ION IRRADIATION DAMAGE IN ER-DOPED SILICA PROBED BY THE ER-3+ LUMINESCENCE LIFETIME AT 1.535 MU-M

The effect of MeV ion irradiation damage on the luminescence lifetime of erbium-doped silica glass films has been studied. The 10-mum-thick films were first implanted with 3.5 MeV Er at a fluence of 5 x 10(15) cm-2. When optically pumped at 488 nm, the films show a clear photoluminescence spectrum centered around 1.535 mum, corresponding to the 4I13/2-->4I15/2 transition of Er3+ (4f11), with a luminescence lifetime of 5.5 ms. After thermal annealing at 900-degrees-C, the lifetime increases to 14.1 ms. Radiation damage was then introduced in the annealed films using 1 MeV He, 3.5 MeV C, 5.5 MeV Si, or 8.5 MeV Ge ions. The lifetime is decreased by irradiation with fluences as low as 10(11) ions/cm2 and continues to decrease with fluence until saturation occurs above almost-equal-to 10(14) ions/cm2. The saturation lifetime is ion-mass dependent and ranges from 6.6 to 8.5 ms. The lifetime changes are explained in terms of nonradiative energy transfer processes caused by irradiation-induced defects in the silica. A model for lifetime changes as a function of ion fluence is derived, assuming an inverse relation between the nonradiative lifetime and the defect density. Fits to the data show that the defect generation rate is a sublinear function of the ion fluence. The ion damage effects are governed by the electronic component of the energy loss along the ion trajectories.