A systematic and comparative study of luminescence and optical absorption properties of the trivalent rare earth neodymium ion in the Bi4Ge3O12 and Bi12SiO20 crystal lattices is presented. The incorporation of Nd3+ ions into these crystals is more easily achieved in the first one than in the latter. In both matrices their intrinsic emission gives rise to a radiative energy transfer between the host and the impurity ion. On the other hand most of the Stark energy levels have been identified for both matrices. A calculation of the Ω2, Ω4 and Ω6 Judd-Ofelt parameters is given for each crystal. © 2001 Elsevier Science B.V.