Knowledge Bank

The optical absorption and fluorescence spectra of the paramagnetic rare-earth ion $Tb3+$ in $TbPo4$, were recorded. The spectra show that this ionic insulator orders antiferromagnetically below $TN=2.2$K. The parameters of the crystal-field Hamiltonian for the $Tb3+$ in $TbPO4$ could be determined. With these parameters a classical expression was derived for the electrical crystal-field energy as a function of the orientation ($\theta ,\phi$) of the magnetic moments in the magnetically ordered state.