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The crystal structures, electronic structures, and optical properties of Y-doped gamma-Si3N4 were studied by using first-principles calculations based upon the density functional theory with Perdew-Burke-Enzerh (PBE) generalized gradient approximation (GGA). The band gap (E-g) of Y-doped gamma-Si3N4 is found to significantly decrease in comparison to that Of gamma-Si3N4. The calculated E-g suggests that gamma-Si3N4 doped with low Y content can be used in the window or absorption material of solar cell, while those doped with high Y concentrations can show metal behavior. The calculation of optical properties shows that the static dielectric constant of gamma-Si3N4 doped with Y is much higher than that of the undoped gamma-Si3N4, implying its special applications in electronics and optics. (C) 2008 Elsevier B.V. All rights reserved.