Gas discharge lamp for producing light

FIELD OF THE INVENTION:

The invention relates to a gas discharge lamp for producing light, in particular to a low-pressure discharge lamp and a high-pressure discharge lamp.

BACKGROUND OF THE INVENTION:

Unless otherwise indicated, the term "light" is used in its broadest sense to encompass the visible light, ultra-violet (UV) and infra-red (IR) ranges.

Historically, discharge lamps have been split into two main types - low pressure discharges and high pressure discharges. High pressure discharges are also called high- intensity discharges (HID). Although the two types share many similarities in construction, there are several important differences:

- low pressure discharge lamps offer high efficacy at lower luminance - for example, fluorescent lamps for office lighting. High intensity discharges offer very high brightness - for examples spot lights for shop lighting. - they operate in different physical and chemical modes. Low pressure discharges operate typically at total pressures below 10 mbar (mainly provided by the pressure of a buffer gas), with a partial pressures of the active or radiating species of about 0.01 mbar (mercury vapor pressure, for example). Low-pressure discharges may be described as a non-thermal equilibrium discharge because the electron temperature (also known as the average kinetic energy of free electrons) and the gas temperature are very different. The low- pressure discharge normally has a diffuse appearance. HID lamps operate at pressures typically above 1 bar (also provided by the pressure of a buffer gas). Light is emitted by both the buffer gas and active species in the form of additives with a partial pressure above 1 mbar. The HID discharges may be described as a so called local thermal equilibrium discharge because the electron temperature is only slightly higher than the temperature of the gas in the discharge. The high-pressure discharge normally has a less-diffuse appearance due to the constriction of the discharge arc.

For both low- and high-pressure lamps, the discharge vessel is usually constituted by a light-transmitting envelope enclosing a fill in a gastight manner. The

discharge vessel is generally circular and comprises both elongate and compact embodiments. Normally, the means for generating and maintaining a discharge in the fill are electrodes arranged near the fill supplied by a current operating at low frequencies or DC. Alternatively, the fill may be excited by so-called electrode-less means where use is made of a capacitively or inductively induced alternating electromagnetic field in the RF or microwave frequency range.

In the known low-pressure discharge lamps comprising mercury vapor in the fill, the light emitted by the excited mercury atoms is mainly ultraviolet radiation at a wavelength of approximately 254 nanometer. Typically, this ultraviolet radiation is subsequently absorbed by a luminescent layer, for example a phosphor, applied to the inside of the discharge vessel 20 which converts the absorbed ultraviolet radiation into, for example, visible radiation of a predetermined color. However, energy is lost during this conversion by the luminescent layer by the production of heat, reducing the efficiency of the mercury vapor discharge lamp. Additionally, mercury is undesirable because of its toxicity and its adverse effects on the environment.

Low-pressure discharge lamps using a fill with transition metal halides are known from the unpublished European patent application EP 06 113 933.3. The application describes the use of Group IVB (M=Ti, Zr, Hf) halides which emit mainly UV and blue radiation from atomic M-lines, ionic M+-lines and molecular M-halide band systems. However, this means that a phosphor is still required to achieve a broad spectrum of output radiation, and thus the attainable luminous efficacy is limited.

SUMMARY OF THE INVENTION:

It is an object of the invention to provide a low-pressure discharge lamp which is essentially mercury free, and which provides output light over a broad spectrum of wavelengths with a higher luminous efficacy.

According to a first aspect of the invention the object is achieved by providing a gas discharge lamp for producing light, comprising: a gas discharge vessel comprising a fill of a buffer gas and an active constituent; an exciter for exciting the fill to cause a light emitting discharge; wherein the active constituent comprises: a halogen selected from the group consisting of fluorine F, chlorine Cl, bromine Br, and iodine I; a transitional metal selected from Group IVB, VB, VIB or VIIB of the periodic table, and sulfur; in amounts such that, when excited, the discharge fill emits light.

