WO2008120171A2

WO2008120171A2 - Discharge lamp comprising a low stability halogen donor material

Info

Publication number: WO2008120171A2
Application number: PCT/IB2008/051208
Authority: WO
Inventors: Achim G. R. Koerber; Rainer Hilbig; Daiyu Hayashi; Stefan Schwan
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2007-04-03
Filing date: 2008-04-01
Publication date: 2008-10-09
Also published as: WO2008120171A3

Abstract

The invention relates to a discharge lamp comprising a low stability halogen donor material. This material may be used to dose halogen, e.g. for formation of volatile metal halides or for controlled dosing of halogen in discharge lamps.

Description

Discharge lamp comprising a low stability halogen donor material

FIELD OF THE INVENTION

The present invention is directed to novel materials for light emitting devices, especially to the field of novel materials for discharge lamps.

BACKGROUND OF THE INVENTION

Discharge lamps form one of the most prominent, widely used and popular forms of lighting. Usually, these discharge lamps comprise metal halides, which are commonly dosed as solid compounds into gas discharge lamps using a glove box containing a dry, oxygen- free atmosphere (usually argon).

However, this procedure bears drawbacks for volatile (metal) halides having a vapor pressure >10Pa at room temperature or liquid or gaseous (metal) halides, because there is always the danger the glove box atmosphere will be contaminated and / or the metal halides will evaporate during closing of the lamp volume with the flame of an argon plasma torch. The same problems apply also to Liquid or gaseous (metal) halides or halogens X₂ (X = Cl, Br, I), because liquids or reactive gases are also very often not easily handled within a glove box.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an illumination system that is at least partly able to overcome the above-mentioned drawbacks and especially allows building a discharge lamp where a controlled dosage of halogen compounds is possible for a wide range of applications.

This object is solved by an illumination system according to claim 1 of the present invention. Accordingly, an illumination system, especially a discharge lamp, is provided comprising at least one low stability halogen-containing material with a negative standard enthalpy of formation of <86 kJ/mol per halogen atom.

The term "standard enthalpy of formation" especially refers to ΔHf^Θ of the solid state at standard reference conditions (T=298.15K, p=lbar) as defined in physical chemistry, cf. e.g. Hollemann-Wiberg, Lehrbuch der Anorganischen Chemie, 91-100. ed. de Gruyter, 1985, p. 51-53.

It should be noted that according to the present invention, the at least one low stability halogen-containing material may only be present before operation of the illumination system or during an initial phase. This is actually one preferred embodiment of the present invention, as will be described later on. However, there are also applications within the present invention, where the at least one low stability halogen-containing material may be present during the whole pass of operation of the illumination system.

Such an illumination system has shown for a wide range of applications within the present invention to have at least one of the following advantages:

Using such an illumination system, volatile halogen compounds may be obtained without (or with a much less) danger of contamination of e.g. a glove box during build-up of the illumination system

The dosage accuracy of halogen and/or halogen-containing compounds may for a wide range of applications greatly be increased, as will e.g. be shown by the examples and embodiments to follow

The materials used are usually non-toxic and are therefore usable for a wide range of applications within the present invention;

According to a preferred embodiment of the present invention, the at least one low stability halogen-containing material has a negative standard enthalpy of formation of preferably <80 kJ/mol per halogen atom, more preferably <70 kJ/mol per halogen atom, most preferred <60 kJ/mol per halogen atom. This has been shown to be advantageous for a wide range of applications within the present invention.

According to a preferred embodiment of the present invention, the at least one low stability halogen-containing material comprises at least one metal halide with a metal M¹ having a redox potential Eo of >0.82 V.

By doing so, it can be for a wide range of application be ensured that the least one low stability halogen-containing material is not formed again once it may decompose during operation of the lamp and/or that the metal will not overly reduce the performance of the illumination system.

