Graphene-mediated enhanced Raman scattering and coherent light lasing from CsPbI3 perovskite nanorods

Graphene-enhanced Raman scattering has been studied as an optical technique related to the selective electron transfer from graphene to the valence band of the contacted molecule, inducing a pileup of electrons within the conduction band and a “photogating effect” for subsequently illuminated light. Herein, we studied the Raman spectroscopy of CsPbI3 nanorods sandwiched between two layers of graphene, revealing that weak coherent lasing also occurs. The photoluminescence intensity of α-phase CsPbI3 nanorods drastically decreased with increasing graphene coverage, particularly on the top, leading to Raman modes at the first (~241 and ~312 cm−1) and second (~640 cm−1) overtones of polymeric iodides, as well as at ~3492 cm−1. First-principle calculations reveal that the ~3492-cm−1 mode originates from the stimulated coherent light emissions of the highly populated electrons accumulated in the CsPbI3 conduction band, which form because of the electronic resonance induced in the Pb and I degenerate states.