Emission Mossbauer (nuclear gamma-resonance) spectra of237Np resulting from the alpha-decay of241Am in solid solutions AmO2−ThO2 and AmO2−UO2 prepared by precipitation from LiF−NaF eutectic melts under fluorine-oxygen exchange were first investigated in the temperature range from 77 to 296 K. The resonant absorbers are NpO2 and NpAl2. The possibility is stated of managing the form of the emission Mossbauer spectra of237Np in dioxides by the directed change of the matrix stoichiometry or by its irradiation by visible light. At temperatures from 77 to 230 K the authors measured for the first time the NGR absorption spectra of237Np in solid solution NpO2−ThO2 with various concentrations of neptunium dioxide. An increase of the absorption line width (approximately by a factor of 4) with a decrease in the NpO2 contents (to 10 mol.%) was explained by the influence of fast electron exchange between Np4+ and Np5+ states observed in the NpO2−ThO2 solid solution at low concentrations of neptunium dioxide.