The term "redox potential" especially means and/or includes the redox potential whereby the metal with oxidation number zero (i.e. the metal in elemental form) is the reduced part of the redox pair. In case that several redox potentials are known (e.g. the metal may form several oxidized states, such as Au(I) or Au(III)), the term "redox potential Eo of >X V " preferably means that one of these redox potentials is larger than X; however, it is in this case a preferred embodiment that all redox potentials are larger than X.

Preferably the at least one low stability halogen-containing material comprises at least one metal halogenide with a metal M¹ having a redox potential Eo of >0.9 V, more preferred >0.95 V and most preferred >1 V.

According to a preferred embodiment of the present invention, the at least one low stability halogen-containing material comprises at least one material with a standard sublimation enthalpy ΔH^Θ _subi >160 kJ/mol. This condition ensures that the low- stability halogen-containing material is not entering the vapor phase as a gaseous compound during operation of the lamp.

The term "standard sublimation enthalpy" ΔH^Θ _subi especially refers (in case the material is a metal halide) to the reaction enthalpy of the sublimation reaction

MX_n(S) <→ MX_n(g)

at standard reference conditions (T=298.15K, p=lbar).

Preferably the at least one low stability halogen-containing material comprises at least one material with a standard sublimation enthalpy of >180 kJ/mol and more preferred >200 kJ/mol. According to a preferred embodiment of the present invention, the at least one low stability halogen-containing material comprises at least one compound selected out of the group comprising AuCl₃, AuCl, AuBr, AuI, PtCl₄, PtCl₃, PtCl₂, PtBr₄, PtBr₃, PtBr₂, PtI₄, IrCl₃, IrBr₃, IrI₂, IrI, PdI₂, RuCl₃, TeBr₄ or mixtures thereof.

Some properties of some compounds according to this embodiment of the present invention are shown in the - merely illustrative and non-binding - tables I and II:

Table I

Table II

According to a preferred embodiment of the present invention, the illumination system comprises at least one metal precursor compound adapted to react with said at least one low stability halogen-containing material to a metal halide.

Said term "metal precursor compound" especially includes that this compound reacts with said at least one low stability halogen-containing material in a redox and/or halogen exchange reaction. According to a preferred embodiment of the present invention, the said at least one metal precursor compound is a solid and/or non- volatile compound.

The term "non-volatile compound" especially means and/or includes that this compound has at room temperature a vapor pressure of <10Pa, preferably <5 Pa and most preferred <2 Pa.

According to a preferred embodiment of the present invention, the said at least one metal precursor compound comprises a metal M^π selected out of the group comprising Ti, Nb, Ta, W, Mo, Os, Zn, Hg, earth alkali metals, alkali metals, rare earth metals, Al, B, Ga, Sc, Y or mixtures thereof. According to a preferred embodiment of the present invention, the illumination system comprises at least one noble gas and at least one low stability halogen- containing material.

According to a preferred embodiment of the present invention, the said at least one noble gas is selected out of the group comprising He, Ne, Ar, Kr, Xe or mixtures thereof. In most applications within the present invention, if a noble gas and at least one low stability halogen-containing material is used, the following situation can be found: When a lamp containing at least one noble gas and at least one low stability halogen-containing material is heated up for the first time - either by external heating means or by operating the lamp - the low stability halogen-containing material will release free halogen and the operated lamp will radiate the well-known quasi-molecular emission systems of the noble gas - halogen excimers. After switch-off and cooling down of such a lamp the free halogen molecules will stay in the vapor phase and not recombine again into the low stability halogen-containing material, because this recombination reaction is kinetically hampered. Such a lamp will therefore behave further on as a common noble gas - halogen excimer lamp.

According to a preferred embodiment of the present invention, the said metal halide is a volatile metal halide.

