We report on an observation of the luminescence and luminescence excitation spectra of platinum dimers in an argon matrix. Samples were produced by sputtering from a metal target, followed by mass selection of dimer ions and codeposition with electrons and argon on a cold substrate. Emission is induced by Dumping into the 800-815 nm region with a titanium-sapphire laser. Five sharp, intense spectral lines are observed, with an average spacing of 197.4 +/- 3.3 cm(-1) and origin at 10 730.5 +/- 0.6 cm(-1). A much weaker vibrational progression in the emitting state gives omega(e)' = 179.2 +/- 0.6 cm(-1). Fluorescence excitation profiles were also obtained and are well simulated using data from previous gas-phase measurements. A rather wide separation of the origins of excitation and emission indicates rapid intersystem crossing in the excited state, with the possibility that our emission is not to the dimer ground state.