Oxygen-free strontium fluoride crystals containing single monovalent silver ions in a cubic site were grown. Our experiments showed that the Ag+ ion remained chemically stable upon optical irradiation at 222 nm (KrCl excimer). The ion exhibits a strong UV luminescence which presents no thermal quenching up to RT. At this temperature, the emitting level time-constant is 12 μs. An explanation is proposed for the silver photostability by relating it to the large electronic bandgap of the host (11.4 ev). The 222 nm absorbing level lies below the conduction band in a way such that photoionization of Ag+ is avoided, as well as other optically-induced opacity phenomena. A minimum source intensity at threshold is estimated at some 276 kW, when using a Fabry-Perot cavity. This power can normally be achieved with the excimer laser.