Effect of Internal Magnetic Field on the Optical Spectra of Sm³⁺ Ion in TbPO₄, YPO₄ and Their Mixed Crystals

Abstract

The emission and excitation spectra and their polarization properties of Sm³⁺ ion doped as a probe ion in Tb_1−xY_xPO₄ (x=0−1) crystals were investigated. Some of Kramers’ doublet states of Sm³⁺ ion which is degenerate in YPO₄ is split in TbPO₄. The ⁴G_5⁄2↔⁶H_5⁄2 transition was investigated in detail as a typical case. The separation between split states becomes gradually smaller with raising temperature, but the splitting remains even up to 200°K. It is concluded that this splitting is caused by the magnetic interaction between an Sm³⁺ ion and Tb³⁺ ions, and that it is due to the short range ordering and probably of the exchange type. The manners of the change of the polarization properties as well as of the separation width with Tb³⁺ concentration can be explained well with the assumption that the internal magnetic field has the parallel and perpendicular components both increasing in proportion to Tb³⁺ concentration.