The low-pressure discharge lamps from unpublished European patent application EP 06 113 933.3 require a luminescent layer because they suffer from a deficiency of green and red contributions in their spectra. The low-pressure discharge lamp according to the invention generates radiation by the emission from sulfur or a compound with sulfur present in the discharge space 50. While not wishing to be bound by theory, it is believed that molecules of Group IVB, VB, VIB or VIIB sulfides are present in the discharge space 50. Surprisingly, the atoms dissociated by the discharge not only recombine into stable sulfides, such as HfS or HfS2, but the sulfides also produce an intense molecular band radiation in the green and red radiation bands. According to an aspect of the invention, the transitional metal and the halogen are combined in a halide. This provides a convenient way to introduce the transitional metal and the halogen into the fill, for example, as hafnium bromide, zirconium chloride, tantalum chloride, hafnium bromide, hafnium chloride, titanium bromide, rhenium chloride and any combination thereof. According to aspects of the invention, the fill may be prepared using any convenient combinations of compounds and elements to introduce the elements of the active constituent, including:

- wherein the active constituent comprises: a compound of the transitional metal, and the halogen is comprised in a halide; - wherein the transitional metal and the sulfur are combined in a sulfide, and the halogen is comprised in a halide;

- wherein the sulfur is comprised in elemental sulfur.

This provides maximum flexibility during the manufacture of the discharge lamp, according to the invention. According to an aspect of the invention, the lamp is configured for low- pressure discharge, and the sum of elemental molar concentrations of the halogen, the transitional metal and the sulfur is at least IE-11 mol/cc in the gas discharge vessel. This provides a low-pressure discharge lamp with a certain minimum amount of radiation power from the elements of the active constituent. According to an aspect of the invention, the lamp is configured for high- pressure discharge, and the sum of elemental molar concentrations of the halogen, the transitional metal and the sulfur is at least 1E-08 mol/cc in the gas discharge vessel. This provides a high-pressure discharge lamp with a certain minimum amount of radiation power from the elements of the active constituent

BRIEF DESCRIPTION OF THE DRAWINGS:

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

In the drawings:

Figures 1 and 2 show two embodiments of a cross-sectional view of a gas discharge lamp according to the invention,

Figures 3(A and B), 4, 5 and 6 show emission spectra of low-pressure gas discharge lamps according to the invention comprising a fill comprising hafnium bromide, zirconium chloride, tantalum chloride, and hafnium bromide respectively; and

Figures 7, 8, 9, 10 and 11 show emission spectra of high-pressure gas discharge lamps according to the invention comprising a fill comprising hafnium chloride, titanium bromide, zirconium chloride, tantalum chloride, and rhenium chloride respectively. The figures 1 and 2 are purely diagrammatic and not drawn to scale.

Particularly for clarity, some dimensions are exaggerated strongly. Similar components in the figures are denoted by the same reference numerals as much as possible.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS: Figure 1 and 2 show very schematically a cross-sectional view of two embodiments of a discharge lamp 10,15 according to the invention. The gas discharge lamp 10,15 according to the invention comprises a radiation transmitting discharge vessel 20,25 which encloses a discharge space 50 in a gas-tight manner. The discharge vessel 20,25 comprises a gas fill, for example, comprising a buffer gas 60 and an active constituent 70. The gas discharge lamp 10,15 further comprises an exciter 30,35 for causing and maintaining a discharge in the fill. The exciter 30,35 couples energy into the fill, for example, via capacitive coupling, inductive coupling, microwave coupling, or via electrodes.

In the discharge lamp 10,15 according to the invention, the fill 50 comprises an active constituent 70 and a buffer gas 60. The active constituent 70 comprises: - a halogen, for example, fluorine, chlorine, bromine, and/or iodine; a transitional metal selected from Group IVB, VB, VIB or VIIB of the periodic table, and sulfur.

The buffer gas 60 comprises an inert gas, for example, helium, neon, argon, krypton and/or xenon.

