Photoluminescence (PL) of a Sm ³⁺-doped (~0.2 at%) AlN thin film is studied and compared to an undoped film. Being deposited by radio frequency magnetron sputtering, the films demonstrate a high-quality surface morphology, good crystallinity and even elemental distribution, although they appear to be oxygen-rich (AlN _0.9O _0.1). The Sm ³⁺-doped film emits a bright orange-red light at UV excitation. In the PL spectrum, a set of line bunches characteristic of Sm ³⁺ is found: the most intense ones at 580, 621 and 660 nm are identified to be due to radiative transitions from the excited Sm ³⁺ level ⁴G _5/2 to the ground ones ⁶H _5/2, ⁶H _7/2 and ⁶H _9/2, respectively. The PL excitation spectrum, being a broad band below 270 nm with shoulders at ~280–330 and 330–390 nm, demonstrates no characteristic lines of resonant Sm ³⁺ pumping. So, the rare-earth PL is sensitized by AlN-O defects and oxygen centers or Sm ³⁺-O ² …