A new emission, broad and structureless, centered at 260 nm is observed by exciting Ar matrices containing 1% O-2 and similar to 0.2% pyrene at 183 nm (5(1)B(2u) <-- 1(1)A(g) transition in pyrene). The excitation spectrum measured by monitoring the emission at ?260 nm is identical with the excitation spectrum measured by monitoring the fluorescence of pyrene itself at 366.8 MI (1(1)B(2u) --> 1(1)A(g) transition in pyrene). We assign this new emission at 260 nm as being due to an exciplex of charge-transfer nature between pyrene and O-2.