Precise photoluminescence measurements have been carried out on RbCdF₃:Mn²⁺ in the 9-300 K range to explore the structural phase transition of the host lattice at T_c=124 K using the first (M₁) and second (M₂) moments of the emission band together with the lifetime tau as probes. Aside from showing a sensitivity of M₂(T) and tau (T) to the phase transition, the present data reveal that the curve M₁(T) experiences a small but observable change of slope in the vicinity of T_c. It is demonstrated that this jump, Delta _t( delta M₁/ delta T)_P=0.22 cm^-1 K^-1, is mainly associated with the increase experienced by the local thermal expansion coefficient below T_c. The importance of both the implicit and explicit contributions to M₁(T) is analysed throughout this work. Neither the luminescence nor the excitation spectrum shows any evidence of tetragonal distortion in the MnF₆^4- complex. This fact is explained through the R_ax-R_eq=0 2 pm value (where R_ax and R_eq are the axial and equatorial Mn²⁺-F^- distances) at 30 K, and the coupling coefficient V_E=66 cm^-1 pm^-1 with the E_g Jahn-Teller mode of MnF₆^4-. Finally, we have found that this crystal exhibits photochemical reactions under UV light irradiation, leading to the formation of centres that transfer easily to Mn²⁺ ions. These centres give rise to an intense absorption band at 310 nm, analogously to those previously formed under x-irradiation.