GB2484738A

GB2484738A - A sealant comprising a getter for a low pressure discharge lamp

Info

Publication number: GB2484738A
Application number: GB201017891A
Authority: GB
Inventors: Andrew Page
Original assignee: Heraeus Noblelight Analytics Ltd
Current assignee: Heraeus Noblelight Analytics Ltd
Priority date: 2010-10-22
Filing date: 2010-10-22
Publication date: 2012-04-25
Anticipated expiration: 2030-10-22
Also published as: GB2484738B; GB201017891D0

Abstract

There is disclosed a sealant 14 for vacuum sealing the cap portion 10 and body portion 12 of a low pressure discharge lamp, the sealant 14 comprising a getter for controlling the levels of contaminants within the lamp. A method of manufacturing the lamp comprises providing the cap portion 10, the body portion 12, and the sealant 14, and heating the sealant 14 to activate a getter function of the sealant. The sealant is preferably frit glass comprising a mixture of components, such as metal oxides and silicate compounds, vitrified together to form a glass. The low pressure discharge lamp is preferably an RF driven photo-ionisation detector (PID) lamp, the cap portion 10 being forming a window that is transparent to visible light or non-visible light such as vacuum ultraviolet light.

Description

LAMP COMPRISING A GETTER

DESCRIPTION

The present invention relates to a low pressure discharge lamp having an improved getter component.

During the manufacture of low pressure discharge lamps, it is almost impossible to avoid the presence of contaminants in the final lamp. Such contaminants include, but are not limited to, gases such as Oxygen, Hydrogen, and Carbon Dioxide. Over time, these contaminants can progressively degrade the operation of the lamp and cause early failure, limiting the lifetime of the lamp.

As is well known in the art, a getter is a material that has a chemical affinity to certain active gaseous elements and compounds that are present as contaminants within a lamp. Such getters are commonly inserted into lamps to control the levels of contaminants, for example by reacting with the contaminants and trapping the gases in their surface to reduce their levels. The reduced level of contaminants lengthens the lifetimes of the lamps.

Getters can typically be categorised into one of two families, evaporable getters and non-evaporable getters. Evaporable getters can be deposited onto the glass wall of the lamp during processing, being "fired" by heating them. The heating can be achieved by external RF (radio frequency) heating of the getter, which is often in ring form to allow this. Non-evaporable getters include alloys which may be mixed in powder form and sintered onto a base metal substrate such as iron. This approach gives effectively higher surface area which increases the effectiveness. Alloy mixtures of materials such as Zirconium, Vanadium, Cobalt are normally chosen on the basis of some physical aspects of the application such as: Operating temperature, types of contaminant gases, production process, physical size/format to fit application. Non-evaporable getters still require heat activation to perform the getter function at some point during the production process.

One of the problems with known getters is that they can result in shadowing of the light emitted by the lamp, giving an unwanted reduction in light output.

Furthermore, the addition of a getter device and the heating of the getter to perform the getter function constitute additional manufacturing steps, and increase the complexity and overall cost of the device.

It is therefore an aim of the invention to provide a low pressure discharge lamp with an improved getter.

According to a first aspect of the invention, there is provided a low pressure discharge lamp comprising a cap portion and a body portion, the cap portion being vacuum sealed to the body portion by a sealant, and wherein the sealant comprises a getter for controlling the levels of contaminants within the lamp.

Since the sealant incorporates a getter, the levels of contaminants within the lamp can be controlled without needing a separate getter device. The sealant performs the dual functions of both vacuum sealing the cap portion to the body portion and controlling the level of contaminants within the lamp.

The low pressure discharge lamp may be an RF driven lamp wherein an external RF field is applied to the lamp to excite an inert gas within the lamp into a plasma state, thereby emitting light. The light may be non-visible light, and the cap portion may be a window portion for emitting the non-visible light.

Advantageously, the lamp may be a longitudinally excited RF (Radio Frequency) driven PID (Photo Ionization Detector) lamp. The location of the seal in such lamps is at a location that has been found to make the getter sealant particularly effective at controlling contaminants.

A second aspect of the invention provides a sealant for vacuum sealing together a cap portion and a body portion of a low pressure discharge lamp, the sealant comprising a getter for controlling the levels of contaminants within the lamp. Advantageously, the incorporation of a known getter into a known sealant can produce a getter sealant. The getter sealant can perform a getter function without the need for a separate, additional getter.

The term low pressure discharge lamp as used herein indicates that the pressure inside the lamp is lower than atmospheric pressure. The external atmospheric pressure tends to force the cap and body portions together, and means the sealant is typically under compression rather than tension.

The term vacuum sealed means the cap portion is sealed to the body portion with a tight enough seal to maintain a vacuum within the lamp.

Advantageously, the sealant may be a frit glass sealant as frit glass is typically strong under compressive forces. Frit glass comprises a mixture of components which are vitrified together to form a glass, for example such components may include metal oxides such as Lead Oxide and Silicate compounds.

