Deep ultraviolet (UV) photoluminescence (PL) spectroscopy has been employed to study deep impurity transitions in Alx Ga1-x N (0≤x≤1) epilayers. Two groups of deep impurity transitions were observed, which are assigned to the recombination between shallow donors and two different deep level acceptors involving cation vacancies (Vcation) and Vcation complexes in Alx Ga1-x N alloys. These acceptor levels are pinned to two different energy levels common to Alx Ga1-x N alloys (0≤x≤1). The deep impurity transitions related with Vcation complexes were observed in Alx Ga1-x N alloys between x=0 and 1, while those related with Vcation were only observed in Alx Ga1-x N alloys between x=0.58 and 1. This points out to the fact that the formation of Vcation is more favorable in Al-rich AlGaN alloys, while Vcation complexes can be formed in the whole range of x between 0 and 1. The implications of our findings to the UV optoelectronic devices using AlGaN alloys are also discussed.