The term "volatile metal halide" especially means and/or includes that this compound has at room temperature a vapor pressure of >10Pa, preferably >15 Pa. According to a preferred embodiment of the present invention, the said metal halide is selected out of the group comprising TiCl₄, TiBr₄, NbCIs, NbBr₅, TaCl₅, TaBr₅, VOCl₃₅ VCl₄, MoCl₆, MoBr₆, OsCl₈, BCl₃, BBr₃, AlCl₃, AlBr₃, GaCl₃, SnCl₄, SbCl₃, SbBr₃, GeCl₄, GeBr₄, PBr₃, PI₃, PCl₃ or mixtures thereof. Some reaction partners (i.e. one possible low stability halogen-containing material and one metal precursor compound) as well as some of the reaction products (i.e. the metal halide) are shown in the - merely illustrative and non-binding - table III:

Table III

It should be noted that the metal halide is not the only reaction product out of a possible reaction between the low stability halogen-containing material and one metal precursor compound and that more reaction products may be obtained as well, which are - for better readability only - not shown in Table III..

According to one embodiment of the present invention, the said metal precursor compound is (at least before operation of the lamp or during an initial phase of the operation) present in molar excess (halogen converted) of the at least one low stability halogen-containing material.

The term "molar excess (halogen converted)" especially means and/or includes that if the metal halide and/or the at least one low stability halogen-containing material is not a monohalide that this is taken into account. E.g. in case the metal precursor material is Ti, the metal halide is TiCl₄, and the low stability halogen-containing material is AuCl₃ a molar excess means that Ti is present in more than 4/3-times molarity than AuCl₃ so that an excess of Ti metal will be remaining after all AuCl₃ has reacted according to the equation

Ti + 4/3* AuCl₃ ^■* TiCl₄ + 4/3* Au This has surprisingly be found to be advantageous for a wide range of application within the present invention for the following reasons:

If the at least one metal precursor compound is present in molar excess (as defined above) of the at least one metal precursor compound, the actual amount of metal halide present in the illumination system will be set by the amount of low stability halogen- containing material. This allows an exact dosage of the amount of metal halide in the lamp, since according to many embodiments of the present invention, this low stability halogen- containing material has a rather high molecular weight.

If the at least one metal precursor compound is present in molar excess (as defined above) of the at least one metal precursor compound, the excess of this metal precursor compound will act as a "halogen buffer"; that means it will bind any free halogen molecules X₂, which might unintentionally form due to reactions with the discharge vessel material or due to an over-stoichiometric amount of halogen in the dosed materials.

However, according to one alternative embodiment of the present invention, the at least one low stability halogen-containing material is (at least before operation of the lamp or during an initial phase of the operation) present in molar excess (halogen converted) of the at least one metal precursor compound.

This has surprisingly be found to be advantageous for a wide range of application within the present invention for the following reasons: - If the at least one low stability halogen-containing material is presented in excess, for many application it can be reached that the at least one low stability halogen- containing material will decompose during operation of the illumination system. Since not all of this halogen will then react with the said at least one metal precursor compound, there will be a fixed overpressure of halogen in the lamp. - In case there is decomposition of the metal halide, there will be a "feed" of metal halide due to the excess of the at least one low stability halogen-containing material.

According to a preferred embodiment of the present invention, the discharge lamp is a HID lamp, a dielectric barrier discharge (DBD) lamp, a TL, CFL and/or QL low- pressure discharge lamp either operated electrodeless (capacitively or inductively) in the RF or microwave frequency range and/or with internal electrodes at low frequencies or DC.

The present invention furthermore relates to the use of a halide-containing compound with a negative standard enthalpy of formation of <86 kJ/mol per halogen atom as halogen donor during operation of illumination systems, especially a HID metal halide lamp, a mercury ultra-high pressure (UHP) lamp, a dielectric barrier discharge (DBD) lamp, a TL, CFL and/or QL low-pressure discharge lamp either operated electrodeless (capacitively or inductively) in the RF or microwave frequency range and/or with internal electrodes at low frequencies or DC.

