A PHOSPHOR COMBINATION FOR A UV EMITTING DEVICE AND A UV GENERATING DEVICE UTILIZING SUCH A PHOSPHOR COMBINATION

Abstract

A UV emitting device having at least one first phosphor that absorbs UV radiation of a wavelength shorter than 200 nm and at least one second phosphor which absorbs UV radiation of a wavelength between 220 nm and 245 nm. The at least one first phosphor emits UV radiation of a wavelength between 220 nm and 245 nm and the at least one second phosphor emits UV radiation of a wavelength between 250 nm and 315 nm. The at least one first phosphor and the at least one second phosphor are disposed in the form of layers, wherein the at least one first phosphor layer is positioned between a discharge volume and the at least one second phosphor layer.

Claims

1-11. (canceled)

12. A UV emitting device, comprising: at least one first phosphor layer which absorbs UV radiation of a wavelength shorter than 200 nm and emits UV radiation of a wavelength between 220 nm and 245 nm; and at least one second phosphor layer which absorbs UV radiation of a wavelength between 220 nm and 245 nm and emits UV radiation of a wavelength between 250 nm and 315 nm; where the at least one first phosphor layer is positioned between a discharge volume and the at least one second phosphor layer.

13. The UV emitting device of claim 12, further comprising: a UV transparent vessel, the vessel having an inner surface and an outer surface, wherein: the discharge volume is a VUV emitting gas discharge volume contained in the vessel; and the at least one first phosphor layer and the at least one second phosphor layer are either: (a) both disposed on or over the inner surface of the vessel, (b) both disposed on or over the outer surface of the vessel, or (c) the at least one first phosphor layer is disposed on the inner surface of the vessel, and the at least one second phosphor layer is disposed on the outer surface of the vessel.

14. The UV emitting device of claim 12, further comprising a UV-transparent vessel, the vessel having an inner surface and an outer surface, and the vessel comprising a coating disposed directly on the inner surface and/or on the outer surface of the vessel.

15. The UV emitting device of claim 14, wherein the coating comprises Al.sub.2O.sub.3, MgO and/or SiO.sub.2.

16. The UV emitting device of claim 14, wherein the at least one first phosphor layer and the at least one second phosphor layer are disposed on the coating.

17. The UV emitting device of claim 12, wherein the vessel comprises a quartz tube.

18. The UV emitting device of claim 12, wherein the UV emitting device is an excimer lamp.

19. The UV emitting device of claim 12, wherein the UV emitting device is a Xenon excimer UV lamp.

20. The UV emitting device of claim 12, comprising a protective layer of MgO covering an inner surface of the at least one first phosphor layer.

21. A phosphor combination for use in a UV-C and/or UV-B emitting device, comprising: at least one first phosphor that absorbs UV radiation of a wavelength shorter than 200 nm and emits UV radiation of a wavelength between 220 nm and 245 nm; and at least one second phosphor that absorbs UV radiation of a wavelength between 220 nm and 245 nm and emits UV radiation of a wavelength between 250 nm and 315 nm.

22. The phosphor combination of claim 21, wherein the at least one first phosphor is one or more phosphor selected from the group comprising: CaSO.sub.4:Pr,Na, SrSO.sub.4:Pr,Na, LaPO.sub.4:Pr, CaSO.sub.4:Pb, LiLaP.sub.4012:Pr, Y.sub.2(SO.sub.4).sub.3:Pr, LuPO.sub.4:Pr, YPO.sub.4:Pr, GdPO.sub.4:Pr, NaMgPO.sub.4:Pr, KSrPO.sub.4:Pr, LiCaPO.sub.4:Pr, LUPO.sub.4:Bi, YPO.sub.4:Bi, YBP.sub.2O.sub.8:Pr, YAlO.sub.3:Pr, LaMgAl.sub.11O.sub.19:Pr, or Ca.sub.5(PO.sub.4).sub.3F:Pr,K.

