcavity can give rise to a large variety of photoluminescence
spectral signatures depending on the excitation power and collection set-up. We
finally give guidelines to measure the real cavity quality factor by
photoluminescence.
