Absorption and luminescence in PbCl2: I− crystals

The absorption and luminescence on PbCl2: I− crystals were investigated at 6 K by varying the amount of I− ions. In PbCl2: I−, additional absorption bands were observed at 3.99 and 4.15 eV in the energy region lower than the fundamental absorption edge. The absorption coefficient of these bands is proportional to the concentration of I− ions in the crystal, and thus they are attributed to the absorption due to I− ions. The energy separation from the excitonic absorption band of PbCl2 would be mainly related to the difference in electron affinity between chlorine and iodine. Optical excitation in the additional absorption band at 3.99 eV produces a luminescence band peaking at 2.26 eV.It is likely that this band originates from the relaxed state of a localized exciton due to the I− ion.