Characteristic energy losses, luminescence spectra, and their lifetimes for RbI and KI under low energy electron impact

摘要

Evaporated thin films of RbI and KI have been examined at 25ndash;300deg;K under low energy electron impact. The emission of RbI at 470 nm was excited at 3.8 to 5.4 eV electron energy as well as at the first optical exciton (5.7 eV) and above. The 395 nm band was excited at ge;5.1 eV and possibly below this energy. The lifetimes tgr;470and tgr;395at 40deg;K are both 10minus;5sec at ge;5.4 eV electron energy while tgr;395decreases to 3.5 times; 10minus;7sec in the range 4.0 to 4.7 eV. tgr;470decreases below 5.4 eV to 10minus;7sec at 4.4 dV, and is too weak to measure at 4.4 eV. The 400 nm band of KI was excited at 30deg;K in the range 4.2ndash;5.4 eV as well as at and above the first optical exciton, 5.8 eV. The 294 nm band of KI and the 315 nm band of RbI were excited principally at and above the region of the step, 6.2 and 6.0 eV, respectively. The lifetimes of the 376 nm band of KI in the range 25ndash;80deg;K were the same for 4.7 and 6.2 eV electron energy, below and above the first optical exciton energy. For each system the evidence indicates that the low energy emitters can be excited directly. The small Stokes shifts approximate those expected for cubic relaxation. Population of lower energy emitting states from other states lying below the first optical exciton may be responsible for lifetimes anomalies.