Abstract The Ce(III) ion shows luminescence in many solids and in solution, but sometimes the luminescence is unexpectedly absent. Examples are La 2 O 3 :Ce(III),La 2 O 2 S:Ce(III), and the recently reported complexes of Ce(III) with carboxylate-containing ligands. This paper tries to find a general approach to the non-radiative transitions in a diverse series of Ce(III)-containing samples. It turns out that Ce(III) luminescence will appear if the optical absorption of its surroundings is at high energy, preferentially in the vacuum ultraviolet. If the absorption is at lower energy, photoionisation or electron transfer may quench the luminescence.