Electron structure and exciton energy level of HgI2, CH3NH3HgI3 and (CH3NH3)2HgI4

Abstract

The electronic structures and exciton properties of HgI2, CH3NH3HgI3 and (CH3NH3)2HgI4 are reported. Compared with HgI2, organic-inorganic hybrids CH3NH3HgI3 and (CH3NH3)2HgI4 have lower dimension and higher band gap, which show significant excitonic properties. The effective masses of electrons and holes of these three materials were predicted by their energy band structures. Their exciton binding energy at room temperature therein was calculated to be 13.77, 166.81, and 256.00 meV, respectively. HgI2 has low exciton binding energy that cannot exist stably, while CH3NH3HgI3 and (CH3NH3)2HgI4 have strong charge localization and high exciton binding energy. In addition, the UV–vis diffuse reflectance spectra reveal the presence of exciton absorption in CH3NH3HgI3 and (CH3NH3)2HgI4, and the exciton energy levels is confirmed by combining the diffuse reflectance spectra with its exciton binding energy. Importantly, the exciton luminescence peaks of CH3NH3HgI3 and (CH3NH3)2HgI4 were observed at 468 nm and 419 nm in their photoluminescence spectra at room temperature, respectively. This indicates that CH3NH3HgI3 and (CH3NH3)2HgI4 have strong exciton properties and are potential candidates for high-light-yield scintillators and light-emitter applications.