In the embodiment shown in Figure 1 the exciter 30 comprises a set of electrodes 30 supplied by a low frequency or DC current (not shown). In Figure 1 only one electrode 30 of the set of electrodes 30 is shown. The electrodes 30 are electrical connections through the discharge vessel 20 of the gas discharge lamp 10. By applying an electrical potential difference between the two electrodes 30, a discharge is initiated between the two electrodes 30. This discharge is generally located between the two electrodes 30 and is indicated in Figure 1 as the discharge space 50. Figure 2 shows an embodiment of the gas discharge lamp 15 with an exciter

35 comprising an inductive coupler 35 supplied by a RF or microwave frequency source (not shown). The exciter 35 inductively maintains the discharge in the gas discharge lamp 15. Alternatively the inductive coupler 35 may also be used for generating the discharge. The inductive coupler 35, also referred to as power coupler 35, generally comprises a coil wound over a ferrite core, for example Nickel- Zinc ferrite or Manganese-Zinc ferrite. The inductive coupler 35 is arranged in a protrusion 26 in the discharge vessel 25 and generates a varying electromagnetic field inside the discharge vessel 25 at the discharge space 50. The benefits of inductively generating and/or maintaining the discharge in the low-pressure gas discharge lamp 15 is that the electrodes 30, which generally limit the lifetime of low-pressure gas discharge lamps, can be omitted. Alternatively, the inductive coupler 35 may be arranged outside (not shown) of the discharge vessel 25 resulting in a simplification of the manufacturing process for the discharge vessel 25. As will be apparent to the person skilled in the art, an exciter comprising a capacitive coupler may also be used.

If the gas discharge lamp 10,15 according to the invention is configured for low-pressure discharge, a molecular gas discharge takes place which emits radiation comprising the characteristic lines of the fill. In general, light generation in a low-pressure gas discharge lamp is based on the principle that charge carriers, particularly electrons but also ions, are accelerated by an electric field applied between the electrodes 30 in the discharge vessel 20, or by an electromagnetic field applied by the inductive coupler 35 in the discharge vessel 25. Collisions of these accelerated electrons and ions with the gas atoms or molecules in the gas fill in the discharge vessel cause these gas atoms or molecules to be dissociated, excited or ionized. When the atoms or molecules of the gas fill return to the ground state, a more or less substantial part of the excitation energy is converted to radiation. The emission spectrum of the low-pressure gas discharge lamp 10, 15 is

determined by the active constituent 70 of the gas fill, together with, for example, the pressure and temperature inside the discharge vessel 20,25. The active constituent 70 comprises different metal compounds such as metal atoms and molecules which all contribute to the emission spectrum of the low-pressure gas discharge lamp 10, 15 according to the invention.

The low-pressure discharge lamp according to invention generates radiation by the emission from sulfur or compounds with sulfur in the discharge space 50. While not wishing to be bound by theory, it is believed that molecules of Group IVB, VB, VIB or VIIB sulfides are present. During manufacture of the discharge lamp 10, 15, sulfur or a compound of sulfur was introduced into the discharge envelope 20,25 with a Group IVB, VB, VIB or VIIB transition metal halide, for example HfBr4, and a buffer gas 60. During operation, it is believed that the heat of discharge evaporated these filling substances which diffused into the hot central region of the discharge space 50, where they dissociated into their constituent atoms. It is further believed that these atoms not only recombine into very stable mono sulfides, such as HfS, but that it is the presence of theses sulfides which produce the intense molecular band radiation in the green and red radiation bands. This is surprising given their expected unsuitability for use in a discharge lamp. The sulfides of Group IVB, VB, VIB or VIIB transitional metals have very low vapor pressures above their solid or liquid state phases - for example, for solid hafnium di-sulphide HfS2, the vapour pressure is below 10-14 bar at a temperature of 1300 K. Therefore, it is difficult to bring sufficient transitional metal sulfide into the vapor phase at the coldest spot temperatures that are feasible for normally used wall materials of the discharge vessel 20,25. Such wall materials include quartz, aluminium oxide and ceramic materials such as poly crystalline alumina (PCA). Additionally, the spectra of the transition metal sulfides are not generally known to the skilled person. For example, in the case of a fill comprising HfBr4, a buffer gas 60, and sulfur

S, it is believed that, at the coldest spot temperatures (such as about 500 K for low pressure discharge), the hafnium goes into the vapor phase as hafnium tetra halide HfX4, where X is = Cl, Br, I), and sulfur is evaporated as S8. It is further believed that these atoms then recombine into the sulfide HfS. The hafnium and the sulfur are thus brought separately into the vapor phase without, it is believed, forming the very stable HfS2 at the coldest spot. Further, it is believed that the filling HfX4 + S is chemically stable in the closed system - that HfS is formed in the hot regions of the discharge space 50 and that the reverse reaction back-reaction to HfX4 + S 8 takes place in the colder regions of the lamp.

