Far UV emitting device, phosphor (combination), luminaire, disinfection system, and use

FIELD OF THE INVENTION

The invention relates to a far UV emitting device, a phosphor (combination) suitable for being used in such a far UV emitting device, a luminaire comprising said far UV emitting device, a disinfection system comprising said far UV emitting device and/or said luminaire, and use of said phosphor (combination), far UV emitting device, luminaire and/or disinfection system for disinfection purposes.

BACKGROUND OF THE INVENTION

With the increasing threat of aggressive viruses like Covid-19, there is a renewed interest in UV based disinfection. From various studies it has been shown that UVC radiation, i.e. wavelengths in the range of 200 to 280 nm, can effectively render viruses ineffective even at relatively low doses. This makes UV treatment of surfaces and air an interesting candidate to fight the spread of these kind of viruses through contact with contaminated surfaces or aerosols. At the same time, however, it is also known that short wavelength UV radiation can give rise to DNA mutations if the radiation hits the unprotected skin. For lamps/devices using mercury 254 nm radiation, which, for example, are commonly used disinfection low-pressure mercury discharge lamps, this limits the allowable exposure in areas where humans are present or may be present, rendering these state-of-the-art UVC lamps/devices using mercury as the active radiator to have the disadvantage of being essentially unsuitable for disinfection of public spaces in an intrinsically safe manner.

It is known also that far UVC wavelengths, i.e. wavelengths in the wavelength range of 200 to 230 nm, show a higher absorption in the skin and hence have only limited penetration into the living skin. At sufficiently low wavelengths this radiation does not penetrate further than the upper skin layers which consist of dead skin cells. As a result, usage of these very short wavelengths has significantly less detrimental side-effects than the 254 nm radiation that emanates from state-of-the-art UVC lamps/devices using mercury as the active radiator. Many far UVC lamps or devices based on excimer radiation, for example from KrCl excimer, having a main emission peak at 222 nm, or for example KrBr excimer, having a main emission peak at 207 nm, however, produce longer, i.e. deep UVC, 2 wavelengths as a by-product of the intended far UVC wavelengths. In current far UVC lamps/devices these harmful, longer deep UVC wavelengths are suppressed by a filter preventing the emission of the longer wavelengths into the exterior.

This renders the known UVC lamps/devices, having said combination of an excimer lamp/device discharge and especially designed external filters, for example dielectric multilayer band-pass filters, to have the disadvantages of being relatively expensive and laborious to manufacture.

SUMMARY OF THE INVENTION

It is an object of the invention to counteract at least one of the disadvantages of the state-of-the-art UVC emitting devices. Thereto, the invention provides a far UV emitting device having a photon emission for a majority in the far UVC range, wherein the far UV emitting device comprises:

- a far UVC source having a majority of its UVC emission, during operation, in a far UVC wavelength range of 200-230 nm; and

- a deep UVC converting phosphor absorbing and converting deep UVC radiation, arranged downstream of the far UVC source for converting radiation in a UV range of 230-300 nm emitted by the far UVC source during operation into radiation with at least one of a highest converted peak emission and a majority of converted emission at wavelengths longer than 290 nm, said deep UVC converting phosphor being substantially transmissive for the emission from the far UVC source in the far UVC range. Substantially in this respect means at least 50%, such as at least 70% or at least 80%, such as 90%.

The radiation emitted by said far UV emitting device preferably being essentially free from deep UVC (230-280 nm), and optionally also essentially free from UVB (280-320 nm). The far UV emitting device can be integrated into, for example, a HVAC, a washing machine, television screen or display, a luminaire. It can be combined with a separate light source providing visible light or it can be integrated into a single light source emitting both UV and visible light. For further improvement of the desired disinfection, the far UV emitting device can be combined with a separate ion generating device, such as an ionizer, or integrated into a single unit with an ionizer.

Typically, a vacuum UV source and/or a far UVC emitting source is a lamp, but alternatively can be a laser or a LED. Such a lamp comprises:

- a lamp envelope comprising a UV -transmissive wall and enclosing a space in a gastight manner, said space comprising a discharge gas filling; 3

- the far UVC emitting source having at least 30% of its photon emission during operation at least in a far UVC sub-range of a far UVC wavelength range of 200-230 nm; and

- the deep UVC converting phosphor arranged downstream of the far UVC emitting source and having an excitation spectrum at least in a deep UVC sub range of the deep UVC wavelength range of 230-300 nm for converting radiation of the far UVC emitting source emitted in said deep UVC sub range to radiation into UVB and/or longer wavelength ranges during operation, said deep UVC converting phosphor being substantially transmissive for the at least far UVC sub range.

Alternatively this could be phrased as:

A far UV emitting device comprising:

- a lamp envelope comprising a UV -transmissive wall and enclosing a space in a gastight manner, said space comprising a discharge gas filling;

- a far UVC emitting source having at least 30% of its photon emission during operation in a wavelength range of 200-230 nm; and

- a deep UVC converting phosphor arranged downstream of the far UVC emitting source and having an excitation spectrum at least in a part of the wavelength range of 230-300 nm for converting radiation of the far UVC emitting source emitted in the wavelength range of 230-300 nm into radiation in the UVB and/or longer wavelength ranges during operation, said deep UV converting phosphor being transmissive for the emission wavelengths of the far UVC emitting source in the wavelength range of 200-230 nm.