An illumination system according to the present invention may be of use in a broad variety of systems and/or applications, amongst them one or more of the following: Office lighting systems household application systems shop lighting systems, home lighting systems, - accent lighting systems, spot lighting systems, theater lighting systems, fiber-optics application systems, projection systems, - self- lit display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, - indicator sign systems, and decorative lighting systems portable systems automotive applications green house lighting systems

The aforementioned components, as well as the claimed components and the components to be used in accordance with the invention in the described embodiments, are not subject to any special exceptions with respect to their size, shape, material selection and technical concept such that the selection criteria known in the pertinent field can be applied without limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional details, features, characteristics and advantages of the object of the invention are disclosed in the subclaims, the figures and the following description of the respective figures and examples, which —in an exemplary fashion— show several embodiments and examples of illumination systems according to the present invention.

Fig. 1 shows several measurements of emission spectra of a discharge lamp according to Example I of the present invention. Fig. 2 shows a measured and simulated emission spectrum of a discharge lamp according to Example II of the present invention.

Fig.3 shows a measured emission spectrum of a discharge lamp according to Example III of the present invention.

EXAMPLE I:

Fig. 1 refers to Example I which was set up as follows:

A tubular quartz envelope with 24 mm inner diameter and 250 mm length, i.e. a volume of 113 ccm, was filled with 0.049 mg Ti, 0.079mg Nb, 0.84 lmg AUCI₃ and 5 mbar Xe (pressure at room temperature).

85 W of RF power of 13.56 MHz frequency were capacitively coupled into the lamp by means of external aluminum electrodes. At different times and coldest spot temperatures the emission spectra of Figure 1 have been measured:

At the start of the measurement (dotted curve in Figure 1) one recognizes the Xe-lines above 800nm and a small contribution from the XeCl B-X band system (max. at 308nm), which is formed by Xe and Cl released from the AuCl₃. At 1600sec the oven temperature has reached 341⁰C, the AuCl₃ has released all of its Cl and the XeCl band system is very strong (thin black line in Figure 1). After several hundred seconds the TiCl ⁴F- X⁴Φ band system at about 420nm starts to develop. At the end of the measurement - when the temperature is down again - it can be seen most clearly (thick black line in Figure 1). This measurement thus demonstrates that this invention is indeed working for the case of low-pressure ("molecular radiator") lamps.

EXAMPLE II: Fig. 2 refers to Example II which was set up as follows:

A spherical quartz envelope with 32 mm inner diameter, i.e. a volume of 17 ccm, was filled with 0.105 mg Ti, 1.157 mg AuCl₃, 0.36 mg WO₂Cl₂ and 100 mbar Ar (pressure at room temperature). About 630 W of microwave power of 2.45 GHz frequency were coupled into the lamp by placing it into a half-spherical brass resonator. The measured emission spectrum is drawn in Figure 2. The following light technical data have been derived from this measurement: Chromaticity co-ordinates x=0.3955, y=0.3725 corresponding to a color temperature T_C=3574K, HP red =21.37%, general color rendering index Ra₈=94.46, luminous flux Φ=481631m, luminous efficacy η=761m/W, total visible radiation

(400..780nm) P_V1S=243.3W, total photon quantity =9.17E20 /s corresponding to 1.45E18 Photons/joule.

Figure 2 also contains a simulated spectrum (dashed) emitted by three band systems (A-X, B-X and C-X) of the TiO molecule. It is apparent that this simulation matches the experimental spectrum very well over the whole spectral range and that radiation emitted by TiO molecules contributes by far the largest amount of the total emitted radiation.

A thermodynamic calculation shows that the dosed amount OfWO₂Cl₂ just evaporates without taking part in any reactions at low temperatures, whilst the AuCl₃ releases all its chlorine to form TiCU and Cl₂. In the hot, radiating centre of the discharge the polyatomic molecules TiCU and WO₂Cl₂ dissociate into atoms which may recombine into diatomic molecules - especially TiO and TiCl. The narrow band system around 420nm in Figure 2 is due to the ⁴F-X⁴Φ transition in TiCl. The emission spectrum of Figure 2 is, however, dominated by the band systems of TiO.

