Luminescence and damage thresholds of cerium-doped LaF3 for ns-pulsed laser excitation at 248 nm

We have studied time-resolved luminescence spectra and laser damage thresholds of Ce:LaF3 following excitation with 248 nm/14 ns laser pulses at room temperature for the two Ce concentrations 0.03 and 1 mol %. The relative intensities of the 5d-4f bands emitted from Ce3+ at regular and at perturbed lattice sites were found to vary linearly with time for the higher concentration and quadratically for the lower one. This can be explained by radiative energy transfer between the two sites and generation of new perturbed sites at a rate that only shows up for the low Ce concentration. Lifetimes of the respective emission bands were determined to be about 18 ns and 41 ns. Despite resonant absorption of the 5 eV photons, surprisingly high ablation thresholds - 16 J/cm(2) for 0.03% Ce, and 10 J/cm(2) for 1% Ce - were observed by the probe-beam deflection technique. The reason is the strong energy loss due to intense fluorescence and deposition of the nonradiative energy fraction in the bulk rather than at the surface. The depth of energy deposition was revealed by scanning electron microscopy in the form of distinctly different ablation morphologies for the two Ce concentrations.