Abstract:
The invention relates to an UV radiation device, comprising an LED comprising a nitridic material which is arranged to emit first UV radiation in a wavelength range of 200 nm-300 nm and a luminescent material doped with at least one of the following activators selected out of the group Eu 2+ , Ce 3+ , Pr 3+ , Nd 3+ , Gd 3+ , Tm 3+ , Sb 3+ , Tl + , Pb 2+  and Bi 3+ , wherein the luminescent material is configured to convert at least a part of the primary UV radiation into secondary UV radiation, the primary UV radiation and the secondary UV radiation having a different spectral distribution.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to a UV radiation device as well as to a system comprising such UV radiation device. 
       BACKGROUND OF THE INVENTION 
       [0002]    UV radiation devices, e.g. for medical purposes, for air or water purification, or surface cleaning by photochemistry are mostly equipped by amalgam, Hg low-, Hg medium-, or Hg high-pressure discharge lamps. 
         [0003]    The main drawbacks of some of the UV emitting gas discharge lamps known in the art is their rather low lifetime due to the plasma-glass and plasma-phosphor interaction resulting in severe glass solarization, phosphor degradation, and plasma efficiency loss. In addition to that these lamps require a high voltage driver and Hg discharge lamps show a strong dependence on temperature, in particular during start-up of the lamp. 
         [0004]    Therefore there is the need for alternative UV radiation devices that at least partly overcome the above-mentioned drawbacks and which have a longer lifetime. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the present invention to provide a UV radiation device which is at least partly able to overcome the above-mentioned drawbacks and especially allows building a UV radiation device with good or improved lighting features together with an increased lifetime for a wide range of applications. 
         [0006]    This object is solved by a UV radiation device according to claim  1  of the present invention. Accordingly, an UV radiation device for generating UV radiation in a wavelength range from 200-420 nm is provided comprising: 
         [0007]    a LED (light emitting diode) comprising a nitridic material which is arranged to emit first UV radiation in a wavelength range between 200 and 300 nm; 
         [0008]    a luminescent material configured to convert at least a part of the first UV radiation into second UV radiation, the first UV radiation and the second UV radiation having a different spectral distribution, wherein the luminescent material comprises at least one material selected out of the group comprising LiLuF 4 :Pr, CaSO 4 :Pr,Na, SrSO 4 :Pr,Na, BaSO 4 :Pr,Na, LaPO 4 :Pr, YPO 4 :Pr, LuPO 4 :Pr, KYF 4 :Pr, LuPO 4 :Bi, CaLi 2 SiO 4 :Pr,Na, KY 3 F 10 :Pr, YPO 4 :Bi, YAlO 3 :Pr, LaMgAl 11 O 19 :Pr, (Ba 1-x Sr x ) 2 SiO 4 :Pr,Na, NaYF 4 :Pr, SrAl 12 O 19 :Pr,Na, Sr 4 Al 24 O 25 :Pr,Na, LuBO 3 :Pr, YBO 3 :Pr, Y 2 SiO 5 :Pr, Lu 2 SiO 5 :Pr, Y 2 Si 2 O 7 :Pr, Lu 2 Si 2 O 7 :Pr, Lu 3 Al 5 O 12 :Bi,Sc, Lu 3 Al 3 Ga 2 O 12 :Pr, Lu 3 Al 4 GaO 12 :Pr, SrMgAl 10 O 17 :Ce,Na, Lu 3 Al 5 O 12 :Pr, LiYF 4 :Ce, LuF 3 :Ce, YBO 3 :Gd, Lu 3 Al 5 O 12 :Gd, Y 3 A 5 O 5 O 12 :Gd, LaMgAl 11 O 19 :Gd, LaAlO 3 :Gd, YPO 4 :Gd, GdPO 4 :Nd, LaB 3 O 6 :Gd,Bi, SrAl 12 O 19 :Ce, LaPO 4 :Ce, GdMgB 5 O 10 :Ce, LuPO 4 :Ce, CaF 2 :Ce, Y 3 Al 5 O 12 :Pr, LaCl 3 :Ce, SrCl 2 :Ce, (La 1-x Gd)PO 4 :Ce, Ca 2 P 2 O 7 :Eu, YPO 4 :Ce, LaMgAl 11 O 19 :Ce, BaSi 2 O 5 :Pb, Sr 2 MgSi 2 O 7 :Pb, SrB 4 O 7 :Eu, BaSO 4 :Eu, SrSO 4 :Eu, CaSO 4 :Eu, (Sr 1-x Mg x ) 2 P 2 O 7 :Eu, YAl 3 (BO 3 ) 4 :Gd,Pr, LaPO 4 :Tm, LaMgAl 11 O 19 :Gd,Bi, LaMgAl 11 O 19 :Gd,Pr, YAl 3 (BO 3 ) 4 :Gd,Bi, wherein x is in the range of 0 to 1.0. 
         [0009]    Surprisingly it has been found that such a UV radiation device has for a wide range of applications within the present invention at least one of the following advantages: 
         [0010]    little dependence of the spectrum and intensity on temperature; 
         [0011]    no toxic components such as Hg; 
         [0012]    emission spectrum can be optimally adjusted to the action curve of the application area aimed at; 
         [0013]    long lifetime; 
         [0014]    high irradiance. 
         [0015]    These luminescent materials have shown to be suitable due to their emission and absorbance features. 
         [0016]    According to a preferred embodiment of the invention, the nitridic material is either (Al,Ga,In)N or BN. The term “(Al,Ga,In)” indicates that the corresponding material may comprise aluminum, gallium or indium. It also indicates that such material may comprise metals selected from the group consisting of calcium, strontium and barium. Thus, the material may for instance comprise aluminum and gallium or only indium, etc. 
