The localized surface plasmon resonance (LSPR) behavior of indium-doped ZnO (IZO) nanocrystals synthesized in different solvents was studied. 1-octadecanol, oleic acid, oleyl alcohol, oleyl amine and 1-octadecene were used as solvent(s) and co-solvent(s) in the pyrolysis synthesis of indium-doped ZnO (IZO) nanoparticles. The results showed that the nanocrystals from a solvent system consisting of 1-octadecene, 1-octadecanol, and oleic acid exhibited enhanced LSPR near-infrared radiation absorption without sacrificing transparency in the visible region. The indium-rich core verified using ICP and XPS analysis was shown to be critical for the enhancement. The reaction mechanism of solvents on the generation of indium-rich core was elucidated through a systematic study of the reaction parameters. The interaction between the activating agent, inhibiting agent and solvent, and their effect on tuning the reactivity of dopant and host precursors were important for the formation of a nanostructure with a dopant-rich core. The solvent effect was also found in the synthesis of gallium-doped ZnO and confirmed to be a general phenomenon in the preparation of doped ZnO nanoparticles.