Zinc sulphide phosphor

The luminescent properties of zinc sulphide phosphors change considerably with the introduction of iron into the crystal. In particular, if the iron... 

The most important phosphors are sulphides and oxides of transition metals. The sulphides of zinc and of cadmium are the most important materials of the sulphide type. An important condition of achieving a highly efficient phosphor is to prepare a salt of the highest possible chemical purity. The emission of zinc sulphide can be shifted to longer wavelengths by increasingly replacing the zinc ions with cadmium. 

Some oxide-type minerals have been found to luminesce when irradiated. A simple example is ruby (aluminium oxide with chromium activator), which emits bright-red light. The phosphors are incorporated into colour television screens to emit the colours blue (silver-activated zinc sulphide), green (manganese-activated zinc orthosilicate), and red (europium-activated yttrium vanadate). 

Another volumetric process which has been recommended consists in reducing the sulphuric acid or sulphate (excepting barium sulphate) by heating with a mixture of hydriodic acid, phosphorus and phosphoric acid, absorbing the resulting hydrogen sulphide in a solution of zinc acetate, and estimating the precipitated zinc sulphide iodo-metrically.2... 

In the case of modification B, the sulphide sulphur fixed as zinc sulphide is distilled in distillation apparatus as hydrogen sulphide after adding phosphoric acid, and collected in a receiver containing zinc acetate solution. Further treatment is as for modification A. 

Sulphide-type phosphors are produced from pure zinc or cadmium sulphide (or mixtures thereof) and heating them together at about 1000 °C with small quantities (0.1-0.001 per cent) of copper, silver, gallium, or other salts, which are termed activators. 

Copper-activated zinc and cadmium sulphides exhibit a rather long afterglow when their irradiation has ceased, which is favourable for application in radar screens and self-luminous phosphors. 

Phosphorus at 200° C. in a sealed tube gives phosphoric acid and hydrogen sulphide.3 Nascent hydrogen, for example from zinc and sulphuric acid, yields hydrogen sulphide,4 as also do phosphorous acid,5 titanous chloride, and even stannous chloride 6... 

Aqueous solutions of the salts, or of tellurium dioxide in acids, easily undergo reduction.to elementary tellurium. Phosphorus, phosphorous acid,-7 hypophosphorous acid,8 sulphurous acid,9 thiosulphuric acid,10 hyposulphurous acid,11 hydriodic acid,12 hydrogen sulphide,13 ferrous salts, stannous salts,14 hydrazine 15 and phenylhydrazine, as well as various metals,18 e.g. zinc, iron, tin, cadmium, antimony and copper, are able to effect this reduction. 

Dimetaphosphates of copper, manganese, cobalt and zinc are said to be formed when an oxide or nitrate of these metals is heated with an excess of phosphoric acid between 316° and 400° C.2 The zinc salt had the formula ZnP208.4H20, and when treated with alkali sulphides gave the alkali salts K2P206.2H20, etc. Other authorities, however, have adduced reason for supposing that these salts are tri- or tetra-metaphosphates.4... 

Solutions of tungstates containing ammonium sulphide yield with hydrochloric acid a brown j recipitate of tungsten trisulphide. The addition of zinc chloride to a tungstate solution produces a yellow precipitate which becomes blue on warming with dilute hydrochloric or sulphuric acid. When excess of hydrochloric acid is added to a solution of alkali tungstate and the mixture reduced by means of zinc, brilliant colours, from red to blue, are produced if phosphoric acid is used, a fine blue precqntate results. 

The blocks appear to possess the typical characteristics of an antiwear /friction reducing film formation. Table 1 shows that it can be hypothesised, based on previous work, that significant levels of zinc phosphate, iron sulphide and molybdenum disulphide may be present on the block substrate. Future analysis with XPS (X-ray Photoelectron Spectroscopy) equipment will be used to confirm this. Analysis of the rings suggest a slightly different surface composition may be present with an obvious lack of any Phosphorous. This was seen throughout all test samples. The lack of any detectable level of Phosphorous on the rings cannot be accounted for at present. 

---