U.S. Philips Corporation

U.S. Phillips Corporation

Wilhelmus Mp Van Kemenade

Cornelis Reinder Ronda

Volker U Weiler

Johannes A Peek

Annette Johnen

Christianus J Roozekrans

Henricus C Verhaar

Henriette J Talen-Van Der Mheen

Pieter J Van Der Wel

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.

Method of coating a luminescent material

A discharge vessel (10) encloses a discharge space (12) in a gastight manner, electrodes (21a, 21b) being arranged in the space and having a first (22a, 22b) and a second fastening (22a', 22b'). At least one of the electrodes (21a) is surrounded by a screen (23) which has a smallest width W, in a plane transverse to the tube axis (11) and transverse to the direction from the first (22a) to the second fastening (22a'), which width is smaller than the distance D between the fastenings (22a, 22a'). The screen (23a) has a length L in the direction of the tube axis (11) which lies between once and three times the smallest width W. The lamp consumes comparatively little mercury in the case of cold ignition.

Low-pressure mercury lamp with specific electrode screens

The invention relates to a method of coating a luminescent material with a 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. The invention also relates to a coated luminescent material and to a low-pressure mercury discharge lamp. According to the invention, 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 low-pressure mercury vapor discharge lamp according to the invention is provided with a discharge vessel having a tubular portion and a first and a second end portion. The discharge vessel encloses a discharge space provided with a filling of mercury and a rare gas in a gastight manner. Each end portion supports an electrode which is arranged in the discharge space. Current supply conductors extend from the electrodes through the end portions to outside the discharge vessel. The tubular portion of the discharge vessel is provided with a metal oxide layer on a surface which faces the discharge space. The first and the second end portion are also provided with metal oxide layers at surfaces which face the discharge space. The lamp according to the invention has a comparatively low mercury consumption.

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Eindhoven, Netherlands

Wilhelmus Mp Van Kemenade