Two sets of AlN/AlxGa1-xN quantum wells (QW) have been grown by metalorganic chemical vapor deposition (MOCVD). The first set consists of five samples of AlN/AlxGa1-xN QWs with (x - 0.65) with well width, Lw, varying from 1 to 3 nm. The second set consists of four samples of AlN/AlxGa1-xN with (U = 1.5 nm) with Al composition, x, varying from 0.70 to 0.85. Low temperature photoluminescence (PL) spectroscopy has been employed to study the Lw dependence of the PL spectral peak position, emission efficiency, and line width. Our results have shown that these AlN/AlGaN QW structures exhibit polarization fields of - 4 MV/cm. Due to effects of quantum confinement and polarization fields, AlN/AlGaN QWs with Lw between 2 and 2.5 nm exhibit the highest quantum efficiency. The dependence of the emission linewidth on Lw yielded a linear relationship. The implications of our results on deep ultraviolet (UV) optoelectronic device applications are also discussed.