(Lu0.995-xMxCe0.005)(2)SiO5 (M=Li, Mg and Sc, x=0.00-0.01) phosphors were synthesized via a sol-gel technique, the luminescence enhancement effect by Li+, Mg2+, or Sc3+ codoping is comprehensively investigated by XRD, Raman, thermoluminescence and X-ray absorption near edge structure (XANES) spectra. The underlying reason of enhanced luminescence by ion codoping is revealed, and a mechanism of the luminescence enhancement effect based on the valence state variation of cerium is proposed. It can be safely concluded that the enhanced luminescence of Lu2SiO5:Ce3+ by ion codoping essentially originates from the increase in the population of Ce3+, which is directly proved by XANES. The difference in luminescence enhancement effect for different codopants can be reasonably explained by the electronegativity of the codopant. (C) 2015 Elsevier B.V. All rights reserved.