Sulfide phosphor

The photometer is adequately described in Figure 3-2. In the phosphor-photoelectric detector (2.10), the x-ray beam strikes a silver-activated zinc sulfide phosphor to produce blue-violet light that is changed by the multiplier phototube (Type 931-A) into an electric current that is amplified and read on a suitable micro- or milliammeter. A stable power supply for both x-ray tube and detector circuit are essential, as is clear from the circuit diagrams.10... 

The main sulfide phosphors are the group II-V ones based on high purity zinc and cadmium sulfides activated by dopants, primarily using copper and silver but also manganese, gold and rare earths. The nature and concentration of the activator, the composition of the flux and the firing conditions, normally in furnaces at 800-1500 °C, influence the luminescent properties. 

The manufactnring process for the important zinc and cadmium sulfide phosphors involves precipitation of the sulfide from purified salt solutions, e.g. the snlfate, with hydrogen snlfide. For ZnS Cu, the copper activator is added, as a readily decomposed derivative, to the sulfides and after grinding the components are fired in fnmaces at temperatures in the range 800-1200 °C. ZnS Ag, the bine phosphor nsed in CRTs, is prepared by firing zinc sulfide with silver nitrate at 1000 °C, nsnally in the presence of sodinm chloride to give the co-activating chloride ions. 

Zinc and Cadmium Sulfides and Sulfoselenides. The raw materials for the production of these sulfide phosphors are high-purity zinc and cadmium sulfides, which are precipitated from purified salt solutions by hydrogen sulfide or ammonium sulfide [5.291], [5.296], [5.307], [5.310], The concentration of contaminants such as Fe, Co, or Ni must be below 1 % of the activator concentration. The Zn, Cd S can be produced by mixing precipitated zinc sulfide and cadmium sulfide. However, coprecipitation from mixed zinc-cadmium salt solutions is preferred because of the better homogeneity. 

The most important activators for sulfide phosphors are copper and silver, followed by manganese, gold, rare earths, and zinc. The charge compensation of the host lattice is effected by coupled substitution with mono- or trivalent ions (e.g., Cl or Al3+). In addition, disorders, such as unoccupied sulfur positions, can also contribute to charge compensation. 

Industrial silver-activated zinc sulfide phosphors use the intense blue emission exclusively. The ZnS Ag phosphor for cathode ray tubes is obtained by firing zinc sulfide and silver nitrate at ca. 1000 °C in the presence of sodium chloride (coactivator Cl-) [5.318]. The afterglow can be further reduced by addition of 10-3-10-4% of nickel ions. 

Among the long afterglow alkaline-earth sulfides, only (Ca, Sr)S Bi3+, CaS Bi3+, and CaS Eu2+, Tm2+ still have any real importance because their respective blue, violet, and red luminescence cannot yet be achieved with the less hydrolysis-sensitive zinc sulfide phosphors. The last-mentioned phosphor gives an intensive red afterglow and can substitute the red zinc-cadmium phosphor. 

The oxidation state of the activators can be influenced by the choice of the furnace atmosphere. As in the case of the sulfide phosphors, contamination by Fe, Co, or Ni greatly reduces the quantum yield. 

A dead layer usually exists on the surface of phosphor particles, which degrades the phosphors due to crystal defects, residues, oxidation, contamination, etc. A surface treatment with an acid wash is widely used in industry to improve the quality of oxide and sulfide phosphors. Chemical etching on phosphors can also be used to investigate the microstructure properties of the phosphor particles. " ... 

Nakamura, T., Kamiya, M., Watanabe, H., and Nakanishi, Y, Preparation and characterization of zinc sulfide phosphors coated with barium titanate using sol-gel method, J. Electrochem. Soc., 142, 949, 1995. 

Synonyms phosphorus sulfide phosphoric sulfide phosphorus persulfide sulfur phosphide, thiophosporic anhydride... 

The sintered block should have a light yellow color. Its excitation characteristics are the same as those of the corresponding sulfide phosphor, but the emission color is a yellowish-green. 

For sulfide phosphors, the host lattices are mostly tri-element compounds in nature, and they can be represented by MaM Sm, where M and M" can be selected from the following ... 

Fig. 2.7 Flow diagram describing the design of white-emitdng oxide and sulfide phosphors for blue LEDs...

Furthermore, the flowcharts of design and preparation of white-emitting oxide and sulfide phosphors for UV LEDs are also shown, respectively in Fig. 2.8. 

Yang and Chen [41] reported the Ba2ZnS3 Ce ", Eu" " sulfide phosphor, which... 

Table 16.5 Luminescent properties of long-persistent sulfide phosphors...

Other inorganic acids, such as sulfamic, methylsulfuric, or hydrobromic, do not corrode tantalum, nor do the anhydrous acid gases, hydrogen sulfide, phosphorous chlorides, SO2, SOCI2, and chlorine oxides. ... 

D. Li, B.L. Clark, D A. Keszler, P. Keir, J.F. Wager, Color control in sulfide phosphors turning up the light for electroluminescent displays, Chem. Mater. 12 (2000) 268-270. 

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