Electric lamp and discharge devices – With luminescent solid or liquid material – With gaseous discharge medium
Reexamination Certificate
2002-04-25
2004-11-23
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
With gaseous discharge medium
C313S582000, C252S30140R
Reexamination Certificate
active
06822385
ABSTRACT:
The invention relates to a gas discharge lamp fitted with a gas discharge vessel filled with a gas suitable for supporting a gas discharge emitting VUV radiation, with a luminophore coating containing a down conversion luminophore and with means for igniting and maintaining a gas discharge.
Conventional fluorescent lamps are mercury gas discharge lamps, the light emission of which is based on mercury low pressure gas discharge. A mercury low pressure gas discharge emits radiation mainly in the near UV with a maximum at 254 nm which is converted into visible light by UV luminophores.
The mercury gas discharge lamp has a refined technology and with regard to the lamp efficiency &eegr;
lamp
can only be matched or exceeded with difficulty by other lamp technologies.
The mercury in the gas filling is however increasingly regarded as an environmentally harmful and toxic substance which should be avoided as far as possible in modern mass production because of environmental risks in use, production and disposal. Therefore for some time efforts have been concentrated on the development of alternative lamp technologies.
One of the mercury-free or low-mercury alternatives to the conventional mercury gas discharge lamp is the xenon low pressure gas discharge lamp which has a gas filling containing mostly xenon. A gas discharge in a xenon low pressure gas discharge lamp emits vacuum ultraviolet radiation (VUV radiation) in contrast to the UV radiation of the mercury discharge. The VUV radiation is generated by excimers e.g. Xe
2
*, and is a molecular band radiation with a broad spectrum in the range about 172 nm. Using this lamp technology discharge efficiencies &eegr;
dis
of 65% are achieved.
Another advantage of the xenon low pressure gas discharge lamp is the short response time of the gas discharge which makes it useful as a signal lamp for automobiles, as a lamp for copier or fax devices and as a water disinfection lamp.
However although the xenon low pressure gas discharge lamp has achieved a discharge efficiency &eegr;
dis
which is comparable to that of the mercury gas discharge lamp, the lamp efficiency &eegr;
lamp
of the xenon low pressure gas discharge lamp is still clearly lower than that of the mercury gas discharge lamp.
In principle the lamp efficiency &eegr;
lamp
consists of the components discharge efficiency &eegr;
dis
, luminophore efficiency &eegr;
phos
, the proportion of the generated visible light which leaves the lamp &eegr;
esc
and the proportion &eegr;
vuv
of UV radiation generated by the luminophore:
&eegr;
lamp
=&eegr;
dis
·&eegr;
phos
·&eegr;
esc
·&eegr;
vuv
.
One handicap of the conventional xenon low pressure gas discharge lamp lies in the conversion, ineffective in principle, of an energy-rich VUV photon with wavelength of around 172 nm into a comparatively low energy photon from the visible spectrum of 400 nm to 700 nm through the luminophore coating of the lamp. Even if the quantum efficiency of the luminophore is close to 100%, by conversion of a VUV photon into a visible photon, on average 65% of the energy is lost due to radiationless transition.
Surprisingly however it has already been possible to develop VUV luminophores which achieve a quantum efficiency of more than 100% for conversion of VUV photons into visible photons. This quantum efficiency is achieved in that a VUV quantum with an electron energy of 7.3 eV is converted into two visible quantums with an electron energy of 2.5 eV. Such luminophores for xenon low pressure gas discharge lamps are known for example from René T. Wegh, Harry Donker, Koentraad D. Oskam, Andries Meijerink “Visible Quantum Cutting in LiGdF
4
:Eu
3+
through Downconversion” Science 283, 663.
In analogy to the multiphoton luminophores known for some time, which through “up conversion” generate from two visible long-wave photons one short-wave photon, these new luminophores, which generate from one short-wave photon two long-wave photons, are known as down conversion luminophores.
But although the quantum efficiency of the known down conversion luminophores is high, this does not mean that consequently the luminophore efficiency &eegr;
phos
is high. The luminophore efficiency &eegr;
phos
is influenced not only by the quantum efficiency but also by the capacity of the luminophore to absorb the VUV radiation to be converted. The absorption capacity of the known down conversion luminophores is however quite low. Too much energy is lost through undesirable absorption in the lattice and hence the occupation of the excited states reduced.
It is an object of the present invention to develop a gas discharge lamp fitted with a gas discharge vessel filled with a gas suitable for gas discharge which emits VUV radiation, with a luminophore coating which contains a down conversion luminophore and with means for igniting and maintaining a gas discharge, and with improved efficiency.
According to the invention this object is achieved by a gas discharge lamp fitted with a gas discharge vessel filled with a gas filling suitable for supporting a gas discharge emitting VUV radiation, with a luminophore coating containing a down conversion luminophore and with means for igniting and maintaining a gas discharge, in which the down conversion luminophore contains a pair of activators of a first lanthanoid ion and a second lanthanoid ion and a sensitizer selected from the group of the cerium (III) ion, praseodymium (III) ion, neodymium (III) ion, samarium (III) ion, europium (III) ion, gadolinium (III) ion, terbium (III) ion, dysprosium (III) ion, holmium (III) ion, erbium (III) ion, thulium (III) ion, ytterbium (III) ion and lutetium (III) ion.
Particularly advantageous effects in relation to the state of the art are obtained by the invention if the first lanthanoid ion is the gadolinium (III) ion and the second lanthanoid ion is selected from the holmium (III) ion and the europium (III) ion.
As part of the present invention it is preferred for the down conversion luminophore to contain as the first lanthanoid ion the gadolinium (III) ion and as the second lanthanoid ion the holmium (III) ion and a co-activator selected from the group of the terbium (III) ion, ytterbium (III) ion, dysprosium (III) ion, europium (III) ion, samarium (III) ion and manganese (II) ion.
It can also be preferred that the host lattice of the down conversion luminophore is a fluoride.
It is particularly preferred that the down conversion luminophore contains the first lanthanoid ion in a concentration of 10.0 to 99.98 mol %, the second lanthanoid ion in a concentration of 0.01 to 30.0 mol % and the sensitizer in a concentration of 0.01 to 30 mol %.
According to one embodiment of the gas discharge lamp according to the invention the down conversion luminophore contains the sensitizer in a concentration of 0.5 mol %.
In a different embodiment of the invention the down conversion luminophore contains the co-activator in a concentration of 0.01 to 30 mol %.
According to a further embodiment of the invention the down conversion luminophore contains a co-activator in a concentration of 0.5 mol %.
The invention also relates to a down conversion luminophore which contains in a host lattice a pair of activators of a first lanthanoid ion and a second lanthanoid ion and a sensitizer selected from the group of the cerium (III) ion, praseodymium (III) ion, neodymium (III) ion, samarium (III) ion, europium (III) ion, gadolinium (III) ion, terbium (III) ion, dysprosium (III) ion, holmium (III) ion, erbium (III) ion, thulium (III) ion, ytterbium (III) ion and lutetium (III) ion.
The luminophore is characterized by a high quantum efficiency, a high absorption of VUV photons and also a high chemical resistance and is therefore particularly suited for commercial applications including in plasma screens. Such a luminophore can advantageously also be used for signaling lamps in motor vehicles.
The invention is now described in more detail.
A gas discharge lamp according to the invention comprises a gas discharge vessel with a gas filling and with at least one wall which
Meijerink Andries
Oskam Koert
Bartlett Ernestine C.
Colón German
Koninklijke Philips Electronics , N.V.
Patel Ashok
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