         [0017]    According to a preferred embodiment of the invention, the luminescent material is selected out of the group comprising fluorides, phosphates, aluminates, borates, silicates or sulphates or mixtures thereof. These materials have shown in practice to be suitable materials within the inventive UV radiation device. 
         [0018]    According to a preferred embodiment of the invention, the luminescent material is provided substantially in ceramic form. 
         [0019]    The term “substantially” herein, such as in “substantially all light” or in “substantially consists”, will be understood by the person skilled in the art. The term “substantially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term “substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of”. The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”. For instance, a phrase “item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term “comprising” may in an embodiment refer to “consisting of” but may in another embodiment also refer to “containing at least the defined species and optionally one or more other species”. 
         [0020]    Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. 
         [0021]    The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation. 
         [0022]    The term “ceramic material” in the sense of the present invention means especially a crystalline or polycrystalline compact material or composite material with a controlled amount of pores or which is pore free. 
         [0023]    The term “polycrystalline material” in the sense of the present invention means especially a material with a volume density larger than 90 percent of the main constituent, consisting of more than 80 percent of single crystal domains, with each domain being larger than 0.5 μm in diameter and having different crystallographic orientations. The single crystal domains may be connected by amorphous or glassy material or by additional crystalline constituents. In the sense of the present invention, the term “LED” may also refer to a plurality of LEDs. 
         [0024]    The terms “UV radiation” especially relates to light having a wavelength in the range of about 200 nm-420 nm. UV radiation may be sub-divided into “UV-C radiation” that especially relates to light having a wavelength in the range of about 200 nm-280 nm, “UV-B radiation” that especially relates to light having a wavelength in the range of about 280 nm-315 nm and “UV-A radiation” that especially relates to light having a wavelength in the range of about 315 nm-420 nm. 
         [0025]    In the term “Y 3 Al 5 O 2 :Gd”, “Gd” indicates that part of the metal ions is replaced by Gd (in this example Gd 3+ replaces Y 3+ ). For instance, assuming 2% Gd in Y 3 Al 5 O 12 :Gd, the correct formula could be (Y 2.98 Gd 0.02 )Al 5 O 12 . 
         [0026]    According to a preferred embodiment of the invention, the UV radiation device further comprises a polymer material selected out of the group comprising PVF (polyvinyl fluoride polymer), PVDF (polyvinylidene fluoride polymer), PTFE (polytetrafluoroethylene polymer), PFA (perfluoroalkoxy polymer), FEP (fluorinated ethylene propylene polymer), ETFE (ethylene tetra-fluoro ethylene polymer), PEEK (polyarylethe-retherketone polymer), PFPE (perfluoropolyether polymer) or mixtures thereof. These polymer materials have proven themselves in practice, particular due to their wide band gap. 
         [0027]    Especially preferred is FEP as a polymer material, since it has a wide band gap and is thus UV transparent. 
         [0028]    This polymer material can be used either as a filler material (e.g. in case when the luminescent material is not provided as a ceramic) or as an optical (e.g. lens) material. 
         [0029]    According to a preferred embodiment of the invention, the luminescent material is essentially provided in particle form with the particles having an average particle size in the range of 0.1 μm-100 μm. 
         [0030]    According to a preferred embodiment of the invention, the luminescent material is essentially provided in particle form with the particles being coated by an inorganic material with a band gap of ≧5.0 eV. 
         [0031]    According to a preferred embodiment of the invention, the luminescent material is essentially provided in particle form with the particles being coated by an inorganic material selected out of the group comprising AlN, Al 2 O 3 , Ln 2 O 3 (Ln=Sc, Y, Lu), MgO, (Y 1-x Lu x ) 3 (Al 1-y Sc y ) 5 O 12 , SiO 2  or mixtures thereof, wherein x is in the range of 0-1.0. 
         [0032]    According to a preferred embodiment of the invention, the UV radiation device further comprises an encapsulation material for encapsulation of the LED, and scattering particles that are dispersed in the encapsulation material. The scattering particles increase the amount of UV light that is coupled out of the UV radiation device and hence increase the device efficiency. 
         [0033]    According to a preferred embodiment of the invention, the nitridic material comprises Al x Ga 1-x In y N, with 0≦x+y≦1. These materials have direct band gaps that can be used to generate radiation in the UV wavelength range. 
         [0034]    According to a preferred embodiment of the invention, the scattering particles comprise one or more of the materials selected from boron nitride and aluminum. These materials show good scattering properties for radiation in the UV-B/C range. 
         [0035]    According to a preferred embodiment of the invention, the UV radiation device of further comprises a first surface for mounting of the LED, a second surface opposite to the first surface for exiting the UV radiation during operation of the device, and a UV reflective surface between the first surface and the second surface, and wherein the concentration of the scattering particles in the encapsulation material is graded from a first concentration in a first portion of the encapsulation material to a second concentration in a second portion of the encapsulation material, such that the first concentration is higher than the second concentration, and wherein the first portion is positioned between the reflective surface and a light-emitting surface of the LED substantially parallel to the reflective surface, and wherein the second portion is positioned between the second surface and a light-emitting surface of the LED substantially parallel to the second surface. The chance that radiation is being absorbed by the LED, for example, larger for light emitted in the first portion compared to the second portion. 
         [0036]    According to a preferred embodiment, only the first portion of the encapsulation material comprises scattering particles. Having a higher concentration of the scattering particles in the first portion compared to the second portion, or no scattering particles in the second portion, will reduce the mount of radiation that gets lost in the first portion. 
