The optical absorption spectrum of Ni²⁺ ion doped in lecontite (sodium ammonium sulphate dihydrate) single crystal has been studied at room and liquid air temperatures. All the bands could be assigned assumingO_h symmetry for the Ni²⁺ ion in the crystal. The splitting of³T_1g (F) band at liquid air temperature has been attributed to spin-orbit interaction. The crystal field and spin-orbit parameters derived areD_q=1000 cm⁻¹;B=740 cm⁻¹;C/B=4.27 and ζ=600 cm⁻¹. All the bands observed show a blue shift when the crystal was cooled to liquid air temperature.

The true potential energy curves for some electronic states of CuF, CuO, CuSe and CuTe molecules have been constructed by the method of Lakshman and Rao (RKR method as modified by Lakshman and Rao). The ground-state dissociation energies evaluated by the method of curve fitting using the H-H function agree well with the values reported earlier. Ther-centroids and Franck-Condon factors for various band systems of the above diatomic molecules have been computed.

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.