Acta Technica 33. (1961)

1-2. szám - Gergely, Gy.: On the Voltage Dependence of Cathodoluminescence

GY. GERGELY of the crystals by chemical treatment [2]. Recent experiments dealing with the effect of various excitation conditions on the form of the Lv curve and the value of Vd have shown that the dead voltage cannot be suppressed [7]. The failure of chemical experiments agrees with the assumption that the inactivity of the surface layef of luminescent crystals is not due to a real dead layer (lack of luminescent centers in the surface layer) but may be explained rather by radiationless transitions of internal secondaries (electrons and holes) which are released near the crystal surface. Such radiationless transi-tions can take place in consequence of surface recombination, as suggested by Broser [8]. For sufficiently high values of the surface recombination velocity, the bulk of released secondaries in the surface layer must suffer radiationless recombination on the surface. The chance of low energy internal secondaries to recombine on the surface strongly decreases with the distance of the electrons and holes from the crystal surface. Thus the surface loss of cathodoluminescence must gradually decrease with increasing accelerating voltage (penetration depth) of the exciting primaries. The low voltage tail of the experimental Lv curve confirms these supposition. Fig. 1. Cathodoluminescence brightness versus accelerating voltage

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