A two-dimensional luminescent cadmium(II) coordination polymer, [Cd(modbc)₂]_n (Cd-P); modbc = 2-methyl-6-oxygen-1,6-dihydro-3,4′-bipyridine-5-carbonitrile, was successfully synthesized by a solvothermal reaction and fully characterized. Cd-P exhibited excellent luminescence emission, and detected Cu²⁺, Co²⁺, Fe²⁺, Hg²⁺, Ni²⁺ and Fe³⁺ ions with high sensitivity and showed good anti-interference performance. After encapsulation of Tb³⁺ ions in Cd-P, the as-obtained fluorescent functionalized Tb³⁺@Cd-P maintained distinct chemical stabilities in different pHs and metal salt solutions. Subsequently, we explored the potential application of Tb³⁺@Cd-P as a probe for Fe³⁺ ions. A new and convenient method for individual identification of Fe³⁺ ions by the combination of Cd-P and Tb³⁺@Cd-P was successfully established. A possible sensing mechanism is discussed in detail.