In the context of this invention the following definitions apply:

Vacuum UV, also referred to as VUV, is UV in the wavelength range of 10- 200 nm;

Far UVC is UV in the wavelength range of 200-230 nm;

Deep UVC is UV in the wavelength range of 230-300 nm or 230-280 nm;

UVB is UV in the wavelength range 300-320 nm or 280-320 nm;

UVA is UV in the wavelength range of 320-380 nm;

Visible light is light in the wavelength range of 380-700 nm;

IR light is light in the wavelength range of 700-100000 nm.

A phosphor comprises a luminescent, a phosphorescent, and/or a fluorescent material.

The percentage of photon emission by the far UV emitting source in the far UVC range is considered to relate to the total emission of the far UVC emitting source in the 4 wavelength range from 200 nm to 700 nm, only, i.e. only to the visible light wavelength range and the UVA, UVB and UVC range (hence, the vacuum UV range and IR range being excluded).

Downstream is defined as the direction from the discharge inside the far UV emitting device, where the UV radiation is generated, to the exterior/environment of the far UV emitting device.

Preferably the far UVC emitting source has a majority of its photon emission during operation in a far UVC sub-range of a far UVC wavelength range of 200-230 nm, such as at least 50%, preferably at least 70%, more preferably at least 85% ,such as at least 90%.

Preferably the deep UVC converting phosphor has a transmissivity for wavelengths in the far UVC sub-range of the far UVC wavelength range of 200-230 nm of at least 50%, preferably at least 75%, more preferably at least 90%, such as at least 95%.

The vacuum UV source can be a laser, such as Ar2, Kn, F2, Xe2 or ArF lasers, emitting respectively at 126 nm, 146 nm, 157 nm, 172 & 175 nm, and 193 nm. Alternatively, said laser can be a far UVC source which, for example, exploits a nonlinear optical property possessed by certain materials known as ‘second harmonic generation’ (SHG) or ‘frequency doubling’. The blue light output by the laser diode has a wavelength, Z. in the range 410 nm- 460 nm. This blue light ‘pumps’ a frequency-doubling component and is converted to UVC light with wavelength X/2 which is in the range 205 nm - 230 nm. The frequency-doubling process, which is the same as ‘wavelength-halving’, can be thought of as pairs of blue photons combining to form single UVC photons. The emitted light has the features characteristic of a UVC laser. The emitted wavelength is essentially monochromatic, yet a deep UVC converting phosphor preferably is still used to filter out by conversion deep UVC radiation, if any.

The far UV emitting device could have the feature that it comprises a lamp envelope comprising a UV -transmissive wall and enclosing a space in a gastight manner, said space comprising a discharge gas filling; wherein, during operation, the discharge gas filling is the far UVC source, and wherein the deep UVC converting phosphor has an excitation spectrum at least in a deep UVC sub range of the deep UVC wavelength range of 230-300 nm . Then, typically, the far UV emitting device could have the feature that the discharge gas comprises a mixture of Kr and Cl and/or Br, and optionally additional, rare gases of Ne, Ar and/or He, such that during operation excimers of KrCl and/or KrBr are formed for emitting far UVC radiation upon dissociation of KrCl and KrBr.. 5

Yet, the far UV emitting device could have the feature that it further comprises a lamp envelope comprising a UV -transmissive wall and enclosing a space in a gastight manner, said space comprising a discharge gas filling, wherein, during operation, the discharge gas filling is a VUV discharge source having a majority of its emission in the wavelength range of 100-200 nm, and the far UVC source is a VUV converting phosphor excited by the VUV discharge source.

The far UV emitting device could comprise a CathodeLuminescent Lamp (CLL). Cathodoluminescence typically takes place when a phosphor emits light upon excitation by accelerated electrons striking the phosphor. Electrons are typically emitted from a cathode via either thermionic emission or field emission. In thermionic emission, the cathode is heated to make it emit electrons and it could take several minutes to “warm up”. In contrast, the field emission enables switching on instantly by placing the cathode in a strong electric field. Carbon fibers, for example, work well as field emission cathode material. A compact power source for the CLL fits around the glass light bulb with minimal effect on its size. CLLs rely on the same principle as cathode-ray tube televisions. In cathodoluminescent technologies, a vacuum tube contains a negatively charged electrode (cathode) at one end and a positively charged, phosphor-coated electrode (anode) at another, opposite end. The cathode serves as an electron gun from which emitted electrons accelerate toward the anode at the opposite end, giving the electrons an energy in the range of 2-30 keV, and striking the far UVC generating phosphor, which converts the energy, at least partly, into far UVC radiation. Hence, the far UVC source is the far UVC generating phosphor excited by the electrons.

The far UVC source, or probably in the future the vacuum UV source, can be a LED, for example, one using aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN) or mixed compositions thereof (InAlGaN). Though the efficiency of these LEDs is not yet high, i.e. about 1%, they can already be used in practice in the far UV emitting device according to the invention. Any deep UVC radiation generated by such a LED is then converted by the deep UVC converting phosphor into longer wavelengths.

