Low luminescence efficiency of rare-earth ions doped upconversion (UC) nanomaterials is still a major limitation for their applications. Here, based on bismuth oxychloride nanosheets that show efficient photocarriers separation due to combining spontaneous polarization and layered semiconductor, we report a new carbon heterovalent doping strategy for efficient UC luminescence enhancement by suppressing the intermediate excited states of Er3+ ions. The first-principles calculations and photoelectrochemical characterizations provide evidences that the replacement of C ions for Cl strengthen the spontaneous polarization and inter electric field (IEF) of bismuth oxychloride nanosheets, which further improve the photocarriers separation efficiency. Under 808 or 980 nm excitation, the emission intensity of I-4(13/2) energy level of Er3+ ions (1550 nm) increase slightly with C doping, but the its decay time and the visible UC emission are improved tremendously at the same time. We show that the recombination rate of intermediate excited state electrons of Er3+ ions with the ground state is inhibited by the enhanced IEF, which promotes the energy reabsorption transition to upper energy levels, thus enhancing the visible UC emission. This work not only may provide a new insight into the method for engineering of UC emissions but also deepen the understanding for layered semiconducting material to modify the transition of Lanthanide ions. (C) 2020 Elsevier Inc. All rights reserved.