[en] Fluorescence spectroscopy was used to study the Ca²⁺/UO₂²⁺/CO₃^2- solution system at different ionic strengths. Fluorescent titrations confirmed formation of Ca₂UO₂(CO₃)₃ complex for which the values of log β₂₁₃ were measured at 0.1, 0.3, 0.7, 1.0 and 3.0 m (NaClO₄) at pcH = 8.1. Specific interaction theory (SIT) was used to correlate the log β₂₁₃ values as a function of ionic strength. The value obtained for log β₂₁₃⁰(I = 0) wsas 29.8 ± 0.7, indicating that Ca₂UO₂(CO₃)₃ was the predominant specie at the pH 8 in calcium rich, oxic waters. (orig.)