Abstract
Time-resolved photoluminescence spectra of various grade CaF2 single crystals were measured to examine effectiveness as a diagnosis for ArF excimer laser damage. Luminescence upon exciting with ArF laser light was classified into four bands from the peak position and lifetime, i.e., (1) 274 nm, 1 microsecond(s) , (2) 541 nm, 1 ms, (3) 418 nm, 700 ns, and (4) a doublet band 309 and 330 nm, 30 ns. Band 1 is emitted via 2-photon absorption processes and the origin is the relaxation of self-trapped exciton generated by band-to-band excitation. Therefore, this band is intrinsic to CaF2 crystals. On the other hand, the bands 2, 3 and 4 originate from trace impurities. Tb3+, Eu2+ and Ce3+, respectively. These luminescence bands occurred via on-photon absorption processes. When the band 2 (yellow green light) was clearly observed during the laser irradiation, the intense absorption band due to an F center associated with a trivalent yttrium ion was induced after prolonged irradiation. On the other hand, the band 3 (blue light) had no relationship with color center formation. It was suggested that photo-oxidation of trivalent rare earth ions has a correlation with color center formation.
