Search

Optically transparent LiF thin films thermally evaporated on glass and Si(100) substrates were used for advanced diagnostics of proton beams of energies from 1.4 to 7 MeV produced by a linear accelerator for protontheraphy under development at ENEA C.R. Frascati. The proton irradiation induces the formation of stable colour centres, among them the aggregate F2 and F3 + optically active defects. After exposure of LiF films grown on glass perpendicularly to the proton beams, their accumulated transversal spatial distributions were carefully measured by reading the latent two-dimensional (2-D) fluorescence images stored in the LiF thin layers by local formation of these broad-band visible light-emitting defects with an optical microscope under blue lamp excitation. Taking advantage from the low thickness of LiF thin films and from the linear behaviour of the integrated F2 and F3 + photoluminescence intensities up to the irradiation fluence of ∼5x1015 p/cm2, placing a cleaved LiF film grown on Si substrate with the cutted edge perpendicular to the proton beam, the 2-D fluorescence image of the film surface could allow to obtain the depth profile of the energy released by protons, which mainly lose their energy at the end of the path. © Published under licence by IOP Publishing Ltd.

The advanced optical and electronic characterization of primary F-defects and metallic lithium colloids in lithium fluoride thin films produced by ion-assisted thermal deposition with Xe low-energy ions (< 200 eV) on transparent amorphous substrates is presented and discussed. The volume concentrations of defects and Li nano-clusters have been estimated by applying a best-fit procedure based on a comprehensive theoretical modelling to the spectro-photometric measurements. The appreciable presence of Li metal at the film surface was clearly demonstrated by X-ray photoelectron spectra. Advanced optical microscopy confirms the negligible formation of other types of more complex luminescent colour centres.

Optical absorption and photoluminescence spectra were measured on gamma colored lithium fluoride crystals at five different irradiation doses. By accurate Gaussian best-fit procedures of the absorption measurements the peak intensity of F and M bands and the concentrations of F, F2 and F3+ color centers in gamma irradiated LiF crystals at different doses were obtained. A quadratic relationship between F and F2 defect concentrations as a function of the irradiation dose was found. Photoluminescence measurements, excited by an Argon laser at 457.9 nm, were used to study the effect of the laser power on the F2 and F3+ emission spectra of gamma irradiated LiF crystals. The influence of the triplet state on the optical cicle of F3+ color center was highlighted for several excitation laser power and the ratio of the transitions probability W1 and W2 to and from the triplet state was derived.