         [0037]    According to a preferred embodiment, the luminescent material comprises luminescent material particles that are dispersed in the encapsulation material or that dispersed in a layer forming a light exit surface during operation of the device. Luminescent particles dispersed in the encapsulation material may also act as scattering particles for scattering the UV-B/C radiation. Having the luminescent material dispersed in a layer forming a light exit surface will reduce the temperature of the luminescent material during operation of the radiation device, and hence, it may improve the life-time of the luminescent material. 
         [0038]    The present invention further relates to a system comprising a UV radiation device for one or more of the following applications: 
         [0039]    medical therapy; 
         [0040]    cosmetic skin treatment; 
         [0041]    water and/or air purification; 
         [0042]    photochemical synthesis of products. 
         [0043]    These applications will be furthermore discussed in more detail. 
       I. System for Medical Therapy 
       [0044]    In case the UV radiation device according to the invention is used for medical therapy (e.g. treatment of skin diseases such as Psoriasis), it is especially preferred that the luminescent material has its emission peak in the wavelength range of 300 nm-320 nm. 
         [0045]    Especially preferred luminescent materials are selected out of the group comprising: 
         [0046]    Lu 3 Al 4 GaO 12 :Pr 
         [0047]    SrMgAl 10 O 17 :Ce,Na 
         [0048]    Lu 3 Al 5 O 12 :Pr 
         [0049]    LiYF 4 :Ce 
         [0050]    LuF 3 :Ce 
         [0051]    YBO 3 :Gd 
         [0052]    Lu 3 Al 5 O 12 :Gd 
         [0053]    Y 3 Al 5 O 12 :Gd 
         [0054]    LaMgAl 11 O 19 :Gd 
         [0055]    YAl 3 (BO 3 ) 4 :Gd,Pr 
         [0056]    LaAlO 3 :Gd 
         [0057]    YPO 4 :Gd 
         [0058]    GdPO 4 :Nd 
         [0059]    LaB 3 O 6 :Gd,Bi 
         [0060]    SrAl 12 O 19 :Ce 
         [0061]    LaPO 4 :Ce 
         [0062]    GdMgB 5 O 10 :Ce 
         [0063]    LuPO 4 :Ce 
         [0064]    CaF 2 :Ce 
         [0065]    Y 3 Al 5 O 12 :Pr 
         [0066]    YAl 3 (BO 3 ) 4 :Gd,Pr 
         [0067]    YAl 3 (BO 3 ) 4 :Gd,Bi 
         [0068]    with Lu 3 Al 5 O 12 :Pr and/or YAl 3 (BO 3 ) 4 :Gd,Pr and/or YAl 3 (BO 3 ) 4 :Gd,Bi being more especially preferred. 
         [0069]    In case that a polymer is used in the UV radiation device, FEP is especially preferred. 
         [0070]    In case that the luminescent material is provided in particle form, an average particle size in the range of 10 μm-50 μm is especially preferred. 
       II. System for Cosmetic Skin Treatment 
       [0071]    In case the UV radiation device according to the invention is used for cosmetic skin treatment (e.g. a tanning device), it is especially preferred that the luminescent material has its emission peak in the wavelength range of 310 nm-340 nm. 
         [0072]    Especially preferred luminescent materials are selected out of the group comprising: 
         [0073]    Lu 3 Al 5 O 12 :Pr 
         [0074]    LiYF 4 :Ce 
         [0075]    LuF 3 :Ce 
         [0076]    YBO 3 :Gd 
         [0077]    Lu 3 Al 5 O 12 :Gd 
         [0078]    Y 3 Al 5 O 12 :Gd 
         [0079]    LaMgAl 11 O 9 :Gd 
         [0080]    LaAlO 3 :Gd 
         [0081]    YPO 4 :Gd 
         [0082]    GdPO 4 :Nd 
         [0083]    LaB 3 O 6 :Gd,Bi 
         [0084]    SrAl 12 O 19 :Ce 
         [0085]    LaPO 4 :Ce 
         [0086]    LaPO 4 :Tm 
         [0087]    GdMgB 5 O 10 :Ce 
         [0088]    LuPO 4 :Ce 
         [0089]    CaF 2 :Ce 
         [0090]    Y 3 Al 5 O 12 :Pr 
         [0091]    LaCl 3 :Ce 
         [0092]    SrCl 2 :Ce 
         [0093]    (La 0.5 Gd 0.5 )PO 4 :Ce 
         [0094]    with LaPO 4 :Ce, YPO 4 :Ce and LaPO 4 :Tm (also mixtures of LaPO 4 :Ce YPO 4 :Ce/LaPO 4 :Ce and LaPO 4 :Tm) being more especially preferred. 
         [0095]    In case that a polymer is used in the UV radiation device, FEP is especially preferred. 
         [0096]    In case that the luminescent material is provided in particle form, an average particle size in the range of 10 μm-50 μm is especially preferred. 
         [0000]    III. System for Water and/or Air Purification 
         [0097]    In case the UV radiation device according to the invention is used for water and/or air purification, it is especially preferred that the luminescent material has its emission peak in the wavelength range of 220 nm-260 nm. 
