A luminescent Ln-CP film of [Tb₂(BDC)₃(H₂O)₄]_n (1) [BDC: p-Benzenedicarboxylate anion] is fabricated using electrodeposition method on FTO (fluorine-doped tin oxide glass). It is a one-step and highly effective electrochemical method at room temperature. The influence of reaction conditions on the thickness of film 1 was investigated. A smooth and adherent thin film 1 is obtained at the appropriate concentrations of Tb(NO₃)₃ (0.01 M) and H₂BDC (0.015 M) with 0.3 mA cm⁻² (0.050 M NH₄NO₃) for 20 minutes. The composition of the film was confirmed by X-ray diffraction. The sensing properties of the film have been studied. The results show that thin film 1 exhibits selective detection of Cu²⁺ in DMF solution. The luminescent intensity is inversely proportional to the concentration of Cu²⁺ ions and displays a linear region over the range of 1 × 10⁻⁵ −1 × 10⁻³ M. Furthermore, a probable quenching mechanism is discussed.