Er³⁺-doped multicomponent RE₂Zr₂O₇ (RE = Y, Lu, Gd, La, and Yb) ceramics with tailored non-equimolar ratios were synthesised via combustion synthesis to explore whether configurational entropy influences their photoluminescent properties. The compositions located near the pyrochlore–defect fluorite boundary showed slight structural deviations related to cation-size effects. In contrast, compositions designed to stabilise the defect fluorite structure were readily obtained as single-phase ceramics after sintering at 1650 °C for 4 h in air and served as high, medium, and low entropy model systems. Their photoluminescent properties indicate that increasing configurational entropy is closely associated with enhanced down-shifting and up-conversion emission compared with the low entropy control sample. These results demonstrate that entropy-guided compositional design enables robust stabilisation of the defect fluorite structure and provides an effective route for improving luminescent performance of Er-doped RE₂Zr₂O₇ ceramics.