Suitable lamp types as UV emitting device are:

A) Low pressure discharge lamp with a rare gas or rare gas mixture and with coiled electrode with emitter, i.e. lamps similar to a normal fluorescent lamp, but without mercury in its filling. Examples include pure Xe, aNe/Xe mixture preferably having aNe percentage of >= 90%, typically with a prime emission wavelength at 147 nm. 6

B) A pure Xe discharge lamp using external electrodes and capacitively operated, either in a coaxial geometry, i.e. ‘industrial’ type discharge lamps, with a radial discharge, or an axial geometry as for example marketed by Ushio, or planar geometry as for example marketed as the Osram Planon lamp. All these lamps emit primarily at 172 nm.

C) A pure Xe discharge lamp based on a micro-hollow cathode design, for example of an Eden-Park type, emitting primarily at 172 nm.

Typically the invention relates to three basic configurations, i.e.:

1) A combination of:

- a low pressure excimer lamp, for example Kr2, F2, ArBr, ArCl, KrI, ArF excimers lamps, or Xe or Ne/Xe discharge lamp which produces vacuum UV light, also referred to as VUV light, at 147 nm, or a medium pressure Xe discharge lamp which produces VUV light at 172 nm, with

- a far UVC emitting/generating phosphor that converts VUV light into the desired far UVC light, and with

- a deep UVC converting phosphor for converting undesired by-product emission radiation of the far UVC emitting source in the deep UVC wavelength range of 250-275 nm, preferably in the wavelength range of 230-280 nm, more preferably in the wavelength range of 230-300 nm, into radiation of wavelengths longer than 300 nm, for example in the UVB range for vitamin D generation and/or skin treatment, or in the UVA or visible wavelength range;

2) A combination of:

- a normal KrCl or KrBr excimer lamp generating and directly emitting radiation in a far UVC sub-range of a far UVC wavelength range, i.e. mainly at 222 or 207 nm wavelengths, with

- a deep UVC converting phosphor for converting undesired by-product radiation of the far UVC emitting source in the deep UVC wavelength range of 250-275 nm, preferably in the wavelength range of 230-280 nm, more preferably in the wavelength range of 230-300 nm, into radiation of wavelengths longer than 300 nm, for example in the UVB range for vitamin D generation and/or skin treatment, or in the UVA or visible wavelength range; 7

3) A combination of:

- a cathodeluminescent lamp generating accelerated electrons in a space evacuated from gas, with

- a far UVC emitting/generating phosphor that converts energy of the accelerated electrons striking the far UVC emitting/generating phosphor, and with

- a deep UVC converting phosphor for converting undesired by-product radiation of the far UVC emitting source in the deep UVC wavelength range of 250-275 nm, preferably in the wavelength range of 230-280 nm, more preferably in the wavelength range of 230-300 nm, into radiation of wavelengths longer than 300 nm, for example in the UVB range for vitamin D generation and/or skin treatment, or in the UVA or visible wavelength range.

Far UVC sources that have deep UVC emitted as a by-product are typically more efficient than far UVC sources emitting only far UVC radiation. It is therefore beneficial to use far UVC sources that have deep UVC as a by-product and to eliminate in a later stage the undesired deep UVC, rather than using pure far UVC sources.

Hence, in both basic configurations the unwanted higher wavelengths are absorbed by the deep UVC converting phosphor, which is at least substantially transparent for the far UVC sub-range of the far UVC radiation. Because this deep UVC converting phosphor converts the undesired deep UVC wavelengths into visible light, UVA and/or UVB, the emitted radiation from the resulting lamp will be much safer than known low mercury pressure discharge lamps used for germicidal purposes, while being germicidally effective and without the need for an (expensive) dielectric multilayer bandpass filter. An additional benefit if the deep UVC is converted into visible light, is that it is immediately recognizable when the lamp is on. Hereby it is noted that UV light is not visible for the human eye but could be made visible, for example by the deep UVC converting phosphor, or by using a third, optionally remote, phosphor.

Typically, in the KrCl or KrBr excimer lamps the original fill gas, in off-state, is a mixture that contains at least Kr and Cl, Br or a mixture thereof and optionally additional rare gases like Ne, Ar and He. The emitting KrBr or KrCl species are only formed temporarily in the discharge, and break down into Kr and halogen species after emitting their energy in the form of a far UVC photon. 8

The low pressure lamp can be in many ways similar to the current UV disinfection lamps, using wounded tungsten electrodes with an oxide emitter, and low- or high frequency AC current running through the lamp, yet comprises a fused quartz lamp envelope, for example made from Suprasil, and a lamp filling comprising or consisting of either Xe or a mixture of Xe and Ne, or a mixture of Ne, Ar and Xe at a low pressure rare gas filling. For the gas mixture a 0.5-5% fraction of Xe in Ne is preferred, as this makes it relatively easy to start the lamp. Depending on the inner diameter, a 100-1000 Pa total pressure is preferred for diameters of 8-20 mm, whereas 600-4000 Pa are preferred for lamps with inner diameters of less than 8 mm. Instead of wound tungsten electrodes with oxide emitter coating it is also possible to use cold-cathode electrodes, especially in narrowdiameter lamps. In these types of discharge lamps, it is also preferred to use AC operation of the discharge in order to avoid cataphoretic effects that could deplete the discharge of Xe atoms on one side of the tube. Typically these lamps could be driven by a standard driver or HF ballast.