The evaporated species are HfX4 and S8. The skilled person would not expect that dissociation of these molecules by electrons in the heat of discharge would lead to a sulfide like like HfS. He would expect Hf, X, HfXl, etc. and S, S2, S3, etc. It is believed that atomic Hf and atomic sulfur recombine to form hafnium mono-sulphide HfS. This special recombination is surprising to the skilled person because this happens under presence of the plasma and does not result in the original molecules supplied in the gas fill 50. It is further believed that the intense molecular radiation produced results from HfS because the formation of HfS is the main channel for recombination, or the molecular band emission of interest is a very strong transition, or a mixture of both. From the measurements and calculations, it is believed that HfS produces up to 80% of the total amount of light emission.

As the invention demonstrates an indirect way of providing the required emission species to the discharge, it will be obvious to the skilled person that other starting compounds may be introduced into the discharge vessel 20,25. For example:

- a pure Group IVB and Group VB, Group VIB or Group VIIB metals together with an halogen and oxygen;

- a sulfide of a Group IVB and Group VB, Group VIB or Group VIIB metal together with a halide;

- a suitable compound of a Group IVB and Group VB, Group VIB or Group VIIB metal together with a halide and sulfur, and - or other compounds of those elements provided that the sum of the elemental molar concentrations of the transition metal and the halogen and the sulfur is within the right ranges. In a preferred embodiment of the low-pressure discharge lamp 10, 15 according to the invention, the sum of elemental molar concentrations of the halogen, the transitional metal and the sulfur is at least IE-11 mol per cubic centimeter (cc) in the gas discharge vessel (20). For low-pressure discharges the generated radiation power is directly proportional to the radiator concentration c _rad (that is the elemental concentrations of the transition metal and the halogen and the sulfur:

P _rad =h*v*exp(-E _k /kT) *A _lk *V*N _A * c _rad .

The lower limit (1.E-I lmol/cc) is therefore determined by a certain minimum amount of radiation power P _rad per volume V.

A possible upper limit (l.E-6mol/cc) corresponds to a summed elemental pressure of approximately 0.2 bar.

The low-pressure discharge lamp according to the invention may be used in new generations of Tubular Fluorescent (TL) or Compact Fluorescent Lamp (CFL) low- pressure discharge lamps, or in Quality Lighting (QL) .which are inductively coupled low- pressure fluorescent lamps. Figures 3(A and B), 4, 5 and 6 show emission spectra of low-pressure gas discharge lamps according to the invention comprising a fill comprising hafnium bromide, zirconium chloride, tantalum chloride, and hafnium bromide, respectively.

EXAMPLE 1 A discharge vessel 20, 25 in the form of a tubular quartz envelope with 24 mm inner diameter and 250 mm length, i.e. a volume of 113 cc, was filled with:

- a buffer gas 60 of 5 mbar (pressure at room temperature) Xe, and

- an active constituent 70 of 0.8 mg HfBr4 and 0.05 mg elemental sulfur. The fill was excited using 93 W of RF power at 13.56 MHz. This was capacitively coupled into the discharge space 50 by means of external aluminium electrodes.

At a coldest spot temperature of 259 ⁰ C the emission spectrum 110 of Figure 3 A and 3B was measured. Figures 3 A and 3B depict the lamp emission spectrum 110, with wavelength in nanometers (nm) increasing along the horizontal axis and intensity in Watts per nanometer increasing along the vertical axis. Figures 3A and 3B depict the predicted spectrum emitted by five band systems of the HfS molecule: - A ¹ E - X ¹ E 112; - B ¹ II - X ¹ E 113, - D ¹ II - X ¹ E 115, - E ¹ LI - X ¹ E 116, and - F ¹ E - X ¹ E 117.

