A new luminescence due to an exciton–exciton collision process in lead iodide induced by two-photon absorption

Photoluminescence properties of highly excited lead iodide have been investigated through two-photon absorption for band-to-band transitions at low temperature and a new luminescence band is observed. The intensity of the new luminescence band increases as 4th power of the excitation intensity and the peak energy is about 23 meV lower than the lowest exciton energy, whose value is almost equal to the energy difference between the n=1 and 2 excitonic states of lead iodide. These results indicate that the new luminescence band observed originates from an exciton–exciton collision process, in which one of the two excitons scatters into the n=2 excitonic state and the other radiatively recombines.