Alternatively, a higher pressure lamp having a total pressure of typically 80- 1000 mbar, such as 100-600 mbar (1 mbar = 100 Pa) for example with pure Xe, can be used in a dielectric barrier discharge configuration. In this type of lamp the spectrum has a peak around 172 nm, originating from the Xe discharge. This kind of lamp configuration has the advantage that the Stokes shift of the far UVC phosphor is smaller, which could potentially lead to a relatively high overall lamp efficiency. It is noted hereby that the discharge efficiency to produce photons is also higher in these lamps as compared to typical KrCl and KrBr lamps, which more than counters the Stokes shift losses.

Besides these preferred excitation sources, there are multiple other VUV lamp sources that emit radiation at wavelengths shorter than 200 nm, which could be used to excite phosphors that emit in the far UVC 200-230 nm range. These include various excimer sources using mixtures of halogens and rare gases, and deuterium lamps. In all these and previous mentioned cases no mercury is dosed.

In any of the lamps of the first basic configuration, preferably a phosphor coating is deposited on the inside of the discharge vessel, which converts the discharge radiation into the desired spectrum, which should preferably be concentrated around 200-230 nm in order to avoid skin damage on the one side in the wavelength range longer than X > 230 nm, X being the wavelength, and ozone generation on the other side, i.e. for X < 200 nm. Having the phosphor on the inside of the discharge vessel also has the advantage that the vessel only needs to be transparent to X > 200 nm which makes it possible to use cheaper wall 9 materials like fused quartz. Other suitable materials are sapphire, which is hard durable, yet expensive, but is transmissive for radiation down to about 140 nm; CaF2 which is resistant to Fluorine corrosion, yet is hygroscopic and brittle, but is transmissive to about 120 nm; and MgF2 which does not absorb water, yet has transmission less than CaF2 and is brittle, but is transmissive to about 120 nm. Other suitable materials are, for example, LiF2, BaF2, NaF, KBr, Y3AI5O12 (YAG = Yttrium Aluminate Garnet), spinel (MgAhO4), A10N (AI23O27N5), and PCA (polycrystalline alumina).

As it is difficult to find a phosphor that completely cuts off at 230 nm, it is likely that some spectral contents above 230 nm will remain. To give one example, Y<i- _X )PO4:Pr _x ³⁺ is a phosphor which converts vacuum UV radiation into a spectrum between 225- 280 nm. This spectrum is not yet optimal, and should preferably be pushed to lower wavelengths. Also with other phosphors that produce more radiation in the 200-230 nm range, typically some residual radiation in the wavelength range longer than 230 nm occurs. In these cases, to filter these parts of the spectrum out, use is made of a second phosphor layer, or an absorption layer, that is present downstream of the first phosphor. This second layer should be as good as possible transparent for the radiation emitted by the far UVC emitting source in the far UVC sub-range in the region of 200-230 nm, in order to retain as much as possible the useful far UVC radiation in this region, but absorb as much as possible of the deep UVC sub-range of the deep UVC radiation in the range 230-300 nm, in order to improve the balance between the useful radiation far UVC radiation between 200-230 nm and the harmful deep UVC radiation above 230 nm. It depends on the wavelengths emitted by the first, far UVC emitting phosphor in the deep UVC sub-range, which wavelengths need to be absorbed by the second, deep UVC converting phosphor.

A good candidate identified as a first, far UVC emitting phosphor is Ca<i- _X - y)SO4:Pr _x ³⁺ ,M _y ⁺ where M ⁺ is an alkaline metal ion like Li ⁺ or Na ⁺ , which are typically added for charge compensation of the Pr ³⁺ dopant in the CaSCfi host material. It has quite some emission intensity in the 230-270 nm deep UVC sub-range which needs to be filtered out. Ideally, the emission spectrum of the first phosphor should be shifted a bit further to shorter wavelength. But there will always be some intensity in said 230-270 nm range. Yet, CaSO4 has the disadvantage of having (some) absorption in the 200-230 nm wavelength range, rendering it less suitable for the intended use of the deep UVC converting phosphor. Potential deep UVC converting materials, also referred to as second phosphor, to filter this deep UVC out, are lanthanides as they have 4P ¹ df'^Sd ¹ transitions which give strong absorption bands, often in the deep UVC and often not too broad. The best lanthanide candidates are Ce ³⁺ phosphors, as it has only one 4f electron and therefore only five 5d ¹ energy levels, which can be spaced apart depending on the crystal structure of the host lattice. All other lanthanides have many df'^Sd ¹ energy levels and therefore have a somewhat less chance on significant spacing in energy between them.