Terms, such as "B ¹ FI" or "X ¹ E", are commonly used to denote the electronic states of molecules.

For clarity, Figure 3 has been divided into two parts, 3A and 3B. Both Figures 3 A and 3B show the identical lamp emission spectrum 110. However, Figure 3 A depicts only the A 112, D 115 and F 117 parts of the predicted spectrum, and Figure 3B depicts only the B 113 and E 116 parts of the predicted spectrum. This simulation 112 - 117 matches the structure of the emitted spectrum 110 quite well in the green and red visible radiation ranges,

and also in the near infrared (IR) range. From calculation, it is believed that the radiation emitted by HfS molecules contribute about 80% of the total emitted radiation 110.

EXAMPLE 2 Similarly to Example 1, a tubular quartz envelope with 24 mm inner diameter and 250 mm length, i.e. a volume of 113 cc, was filled with 5 mbar Xe and 0.05 mg of elemental sulfur. However, for Example 2, 0.3 mg ZrCW was added to the fill 50

The fill 50 was excited using 91 W of RF power at 13.56 MHz frequency which was capacitively coupled into the lamp by means of external aluminium electrodes. At a coldest spot temperature of 172 ⁰ C the emission spectrum 120 of Figure 4 was measured. Figure 4 depicts the lamp emission spectrum 120, with wavelength in nanometers (nm) increasing along the horizontal axis and intensity in Watts per nanometer increasing along the vertical axis. The measured spectrum 120 comprises a UV-blue part 122 from approximately 250 to 550nm, and a red-infrared part 124 from approximately 550 to 950nm. It is believed that the UV-blue emission part 122 is mainly due to line like emission of atomic Zr above a continuous spectrum of diatomic sulfur. The emission 124 longer than 550 nm is believed mainly to be due to ZrS. From calculation, it is believed that the radiation emitted by ZrS molecules contributes about half to the total emitted radiation 120.

EXAMPLE 3:

Similarly to Example 1, a tubular quartz envelope with 24 mm inner diameter and 250 mm length, i.e. a volume of 113 cc, was filled with 5 mbar Xe and 0.05 mg of elemental sulfur. However, for Example 3, 0.4 mg TaC15 was added to the fill 50.

The fill 50 was excited using 91 W of RF power at 13.56 MHz which was capacitively coupled into the lamp by means of external aluminium electrodes.

At a coldest spot temperature of 340 ⁰ C the emission spectrum 130 of Figure 5 was measured. For comparison, the emitted spectrum 132 without sulfur - i.e. for pure tantalum chloride - was measured, and also shown in Figure 5.

The main difference between the two spectra 130,132 is in the red wavelength range 500 to 700 nm - the intensity of emission 130 in this range by the discharge lamp according to the invention is greater than the emission 132 using tantalum chloride, and it is believed to be due to the presence of TaS in the discharge space 50.

EXAMPLE 4:

A discharge vessel 20, 25 in the form of a tubular quartz envelope with 48 mm inner diameter and 100 mm length, i.e. a volume of 180 cc, was filled with:

- a buffer gas 60 of 2 mbar (pressure at room temperature) Xe, and

- an active constituent 70 of 0.9 mg HfBr4, 0.08 mg of elemental sulfur and 0.13 mg of metallic Hf.

The fill 50 was excited using 270 W of RF power at 8 MHz frequency which was inductively coupled into the lamp by means of an air coil with 7 windings put on the outer surface of the quartz envelope.

At a coldest spot temperature of about 200 ⁰ C the first emission spectrum 140 of Figure 6 was measured. Figure 6 depicts the lamp emission spectra 140, 142, with wavelength in nanometers (nm) increasing along the horizontal axis and intensity in relative units increasing along the vertical axis. In this figure the two emission spectra 140, 142 are depicted using different vertical scales (left scale for spectrum 140, right scale for spectrum 142) to allow an easier comparison of corresponding spectral features. The second emission spectrum 142 shows the measured spectrum at lower wall temperatures, where, it is believed, the contribution of the five band systems (A-X, B-X, D-X, E-X and F-X) of the HfS molecule is less prominent. Comparing the spectra 140, 142, it is believed that the difference is due to the emission of HfS. This is also suggested by comparing the spectra 140, 142 with those 110, 112-117 of Figure 3. In the case of Example 4, the radiation emitted by HfS molecules is believed to contribute about 50% to the total emitted radiation 140.

