  The photoluminescence (PL) spectrum of a two-dimensional electron gas (2DEG)
in the fractional quantum Hall regime is studied. The response of the 2DEG to
an optically injected valence hole depends on the separation d between the
electron and hole layers. At d smaller than the magnetic length lambda, the PL
spectrum shows recombination of neutral (X) and charged (X-) excitons. At
d>lambda, the hole binds one or two Laughlin quasielectrons (QE) of the 2DEG to
form fractionally charged excitons (FCX), hQE or hQE2. Different FCX states
have different optical properties, and their stability depends critically on
the presence of QE's in the 2DEG. This explains discontinuities observed in the
PL spectrum at such (Laughlin) filling factors as nu=1/3 or 2/3.
