WO2011121497A1

WO2011121497A1 - Uv-c-emitting discharge lamp

Info

Publication number: WO2011121497A1
Application number: PCT/IB2011/051248
Authority: WO
Inventors: Georg Greuel; Thomas Juestel
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2010-03-31
Filing date: 2011-03-24
Publication date: 2011-10-06

Abstract

The invention relates to a discharge lamp with a novel Yttrium/Lutetium/Gadolinium fluoride Praseodymium phosphor with excellent UV-C spectral properties.

Description

UV-C-EMITTING DISCHARGE LAMP

FIELD OF THE INVENTION

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

BACKGROUND OF THE INVENTION

Fluorescent lamps which comprise an UV emitting phosphor are widely applied for cosmetic and medical purposes. These lamps usually generate UV light by e.g. utilizing a Hg low-pressure discharge and a luminescent screen comprising UV-B or a UV-A phosphors or a blend of several UV-A/B phosphors. Most commonly applied phosphors are LaP0₄:Ce, SrAli₂0i₉:Ce,Na, or LaB₃0₆:Bi,Gd as UV-B emitter and (Y,Gd)P0₄:Ce, Ba- Si₂0₅:Pb, or SrB₄0₇:Eu as UV-A emitter

However, Hg discharge lamps for disinfection or purification purposes does not use any luminescent screen, since the spectral power distribution of the emission spectrum of a low or medium pressure Hg discharge nicely coincides with the GAC and with the absorption edge of molecular Oxygen and water.

The main drawback of the presently applied low- and medium-pressure Hg discharge lamps is their strong dependence of the radiation output from the (water, air) temperature. This is caused by the vapor pressure of liquid Hg, which is a sensitive function of the temperature.

Moreover, the chemical interaction of the Hg discharge with the glass vessel causes the formation of color centers, which in turn causes an efficiency reduction. Formation of an absorbing layer due to color centers is reduced, once nanoscale particles or phosphor particles are coated on top of the glass surface. Therefore, low- and medium pressure Hg discharge lamps show strong degradation and must be replaced after about 1000 h operation.

A similar maintenance problem is known from UV-C emitting Xe excimer discharge lamps, equipped by a luminescent screen, which comprises a Bi³⁺ activated phosphor, viz. YP0₄:Bi or LuP0₄:Bi. Therefore there is the need for alternative phosphors, especially for UV-C lamps, which are at least partly overcoming the above-mentioned drawbacks and which have a longer lifetime.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a discharge lamp which is at least partly able to overcome the above-mentioned drawbacks and especially allows building a discharge lamp with good or improved lighting features together with an increased lifetime for a wide range of applications.

This object is solved by a discharge lamp according to claim 1 of the present invention. Accordingly, an discharge lamp, preferably a low-pressure gas discharge lamp, is provided, whereby said discharge lamp is provided with a discharge vessel comprising a gas filling with a discharge-maintaining composition, wherein at least a part of a wall of the discharge vessel is provided with a luminescent material comprising A(Yi__x__a__yLu_xGd_y)F4:Pr_a , whereby A is an alkali metal or a mixture thereof, x is >0 and <1 , y is >0 and <1 (with x+y < 1-a) and a is >0 and <0.1.

Surprisingly it has been found that such a discharge lamp has for a wide range of applications within the present invention at least one of the following advantages:

An improved lamp efficacy due to the optimized emission spectrum to the action curve of the application and due to less re-absorption by the phosphor layer

A improved stability of the UV-C output and thus improved operational lifetime of the UV light source

an adjustable UV-C emission spectrum;

weaker dependence of the lamp efficacy on the temperature

improved flexibility of the lamp with respect to its geometry and to switching cycles Preferably the discharge lamp is a Xe, Ne, or Xe/Ne excimer discharge lamp. According to a preferred embodiment of the present invention, either x is >0 and <1 , y is >0 and <1 or both, i.e. that the phosphor material comprises Yttrium and one or both of Lutetium and Gadolinium. This has been found to be advantageous for many applications within the present invention due to the good spectral properties of the phosphors with this structure.

According to a preferred embodiment, A is selected out of the group comprising Rb, Cs, K and mixtures thereof. This has been found to be advantageous for many appli- cations within the present invention due to the good spectral properties of the phosphors with this structure.

According to a preferred embodiment, at least a part of a wall of the discharge vessel is provided with a basic metal oxide, preferably selected out of the group MgO, MgAl₂0₄, A1₂0₃, or Ln₂0₃ (Ln = Sc, Y, La, Gd, Lu) or mixtures thereof. This has been shown to be advantageous for many applications within the present invention due to observed reduction of decrease of the radiation output over lifetime.

The basic metal oxide is preferably provided as a nanoscale particle material with an average particle size of >10 nm and < 1 μιη, preferably >100 nm and < 500nm. Pre- ferably they are provided either together with the luminescent material (e.g. that a layer is formed comprising both materials) or as a layer on top or underneath the luminescent material.

