U.S. Philips Corporation

U.S. Phillips Corporation

Volker U Weiler

Cornelis Reinder Ronda

Ulrich H Kynast

Wilhelmus Mp Van Kemenade

Johannes A Peek

Annette Johnen

Wilhelm A Groen

Bennie Josephus De Maagt

Wilhelmus M P Van Kemenade

Cornelis J M Denissen

A low-pressure mercury vapor discharge lamp is provided with a discharge vessel 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 (,) arranged in the discharge space. An electrode shield (,) encompasses the electrodes (,) and is covered with a material which reacts with or forms an alloy with alkaline earth metals, which material is released by the electrode (,).

Low-pressure mercury vapor discharge lamp with electrode shield

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 luminescent screen includes a luminescent zeolite containing rare earths, such as terbium (Tb), and europium (Eu), and an oxide of a transition metal, such as, molybdenum (Mo), tungsten (W), niobium (Nb), and tantalum (Ta). It was found that a zeolite containing both terbium, and tungsten oxide had an absorbability that was approximately 60 times as high as that of a zeolite containing only terbium, thus increasing the luminescent efficiency of the zeolite.

Luminescent screen including a luminescent zeolite

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.

The invention relates to a luminescent zeolite of the Faujasite type containing Ce.sup.3+ ions. Such a zeolite can for instance be used in the luminescent screen of a low pressure mercury discharge lamp for use in photochemical processes. According to the invention the zeolite further contains cations S.sup.n+, wherein n.gtoreq.2 and the sum of the amount of Ce.sup.3+ ions and the amount of cations S.sup.n+ per unit cell of the zeolite is at least 16. The zeolite exhibits a high quantum efficiency for converting UV radiation of 254 nm into radiation having an emission maximum between 315 and 400 nm, even in case the Ce.sup.3+ ion content is relatively low.

Luminescent zeolite

The invention relates to a luminescent screen and to a low pressure mercury discharge lamp comprising such a luminescent screen. According to the invention the luminescent screen comprises a zeolite containing trivalent Ce. The luminescent screen exhibits a large quantum efficiency for converting UV radiation of 254 nm into radiation having an emission maximum at approximately 346 nm.

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Aachen, Germany

Volker U Weiler