Method of coating red-luminescing phosphor particles with hematite

US5387436A · kind A · utility

Assignee

• U.S. Philips Corporation · US

Inventors

• Cornelis Reinder Ronda · Aachen, DE
• Guido Hutten · Besigheim, DE
• Michael Bredol · Aachen, DE
• Ulrich Kynast · Roetgen, DE
• Thomas Rink · Waldfenster, DE

Key dates

• Filing date: Nov 16, 1993
• Grant date: Feb 7, 1995
• Expiry date: Nov 16, 2013

Classification

• Technology area (CPC H): Electricity
• CPC primary: H01J29/20
• WIPO field: Basic materials chemistry
• WIPO sector: Chemistry

Abstract

The invention relates to a method of coating red-luminescing phosphor particles with hematite (.alpha.--Fe.sub.2 O.sub.3), whereby first Fe(OH).sub.3 is deposited on the phosphor particles and subsequently converted into .alpha.--Fe.sub.2 O.sub.3 at a raised temperature. A good adhesion of the hematite pigments to the phosphor particles is achieved in that first an aqueous solution of an iron(III) salt and a complexing agent is prepared, in which the complexing agent and its concentration are so chosen that in combination with Fe.sup.3+ ions complex ions are formed which on the one hand do not yet precipitate at a pH-value which is at least 0.5 higher than the value at which the phosphor particles just fail to be chemically attacked anymore, and which are dissociable at a further increase in the pH-value so that Fe(OH).sub.3 is formed, in that subsequently, if the pH-value is not yet high enough, a basic substance is added to the mixture, in that the pH-value is increased to a value which is at least 0.5 below the value at which Fe(OH).sub.3 starts to precipitate and at least 0.5 higher than the value at which the phosphor particles just fail to be chemically attacked anymore, in t…