         [0098]    Especially preferred luminescent materials are selected out of the group comprising: 
         [0099]    LiLuF 4 :Pr 
         [0100]    CaSO 4 :Pr,Na 
         [0101]    SrSO 4 :Pr,Na 
         [0102]    LaPO 4 :Pr 
         [0103]    YPO 4 :Pr 
         [0104]    LuPO 4 :Pr 
         [0105]    KYF 4 :Pr 
         [0106]    LuPO 4 :Bi 
         [0107]    CaLi 2 SiO 4 :Pr,Na 
         [0108]    KY 3 F 10 :Pr 
         [0109]    YPO 4 :Bi 
         [0110]    YAlO 3 :Pr 
         [0111]    LaMgAl 11 O 19 :Pr 
         [0112]    (Ba,Sr) 2 SiO 4 :Pr,Na 
         [0113]    NaYF 4 :Pr 
         [0114]    SrAl 12 O 19 :Pr,Na 
         [0115]    Sr 4 Al 24 O 25 :Pr,Na 
         [0116]    LuBO 3 :Pr 
         [0117]    YBO 3 :Pr 
         [0118]    with YPO 4 :Bi being more especially preferred. 
         [0119]    In case that a polymer is used in the UV radiation device, FEP is especially preferred. 
         [0120]    In case that the luminescent material is provided in particle form, an average particle size in the range of 10 μm-50 μm is especially preferred. 
       IV. System for the Photochemical Synthesis of Products 
       [0121]    In case the UV radiation device according to the invention is used for equipment for photochemical synthesis of products (e.g. a chemical reactor for the photochemical synthesis of Vitamin D 3 ), it is especially preferred that the luminescent material has its emission peak in the wavelength range of 240 nm-280 nm. 
         [0122]    Especially preferred luminescent materials are selected out of the group comprising: 
         [0123]    KY 3 F 10 :Pr 
         [0124]    YPO 4 :Bi 
         [0125]    YAlO 3 :Pr 
         [0126]    LaMgAl 11 O 19 :Pr 
         [0127]    (Ba,Sr) 2 SiO 4 :Pr,Na 
         [0128]    NaYF 4 :Pr 
         [0129]    SrAl 12 O 19 :Pr,Na 
         [0130]    Sr 4 A 24 O 25 :Pr,Na 
         [0131]    LuBO 3 :Pr 
         [0132]    YBO 3 :Pr 
         [0133]    Y 2 SiO 5 :Pr 
         [0134]    Lu 2 SiO 5 :Pr 
         [0135]    Y 2 Si 2 O 7 :Pr 
         [0136]    Lu 2 Si 2 O 7 :Pr 
         [0137]    Lu 3 Al 5 O 12 :Bi,Sc 
         [0138]    with YBO 3 :Pr, Y 2 SiO 5 :Pr (also mixtures of YBO 3 :Pr and Y 2 SiO 5 :Pr) being more especially preferred. 
         [0139]    In case that a polymer is used in the UV radiation device, FEP is especially preferred. 
         [0140]    In case that the luminescent material is provided in particle form, an average particle size is preferably in the range of 0.1 μm-100 μm, more preferably in the range of 10 μm-50 μm. 
         [0141]    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 
         [0142]    Additional details, features, characteristics and advantages of the object of the invention are disclosed in the dependent claims, the figures and the following description of the respective figures and examples, which—in an exemplary fashion—show several embodiments and examples of a UV radiation device or a system comprising such UV radiation device according to the invention. 
           [0143]      FIG. 1  shows a schematic cross-sectional view of a UV radiation device according to a first embodiment of the invention 
           [0144]      FIG. 2  shows emission spectra of LEDs according to Example I of the invention 
           [0145]      FIG. 3  shows emission spectra of LEDs according to Example II of the invention 
           [0146]      FIG. 4  shows emission spectra of LEDs according to Example II of the invention 
           [0147]      FIG. 5  shows emission spectra of LEDs according to Example IV of the invention 
           [0148]      FIG. 6  shows emission spectra of LEDs according to Example V of the invention 
           [0149]      FIG. 7  shows emission spectra of LEDs according to Example VI of the invention 
           [0150]      FIG. 8  shows emission spectra of LEDs according to Example VII of the invention 
           [0151]      FIG. 9  shows emission spectra of LEDs according to Example VIII of the invention 
           [0152]      FIG. 10  shows a schematic cross-sectional view of a UV radiation device according to a second embodiment of the invention 
           [0153]      FIG. 11  shows a schematic cross-sectional view of a tanning device according to the invention 
           [0154]      FIG. 12 a    and  FIG. 12 b    shows a schematic cross-sectional view of a purification system according to the invention. 
           [0155]      FIGS. 13A and 13B  show a schematic cross-sectional view of a UV radiation device according to a second and third embodiment of the invention, respectively. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0156]      FIG. 1  shows a schematical cross-sectional view of a UV radiation device  1  according to a first embodiment of the present invention. It comprises a first LED  10  placed in an aluminum mirror  50  which is surrounded by a heat sink  60 . In the line of the optical path from the LED  10  is provided the luminescent material  20  in form of particles. The luminescent material  20  is embedded in a polymer  30  which also forms a lens  40  to focus the light emitted by UV radiation device  1 . In an alternative embodiment, the luminescent material may be present in the form of a ceramic plate on top of the LED  20 . 
         [0157]    The UV radiation device  1  is driven via a LED driver  80  which is connected with the UV radiation device  1  via a wire, preferably an aluminum wire  70 . 
         [0158]    The invention will furthermore be understood by the following inventive Examples which are merely for illustration of the invention only and non-limiting. 