The getter is typically a non-evaporable getter to avoid the getter from discolouring the cap portion. The getter may continue to perform a getter function during the normal operation of the lamp.

A third aspect of the invention provides a method of manufacturing a lamp comprising a cap portion and a body portion, the method comprising providing the cap portion, the body portion, and a sealant; and heating the sealant to activate a getter function of the sealant for controlling the level of contaminants within the lamp.

Advantageously, the step of heating the sealant may further seal the cap portion to the body portion of the lamp, such that only one manufacturing step is required for both for forming the seal and performing the getter function.

Alternatively, the cap and body portions may be sealed together by the sealant, and the sealant subsequently re-heated below the seal formation temperature to perform the getter function.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figures 1 a and I b show schematic side and plan diagrams of a lamp with a sealant for performing a getter function according to an embodiment of the invention; and Figure 2 shows a flow diagram of a method for manufacturing a lamp according to an embodiment of the invention.

Figure 1 a shows a schematic side diagram of a low pressure discharge lamp comprising a cap portion 10 and a body portion 12. Figure lb shows a plan diagram of the lamp when viewing the lamp from a direction A indicated in Figure Ia. The cap portion 10 supports any electrodes that may be present within the lamp, and the body portion together with the cap portion contain an inert low-pressure gas. The cap portion 10 is sealed to the body portion 12 by a sealant 14.

The sealant 14 comprises a getter for performing a getter function. The getter function is realised by heat activating the getter during production of the lamp, and/or during the use of the lamp.

In an embodiment, the low pressure discharge lamp is an RF driven lamp, wherein an RF field excites the gas in the lamp to a plasma state, emitting light.

The cap portion may be a window portion that is transparent to visible light or non-visible light, for example Vacuum Ultra Violet (VUV) light. The window portion may for example be formed of a crystal of Magnesium Fluoride, Calcium Fluoride, Lithium Fluoride, Sapphire, Quartz.

The lamp may be driven with longitudinal or transverse RF radiation. The seal has been found to perform a particularly effective getter function when the lamp is longitudinally excited, due to the location of the seal of the lamp.

Alternatively, the low pressure discharge lamp comprises electrodes within the cap and/or body portion for exciting the low-pressure, inert gas.

Fig. 2 shows a flow diagram of a method for manufacturing a lamp according to an embodiment of the invention. The method comprises providing 20 a cap portion, a body portion, and a sealant, and heating 22 the sealant to activate a getter function of the sealant to control the level of contaminants within the lamp.

In one embodiment, the cap portion and the body portion are spaced apart by the sealant and the sealant is heated to form vacuum seal. The cap portion and the body portion may be filled with low pressure gas and the getter in the still-hot sealant can reduce the level of contaminants within the gas. Alternatively, the sealant may be allowed to cool, and then subsequently re-heated after filling with the gas to perform the getter function.

Claims

CLAIMS1. A low pressure discharge lamp comprising a cap portion and a body portion, the cap portion being vacuum sealed to the body portion by a sealant, and wherein the sealant comprises a getter for controlling the levels of contaminants within the lamp.
2. The low pressure discharge lamp of claim 1, wherein the sealant is a frit glass sealant.
3. The low pressure discharge lamp of claim 1 or 2, wherein the cap portion is a window portion for emitting non-visible light.
4. The low pressure discharge lamp of claim 1 or 2, wherein the cap portion is a window portion for emitting visible light.
5. The low pressure discharge lamp of claim 1, 2, or 3, wherein the lamp is a longitudinally excited RF driven Photo lonisation Detector (PID) lamp.
6. The low pressure discharge lamp of claim 1, 2, or 3, wherein the lamp is a transversely excited RF driven Photo lonisation Detector (PID) lamp.
7. The low pressure discharge lamp of claim 1, 2, 3, or 4, wherein the cap portion comprises electrodes for driving the lamp.
8. The low pressure discharge lamp of claim 1, 2, 3, 4, or 7, wherein the body portion comprises electrodes for driving the lamp.
9. The low pressure discharge lamp of any preceding claim, wherein the getter is a non-evaporable getter.
10. A sealant for vacuum sealing together a cap portion and a body portion of a low pressure discharge lamp, the sealant comprising a getter for controlling the levels of contaminants within the lamp.
11. A method of manufacturing a lamp comprising a cap portion and a body portion, comprising: -providing the cap portion, the body portion, and a sealant; and -heating the sealant to activate a getter function of the sealant for controlling the level of contaminants within the lamp.
12. The method of claim 11, wherein the step of heating the sealant further seals the cap portion to the body portion of the lamp.
13. The method of claim 11 or 12, further comprising re-heating the sealant to activate the getter function of the sealant for controlling the level of contaminants within the lamp.
14. A low pressure discharge lamp substantially as described herein or with reference to the accompanying drawings.
15. A method of manufacturing a lamp substantially as described herein or with reference to the accompanying drawings.