Resonant Secondary Emission and Its Excitation Energy Dependence in Monoclinic Zinc Diphosphide

Abstract

Resonant secondary emission of monoclinic zinc diphosphide (β-ZnP 2 ) has been investigated in detail under excitation into the energy range from the interband to the exciton-bands region. In addition to the 1LO line of 32.2 meV already reported, we have found more than 30 resonant Raman lines ranging from 9.4 meV to 58.9 meV by varying the excitation energy. These lines are observed distinctly when their scattered energies fall into the vicinity of the 1s exciton energy. It is confirmed that among phonons of 72 modes the LO phonon of 32.2 meV preferentially governs the relaxation processes of exciton polaritons in β-ZnP 2 . We have also observed a significant intensity decrease of the exciton polariton luminescence when the excitation energy is lowered across the 1s longitudinal exciton energy E L . A brief discussion is made in this connection.