EXAMPLE III:

Fig. 3 refers to Example III which was set up as follows:

A tubular quartz tube with 40 mm inner diameter and 90 mm length, i.e. a volume of 145 ccm, was filled with 0.84 mg ZrCU, 0.47 mg MoCl₃, 0.25 mg AuCl₃ and 18 mbar Xe (pressure at room temperature). A sufficient amount of oxygen was delivered by reactions with the quartz wall material. 280 W of RF power of 14 MHz frequency were inductively coupled into the lamp by means of an external air coil on the burner (1 mm silver wire, 7 windings). At a coldest spot temperature of 240 ⁰C the emission spectrum of Figure 3 has been measured. The emission of the embodiment lamp 3 between 500 nm and 660 nm is mainly due to radiation from the diatomic ZrO.

The desired, volatile molybdenum chloride would be MoCU. However, MoCU cannot (or only with great difficulty) be filled into the lamp within a glove box, because it has a high vapor pressure at room temperature. Therefore, the readily available, non-volatile M0CI3 plus AuCl₃ was dosed to form the volatile MoC^ during the first heating-up of the lamp as described above.

The particular combinations of elements and features in the above detailed embodiments are exemplary only; the interchanging and substitution of these teachings with other teachings in this and the patents/applications incorporated by reference are also expressly contemplated. As those skilled in the art will recognize, variations, modifications, and other implementations of what is described herein can occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention's scope is defined in the following claims and the equivalents thereto. Furthermore, reference signs used in the description and claims do not limit the scope of the invention as claimed.

Claims

CLAIMS:

1. Illumination system, especially a discharge lamp, comprising at least one low stability halogen-containing material with a negative standard enthalpy of formation of <86 kJ/mol per halogen atom.

2. Illumination system according to claim 1, whereby the at least one low stability halogen-containing material comprises at least one material with a standard sublimation enthalpy ΔH^Θ _subi >160 kJ/mol.

3. Illumination system according to claim 1 or 2 , whereby the at least one low stability halogen-containing material comprises at least one compound selected out of the group comprising AuCl₃, AuCl, AuBr, AuI, PtCl₄, PtCl₃, PtCl₂, PtBr₄, PtBr₃, PtBr₂, PtI₄, IrCl₃, IrBr₃, IrI₂, IrI, PdI₂, RuCl₃, TeBr₄ or mixtures thereof

4. Illumination system according to any of the claims 1 to 3 furthermore comprising at least one noble gas., preferably selected out of the group comprising He, Ne, Ar, Kr, Xe or mixtures thereof.

5. Illumination system according to any of the claims 1 to 4, furthermore comprising at least one metal precursor compound adapted to react with said at least one low stability halogen-containing material to a metal halide.

6. Illumination system according to claim 5, whereby said at least one metal precursor compound is a solid and/or non- volatile compound.

7. Illumination system according to any of the claims 1 to 6, whereby said at least one metal precursor compound comprises a metal M^π selected out of the group comprising Ti, Nb, Ta, W, Mo, Os, Zn, Hg, earth alkali metals, alkali metals, rare earth metals, Al, B, Ga, Sc, Y or mixtures thereof.

8. Illumination system according to any of the claims 1 to 7, whereby said metal halide is a volatile metal halide.

9. Illumination system according to any of the claims 1 to 8, whereby the discharge lamp is a HID lamp, a dielectric barrier discharge (DBD) lamp, a TL, CFL and/or QL low-pressure discharge lamp either operated electrodeless, capacitively or inductively, in the RF or microwave frequency range and/or with internal electrodes at low frequencies or DC.

10. A system comprising an illumination system according to any of the claims 1 to 9, the system being used in one or more of the following applications:

Office lighting systems household application systems shop lighting systems, - home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, fiber-optics application systems, - projection systems, self-lit display systems, pixelated display systems, segmented display systems, warning sign systems, - medical lighting application systems, indicator sign systems, and decorative lighting systems, portable systems, automotive applications, - green house lighting systems.