THERE has been much discussion about the existence of re-trapping (electronic recapture) in phosphorescence1. One of my experiments seems to demonstrate the existence of re-trapping: electrons leave the deep traps and get into the short-life traps. I used a calcium sulphide, (bismuth activator) phosphor of very long afterglow. This sulphide was strongly excited by ultra-violet radiations of about 0.36 µ from a mercury vapour arc; it was then heated up to 135° C. until complete extinction was reached. When the sulphide had cooled down to room temperature, it was submitted to the infra-red radiations of a 300-W. electric lamp filtered by a black manganese–iron glass with transparent range of 0.8 µ–4µ with some peaks between 1 µ and 4 µ.