Charge transfer and f-f transitions studied by photoacoustic spectroscopy of [R(NO3)(2)(PicBH)(2)]NO3 and [R(NO3)(3)(PicBH)(2)] complexes (R-rare earth ion) Guskos N, Papadopoulos G, Majszczyk J, Typek J, Wabia M, Likodimos V, Paschalidis DG, Tossidis IA, AidinisC ActaPhysicaPolonicaA103 (2-3): 301-313 (2003)