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AssigneeU.S. Philips Corporation
InventorsCornelis R. Ronda, Volker U. Weiler, Annette Johnen, Johannes A. F. Peek, Wilhelmus M. P. Van Kemenade
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A luminescent material coated with a crystalline layer of a metal oxide M.sub.2 O.sub.3 wherein a metal M is chosen from the group formed by Y and Al is shown. According to this method the luminescent material is first introduced into a solution of a salt of the metal M, then a compound of the metal M is deposited on the luminescent material through homogeneous precipitation, and subsequently the luminescent material is separated from the solution, dried, and heated. It is achieved thereby that the luminescent material will absorb mercury to a low degree only, and that accordingly the color point of a low-pressure mercury discharge lamp whose luminescent layer comprises a luminescent material coated in accordance with the invention only shows a small shift as the lamp ages.
A coated luminescent material, the luminescent material coated with a crystalline layer of a metal oxide of the formula M.sub.2 O.sub.3 wherein M is a metal selected from the group consisting of Y and Al and the layer is provided on the luminescent material in the following manner:
A low-pressure mercury discharge lamp provided with a luminscent screen provided with a coated luminescent material, the coated luminescent material coated with a crystalline layer of a metal oxide of the formula M.sub.2 O.sub.3 wherein M is a metal selected from the group consisting of Y and Al and the layer is provided on the luminescent material in the following manner:
A low-pressure mercury discharge lamp as claimed in claim 16, wherein the coated luminescent material is barium-magnesium aluminate activated by bivalent europium.
Dependencies are inferred from the claim text.