화학공학소재연구정보센터
Journal of Physical Chemistry, Vol.98, No.51, 13575-13582, 1994
Effect of Laser-Pulses on the Photoelectron Emission from Na+(C222)Na-
Photoemission from crystalline Na+(C222Na- has been measured from 240 to 900 nm. Pure sodium cryptand sodide crystals have an emission peak at approximate to 290 nm (approximate to 4.3 eV) and a very low emission on the low-energy side above 400 nm. The photoemission threshold of this sodide is approximate to 3.1 eV. Most crystalline samples contain, however, both defect sites and defect electrons. As a result, the photoemission spectrum yields an additional shoulder at 360 nm (3.4 eV) and peaks and shoulders in the range of 500-700 nm. Electron emission from polycrystalline samples of Na+(C222Na- is strongly affected by a 7 ns pulsed Nd:YAG laser at 532 nm. The laser pulses result in transient depletion of shallowly trapped electrons and the creation and/or occupancy of defect sites. By comparing the photoemission currents before and after the laser pulses upon illumination at 400 and 600 nm, the energy legions of electron depletion and enhancement can be identified. The kinetics of photoemission decay and/or growth after the laser pulse can be related to the competition between decay of the excess electron population and photon-induced repopulation of empty traps.