Host excitation of luminescence from KI:Tl+ and RbI:Tl+ by slow electron impact

The luminescence of KI:Tl+ and RbI:Tl+ evaporated thin films in the range 30–300 °K is excited by electron impact from ∼4 to ?8 eV. Emission at 410 nm from KI:Tl+ at 300 °K was excited throughout the range 4.1–5.7 eV (the first optical exciton) and above. For 6.6 eV excitation at 70 °K, the emission spectrum may contain unresolved contributions from the host at 376 and 410 nm as well as from the activator at 336 and 430 nm, the last being much the strongest. Optical absorption is known to excite intrinsic luminescence bands at 410, 376, and 300 nm. In RbI:Tl+, the low-energy emission at 430 nm and 300 °K was excited by electron impact throughout the range 4.0–5.7 eV (the first optical exciton) and above. The temperature dependence of the lifetime for the 430 nm bands of KI:Tl+ agrees with results from the literature, while that of the intensity dependence agrees only in part. Characteristic electron energy losses of the host lattice are unmodified by Tl+ and the luminescence intensity is high, indicating host sensitization.