1) The Institute Physical and Chemical Research(RIKEN), Hirosawa 2-1, Wako, Saitama 351, Japan
2) Japan Atomic Energy Research Institute(JAERI), Sirakawa 2-4, Tokai, Ibaragi 319-11, Japan
3) Korea Institute of Geology Mining and Materials, Taejon 305-350, Korea
4) Osaka Institute of Technology, Kitayama 1-79-1, Hirakata 573-01, Japan
Luminescence spectra and their decay curves are measured for a-alumina irradiated by various ions and at different temperatures. The time-integrated luminescence spectrum is principally composed of bands well known by electron and photon irradiation, whereas decay measurements show that almost all the bands cannot be recognized in a time range earlier than few hundreds ns except for the 326-nm band and a 100-ps-lived band. Excitation density (ED) dependence of the luminescence efficiency and the decay rate, and their temperature dependence, suggest not only radiative distant interaction between the excited states but also stimulated emission. The time-resolved spectra can discern obviously a 100-ps-lived broad band which has not yet been reported. This may be ascribed to a complex between adjacent excited states, considering the superlinear dependence of its luminescence efficiency on ED and temperature independence of the decay rate.
Physical Review B, 60(1999)12626.