In a second embodiment of the invention, the discharge lamp 10, 15 may be configured for high-pressure discharge or high-intensity discharge (HID). No major differences in the context of the invention are required, except for the fill amounts. It will be apparent to the skilled person how to dimension and arrange the construction to accommodate the higher pressures and higher intensity of discharge.

High-pressure lamps using a fill 50 comprising hafnium bromide or hafnium chloride are known from US patent 5,8444,365. However, similar to the situation for low- pressure discharge lamps, discharges containing transition metal halides emit atomic or ionic line radiation located mainly in the UV or blue spectral range. Molecular radiation from stable transition metal halides is mainly found in the UV and the near-IR. Therefore, transition metal HID discharges are generally deficient of green and red radiation.

Similarly to the first embodiment, the starting compounds introduced into the discharge vessel 20,25 may be potentially be any combination, provided that the sum of the

elemental molar concentrations of the transition metal and the halogen and the sulfur is within the right ranges. In a preferred embodiment of the high-pressure discharge lamp 10, 15 according to the invention, the sum of elemental molar concentrations of the halogen, the transitional metal and the sulfur is at least 1E-08 mol per cubic centimeter in the gas discharge vessel 20,25.

The lower limit (l.E-8mol/cc) for HID discharge lamps is - similar to the situation for low-pressure discharge lamps - determined by a certain minimum amount of radiation power P _ra d per volume V. It is 3 orders of magnitude higher than the "low-pressure limit", because also the desired power densities are about 3 orders of magnitude higher for HID discharge lamps.

A possible upper concentration limit c _up (=l.E-4mol/cc) corresponds to a high pressure discharge with a pressure p _up of about 20bars take the common estimate T _e ff ~ 2500K.

Without being bound to theory, it believed that 20 bars will be about the limit of reachable summed elemental pressures, because this pressure has to be exceeded by the vapor pressures of the evaporated filling substances at the coldest spot temperature T _cs . If some part of the dosed fill is not evaporated, but remains as a solid or liquid condensate at the coldest spot, then the specification of an upper limit for the filling concentration loses its significance, because any higher amount would yield the same gas composition in the operating lamp.

Figures 7, 8, 9, 10 and 11 show emission spectra of high-pressure gas discharge lamps according to the invention comprising a fill 50 comprising hafnium chloride, titanium bromide, zirconium chloride, tantalum chloride, and rhenium chloride respectively.

EXAMPLE 5

A discharge vessel 20, 25 in the form of a spherical quartz vessel of 32.5 mm inner diameter, i.e. a volume of 18 cc was filled with:

- a buffer gas 60 of 100 mbar (pressure at room temperature) Ar, and

- an active constituent 70 of 0.8 mg HfCW and 0.1 mg elemental sulfur. The fill 50 was excited using a 2.45 GHz microwave resonator at about 600

W.

Figure 7 shows the emitted spectrum 210 of Example 5. Figure 7 depicts the lamp emission spectrum 210, with wavelength in nanometers (nm) increasing along the horizontal axis and intensity in Watts per nanometer increasing along the vertical axis.

For comparison a second lamp, similar to that of Example 5, was filled with 0.82 mg HfCW and 100 mbar Ar - that is, no sulfur was added. When excited in the same way as Example 5, this second lamp emitted a much broader spectrum 212 with larger blue and far-red contributions, but without the strong radiation bands between 500 nm and 600 nm. While not wishing to be bound by theory, it is believed that the radiation bands between 500 nm and 600 nm are caused by molecules of HfS, present in the discharge space.

