We report what is believed to be the first observation of permanent photoreduction of Eu<sup>3+</sup> to Eu<sup>2+</sup> in transparent and colorless Eu<sup>3+</sup> -doped fluorozirconate glass at room temperature, using an infrared femtosecond laser. Difference absorption and electron-spin-resonance spectra of the glass before and after laser irradiation showed that a portion of the Eu<sup>3+</sup> ions in the focused part of the laser inside the glass were reduced to Eu<sup>2+</sup> ions after laser irradiation. It is suggested that Eu<sup>3+</sup> ions act as electron-trapping centers, whereas active sites in the glass matrix act as hole-trapping centers, leading to the formation of Eu<sup>2+</sup> ions. The observed phenomenon is inferred to be useful in the fabrication of optical memory devices with high storage density and waveguide-type micro-optical devices.
© 1999 Optical Society of America
(130.3120) Integrated optics : Integrated optics devices
(140.3450) Lasers and laser optics : Laser-induced chemistry
(140.3460) Lasers and laser optics : Lasers
(160.4670) Materials : Optical materials
(160.5690) Materials : Rare-earth-doped materials
Jianrong Qiu*, K. Kojima, K. Miura, T. Mitsuyu, and K. Hirao, "Infrared femtosecond laser pulse induced permanent reduction of Eu3+ to Eu2+ in a fluorozirconate glass," Opt. Lett. 24, 786-788 (1999)