Luminescence from size-quantized exciton states of PbI2

We have measured bound exciton luminescences from PbI2 microcrystallites in the shape of a platelet embedded into E-MAA copolymer at 4.2 K. An energy shift of the bound exciton from the free exciton increases as the thickness of the crystallite decrease, and amounts to 51 meV in the crystallite with a monolayer, which is about seven times as large as that of the bulk crystal. This fact strongly suggests that the binding energy of the free exciton becomes larger both for the size confinement and dielectric screening effects.