Experimental Study of the Mechanism of Thermoluminescence in Irradiated Sodium Chloride

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Abstract
The general configuration of the emission spectrum of synthetic NaCl crystals which had been irradiated with 7 × 105r of x-rays at room temperature and were then permitted to luminesce at 500°K was determined, and bands were located with maxima at 362, 418, 432, and 525 millimicrons. The glow curves for NaCl crystals irradiated with x-rays or ultraviolet light were investigated, and eight bursts of light (glow peaks) were found with peaks at temperatures between 334 and 625°K. The relative contribution of the different bursts to the total glow curve was determined as a function of the amount of x-ray irradiation. The activation energies for five of the bursts were measured and in each case turned out to be about 1.25 ev. It is suggested that these results indicate that the thermoluminescence takes place by means of a two-stage process of the following sort. The first stage, which is the same for all the bursts and is thermally activated with the measured activation energy, takes place when trapped electrons are raised from F-centers into the conduction band. In the second stage, electrons in the conduction band fall into different empty energy levels, there being one type of level for each burst. The large observed differences between the peak temperatures of the different bursts is then due to large variations in the probabilities of this second process for different levels.