       Example I 
       [0159]    Example I refers to a UV radiation device according to  FIG. 1 , having an UV radiation source comprising a 230 nm emitting (Al,Ga)N die and a luminescent screen comprising YPO 4 :Bi (Al 2 O 3 ) as a luminescent material. It can especially be used for air, water or surface disinfection devices and was made the following way: 
         [0160]    A microscale Al 2 O 3  coated YPO 4 :Bi(0.8%) phosphor powder is coated onto the (Al,Ga)N die, typically 1 mm 2  in size, by electrophoretic powder deposition (EPD). The phosphor layer thickness is between 10 and 50 μm. Then the coated chip is mounted inside an Al coated metal heat sink and electrically connected by Ag wires (alternatively Au wires could be used) to the driver. The heat sink is filled up by molten FEP (fluorinated ethylene propylene polymer). To complete the LED package, a transparent FEP cap is attached to the filled heat sink. 
         [0161]    The UV radiation device is driven by a low voltage driver that supplies direct current and a forward voltage between 2 and 20 V. 
         [0162]      FIG. 2  shows three emission spectra of UV radiation devices according to this Example I, referred to as LED 1 , LED 2  and LED 3 , having different luminescent material layer thicknesses between 20 and 60 μm, wherein LED 1  has the smallest layer thickness and LED 3  the largest layer thickness. 
       Example II 
       [0163]    Example II refers to a UV radiation device according to  FIG. 1 , having an UV radiation source comprising a 240 nm emitting (Al,Ga)N die and a luminescent screen comprising Lu 3 Al 5 O 12 :Pr as a luminescent material. It can especially be used for medical equipment for psoriasis treatment and was made the following way: 
         [0164]    A ceramic body (100 μm thickness) made out of microscale cubic Lu 3 Al 5 O 12 :Pr(0.3%) powder is deposited onto the (Al,Ga)N die, typically 1 mm 2  in size. Then the ceramic/chip assembly is mounted inside an Al coated metal heat sink and electrically connected by Ag wires (alternatively Au wires could be used) to the LED driver. The heat sink is filled up by molten FEP (fluorinated ethylene propylene polymer). To complete the LED package, a transparent FEP cap is attached to the filled heat sink. 
         [0165]    The UV radiation device is driven by a low voltage driver that supplies direct current and a forward voltage between 2 and 20 V. 
         [0166]      FIG. 3  shows three emission spectra of UV radiation devices according to this Example II, referred to as LED 1 , LED 2  and LED 3 , having different luminescent material layer thicknesses between 20 and 60 μm, wherein LED 1  has the smallest layer thickness and LED 3  the largest layer thickness. 
       Example III 
       [0167]    Example III refers to a UV radiation device according to  FIG. 1 , having an UV radiation source comprising a 240 nm emitting (Al,Ga)N die and a luminescent screen comprising YAl 3 (BO 3 ) 4 :Gd,Pr as a luminescent material. It can especially be used for medical equipment for psoriasis treatment and was made the following way: 
         [0168]    The microscale Al 2 O 3  coated YAl 3 (BO 3 ) 4 :Gd(10%)Pr(1%) luminescent material powder is coated onto the (Al,Ga)N die, typically 1 mm 2  in size, by electrophoretic powder deposition (EPD). The luminescent material layer thickness is between 10 and 50 μm and the layer density is between 20 and 50%. Then the coated chip is mounted inside an Al coated metal heat sink and electrically connected by Ag wires (alternatively Au wires could be used) to the LED driver. The heat sink is filled up by molten FEP (fluorinated ethylene propylene polymer). To complete the LED package, a transparent FEP cap is attached to the filled heat sink. 
         [0169]    The UV radiation device is driven by a low voltage driver that supplies direct current and a forward voltage between 2 and 20 V. 
         [0170]      FIG. 4  shows three emission spectra of UV radiation devices according to this Example III, referred to has LED 1 , LED 2  and LED 3 , having different luminescent material layer thicknesses between 20 and 60 μm, wherein LED 1  has the smallest layer thickness and LED 3  the largest layer thickness. 
       Example IV 
       [0171]    Example IV refers to a UV radiation emitting device according to  FIG. 1 , having an UV radiation source comprising a 240 nm emitting (Al,Ga)N die and a luminescent screen comprising SrAl 12 O 19 :Ce(5%)Na(5%) as a luminescent material. It can especially be used for medical equipment for psoriasis treatment and was made the following way: 
         [0172]    The microscale Al 2 O 3  coated SrAl 2 O 19 :Ce(5%)Na(5%) luminescent material powder is coated onto the (Al,Ga)N die, typically 1 mm 2  in size, by electrophoretic powder deposition (EPD). The luminescent material layer thickness is between 10 and 50 μm and the layer density is between 20 and 50%. Then the coated chip is mounted inside an Al coated metal heat sink and electrically connected by Ag wires (alternatively Au wires could be used) to the LED driver. The heat sink is filled up by molten FEP (fluorinated ethylene propylene polymer). To complete the LED package, a transparent FEP cap is attached to the filled heat sink. 
         [0173]    The UV radiation device is driven by a low voltage driver that supplies direct current and a forward voltage between 2 and 20 V. 
         [0174]      FIG. 5  shows three emission spectra of UV radiation devices according to this Example IV, referred to as LED 1 , LED 2  and LED 3 , having different luminescent material layer thicknesses between 20 and 60 μm, wherein LED 1  has the smallest layer thickness and LED 3  the largest layer thickness. 
       Example V 
       [0175]    Example V refers to a UV radiation device according to  FIG. 1 , having an UV radiation source comprising a 240 nm emitting (Al,Ga)N die and a luminescent screen comprising YBO 3 :Pr as a luminescent material. It can especially be used for photochemical production of Vitamin D and was made the following way: 
         [0176]    The microscale Al 2 O 3  coated YBO 3 :Pr (2%) phosphor powder is coated onto the (Al,Ga)N die, typically 1 mm 2  in size, by electrophoretic powder deposition (EPD). The phosphor layer thickness is between 10 and 50 μm and the layer density is between 20 and 50%. Then the coated chip is mounted inside an Al coated metal heat sink and electrically connected by Ag wires to the LED driver. The heat sink is filled up by molten FEP (fluorinated ethylene propylene polymer). To complete the LED package, a transparent FEP cap is attached to the filled heat sink. 
