A New Luminescence under High-Density Excitation in PbI2 Possibly Due to a Self-Trapped Excitonic Molecule

A new luminescence band has been found in the temperature range from 40 to 80 K under high-density excitation of 2H-PbI 2 . The decay time of this luminescence at 58 K is about 400 ps, which is twice as large as that due to the excitonic molecule, and both the Stokes shift and the half-width are about 0.01 eV. These experimental facts suggest that the new luminescence comes from radiative annihilation of the self-trapped excitonic molecule leaving the exciton in the distorted lattice.