Method of preparing a luminescent Eu2+ activated strontium aluminate, aluminate obtained by said method and low-pressure mercury vapour discharge lamp provided with such an aliminate

摘要

Method of preparing a luminescent Eu²⁺ activated strontium aluminate defined by the formula Sr₄Al₁₄O₂₅:Eu²⁺ in which a mixture comprising SrO, Al₂O₃ and Eu₂O₃ or compounds yielding these oxides upon an increase of temperature is heated in a weakly reducing atmosphere at a temperature of 1100 to 1500°C, in which per mol of the Al present a combination of between 0.1 and 5 mol % of B₂O₃ or compounds yielding B₂O₃ upon an increase of temperature, and between 0.1 and 10 mol % of at least one of the fluorides and/or chlorides of Ba, Sr, Cs and/or Al and/or RbCl is added to the mixture as a flux, whereafter the mixture is subjected to a first heat treatment at 1100 to 1500°C. Between 0.1 and 10 mol % of at least one of the ammonium halogenides is added to the product thus obtained per mol of the Al present and the mixture thus obtained is subsequently subjected to a second heat treatment at a temperature of 700 to 1200°C.