We have systematically investigated the X-ray-induced radiophotoluminescence (RPL) bands in a silver-activated phosphate glass (PG:Ag), and we have ascribed these bands to Ag 0 , Ag 2+and Ag 2 + centres, using optical characterisation such as absorption, excitation, emission and lifetime measurements. The absorption spectrum of PG:Ag irradiated with X-rays was decomposed into six Gaussian bands on the basis of its strong analogy with irradiated silver-activated sodium chloride (NaCl:Ag). We confirmed that blue emission peaking at 450 nm was connected with the 270 and 345 nm bands of the excitation spectrum, while orange emission peaking at 560 nm was associated with the 308 nm excitation band. Each band of the excitation spectrum was in turn attributed to an Ag 2 + , Ag 0 or Ag 2+ centre by analogy with the RPL of NaCl:Ag. The excited-state lifetimes for each emissive process were also determined for different X-ray doses. In conclusion, we determined that both blue and orange emissions result from radiation-induced (rather than intrinsic) properties in the range of 1.22 -24.5 Gy.

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Laser-active F 2 centers were produced in lithium fluoride ͑LiF͒ at a concentration of 2 ϫ10 18 cm Ϫ3 by irradiating focused femtosecond ͑fs͒ laser pulses from a mode-locked titanium sapphire laser ͑wavelength ϳ800 nm, emission pulse duration ϳ100 fs). This technique was used to write waveguides embedded in LiF crystals. A refractive index change estimated from a guide propagation method was approximately ϩ1% at a wavelength of 633 nm. Refractive index-modulated volume-type gratings were also encoded inside LiF crystals by a single interfered fs laser pulse. The distributed feedback laser structure was fabricated using the gratings thus encoded, which exhibited a room-temperature F 2 -color center laser oscillation at 707 nm. This demonstrates a DFB color center laser operating at room temperature utilizing photon written, permanent Bragg gratings.

We report, for the first time, simultaneous fabrication of laser-active F2 and F3+ colour centres in lithium fluoride and permanent periodic gratings with fringe spacings as fine as sub-micron size by two interfering infrared femtosecond (fs) laser pulses. In particular, the optical properties (absorption and luminescence) of F2 and F3+ colour centres produced by a single fs laser pulse are compared with those created by damage from radiation such as x-rays. The present technique of simultaneously fabricating laser-active colour centres and functional fine-periodic structures in photo-insensitive transparent materials may well be a useful method for making miniaturized optical devices.

We have systematically investigated the origin and optical properties of the X-ray-induced colour centres based on the blue and red radiophotoluminescence (RPL) in a silver-activated phosphate glass. The induced-absorption band was decomposed into six Gaussian bands on the basis of its strong analogy with silver-activated sodium chloride. We have ascribed these bands to Ag 0 , Ag 2+ , Ag 2 + and other silver ion species by means of optical and thermal measurements such as colour centre formation and dissolusion by highly successive femtosecond-pulse irradiation, excited-state lifetime and thermal annealing characteristics.The data confirmed that the blue RPL at 450 nm could be attributed to the 270 and 345 nm bands due to the Ag 2 + and Ag 0 centres, respectively, and that the orange RPL at 560 nm was associated with the 308 nm band due to the Ag 2+ centres.