Decay of Zinc Sulphide Type Phosphors

IN the derivation of the decay curve for phosphors of the recombination type with traps at one single depth, Randall and Wilkins¹ have assumed that there is no retrapping of electrons. In a subsequent paper² they show, however, that the cross-sections for electron capture of the traps and the `empty' luminescence centres are about equal. After a long decay period there are many more empty traps than empty luminescence centres and consequently retrapping must be important.