Optical absorption of Er³⁺ ion in Er(NO₃)₃·5H₂O, NH₄NO₃, Mg(NO₃)₂·6H₂O, KNO₃ and NaNO₃ complexes has been studied. The second derivative spectra of these Er³⁺ complexes exhibited splittings in the⁴I_9/2,⁴F_9/2,⁴F_7/2,⁴F_5/2 and²H_9/2 levels. These splittings have been tentatively explained as due to a cubic crystalline field. The partial derivatives for Er³⁺ ion have been calculated in terms of Racah (E^k) parameters. The results of a least squares fit of the energy levels and oscillator strengths of the bands are reported in terms of interaction parameters and Judd-Ofelt parameters. Radiative transition probabilities for various fluorescence levels are theoretically estimated. The lifetime of the⁴G_11/2 level is found to be lowest in all nitrate complexes.