Huge exchange energy and fine structure of excitons in an organic-inorganic quantum well material

Photoluminescence and spin-flip Raman scattering of excitons in an organic-inorganic quantum well material ${({\mathrm{C}}_{4}{\mathrm{H}}_{9}\mathrm{N}{\mathrm{H}}_{3})}_{2}\mathrm{Pb}{\mathrm{Br}}_{4}$ have been investigated at low temperature. The estimated exchange energy of the exciton is greatly enhanced by strong confinement and by image charge effects, and ranges from $28\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}32\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. These values are one or two orders of magnitude larger than those for quantum wells made from the more usual inorganic materials. The ratio of the oscillator strength of the dipole-allowed exciton to that of the dark (dipole-forbidden) exciton is estimated to be of order 800.