The wall has an inner side facing the discharge and downstream from the inner side an outer side facing away from the discharge. Usually the phosphor converting materials are provided on the inner side of the wall. On the condition that the wall material is transmissive for the prime excitation wavelength of the discharge, e.g. 147 or 172 nm, the phosphors could be deposited on the outer side of the wall of the discharge vessel. In any case the second, deep UVC converting phosphor can be deposited on either the inside or outside of the discharge vessel, or even on a remote output window of a lamp module, but at least downstream of the first, far UVC emitting phosphor. In most cases for cost reasons wall materials will be chosen that the first, far UVC emitting phosphor will be positioned on the inside of the discharge vessel.

The far UV emitting device may have the feature that the first and second phosphor layer are spaced apart, for instance in that the UV-emitting device has a doublewalled envelope. The space in between these layers can or is then used for enhanced disinfection of air, which is naturally or mechanically moved through that space, as the radiation to be filtered out is actually quite germicidally effective. In that way, the harmful light is still used for disinfection, and the photons which are not absorbed by germs will be absorbed by the second phosphor, which converts it into other potentially useful far UVC light that is safer to use in the presence/direct contact with humans.

In view of the foregoing description and advantages of the far UV emitting device according to the invention, the far UV emitting device could have the following features:

The far UV emitting device could have the feature that the deep UVC converting phosphor is provided as a coating on the wall.

The far UV emitting device could have the feature that the far UVC emitting source is chosen from the group of a discharge gas composition and a VUV converting phosphor.

The lighting device could have the feature that the discharge gas comprises a mixture of Kr and Cl and/or Br, and optionally additional, rare gases of Ne, Ar and/or He, such that during operation excimers of KrCl and/or KrBr are formed for emitting far UVC upon dissociation of KrCl and KrBr. 11

The far UV emitting device could have the feature that the VUV converting phosphor is provided on a first UV transmissive carrier and the deep UVC converting phosphor is provided on a second UV transmissive carrier downstream of the VUV converting phosphor, the VUV converting phosphor and the deep UVC converting phosphor being mutually spaced by a gap. Said gap is for enabling natural convective or forced air flow in between the VUV converting phosphor and the deep UV converting phosphor.

The far UV emitting device could have the feature that the discharge gas filling is a VUV emitting source and is chosen from a low pressure Xe, Ne/Xe, or Ne/Ar/Xe filling, and from a medium pressure Xe2 discharge, wherein low pressure is in the range of 100 Pa to 4000 Pa, and medium pressure is in the range of 3000 Pa to 80000 Pa.

The far UV emitting device could have the feature that the VUV converting phosphor is at least one of Ca<i- _x -y)SO4:Pr _x ³⁺ ,My ⁺ ; Sr(i- _x -y)SO4:Pr _x ³⁺ ,M _y ⁺ ; LiLu(i- _X )F4:Pr _x ³⁺ ; LiY(i- _X )F4:Pr _x ³⁺ ; and La -xTCh: Pr _x ' ¹ wherein M ⁺ is at least one of Li ⁺ and Na ⁺ .

The far UV emitting device could have the feature that 0.002 <= x <= 0.2, preferably 0.02 <= x <= 0.1. The far UV emitting device could have the feature that 0 <= y <= 0.2. The far UV emitting device could have the feature that x=y.

The far UV emitting device could have the feature that the deep UVC converting phosphor comprises an activator from the group Ce ³⁺ , Gd ³⁺ , Tm ³⁺ , Bi ³⁺ , Pb ²⁺ . Gd ³⁺ as activator is interesting, provided that emission by the far UVC emitting source in the deep UVC is only in the deep UVC sub-ranges of 245-255nm and/or 270-280 nm, because there Gd ³⁺ has relatively intense absorption/excitation lines. Yet for Gd ³⁺ nearly any host lattice would work.

The far UV emitting device could have the feature that the deep UVC converting phosphor is at least one of Lu<i- _X )AG:Bi ³⁺ Gd _x ³⁺ , Sc(i- _X )PO4:Ce _x ³⁺ ; Lu<i- _X )PO4:Ce _x ³⁺ ; Y(i- _X )PO4:Ce _x ³⁺ ; Gd<i- _X )PO4:Ce _x ³⁺ ; and Sr(i- _X )SiO3:Pb _x ²⁺ , wherein 0.01 <= x <= 0.2. If we add Gd ³⁺ or Tm ³⁺ as activator, then x can even be 1. LuAG is an abbreviation for Lutetium Aluminum Garnet, i.e. LU3AI5O12.

The far UV emitting device could have the feature that it comprises one of the following combinations of the far UVC emitting source and deep UVC converting phosphor:

- KrCl excimer and Y(i- _X )PO4:Ce _x ³⁺ , wherein 0.002 <= x <= 0.1;

- Xe2, Ca<i- _x -y)SO4:Pr _x ³⁺ ,Nay ⁺ and Y(i- _Z )PO4:Ce _z ³⁺ , wherein 0.002 <= x <= 0.1, 0 < y <= 0.1, and 0.002 <= z <= 0.1;

- KrCl excimer and Sc(i- _X )PO4:Ce _x ³⁺ , wherein 0.002 <= x <= 0.1; 12

- Xe2, Ca(i-x-y)SO4:Pr _x ³⁺ ,Nay ⁺ and Sc(i- _Z )PO4:Ce _z ³⁺ , wherein 0.002 <= x <= 0.1, 0 < y <= 0.1, and 0.002 <= z <= 0.1;

- ArBr (emitting at 165nm) (or F2 emitting at 158nm) excimer, La<i- _x) PO4:Pr _x ³⁺ , and Gd(i- _x) PO4:Ce _x ³⁺ .

