F. F. Mikus
Sylvania Electric Products, Inc. Towanda, Pennsylvania
I
Simple Preparations of Phosphors
and evaporate to dryness at 120°C. Intimately mix 2 g of finely divided NaCl with the ZnS. Transfer to a silica crucible, cover and place in a furnace a t 900°C. Fire at t,his temperature for two hours and while still covered remove crucible from the furnace to cool to room temperature before examining under UV. A blue luminescence will be observed. Z n S Activated by M n . Repeat except that 4.5 g MnClz is substituted for Agli01. A yellow luminescence will be observed. Z n S Activated by Cu. Repeat except that 40 mg of CuSO4.5Hz0 is substituted for AgiVO8. A green luminescence with a longer period of emission after removal from source of excitation (afterglow) than that of ZnS:Ag or ZnS:Mn will be observed. Zinc sulfide and cadmium sulfide form solid solutions throughout the entire concentration range. When these are used as host crystals with silver as activator, the spectrum changes progressively from the blue region to infrared as the CdS content increases from 0 to 100%. This call be demonstrated by performing the following experiment. Add 61 g ZnS and 39 g CdS t o 2.5 ml of AgSOi solution containing 8 mg AgiXO?, and evaporate to dryness a t 120°C. Intimately mix 2 g of finely divided KaCl with the above mixture. Transfer to a silica crucible, cover and place in a furnace at 800°C. ].'ire for 2 hours and while still covered remove from furnace to cool to room temperat,ure. This phosphor emits most strongly at 5200A. Repeat except that 40 g of ZnS and $0 g CdS are used. The peak emission occurs at 5740A. Experiments Repeat except that 32 g of ZuS and 6 8 g of CdS arz I'rrparation of a Phosphor at Room T e m p e r a t ~ r e . ~ used. The peak emission occurs at 6100A. KC1 erystals are placed within 1 cm of SbCL under a 365OA UV light source in a dark room or a dark box. Bibliography The initially uonluminescent KC1 crystals will begin to GARLICK, G. F. J., "Luminescent, Materials," Oxford University show a yellow luminescence as the molecules of SbC5 Press, London, 1949. volatilize and come in contact with the RC1. Grinding GRAY,T. J., "The Defect Solid State," Interscience Publishers, the KC1 crystals with ShCla in a mortar will accelerate Inc., New York, 1957. the process. KaosEn. F. A,. "Some Asoects of the Luminescence of Solids."
In recent years the volume of literature pertaining to the solid state has been growing larger and larger. About a third of the current physical research is in this field. Phosphor chemistry offers a simple and colorful introduction to this phase of chemistry a t the undergraduate level. The preparation of some phosphors outlined below may be used as experiments in an inorgauic course. Phosphors, materials which exhibit fluorescence aud phosphorescence, are composed of a host crystal or matrix, and an activator or luminescence-promoting material in small quantities. A flux, usually an alkali or alkaline earth halide, may or may not be used to aid in the production of the phosphor. It provides a medium for the transport of materials, increases surface reactivity and increases atomic mobility to facilitate crystal growth. Details of crystal imperfections, color centers, and the mechauism of phosphorescence are beyoud the scope of this paper, but may be found in excellent treatises on the subjects. A muffle furnace capable of maintaining up t o 900°C is needed for firing the materials. Silica crucibles with covers serve as excellent containers for the process. An ultraviolet source' emitting strongly a t 36.50A is used to excite the phosphors to lumiuesceuce. If a dark room is not available, a partially closed wooden box painted black may be used. Purity of materials and precautions to prevent contaminatiou in handling are very important. As little as 3 to 5 ppm nickel will cause zinc sulfide phosphors to become inert. For best results, use luminescent grade ZnS and CdS.
Effect of Various Activators Z n S Actiuated by Ag. Add 20 mg of AgN08 to a slnrrv of 100 rr ZnS in 25 ml of water. Stir thoroughly 1 Lite-Mite made hy Stocker and Yale, Inc., Marhlehead, Mass., is convenient. H. W., "Luminescence of Solids," John Wiley and LEVERENZ, Sons, Inc., New York, 1950.
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E~sevikr~uhiishing~a.,kmsterdam,Holland, 1948. LEYERENZ, H. W., "Luminescence uf Solids," John Wiley and Sons, Ine., New York, 1950. PRINGSHEIM, P., "Fluorescence and Phosphorescence," Interscience Publishers, Inc., New York, 1949. SEITZ,F., "Imperfection in Nearly Perfect Crystals," John Wiley and Sons, Ino., New York, 1952, pp. 3-76. SEITZ,F., AND TURNBULL, D., "Solid State Physics," Academic Press, Inr., New York, 1957, Vd. 5 ; 1959, Vol. 9.
