Eradication of oxygen contamination in production of ZnS:Ag:Cl blue phosphor powder

摘要

It has been pointed out that oxygen contamination of ZnS:Ag:Cl blue phosphor powder mainly comes from the air trapped in inevitably existing pores in heating mixture in crucible. Calculated amount of the trapped air is 2 x 10~(-3) mol per mole a-ZnS in crucible. It is found that addition of AlCl_3 (2 x 10~(-3) mole) eradicates the oxygen gas in heating mixture, by means of formation of Al_2O_3 solid. Segregating Na_2S_4 carries the fine Al_2O_3 particles to the place that Al_2O_3 converts to Al_2S_3 by the concentrated Na_2S_4. The segregation of Na_2S_4 requires a slow cooling from 950 to 850℃. The segregation produces the large yellowish particles ( > 50 μm), which are confirmed as ZnO microcrystals surprisingly. Then, we have proposed a model of the growth of ZnO microcrystals in heated mixture which is a sulfur-rich atmosphere.