         [0177]    The UV radiation device is driven by a low voltage driver that supplies direct current and a forward voltage between 2 and 20 V. 
         [0178]      FIG. 6  shows three emission spectra of UV radiation devices according to this Example V, referred to as LED 1 , LED 2  and LED 3 , having different luminescent material layer thicknesses between 20 and 60 μm, wherein LED 1  has the smallest layer thickness and LED 3  the largest layer thickness. 
       Example VI 
       [0179]    Example VI refers to a UV radiation device having an UV radiation source according to  FIG. 1 , having a 240 nm emitting (Al,Ga)N die and a luminescent screen comprising Y 2 SiO 5 :Pr as a luminescent material. It can especially be used for photochemical production of Vitamin D and was made the following way: 
         [0180]    The microscale Al 2 O 3  coated Y 2 SiO 5 :Pr(2%) phosphor powder is coated onto the (Al,Ga)N die, typically 1 mm 2  in size, by electrophoretic powder deposition (EPD). The phosphor layer thickness is between 10 and 50 μm and the layer density is between 20 and 50%. Then the coated chip is mounted inside an Al coated metal heat sink and electrically connected by Ag wires to the LED driver. The heat sink is filled up by molten FEP (fluorinated ethylene propylene polymer). To complete the LED package, a transparent FEP cap is attached to the filled heat sink. 
         [0181]    The UV radiation device is driven by a low voltage driver that supplies direct current and a forward voltage between 2 and 20 V. 
         [0182]      FIG. 7  shows three emission spectra of UV radiation devices according to this Example VI, referred to as LED 1 , LED 2  and LED 3 , having different luminescent material layer thicknesses between 20 and 60 μm, wherein LED 1  has the smallest layer thickness and LED 3  the largest layer thickness. 
       Example VII 
       [0183]    Example VII refers to a UV radiation device source according to  FIG. 1 , having an UV radiation source comprising a 258 nm emitting (Al,Ga)N die and a luminescent screen comprising LaPO 4 :Ce and YPO 4 :Ce as a luminescent material. It can especially be used for tanning equipment and was made the following way: 
         [0184]    The microscale Al 2 O 3  coated phosphor powders of LaPO 4 :Ce(10%) and YPO 4 :Ce(5%) are blended and the blend is coated onto the (Al,Ga)N die, typically 1 mm 2  in size, by electrophoretic powder deposition (EPD). The phosphor layer thickness is between 10 and 50 μm and the layer density is between 20 and 50%. Then the coated chip is mounted inside an Al coated metal heat sink and electrically connected by Ag wires (alternatively Au wires could be used) to the LED driver. The heat sink is filled up by molten FEP (fluorinated ethylene propylene polymer). To complete the LED package, a transparent FEP cap is attached to the filled heat sink. 
         [0185]    The UV radiation device is driven by a low voltage driver that supplies direct current and a forward voltage between 2 and 20 V. 
         [0186]      FIG. 8  shows three emission spectra of light emitting devices according to this Example according to this Example VII, referred to as LED 1 , LED 2  and LED 3 , having different luminescent layer thicknesses between 20 and 60 μm, wherein LED 1  has the smallest layer thickness and LED 3  the largest layer thickness. 
       Example VIII 
       [0187]    Example VIII refers to a UV radiation device according to  FIG. 1 , having an UV radiation source comprising a 258 nm emitting (Al,Ga)N die and a luminescent screen comprising LaPO 4 :Ce and LaPO 4 :Tm as a luminescent material. It can especially be used for tanning equipment and was made the following way: 
         [0188]    The microscale Al 2 O 3  coated luminescent material powders of LaPO 4 :Ce(10%) and LaPO 4 :Tm(1%) are blended and the blend is coated onto the (Al,Ga)N die, typically 1 mm 2  in size, by electrophoretic powder deposition (EPD). The luminescent material layer thickness is between 10 and 50 μm and the layer density is between 20 and 50%. Then the coated chip is mounted inside an Al coated metal heat sink and electrically connected by Ag wires (alternatively Au wires could be used) to the LED driver. The heat sink is filled up by molten FEP (fluorinated ethylene propylene polymer). To complete the LED package, a transparent FEP cap is attached to the filled heat sink. 
         [0189]    The UV radiation device is driven by a low voltage driver that supplies direct current and a forward voltage between 2 and 20 V. 
         [0190]      FIG. 9  shows three emission spectra of UV radiation devices according to this Example according to this Example VIII, referred to as LED 1 , LED 2  and LED 3 , having different luminescent material layer thicknesses between 20 and 60 μm, wherein LED 1  has the smallest layer thickness and LED 3  the largest layer thickness. 
