Information obtained from optical absorption, excitation, and emission experiments on erbium doped crystalline CsCdBr3 is analyzed, using a semiempirical Hamiltonian, to calculate atomic and crystal-field interaction parameters and electronic state wave functions. A majority of the Er3+ ions substitute at a Cd2+ site giving C-3 upsilon point group symmetry and forming and Er3+ ion dimer center. This dimerization, together with the material’s low phonon energies, and the specific positioning of states in the Er3+ (4f(11)) configuration, produce the interesting and useful emission properties of the material. Comparisons are made with other erbium halide crystals, and interaction parameter and energy-level results for Nd3+ : CsCdBr3 are also presented. The inclusion of second order correlation crystal-field interaction parameters is shown to be essential for accurately characterizing splittings of several J multiplets important in visible emission pathways.