The invention further relates to:

UV conversion phosphor or a combination of VUV converting phosphor and a deep UVC converting phosphor suitable for use in the far UV emitting device according to the invention.

A luminaire comprising a far UV emitting device according to the invention and a driver.

A disinfection system comprising at least one far UV emitting device according to the invention and/or a luminaire according to the invention and a control device. The control device can be a simple switch, remote control, sensor, for example an occupancy sensor, a light sensor, and/or an IR-sensor.

Use for disinfection purposes of a far UV emitting device according to the invention, a phosphor or phosphor combination according to the invention, a luminaire according to the invention, and/or a disinfection system according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further elucidated by means of the schematic drawings, which are by no means intended to limit the scope of the invention but rather to exemplify the ample possibilities of the invention. In the drawings

Fig. 1 shows a schematic view of an far UV emitting device according to the invention;

Figs. 2A-B show respectively a side view and a transverse cross-section of a first embodiment of a far UV emitting device according to the invention;

Fig. 3 shows a side view of a second embodiment of a far UV emitting device according to the invention;

Fig. 4 shows partly worked open perspective view of a third embodiment of a far UV emitting device according to the invention;

Fig. 5A shows both the excitation and emission spectrum of La<i- _X )PO4:Pr _x ³⁺ and

Fig. 5B shows the excitation, reflection and emission spectrum of Lap. PO ₄ :Ce _x ³⁺ ; 13

Fig. 6 shows the emission spectrum of Ca<i- _x -y)SO4:Pr _x ³⁺ ,My ⁺ and absorption spectrum of Sc<i- _X )PO4:Ce _x ³⁺ ; and

Fig. 7 shows the emission spectrum of a discharge comprising KrCl excimers and absorption spectrum of Sc(i- _X )PO4:Ce _x ³⁺ ; and

Fig. 8 shows a fourth embodiment of a far UV emitting device according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows a schematic view of a far UV emitting device according to the invention. The far UV emitting device 200 has a housing 205 which accommodates an optional vacuum UV source 210, for example a laser or a lamp, that issues vacuum UV radiation 215 towards a far UVC source 220. The far UVC source, for example a VUV converting phosphor, if it receives VUV radiation 215 from the vacuum UV source, converts said VUV radiation into far UVC radiation 223 and some deep UVC radiation 227 as a byproduct. Alternatively, there is no VUV source, and the far UVC source 210, for example a laser or a lamp, generates directly far UVC radiation 223 and some deep UVC radiation as a by-product. Said far UVC radiation 223 and deep UVC radiation 227 are emitted towards a deep UVC converting phosphor 230 which is transmissive for the far UVC radiation 223, but converts the deep UVC radiation 227 into longer wavelength radiation 235, for example UVB, UVA and/or visible radiation. Finally, essentially only said far UVC radiation 223 and longer wavelength radiation 235 are emitted from within the housing 205 into the environment.

