We report on the comparative studies of photoluminescence (PL) properties of molecular beam epitaxy grown dilute InAsN epilayers with and without antimony (Sb) flux during the growth. Both samples exhibit strong midinfrared (MIR) emission at room temperature, while the sample with Sb flux has much higher intensity. At low temperatures, these samples exhibit totally different PL features in terms of line width, peak position, intensity, and their dependences on temperature and excitation density. Our results clearly indicate that part of Sb atoms serve as a surfactant that effectively improves the optical quality of MIR dilute nitrides.