SELECTIVE ELECTRON EMISSION FROM F-CENTERS IN CsCl

Abstract

R6sum6.-Les emissions photoelectrique et thernloelectrique ont ete appliquees pour Ctudier les aspects du degagement des electrons a partir des centres F dans CsCI. La courbe de photoemission coincide parfaitement avec la bande d'absorption F. La selectivite spectrale indique que la photoabsorption a lieu seulement a I'etat excite du centre F tandis que la dClocalisation et I'ejection d'klectrons a partir de la surface sont effectuees par energie thermique. Le blanchissement de la bande d'absorption F et la trempe de I'emission photoelectronique correspondante sont accrus par ionisation thermique des centres F. Un pic d'eniission thermique specifique est observe B 360 K, dii aussi aux centres F. L'energie d'activation thermique correspondante est Cgale a 0,95 eV et le facteur de frequence a 1012 s-1. La difference avec I'energie d'activation optique (z 2,3 eV) est expliquke par le principe de Franck-Condon.

Possibilities of Optically Stimulated Exoelectron Emission (OSEE) Registration in the Nano- and Microsecond Range from CsCI

“…The observed emission corresponds to one trap energy level (F-center) only as was shown earlier [5]. One can suggest two possible mechanisms of OSEE from the studies of the CsCl samples: a) photo-thermal process in which after absorption of a photon the electron is raised from the ground state of the F-center to the excited state F* and then is released into conduction band and finally into vacuum by thermal agitation of the lattice [4]; b) re-emission process in which the electron is raised to the conduction band and then into vacuum similarly as in case a), but during its way the electron is captured by other electron traps, where it is staying for some time [lo].…”

“…This may be helpful in solving some problems of the OSEE phenomenon like the rapid increase in the initial parts of the OSEE kinetics, always observed just after starting the optical stimulation. It is well known that the used material (mixture of CsCl and graphite) exhibits exoemission from F-centers, as has been clearly demonstrated in [5].…”

“…Inserting F* from (6) into (5) we fmd the solution of ( 5 ) under conditions n(0) = 0 and 5, < TF% If the light pulse duration is ? : using the conditions 1n, one can obtain…”

Effects of mechanical deformation: Exoemission

“…The first step is the optical transition from the colour centre to the conduction band, and the second step is the thermionic emission from the conduction band to vacuum. The stimulation spectra (i.e., PSEE as a function of the stimulating wavelength) have been studied extensively and found to give information about the colour centres similar to that yielded by their optical absorption spectra (Ford et al 1970;Bichevin et al 1971;Nink and Holzapfel 1973;Maiste et al 1973;Kortov et al 1982;Tale et al 1982).…”