Ion–Ion and Ion–Lattice Interactions in the Optical Spectra of YbPO4Crystal

Abstract

At least nine very sharp lines are observed close to the optical transition between the ground state 2 F 7/2 and the lowest excited state 2 F 5/2 of 4f-electrons of Yb 3+ ions in the emission and excitation spectra of YbPO 4 crystal at low temperatures. It is shown that each line is associated with an excited Yb 3+ ion or a localized (Frenkel type) exciton connected to an entity located at the distance corresponding to each line. The lattice vibration of this crystal interacts strongly with 4f-electrons of Yb 3+ ions, resulting in intense vibronic lines in the absorption spectra and in broadened and deformed lines in the emission spectra even at low temperatures. In contrast, a spectral line at 300 cm -1 in the Raman spectra, which is due to the rotational vibration of the tetrahedral PO 4 molecular complex, is split at low temperatures and broadened with increasing temperature by the interaction with 4f-electrons of Yb 3+ ions.