A Demonstration of the Fluorescent and Phosphorescent Effects of Zinc Sulphide

Abstract

Zinc Sulphide is prepared by the precipitation of a soluble zinc salt by means of a soluble sulphide. The product so obtained is a white, amorphous powder, entirely devoid of luminescent properties. If heated to a high temperature it becomes crystalline. Zinc sulphide occurs naturally as the mineral “wurtzite,” which is usually dark-coloured owing to the presence of impurities, and only very rarely do samples of the natural material possess luminescent properties. Sidot, in 1886, was the first to produce phosphorescent zinc sulphide. He heated crystalline zinc sulphide in a stream of sulphur dioxide and obtained hexagonal crystals, which were phosphorescent and fluorescent. The product so obtained was known as “Sidot blende.” The first application of Sidot blende was for the manufacture of the screen used in the spinthariscope. This is an appliance to demonstrate the scintillations produced by the impact of a particles, from a small amount of radioactive matter, upon a zinc sulphide screen. The first practical application of the luminescent properties of zinc sulphide was the manufacture of self-luminous compound for clock and watch dials. This was made by mixing phosphorescent zinc sulphide with a small amount of radioactive matter. The luminosity of this luminous compound is due almost entirely to the α particles, to which the zinc sulphide responds more effectively than any other known luminescent substance. Luminous compound of this nature was used on a relatively large scale during the War for painting the dials of instruments in warships, aeroplanes, etc.; and also for filling small capillary tubes which were employed as gun-sights for night firing.