         [0191]      FIG. 10  schematically depicts another embodiment of a UV radiation device  200  comprising a module  170 , with a wall  171 , a cavity  172 , and a UV transmissive window  173 . The wall  171  and the UV transmissive window  173  here enclose cavity  172 . The UV radiation device  200  further comprises an LED  90  configured to generate first UV radiation  11 . Here, by way of example two LEDs  90  are depicted, though of course more than two, or only one, may be present. Further, the UV radiation device  200  comprises the luminescent material  2  that is embedded in a matrix  220 . The matrix  220  may comprise a polymer material. The luminescent material  2  is configured to convert at least part of the first UV radiation  11  into second UV radiation  121 . By way of example, the radiation device  200  further comprises the second luminescent material  150 , which provides upon excitation third UV radiation  151 . This third UV radiation  151  will in general have another spectral distribution than the second UV radiation  121 . All light generated by the UV radiation device is indicated with UV radiation device light  5 , which in this schematic embodiment comprises first UV radiation  11 , second UV radiation  121  and the optional third UV radiation  151 . Note that the luminescent material  2  is arranged at a non-zero distance d from the LED(s)  90 . In an alternative embodiment all first UV radiation  11  is converted to second UV radiation  121 , and optionally also into third UV radiation  151 . The UV radiation device  200  may further comprise a UV interference filter (not shown in  FIG. 10 ) that prevents the emission of undesired UV radiation in the wavelength range defined by the filter. The interference filter can be used to reflect short wavelength UV at the position where the longer wavelength UV leaves the device, in this way increasing optical absorption of the short wavelength UV in the luminescent material. Alternatively, it can be used to reflect the long wavelength UV at the site where the short wavelength UV enters the luminescent material, increasing the long wavelength UV radiation at the desired position. Finally, also the two interference filters could be used simultaneously. 
         [0192]      FIG. 11  schematically depicts a tanning device  31  in accordance with an embodiment of the invention. The tanning device  31  comprises a first tanning unit  2   a  and a second tanning unit  2   b  comprising two optical systems  3   a  and  3   b , respectively, wherein the tanning units  2   a ,  2   b  are mutually coupled by means of a hinge  4 . Each optical system  3   a ,  3   b  comprises a housing  5   a ,  5   b  for a UV radiation device  6   a ,  6   b , said housing  5   a ,  5   b  being defined by a reflective backing  7   a ,  7   b . The reflective backing structure  7   a ,  7   b  comprises a parabolic cross-section facetted cylindrical reflector  9   a ,  9   b , a reflective bottom plate  10   a ,  10   b , and a reflective top plate  11   a ,  11   b , both plates  10   a ,  10   b ,  11   a ,  11   b  being connected to said facetted cylindrical reflector  9   a ,  9   b . The UV radiation devices  6   a ,  6   b  used are suitable for emitting UV radiation during operation. For example the UV radiation devices  6   a ,  6   b  may comprise an elongated glass tube in which a plurality of LEDs is mounted on a board and a luminescent material is deposited directly on the LEDs or inside the glass tube, remotely from the LEDs. Alternatively, the UV radiation devices  6   a ,  6   b  may be constructed according to UV radiation device  200 , as shown in  FIG. 10 , with multiple LEDs. In order to obtain an efficient light output of the tanning apparatus  31  a high efficiency reflector design is applied. In the embodiment of the tanning device  31  shown, the orientation between the tanning units  2   a ,  2   b  is adjustable. During operation, the angle α enclosed by both adjacent tanning units  2   a ,  2   b  is preferably about 120° for optimally irradiating a tanning person being situated at a distance of about 25 cm from the hinge  4 . By means of a timer switch  13  contained in the second tanning unit  2   b , the tanning time (commonly up to 15 or 30 minutes) can be adjusted by the person. Both tanning units  2   a ,  2   b  are provided with a handle  14   a ,  14   b  to facilitate transport of the tanning apparatus  31 . The tanning device  31  may further comprise a UV interference filter (not shown in  FIG. 11 ) that prevents the emission of undesired UV radiation in the wavelength range defined by the filter. The interference filter can be used to reflect short wavelength UV at the position where the longer wavelength UV leaves the device, in this way increasing optical absorption of the short wavelength UV in the luminescent material. Alternatively, it can be used to reflect the long wavelength UV at the site where the short wavelength UV enters the luminescent material, increasing the long wavelength UV radiation at the desired position. Finally, also the two interference filters could be used simultaneously. 
         [0193]      FIG. 12 a    schematically depicts a system  100  for the purification of a fluid, in accordance with an embodiment of the invention. Two perforated plates  104  are housed inside a chamber  102 . Perforated plates  104  have UV radiation devices mounted on their surface (see  FIG. 12 b   ). In an embodiment of the invention, perforated plates  104  may be modified to fit into any other container. For example, perforated plates  104  may be modified to fit into cylindrical pipe carrying water. Chamber  102  has an inlet  106  and an outlet  108 . The fluid enters chamber  102  through inlet  106  and passes through perforations in perforated plates  104 . The fluid may be air, water or any other liquid or gas. The micro-organisms present in the fluid, while passing through the perforations in perforated plates  104 , are exposed to UV radiation emitted by the UV radiation devices. The UV radiation is absorbed by the DNA, RNA and protein in the micro-organisms. The UV radiation causes genetic disorder and inactivation of the micro-organisms. Perforated plates  104  expose both front and rear of the micro-organisms to the UV radiation. In an embodiment of the invention, a feedback-based power control unit and feedback units are employed to control amount of power supplied to the UV radiation emitters (not shown in  FIG. 12 a   ). The feedback units provide data about the physical properties of the fluid to the feedback-based power control unit. Depending on the received data, the feedback-based power control unit varies the amount of power supplied to the UV radiation devices. In an alternative embodiment, system  100  has UV-reflecting screens  110 . UV-reflecting screens  110  cover walls of chamber  102 . Any UV radiation incident on UV reflecting screens  110  is reflected back to chamber  102 , increasing density of the UV radiation inside chamber  102 . In an embodiment of the invention, UV-reflecting screens  110  are made of aluminium. In another embodiment the UV-reflecting screens  110  may comprise a TiO 2  photo-catalyst that generates ozone when exposed to UV radiation. 
