Ultraviolet laser and x-ray induced valence changes and defect formation in europium and terbium doped glasses

Abstract

The influence of Eu3+, Eu2+ and Tb3+ ions on x-ray and ultra violet laser induced defects is examined in a fluoride phosphate and an ultraphosphate glass. The defects are characterised by optical absorption, fluorescence and ESR spectroscopy Europium ions cause larger changes in the fluoride phosphate glass whereas terbium ions do in the ultraphosphate glass. Different mechanisms of defect formation are found for x-ray and ultraviolet excimer laser irradiation at 248 nm. X-ray irradiation induces valence changes of a part of the dopant ions into (Eu3+)−, (Eu2+)+ and (Tb3+)+ ions, respectively: By contrast, laser irradiation results in a very hst and complete photo-oxidation of Eu3+ but in a very slight photooxidation of Tb3+. Photoreduction of Eu3+ does not occur. Under x-ray irradiation, the dopants have a similar but small influence on the intrinsic defect formation. Extrinsic rare earth related defect centres replace intrinsic defects. On the contrary the laser induced photo-oxidation of Eu2+ enhances considerably the amount of intrinsic electron centres but suppresses effectively the formation of intrinsic hole centres. However; Tb3+ doping increases both electron and hole centre formation. These peculiarities of Eu2+ and Tb3+ doping result from the coincidence of the laser energy with the 4f-5d transitions of the rare earth ions. The fast and intense laser induced defect formation in the Eu2+ and Tb3+ doped glasses suggests that these dopants are promising candidates for increasing the photosensitivity of glasses.