23. The phosphor combination of claim 21, wherein the at least one second phosphor is one or more phosphor selected from the group comprising: CagLu(PO.sub.4).sub.7:Pr, CagY(PO.sub.4).sub.7:Pr, NaSrPO.sub.4:Pr, NaCaPO.sub.4:Pr, Sr.sub.4Al.sub.14O.sub.25:Pr,Na, SrAl.sub.12O.sub.19:Pr,Na, CaLi.sub.2SiO.sub.4:Pr,Na, KCaPO.sub.4:Pr, LuBO.sub.3:Pr, YBO.sub.3:Pr, Lu.sub.2SiO.sub.5:Pr, Y.sub.2SiO.sub.5:Pr, Lu.sub.2Si.sub.2O.sub.7:Pr, CaZrO.sub.3:Pr,Na, CaHfO.sub.3:Pr,Na, Y.sub.2Si.sub.2O.sub.7:Pr, Lu.sub.3Al.sub.5O.sub.12:Bi,Sc, Lu.sub.2SiO.sub.5:Pr, Lu.sub.3Al.sub.3Ga.sub.2O.sub.12:Pr, Lu.sub.3Al.sub.4GaO.sub.12:Pr, SrMgAl.sub.10O.sub.17:Ce,Na, Lu.sub.3Al.sub.5O.sub.12:Pr, YBO.sub.3:Gd, Lu.sub.3Al.sub.5O.sub.12:Gd, Y.sub.3Al.sub.5O.sub.12:Gd, LaMgAl.sub.11O.sub.19:Gd, LaAlO.sub.3:Gd, YPO.sub.4:Gd, GdPO.sub.4:Nd, LaB.sub.3O.sub.6:Gd,Bi, or SrAl.sub.12O.sub.19:Ce.

24. The phosphor combination of claim 21, wherein the at least one first phosphor is YPO.sub.4:Bi, and the at least one second phosphor is YBO.sub.3:Pr.

Description

[0085] In the following, an embodiment of the present invention is described in greater detail. Reference to the drawings is made, which show

[0086] FIG. 1: on the left side the Xe excimer emission spectrum (solid line) and superimposed with the photoluminescence excitation spectrum (dotted line), and on the right side the photoluminescence emission spectrum exhibited by YPO.sub.4:Bi;

[0087] FIG. 2: an emission spectrum of an Xe excimer discharge lamp with a double layer coating of YPO.sub.4:Bi and YBO.sub.3:Pr; and

[0088] FIG. 3: a preferred embodiment with a layered structure of two phosphors on the outside of a quartz vessel.

[0089] An excimer discharge lamp comprising a double layer coating is disclosed, wherein the first layer comprises YPO.sub.4:Bi (emission maximum 241 nm) and the second layer comprises YBO.sub.3:Pr (emission maximum 265 nm).

[0090] Xe excimer discharge lamp bodies fabricated from high quality synthetic quartz were treated in a coating procedure which involves a four stepped spray coating of the lamp body surface with a first precoating layer of nanometer sized Al.sub.2O.sub.3 particles, a second covering layer of the UV-C emitting phosphor YPO.sub.4:Bi (λ(Em.)max=241 nm), a third covering layer of the UV-C/B emitting Phosphor YBO.sub.3:Pr (λ(Em.)max=265 nm) and a final protective capping layer of SiO.sub.2.

[0091] The base coating given by nanometer sized Al.sub.2O.sub.3 particles is applied onto the lamp vessel via spray coating utilizing a homogeneous 7.5 wt.-% dispersion of γ-Al.sub.2O.sub.3 (Trade name “AluC” provided by Evonik Industries AG, Essen, Germany) in iso-propanol. The coating was then applied in an airbrush spray-coating procedure involving continuous rotation of the lamp body along its longitudinal axis. The as coated lamp body is allowed to dry at room temperature for 20 minutes before it is further dried at 80° C. for 1 h within a furnace.

[0092] The Al.sub.2O.sub.3 coated excimer lamp body is treated in another spray coating step involving a spray paint based on n-butylacetate as dispersing agent charged with 3 wt. % nitrocellulose (Type H7 provided by Hagedorn-NC GmbH, Osnabruck, Germany), 1 wt.-% Al.sub.2O.sub.3(AluC, Evonik), 20 wt. % YPO.sub.4:Bi (all wt. % values are related to the mass of n-butylacetate). In order to increase homogeneity, Al.sub.2O.sub.3 and YPO.sub.4:Bi were gently mixed with 5 wt. % of an organic dispersing additive (Dysperbyk 110, provided by BYK-Chemie GmbH, Wesel, Germany), used relative to the summed up weight of Al.sub.2O.sub.3 and YPO.sub.4:Bi, before dispersion in the homogeneous solution of nitrocellulose in iso-propanol. Homogeneity is achieved via agitation of the as prepared dispersion within a polyethylene bottle lying on a roller band for at least 2 hours. The coating was then applied in an airbrush spray coating procedure involving continuous rotation of the lamp body about its longitudinal axis.

[0093] The so coated lamp body is allowed to dry at room temperature for 1 hour. The drying is followed by a calcination at 500° C. (30 min hold time) to bake out any organic components given by the applied YPO.sub.4:Bi phosphor coating.

