| Abstract: | Recharging processes of chromium ions were investigated for Mg2SiO4:Mg, Cr single crystals using annealing in O2 and in air and γ‐irradiation, as compare to YAG :Ca, Cr single crystals. The formation of tetravalent Cr ions in the Mg2SiO4 :Mg, Cr is related not only to the initial Cr content in the melt, oxygen partial pressure and O2‐ vacancy existing in the crystal, but also to the external field such as γ‐irradiation. The additional absorption after γ‐irradiation shows the decrease in intensity of the absorption of Cr3+ and Cr4+ ions in some part of the spectrum and increase in the other giving evidence on recharging effects between Cr3+ and Cr4+. There arises also color centers observed between 380 nm and 570 nm that may participate in energy transfer of any excitation to Cr4+ giving rise to Cr4+ emission. Opposite to forsterite crystal, absorption spectrum of YAG:Ca, Cr crystal after γ‐irradiation reveals only increase in the absorption of the Cr bands. The observed behavior of the absorption spectrum of YAG:Ca, Cr crystal under influence of γ‐irradiation suggests that γ‐irradiation ionizes only Cr ions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) |