Figures 2A-B show respectively a side view and a transverse cross-section of a first embodiment of a far UV emitting device according to the invention. More specifically, figures 2A and 2B show a coaxial dielectric barrier discharge lamp, also referred to as DBD- lamp, with an annular shaped discharge gap 1. FIG. 2A shows in a longitudinal sectional view an inner part of a DBD-lamp 100. FIG. 2B shows the same DBD-lamp 100 or the same inner part of the DBD-lamp in a cross-sectional view, yet without the corresponding electrodes. The discharge gap 1 of the DBD-lamp is formed by a dielectric inner wall 2 and a dielectric outer wall 3. In these figures the discharge gap 1 is formed by an inner lamp tube having a circumferential wall, functioning as the inner wall 2 and an outer lamp tube having a circumferential wall, functioning as the outer wall 3. The lamp tubes are made of quartz glass, which is a dielectric material, and is transmissive for VUV, far UVC and deep UVC. The inner wall 2 has an inner surface 2a and an outer surface 2b. The inner surface 2a faces 14 the discharge gap 1 and the outer surface 2b is directed in opposite direction. The outer wall 3 has an inner surface 3a and an outer surface 3b analogue. The inner surface 3a like the inner surface 2a of the inner wall 2 faces the discharge gap 1. The outer surface 3 b is directed in opposite direction to the inner surface 3 a The DBD-lamp has two corresponding electrodes 4 arranged at the outer and the inner wall 2, 3. The first electrode is arranged at the outer surface 2b of the inner wall 2 and the second electrode 4b is arranged at the outer surface 3b of the outer wall 3, both the electrodes are shaped as a grid. At the inner surface 3a of the outer wall a deep UVC converting coating layer 5 of Y(i- _X )PO4:Ce _x ³⁺ is provided. The inner surface 2a of the inner wall 2 has no such luminescent coating layer. Instead of this, a directing means 6 in form of a reflective coating layer 6a is arranged at the inner surface 2a of the inner wall 2. This reflective coating is optional, and when not provided UV radiation as generated by the discharge can be emitted inwards into a shielded inner channel 7 surrounded by the inner wall 2 without being partly converted. In the inner channel said unconverted radiation can be used for disinfection of a natural convective or forced air flow 8 flowing through it, with use of the full UVC wavelength range, hence also comprising UVC in both the wavelength ranges between 200-230 nm and 230-300nm. In this case, the reflective coating layer is a layer made of ultrafine particles, such as MgO, SiCh and/or AI2O3. The diameter of the grains, forming that layer is chosen such, that an optimal reflection of the wavelength-range of the generated UV-radiation is realized. Here the filling of the DBD- lamp is discharge gas comprising a mixture of Kr and Cl and Ar, Ne and/or He, together with filling pressures in between 30 mbar and 800 mbar, such as 100 mbar. In this case the generated radiation caused by the dissociation of KrCl peaks at about Z=222 nm, however also some radiation is emitted at about 260 nm as an undesired by-product. The 222nm wavelength range and 260 nm wavelength range are reflected towards the luminescent coating layer on the inner side 3a of the outer wall 3. The phosphor material for that coating layer in this case is Y(i- _X )PO4:Ce _x ³⁺ , which is essentially transmissive for the 222 nm radiation, but is excited by (hence absorbs) the undesired 260 nm radiation. Thus it is attained that the safe 222 nm radiation is emitted into the environment while the harmful 260 nm is blocked from being emitted into the environment. If a single (second) phosphor does not absorb the entire region between 230-300 nm, also a mixture of second phosphors can be used as the second phosphor layer in order to cover the entire region from 230-300 nm.

A similar lamp design as shown in figure 2A/B can be used for a 172 nm Xe2 discharge lamp, yet with a different gas filling, i.e. Xe gas. 15

Figure 3 shows an alternative, second embodiment of the DBD 100 lamp as shown in figure 2A. The double walled lamp is made of VUV and UVC transmissive CaF2 has an outer wall 3 and an inner wall 2 which are spaced apart by a gap 9 though which an air flow 7 can stream. The inner wall forms an annular gastight discharge space 1 which is filled with a discharge gas of pure ArBr at a medium pressure of about 10000 Pa. On an outer surface 2c of the inner wall the electrodes 4 are provided as a mesh structure for generating a discharge and enabling generated VUV light of about 165 nm to pass through. On top of the electrodes a first, far UVC generating phosphor 10, La<i- _X )PO4:Pr _x ³⁺ is provided that converts the VUV into a far UVC subrange of the far UVC wavelength range and which converts also part of the VUV into a deep UVC sub-range of the deep UVC wavelength range. Said combined radiation of far UVC and deep UVC is radiated into the gap 9 through which air 7 flows and both the far UV and deep UV is used for disinfection of said air. On an inner surface 3a of the outer wall a second, deep UVC converting phosphor 5, Gd<i- _X )PO4:Ce _x ³⁺ , is provided which is transmissive for the sub-range of the far UVC wavelength range generated by the first phosphor, but which converts the deep UVC sub-range as generated by the first phosphor into longer wavelength radiation range of 300-380 nm. Said second phosphor prohibits that deep UV is issued to the exterior.

Figure 4 shows partly worked open perspective view of a third embodiment of a far UV emitting device according to the invention. More specifically, Fig. 4 shows a low- pressure discharge lamp 300 with an elongate discharge vessel 303, having a wall 302, and is made of quartz glass transmissive for at least far UVC, i.e. Suprasil. The lamp comprises an electrode 305 at each end, which electrode is a coil formed by a triple coiled tungsten wire 306 supported by conducting lead wires 307, 309 which extend through a quartz glass pinch 311 of a seal 310. The double or triple coiled tungsten wire 306 is provided with an emitter material such as oxides of barium, calcium, and strontium for reducing the work function of the electrode. The seal 310 hermetically seals off the discharge vessel 303. The lead wires 307, 309 are connected to pin-type contacts 313 in the respective end caps 312 which are provided at either end of the lamp 300.

The discharge vessel 303 has a discharge space 317 which is filled with a low pressure rare gas filling, with a pressure in-between 100 Pa and 4000 Pa, typically chosen from Xe, a mixture of Xe and Ne, and a mixture of Ne, Ar and Xe, in the figure the filling is with Xenon to create a Xe discharge and emission thereof during operation of the lamp, yielding a discharge emission that is mainly concentrated around the Xe 147 nm. No mercury is dosed. A first phosphor coating 304 of Ca(i- _x -y)SO4:Pr _x ³⁺ ,Na _y ⁺ , as a far UVC emitting 16 source, is provided on the wall 302 and faces the discharge space 317. Said first phosphor coating 304 converts the 147 nm vacuum UV into far UVC radiation peaking in the far UVC sub-range of 220-230 nm, but also generates some deep UVC radiation in the deep UVC subrange around 250nm as an undesired side-product. A second phosphor coating 308, as a deep UVC converting phosphor, in this case a Y(i- _X )PO4:Ce _x ³⁺ phosphor, is provided in between the first phosphor layer 304 and the wall 302. Said second phosphor 308 is at least transmissive for the radiation of the first phosphor 304 emitted in the far UVC sub-range, i.e. for the emission in the range of 210-230 nm, but is excited by the radiation emitted by the first phosphor 304 in the deep UVC sub-range , i.e. for the emission around the 250 nm wavelength range, and converts said deep UVC radiation into longer, non-harmful radiation wavelengths.

