The steady-state and time-resolved photoluminescence of nine ternary solid solutions, whose general formula is La2xGa2yIn2zO3, used as heterogeneous photocatalysts for the production of hydrogen by water splitting, has been investigated in order to characterize the properties of their electronic excited states. The comparison with the parent binary oxides (LaGaO3, LaInO3 and GaInO3) proved to be essential for understanding the composition of the solids in terms of phases and allowed the different emissions to be assigned to specific crystal structures and band gap transitions. Upholding what was previously deduced by means of the X-ray powder diffraction and micro-Raman techniques, the structural properties of the La2xGa2yIn2zO3 samples were corroborated. By doing so, the employment of photoluminescence as a distinctive feature to strengthen the structural information gathered by other techniques is demonstrated. Moreover, the luminescence lifetimes of the photo-generated electron–hole pairs were measured and analyzed in view of the photocatalytic activity of the samples, with their efficiency being directly proportional to the excited state lifetime. Finally, the metal oxides solid solutions have been found able to emit over the entire visible region up to near-IR. Therefore, they might be appealing panchromatic emitters for display and lightning technologies. •The photoluminescence is useful to gain insight on structural composition of solid solutions.•Determination of electronic lifetimes by both Least-Squares and Maximum Entropy method.•Direct electronic transitions last less than indirect phonon-assisted transitions.•La2xGa2yIn2zO3 are promising panchromatic emitters.•La2xGa2yIn2zO3 have lifetimes ranging from tens of μs up to tens of ms.