[0094] The Al.sub.2O.sub.3 precoated and YPO.sub.4:Bi coated excimer lamp body is further treated in another spray coating involving a spray paint based on n-butylacetate as dispersing agent charged with 3 wt.-% nitrocellulose (Type H7, Hagedorn), 1 wt.-% Al.sub.2O.sub.3(AluC, Evonik), 20 wt.-% YBO.sub.3:Pr (all wt.-% values are related to the mass of n-butylacetate). In order to increase homogeneity, Al.sub.2O.sub.3 and YBO.sub.3:Pr were gently mixed with 5 wt.-% of an organic dispersing additive (Dysperbyk 110, Byk), used relative to the summed up weight of Al.sub.2O.sub.3 and YBO.sub.3:Pr before dispersion in the homogeneous solution of nitrocellulose in iso-propanol. Homogeneity is achieved via agitation of the as prepared dispersion within a polyethene bottle lying on a roller band for at least 2 hours. The coating was then applied in an airbrush spray coating procedure involving continuous rotation of the lamp body along its longitudinal axis. The as coated lamp body is allowed to dry at room temperature for 1 hour. The drying is followed by a calcination at 500° C. (30 min hold time) to bake out any organic components given by the applied YBO.sub.3:Pr phosphor coating. The lamp coating procedure is finally completed by the application of a capping layer of SiO.sub.2 utilizing a mixture of 1:1:0.25 mixture of ethanol, tetraethoxysilane in another, final airbrush spray coating procedure, continuously rotating of the lamp body along its longitudinal axis. The as coated lamp body is allowed to dry at room temperature for 1 hour followed by a final calcination at 500° C. (30 min hold time).

[0095] An Xe excimer lamp was produced in a known way using the so coated quartz tube as a tubular discharge vessel which contains the Xe gas filling as a discharge volume. The emission spectrum of an Xe excimer lamp with this coating is shown in FIG. 2.

[0096] FIG. 3 shows a principal cross section of a lamp according to a preferred embodiment. The embodiment shown in FIG. 3 is radially symmetrical and comprises, from the center to the outside, the following features:

[0097] The center comprises the central electrode 1 which is in the form of a wire electrode. The electrode 1 is surrounded by and centered in a gas volume 2 which contains e.g. a Xe filling at a low pressure. The gas volume 2 is contained inside a discharge vessel 3 which in this case is made from synthetic quartz which is transparent to VUV radiation. The outer surface of the discharge vessel 3 holds a first layer 4 made of a first phosphor which absorbs UV radiation of a wavelength shorter than 200 nm and emits UV radiation of a wavelength between 220 nm and 245 nm. A second layer 5 is provided radially outside the first layer 4 and contains a second phosphor which absorbs UV radiation of a wavelength between 220 nm and 245 nm and emits UV radiation of a wavelength between 250 nm and 315 nm. The arrangement of phosphor layers 4 and 5 is furthermore surrounded by a transparent tube 6, which is made for example from conventional quartz being transparent to wavelengths between 250 nm and 315 nm (and above).

[0098] This arrangement provides for a discharge volume 2 being contained in a synthetic quartz discharge vessel 3, which is on the one hand transparent to the VUV emission of a wavelength shorter than 200 nm and on the other hand can sustain the discharge without being deteriorated physically or chemically by the discharge inside. The first layer 4 can receive the full VUV radiation that is produced by the discharge. The photon conversion efficiency of the first layer 4, which is a pure VUV phosphor, is very high, of the order of 80%. The first layer 4 subsequently produces UV radiation of a wavelength between 220 nm and 245 nm which is absorbed by the second layer 5.

[0099] This layer converts the said radiation to a longer wavelength of 250 nm to 315 nm, which is the desired output of the UV lamp. The outer tube 6 is transparent to this output wavelength and is provided to protect the discharge vessel and the phosphor layers from external influences.

[0100] The quantum efficiency overall is very good because the layered structure of the phosphor ensures that the initial VUV radiation is only received by the first layer and not by a mixture of phosphors, which would be less effective in converting the impinging VUV radiation of less than 200 nm into the longer wavelength of 220 nm to 245 nm, which in turn impinges on a pure layer of the second phosphor with the same advantage.

[0101] Other embodiments which are not shown may provide for a first layer inside the discharge vessel, which first layer would then be coated on its inside surface with a layer of MgO to protect the first layer from chemical and physical effects of the discharge. The second layer could either be provided outside the first layer between the first layer and the discharge vessel, or on the outside of the discharge vessel. These embodiments would allow that the discharge vessel is made of conventional quartz instead of synthetic quartz because the VUV radiation is already converted to longer wavelengths inside the discharge vessel by the first layer of VUV phosphor.