Color centers and charge state change in Ce : YAG crystals grown by temperature gradient techniques

Color centers and impurity defects of Ce:YAG crystals grown in reduction atmosphere by temperature gradient techniques have been investigated by means of gamma irradiation and thermal treatments. Four absorption bands associated with color centers or impurity defects at 235, 255, 294 and 370 nm were observed in as-grown crystals. Changes in optical intensity of the 235 and 370 nm bands after gamma irradiation indicate that they are associated with F+-type color center. Charge state change processes of Fe3+ impurity and Ce3+ ions take place in the irradiation process. The variations of Ce3+ ions concentration clearly indicate that Ce4+ ions exist in Ce:YAG crystals and gamma irradiations could increase the concentration of Ce3+ ions. Annealing treatments and the changes in optical density suggest that a heterovalent impurity ion associated with the 294 nm band seems to be present in the crystals. (c) 2005 Elsevier B.V. All rights reserved.

Color centers and charge state recharge in gamma-irradiated Yb : YAP

Gamma-ray irradiation induced color centers and charge state recharge of impurity and doped ion in 10 at.% Yb:YAP have been studied. The change in the additional absorption (AA) spectra is mainly related to the charge exchange of the impurity Fe2+, Fe3+ and Yb3+ ions. Two impurity color center bands at 255 and 313 nm were attributed to Fe3+ and Fe2+ ions, respectively. The broad AA band centered at 385 nm may be associated with the cation vacancies and F-type center. The transition Yb3+ -> Yb2+ takes place in the process of gamma-irradiation. Oxygen annealing and gamma-ray irradiation lead to an opposite effect on the absorption properties of the Yb:YAP crystal. In the air annealing process, the transition Fe2+ -> Fe3+ and Yb2+ -> Yb3+ take place and the color centers responsible for the 385 nm band was destroyed. (c) 2005 Elsevier B.V. All rights reserved.