Time-resolved photoluminescence (PL) on excitation with an ArF excimer laser and IR–vacuum UV optical absorption induced by irradiation of an ArF excimer laser of commercially available CaF<sub>2</sub> single crystals fabricated by four different manufacturers were measured. Intrinsic PL that was due to self-trapped excitons generated by band-to-band excitation by two-photon absorption processes was observed in all samples. In addition, most samples showed PL originating from traces of lanthanoid (Ln) impurities, Ce<sup>3+</sup>, Eu<sup>2+</sup> (blue emission), or Tb<sup>3+</sup> (yellow-green emission). The PL of Ce<sup>3+</sup> and Eu<sup>2+</sup> had no correlation with color-center formation; however, intense absorption bands arising from an F<sup>−</sup> center associated with a trivalent yttrium ion (YFC) were necessarily induced in the samples that showed yellow-green PL of Tb<sup>3+</sup> under irradiation by ArF excimer laser light. When the yellow-green fluorescent samples were irradiated with ArF excimer laser light, the PL intensity of Tb<sup>3+</sup> and the induced absorption that was due to YFC increased with the irradiated pulse number, and their growth was found to conform to a first-order kinetics. It was concluded that photoelectrons were released from Tb<sup>2+</sup> ions by ArF excimer laser irradiation, and the resulting electrons were trapped at the site of a fluorine vacancy neighboring on Y<sup>3+</sup>. Therefore the intensity of yellow-green PL of Tb<sup>3+</sup> is proposed as an index for diagnosis of resistance to ArF excimer laser damage in CaF<sub>2</sub> single crystals.
© 1999 Optical Society of America
(140.2180) Lasers and laser optics : Excimer lasers
(140.3330) Lasers and laser optics : Laser damage
(160.3380) Materials : Laser materials
(300.2530) Spectroscopy : Fluorescence, laser-induced
(300.6500) Spectroscopy : Spectroscopy, time-resolved
Masafumi Mizuguchi, Hideo Hosono, Hiroshi Kawazoe, and Tohru Ogawa, "Time-resolved photoluminescence for diagnosis of resistance to ArF excimer laser damage to CaF2 single crystals," J. Opt. Soc. Am. B 16, 1153-1159 (1999)