Abrasive is one of the most important factors in chemical mechanical polishing (CMP). In order to improve the polishing qualities of sapphire substrates, the novel Nd3+-doped colloidal SiO2 composite abrasives were prepared by seed-induced growth method. In this work, there were a series of condensation reactions during the synthesis process of Nd3+-doped colloidal SiO2 composite abrasives and the silica cores were coated by shells (which contains SiO2, Nd2Si2O7 and Nd(OH)(3)) via chemical bonds and hydrogen bonds in the Nd3+-doped colloidal SiO2 composite abrasives, which made the composite abrasives core-shell structure more sTable Scanning electron microscopy (SEM) showed that Nd3+-doped colloidal SiO2 composite abrasives were spherical and uniform in size. And the acting mechanisms of Nd3+-doped colloidal SiO2 composite abrasives on sapphire in CMP were investigated. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) analysis and X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the solid-state chemical reactions between the shells (which contained SiO2, Nd2Si2O7 and Nd(OH)(3)) of Nd3+-doped colloidal SiO2 composite abrasives and the sapphire occurred during the CMP process. Furthermore, Nd3+-doped colloidal SiO2 composite abrasives exhibited lower surface roughness and higher material removal rate (MRR) than the pure colloidal SiO2 abrasives in the same polishing conditions, which was attributed to the solid-state chemical reactions between shells of Nd3*-doped colloidal SiO2 composite abrasives and sapphire. (C) 2017 Published by Elsevier B.V.