Emission decay times of F2 color centers in heavily irradiated LiF crystals

The F-2 centers in LiF display an efficient broad emission in the red spectral range when excited in their absorption band located around 450 nm and promising results have been obtained in transferring the optical properties to low-dimensional emitting structures, where their density reaches values higher than 10(17) F-2 /cm(3). The emission decay times measured in the entirely colored LiF crystals irradiated by 3 MeV electrons with increasing doses do not show any variation up to 10(17) F-2/cm(3) and decrease by 20% of the value approaching 10(18)F(2)/cm(3). The values at low concentrations practically coincide with the lifetime of the excited level. The comparison among samples irradiated at different temperatures seems to exclude relevant interactions with the F-3(+) centers, while it supports an energy transfer mechanism with the F-2(+) ones. (C) 2001 Elsevier Science B.V. All rights reserved.