Another potential lanthanide candidate to be used for the second phosphor is Gd ³⁺ based material. By doping the Gd ³⁺ material with e.g. Eu ³⁺ , excitation of Gd ³⁺ will lead to visible (red) emission via energy transfer. Figure 5A shows both the excitation B and emission spectrum A of La<i- _X )PO4:Pr _x ³⁺ + and Figure 5B shows the excitation B, reflection C and emission spectrum A of Gd(i- _X )PO4:Ce _x ³⁺ +. Typically La<i- _X )PO4:Pr _x ³⁺ is excited in the range from 150-200 nm, e.g. by excimers of ArBr or F2 emitting respectively at 165 nm and 158 nm, and has its main emission peak in the far UVC sub-range at about 225 nm, but also having a peaking emission in the deep UVC sub-range at about 260 nm. Gd(i- _X )PC>4:Ce _x ³⁺ forms a good combination with La<i- _X )PO4:Pr _x ³⁺ as the Gd(i- _X )PO4:Ce _x ³⁺ phosphor is well excited in the range 240-300 nm and emits mainly as UVB-UVA radiation in the longer UV wavelength range of 310-380 nm, and partly in the longer, at least visible, wavelength range.

Figure 6 shows the emission spectrum M of Cao.98S04:Pro.oi ³⁺ ,Nao.oi ⁺ and absorption spectrum N of Sco.99P04:Ceo.oi ³⁺ . More specifically, figure 6 shows an example of a Ce ³⁺ absorption spectrum which is suited for absorbing the hazardous radiation in the Ca<i- _X - _y )SO4:Pr _x ³⁺ ,Na _y ⁺ emission spectrum. All 5 5d ³ transitions are present. The largest energy gap is in between the A and B band, but it is at too low energy, and there is no practical material in which that gap is shifted to the 200-230 nm range. For Y(i- _X )PO4:Ce _x ³⁺ it appears that the energy gap between the C and E bands is also significant, and the D band is very weak. In Y(i- _X )PO4:Ce _x ³⁺ the B band seems at a slightly too low wavelength to sufficiently absorb the hazardous radiation for Ca -x-yiSCfi: Pr _x ' '.Na _y ¹ at about 260 nm. For the spectrum in Figure 6 there is a 8 nm shift which approximately equals the spectrum of Sc(i- _X )PO4:Ce _x ³⁺ . Such a Ce ³⁺ phosphor will give UVA emission upon absorbing the harmful radiation from the first phosphor. Sc(i- _X )PO4:Ce _x ³⁺ is expected to give emission in the 330-370 17 nm range. This light could be used for disinfection via photo-catalysis with use of photocatalytic, self-cleaning layers as MgO and TiCh.

The second phosphor can also be used in combination with discharge lamp comprising KrCl in its discharge gas, said KrCl acts as source of far UVC radiation and peaks at 222 nm, see Figure 7, which shows the emission spectrum M of KrCl discharge and absorption spectrum N of Sc(i- _X )PO4:Ce _x ³⁺ . Optionally, Scandium in Sc(i- _X )PO4:Ce _x ³⁺ is at least partly substituted by Yttrium to form (YSc)(i- _X )PO4:Ce _x ³⁺ .

Figure 8 shows a schematic diagram of a cathodeluminescent lamp (CLL) as a fourth embodiment of a far UV emitting device according to the invention. The CLL comprises a lamp envelope 1401 in which a cathode 1407 is arranged. The lamp envelope is evacuated through exhaust tube 1411. The lamp envelope comprises a lamp wall 1403 on which a stacked coating is provided facing the cathode and being spaced from the cathode. The stacked coating comprises a far UVC phosphor layer 1406, a deep UVC converting layer 1413, and an anode 1404. A voltage is applied between the cathode and anode through contacting elements 1405 causing field emission of electrons from the cathode which are accelerated towards the anode while bridging the spacing between cathode and anode. The accelerated electrons pass through the anode layer 1404 deposited on top of the phosphor layers, hit the far UVC phosphor layer 1406 which subsequently emits radiation 1415 comprising far UVC radiation and deep UVC radiation which is converted by the deep UVC converting layer into radiation of longer wavelengths than deep UVC. In the CLL Ca<i- _X - _y )SO4:Pr _x ³⁺ ,Na _y ⁺ can be suitably applied as far UVC emitting phosphor and Sc(i-z)PO4:Ce _z ³⁺ as deep UVC converting phosphor, wherein 0.002 <= x <= 0. 1, 0 < y <= 0. 1, and 0.002 <= z <= 0.1.