         [0194]      FIG. 12 b    is a front view of a perforated plate  104  with UV radiation devices  202  mounted on its surface, in accordance with an embodiment of the invention. Perforated plate  104  has UV radiation devices  202  arranged in an array on its surface. The UV radiation devices  202  may be, for example, according to the UV radiation device as shown in  FIG. 1  and having one LED or alternatively a plurality of LEDs. Alternatively, UV radiation devices  202  may be according to the UV radiation device as shown in  FIG. 10 . Perforated plate  104  has perforations  204  to allow the fluid to pass through. In an embodiment of the invention, perforated plate  104  may be a Printed Circuit Board (PCB). In another embodiment of the invention, perforated plate  104  is a Metal Core Printed Circuit Board (MCPCB). The metal core of the MCPCB makes it a good conductor of heat. The metal core effectively transfers heat generated by UV radiation devices  202  to a heat sink which may be a separate heat sink (not shown in  FIG. 12 a   ) or the fluid (e.g. water) that is purified. Effective transfer of heat to the heat sink keeps UV radiation devices  202  in their ideal operating temperature range, thereby increasing efficiency of the system  100 . A relatively low temperature is required for efficient operation of the LEDs, preferably in the range of 20° C. to 60° C. In an embodiment of the invention, perforations  204  are square in shape. Perforations  204  allow the fluid to pass through and expose the micro-organisms present in the fluid to the UV radiation. Dimensions of perforations  204  determine proximity of the micro-organisms to the UV radiation devices  202 . The dimensions of perforations  204  are decided based on UV radiation emission capacity of UV radiation devices  202 . The dimensions of perforations  204  are relatively large for high power UV radiation emitters  202 , whereas the dimensions of perforations  204  are relatively small for low power UV radiation emitters  202 . 
         [0195]      FIGS. 13A and 13B  show a schematic cross-sectional view of a UV radiation device according to a second and third embodiment of the invention, respectively. Referring to  FIGS. 13A and 13B  together, UV radiation device  330  and  340  comprise a UV LED  302  that is mounted on a sub-mount  301 . The UV LED  302  is encapsulated by an encapsulation material  306 . The side walls  303  are made (or alternatively coated by) from a UV reflective material. During operation, the UV LED  302  generates UV radiation  309  from the side walls of the LED  302  in the direction of the side walls  303 , as well as UV radiation  310  from the top surface of the LED in the direction of the light exiting surface  311  of the UV radiation device. UV radiation device  330  comprises a layer  304  that comprises luminescent material particles  307 . UV radiation device  340  comprises luminescent material particles  307  that are present in the encapsulation material  306 . During operation, at least a part of the UV radiation generated by the UV LED  302  is converted by the luminescent material  307  to second UV radiation. The second UV radiation and optionally the non-converted UV radiation generated by the UV LED  302  exits the UV radiation device  330 ,  340  as UV radiation  308 . The UV radiation device  330 ,  340  further comprise scattering particles  305 . The scattering particles  305  scatter the UV radiation generated by the UV LED  302  which may prevent that part of the UV radiation will be lost in the UV radiation device  330 ,  340  due to internal absorption. For example, the UV radiation  309  may be reflected back by the side walls  303  into the direction of the UV LED  302  and being absorbed there. In this way the scattering particles  305  will minimize the loss of UV radiation and improve the efficiency of the UV radiation device  330 ,  340 . Furthermore, the scattering particles  305  may broaden the angle of the light beam that comprising the UV radiation  308  generated by the UV radiation device during operation. For example, the UV LED  302  may comprise a semiconductor material of group IIIA-nitrides (Al x Ga 1-x-y In y N, with 0≦x+y≦1) that have direct band gaps that can be used to generate electromagnetic radiation in the UV wavelength range. For such materials, e.g. for Al x Ga 1-x N (0&lt;x&lt;1) that is often utilized as the component for LEDs generating UV(-C) radiation, the UV radiation  310  emitted from the AlN layer is TM (Transverse Magnetic)-polarized, and instead of that the UV radiation  309  from the GaN layer is TE (Transverse Electric)-polarized. The light extraction of the TM-polarized light is generally worse than that of TE-polarized light. The use of the scattering particles  305  results in an improved extraction of the (TE polarized) UV radiation  309 , increasing the package efficiency. In a preferred embodiment, the concentration of the scattering particles  305  in the encapsulation material  306  is graded from a first concentration in a first portion of the encapsulation material  306  to a second concentration in a second portion of the encapsulation material  306 , such that the first concentration is higher than the second concentration. The first portion may be mainly transmitting the UV radiation  309 , i.e. that portion of the encapsulation material more close to the submount  301 , for example the portion of the encapsulation material  306  enclosed by the submount  301 , the side walls  303  and an imaginary line  312 . The imaginary line  312  is a line substantially parallel to the submount  301  and that coincides with the top surface of the LED  301 . The second portion may be mainly transmitting the UV radiation  310 , i.e. more close to the light exiting surface  311 , for example that part of the encapsulation material  306  enclosed by the imaginary line  312 , the side walls  303  and the light exit window  311 . In a specific embodiment, only the first portion of the encapsulation material  306  comprises scattering particles  305 . The encapsulation material  306  may be any type of (at least partly) UV transparent polymer (e.g. silicone, PVF, PVDF, PTFE, PFA, FEP, ETFE, PEEK, PFPE or mixtures thereof), glass, ceramic material, etc. The scattering particles  305  may comprise boron nitride, alumina or aluminum, and have a particle size in the rage of 200 nm-5 μm. 
         [0196]    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. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. The invention&#39;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.