Electric lamp and discharge devices – With luminescent solid or liquid material – With gaseous discharge medium
Patent
1995-09-25
1998-02-03
Horabik, Michael
Electric lamp and discharge devices
With luminescent solid or liquid material
With gaseous discharge medium
313637, 2523014R, 2523014P, H01J 162, C09K 1108
Patent
active
057148350
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to fluorescent materials excitable by VUV (Vacuum Ultra Violet) radiation, and fluorescent lamps coated with them.
The present invention is related closely to German Patent Application P 43 11 197.1, to which International Application PCT/DE94/00380, published as WO94/23442, and United States National application Ser. No. 08/491,872, issued as U.S. Pat. No. 5,604,410 VOLLKOMER et al., correspond, in which a novel mode of operation for dielectrically impaired discharges is disclosed. The teaching provided in detail therein enables among others a markedly more efficient generation of UV and VUV radiation, especially by means of excimers--such as Xe.sub.2 *, which emits a molecular band radiation in the range around 172 nm--than was possible previously. Hereinafter, the term VUV radiation will be used to mean particularly electromagnetic radiation at wavelengths in the range between about 145 nm and 185 nm.
BACKGROUND
The primary field of application of modern fluorescent materials in lighting technology, or in other words for converting short-wave electromagnetic radiation into light, is the fluorescent lamp. Such a lamp is based on mercury low-pressure discharge, which outputs energy predominantly in the form of UV radiation. Essentially, this is radiation of an atomic spectral line with a wavelength of about 254 nm.
To meet the increasing demand for environmental awareness, mercury-free UV and VUV radiation sources have increasingly been developed recently. Until now, however, it was possible to attain only relatively low UV and VUV yields (approximately 10% to 20%, at industrially relevant power densities), by comparison with mercury low-pressure discharge (approximately 70%). It was therefore uneconomical to use this mercury-free UV or VUV radiator in an embodiment as a fluorescent lamp for general lighting, and such a use was therefore not considered. Accordingly there was also no need to search for fluorescent materials that are both readily excited in the VUV range and suitable in terms of their emission properties for purposes of general lighting. With the mode of operation described in the aforementioned patent application, it is possible for the first time to attain efficiencies of 65% and more in mercury-free discharges, particularly for generating VUV radiation. The high VUV yields are due in particular to the highly efficient generation of Xe.sub.2 * excimers. The radiation emitted is predominantly in the wavelength range between approximately 145 nm and 185 nm. A genuine alternative to conventional mercury low-pressure discharge has thus been found with a view to efficient radiation generation. However, if the novel radiation source is to be used in general lighting, then the conversion of the short-wave VUV radiation into light, that is, into the visible range of the optical spectrum, must be done.
THE INVENTION
The object of the invention is to provide fluorescent materials that luminesce efficiently in the visible range of the optical spectrum when irradiated with VUV radiation, especially at wavelengths in the range between approximately 145 nm and 185 nm.
A further object of the invention is to provide a fluorescent lamp with a fluorescent material coating suitable for purposes of general lighting, the lamp being based on a VUV radiator that in particular generates wavelengths in the range between approximately 145 nm and 185 nm.
One characteristic variable for the efficiency of the conversion of electromagnetic radiation by fluorescent materials is its wavelength-dependent excitability. This is proportional to the product of the absorption and the quantum efficiency. The latter is the likelihood of the generation of a photon by the fluorescent material after a photon of relatively short wavelengths (relatively high energy) has been absorbed. Maximum excitability accordingly is present if both the absorption and the quantum efficiency are 100%, or in other words every incident photon is absorbed and converted into a photon of longer wavel
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Charles Kittel's "Introduction to Solid State Physics", Sixth Edition, preface pages and pp. 359 through 363.
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Muller Ulrich
Schmidt Dieter
Zachau Martin
Day Michael
Horabik Michael
Patent-Treuhand-Gesellschaft F. Elektrische Gluehlampen mbH
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