Er3+- and Yb3+-doped yttrium calcium oxoborate Er:Yb:YCa4O(BO3)(3) (Er:Yb:YCOB) crystallizes with a fluorapatite-type structure in the monoclinic system. Its lattice vibrational modes were calculated by using space group theory, and Raman spectra were measured at room temperature with different scattering geometry projects. The experiments show that the characteristic lattice vibrational modes of Er:Yb:YCOB crystal arise mainly from the internal vibrations of the BO3, CaO6, and YO6 groups. The three-dimensional network structure of Er:Yb:YCOB crystal is identified, and its excellent nonlinear optical (NLO) properties are mainly attributed to the BO3 clusters that connects all the distorted YO6 and CaO6 octahedral clusters together. The combination of the strong absorption at 976 nm and the strong emission at 1537 nm makes this material very promising for use in an infrared laser system. (C) 2002 Elsevier Science B.V. All rights reserved.