EXAMPLE 6

Similar to Example 5, a spherical quartz vessel of 32.5 mm inner diameter, i.e. a volume of 18 cc was filled with a buffer gas 60 of 100 mbar Ar and an active constituent 70 of 1.04 mg TiBr4 and 0.08 mg S.

The fill 50 was excited using a 2.45 GHz microwave resonator at about 600 W.

Figure 8 shows the emitted spectrum 220 of Example 6. Figure 8 depicts the lamp emission spectrum 220, with wavelength in nanometers (nm) increasing along the horizontal axis and intensity in Watts per nanometer increasing along the vertical axis. For comparison, a simulated emission spectrum 222 of the C ³ δ - X ³ δ transition of TiS is also depicted.

EXAMPLE 7

Similarly to Example 5, a spherical quartz vessel of 32.5 mm inner diameter, i.e. a volume of 18 cc was filled with a buffer gas 60 of 100 mbar Ar and an active constituent 70 of 0.43 mg ZrC14 and 0.1 mg S.

The fill 50 was excited using a 2.45 GHz microwave resonator at about 600 W. Figure 9 shows the emitted spectrum 230 of Example 7, and for comparison, a simulated emission spectrum 232 of the C ¹ E ⁺ - X ¹ E ⁺ transition of ZrS.

EXAMPLE 8

Similarly to Example 5, a spherical quartz vessel of 32.5 mm inner diameter, i.e. a volume of 18 cc was filled with a buffer gas 60 of 100 mbar Ar, and an active constituent 70 of 0.85 mg TaCIs and 0.1 mg S

The fill 50 was excited using a 2.45 GHz microwave resonator at about 600 W.

Figure 10 shows the emitted spectrum 240 of Example 8, and for comparison a simulated emission spectrum of four transitions of TaO 242 (P' ² δ _3/2 - Xi ² δ _3/2 , M ² φs _/2 - Xi ² δ ₃ / ₂ , L ² II ₁ Z ₂ - Xi ² δ ₃ /2 and K ² φ ₅ / ₂ - Xi ² δ ₃ / ₂ ) and a simulated emission spectrum of eight transitions of TaS 244 (K _3/2 - Xi _3/2 , J 5/2 - Xi ₃ / ₂ , N _5/2 - X ₂ 5/2, M _3/2 - X ₂ 5/2, G _3/2 - Xi _3/2 , F 1/2 - Xi ₃ /2, H 5/2 - X ₂ 5/2 and 1 ₃ / ₂ - X _{2 5} / ₂ ) are also depicted.

EXAMPLE 9

Similarly to Example 5, a spherical quartz vessel of 32.5 mm inner diameter, i.e. a volume of 18 cc was filled with a buffer gas 60 of 100 mbar Ar and an active constituent 70 of 0.29 mg ReCl ₃ , 0.2 mg AuCl ₃ and 0.1 mg S.

The fill 50 was excited using a 2.45 GHz microwave resonator at about 600 W.

Figure 11 shows the emitted spectrum 250 of Example 9.

For comparison a second lamp, similar to that of Example 9, was filled with 100 mbar Ar, 0.32 mg ReCl ₃ , 0.2 mg AuCl ₃ - that is, no sulfur was added. This second lamp was excited in the same way as for Example 9, and the emitted spectrum 252 is depicted in Figure 11. The second lamp produced much less visible radiation than the lamp of Example 9. The reason is believed to be because the strong radiation bands between 400 nm and 800 nm, which are characteristic for the emitted spectrum 250 of Example 9, were missing. It is further believed that these strong radiation bands were due to the presence of molecules of ReS in the discharge space during operation.

In summary, the invention is a discharge lamp comprising a halogen selected from the group consisting of fluorine F, chlorine Cl, bromine Br, and iodine I; a transitional metal selected from Group IVB, VB, VIB or VIIB of the periodic table, and sulfur. The presence of the sulfur in the lamp causes an increase in the radiation emitted in the green and/or red radiation bands, thereby improving the spread of colors emitted by such a lamp. This effect is believed to be due to the presence of sulfides of the transitional metal selected from Group IVB, VB, VIB or VIIB in the discharge space. This effect may be utilized in both low-pressure and high-pressure operating modes.