Electronic structure of polycrystalline polyamine copper dinitrate complexes investigated by photoacoustic and electron paramagnetic resonance spectroscopy N.Guskos, G.J.Papadopoulos, V.Likodimos, J.Majszczyk, J.Typek, M.Wabia, E.Grech, T.Dziembowska, A.Perkowska, K.Aidinis Journal of Applied Physics 90 (3), 1436 (2001)