We report on the photoluminescence (PL) of erbium-implanted polycrystalline thin films of AlN. These films were grown by metal-organic chemical vapor deposition on Si substrates. The PL intensity of Er:AlN is compared to the PL of Er in GaN, Si3N4 and SiO2. The strongest PL is observed for Er:Si3N4 , followed by Er:AlN, Er:GaN and Er:SiO2. It is suggested, that the intrinsic radiative lifetime of Er:Si3N4 is the shortest amongst the investigated samples. Electroluminescent devices from all these systems were fabricated, but their performance was very sensitive to the material quality and defect structure of the thin films, impeding a direct comparison of the results.