The major challenges faced by magnetic–luminescent bi-functional nanoparticles include poor luminescence intensity and severe magnetic–luminescence quenching. Introduction of an intermediate layer with localized surface plasmon resonance (LSPR) effects in magnetic–luminescent bi-functional nanoparticles plays a major role in solving these challenges. Herein, a fascinating process of plasmonic energy conversion in Fe₃O₄@WO₃@GdF₃:Eu³⁺ heterostructures, which can enhance the luminescence by LSPR effects of WO₃, is demonstrated. It is proposed that the LSPR of WO₃ is the primary reason for the enhanced luminescence of Fe₃O₄@GdF₃:Eu³⁺. Moreover, saturation magnetization did not significantly decline on introducing WO₃ with LSPR effect. This research conclusion can solve the problems faced by magnetic–luminescent bimodal imaging materials and promote the application of this type of composite materials in tumor therapy and optical confocal microscopy technology.