Phonon Structures in Absorption and Emission on Spectra of Pb⁺⁺ Doped CdI₂ Single Crystal at 10°K

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Optical properties of Pb⁺⁺ ion doped CdI₂ crystal having the layer structure have been studied at low temperature. Absorption spectrum consists of two narrow bands at 3860A and 3830A which are active for E⁄⁄C and E⊥C, respectively. These bands are assigned as due to the allowed transitions from the A_1g ground state to the excited A_2u and E_u states of Pb⁺⁺ ion in the crystal field of D_3d symmetry. Emission spectrum consists of two narrow bands at 3900A and 3970A and a broad band at 5180A. The 3900A band emission is polarized parallel to the C-axis. The narrow emission bands have the mirror image relations with absorption bands. Both emission and absorption bands show the complex phonon structures. The main phonons relevant to the structures have energies 16, 49, 64, 70 and 100cm⁻¹ and the last one appears most prominently.