Acta Technica 33. (1961)

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

ON THE VOLTAGE DEPENDENCE OF CATHODOLUMINESCENCE GY. GERGELY TELECOMMUNICATION RESEARCH INSTITUTE, BUDAPEST [Manuscript received May 20, 1960] Introduction The voltage dependence of cathodoluminescence emission was studied by the author in some recently published papers [1, 2]. In accordance with the results of other authors [3 — 6], above 3 — 5 kV a strictly linear brightness versus voltage relationship was found. The voltage dependence of various types of luminescent and scintillator crystals exhibits the same character. Fig. 1 shows such a typical curve. An attempt was made to explain the linear behaviour of the brightness, Lv versus accelerating voltage, V0 curve by the following two assumptions: 1. The intrinsic efficiency, r]0 of cathodoluminescence is constant and independent of the accelerating voltage. 2. A thin non-luminescent layer (dead layer) exists [6] on the surface of the luminescent crystals. It will be shown in this paper that the dead layer effect can be attributed to surface recombination of released secondaries. The magnitude of the diffu­sion length of internal secondaries in luminescent crystals can be approximately calculated from the Lv versus V0 curve. Some properties of the dead layer The experimentally determined value of efficiency, rj„, for V0 voltage is less than rj0. The apparent reduction in efficiency is caused by the loss of incident cathode rays on the dead layer. The magnitude of surface losses can be characterized by the interception of the linear section of the Lv curve with the horizontal V0 axis on Fig. 1. This point of interception is called the dead voltage Vd [6]. As described in one of the previous papers [2], the magnitude of Vd can be increased by applying artificial surface films (aluminium coating or colloidal binder film) and by the distortion of the crystal surface (ion bombard­ment damage, photolysis, grinding of the crystals). On the other hand, dead voltage cannot be reduced by removing the 100—2000 A thick surface layer

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