According to a preferred embodiment, at least a part of a wall of the discharge vessel is provided with a further luminescent material selected out of the group comprising (Yi__x__aLu_x)B0₃:Pr_a, (Y^Lu^PO^Pr,, (Y₁__x__aLu_x)P0₄:Bi_a, L_ai__aP0₄:Pr_a, (Y_!__x__aLu_x)A10₃:Pr_a, (Cai__x__2aSr_x)₂P₂0₇:Pr_aNa_a, (Cai__x__2aSr_x)Ali₂0i₉:Ce_aNa_a, or (Lai__x__aGd_x)P0₄:Ce_a with x >0 and <1 and a is >0 and <0.1 (for all materials) or mixtures thereof.

By doing so for many applications optimization of the lamp spectrum to the action spectrum of the given application is feasible.

The present invention furthermore relates to the use of A(Yi__x__a__yLu_xGd_y)F₄:Pr_a

, whereby A is an alkali metal or a mixture thereof, x is >0 and <1, y is >0 and <1 (with x+y < 1-a) and a is >0 and <0.1 as an activator in UV-C emitting illumination systems.

A system comprising a discharge lamp as described or making use of the phosphor material as described above may be used in one or more of the following applica- tions:

Equipment for medical therapy

Equipment for cosmetical skin treatment (e.g. tanning devices)

Water sterilization and/or purification applications, e.g. by the photochemical activation of Cl₂ or C10₂

- chemical reactors, e.g. for the photochemical synthesis of advanced chemical products, e.g. Vitamin D₃

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, discharge lamp selec- tion and technical concept such that the selection criteria known in the pertinent field can be applied without limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional details, features, characteristics and advantages of the object of the invention are disclosed in the sub-claims, the figures and the following description of the respective figures and examples, which - in an exemplary fashion - show several embodiments and examples of discharge lamps according to the invention.

Fig. 1 shows a very schematic cross-sectional view of a discharge lamp according to a first embodiment of the present invention.

Fig. 2 shows an XRD spectrum of a first luminescent material according to the present invention (Example I)

Fig. 3 shows the excitation, emission and reflection spectrum of the material of Fig. 2

Fig. 1 shows a very schematic cross-sectional view of a discharge lamp according to a first embodiment of the present invention. The discharge lamp 10 (which is prin- cipally prior art) comprises a glass tube 14 in which a phosphor 12 is provided. This phosphor comprises the luminescent material of the present invention. Depending on the application also further phosphors and basic metal oxide nanoparticle may be present in this area. Furthermore two electrodes (e.g. made of Al) 18 are provided.

The invention will furthermore be understood by the following Inventive Ex- ample which is merely for illustration of the invention only and non- limiting.

EXAMPLE I

Example I refers to KLuF₄:Pr (10%), which was made by blending a suitable mixture of LuF₃, PrF₃, and KF in a C-crucible, annealing at 700 and then at 900 °C under CO for 2 h.

Fig. 2 shows the XRD spectrum, Fig. 3 shows the excitation (left spectrum), the emission spectrum (right spectrum) and the reflection spectrum (upper right spectrum) of the material of Example I. It can clearly be seen that this material is an excellent material of use in discharge lamps for UV-C radiation 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 re- cited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. The invention's scope is defined in the following claims and the equivalents thereto. Furthermore, reference signs used in the description and claims do not limit the scope of the invention as claimed.

Claims

CLAIMS:

1. Discharge lamp, provided with a discharge vessel comprising a gas filling with a discharge-maintaining composition, wherein at least a part of a wall of the discharge vessel is provided with a luminescent material comprising A(Yi__x__a__yLu_xGd_y)F₄:Pr_a, whereby A is an alkali metal or a mixture thereof, x is >0 and <1, y is >0 and <1 (with x+y < 1-a) and a is >0 and <0.1.

2. The discharge lamp of Claim 1, whereby the discharge lamp is a Xe, Ne, or Xe/Ne excimer discharge lamp.

3. The discharge lamp of Claim 1 or 2, whereby either x is >0 and <1, y is >0 and

<1 or both.

4. The discharge lamp of any of the Claims 1 to 3, whereby A is selected out of the group comprising Rb, Cs, K and mixtures thereof.

5. The discharge lamp of any of the Claims 1 to 4, whereby at least a part of a wall of the discharge vessel is provided with a basic metal oxide, preferably selected out of the group MgO, MgAl₂0₄, A1₂0₃, or Ln₂0₃ (Ln = Sc, Y, La, Gd, Lu) or mixtures thereof.

6. The discharge lamp of any of the Claims 1 to 5, whereby at least a part of a wall of the discharge vessel is provided with a further luminescent material selected out of the group comprising (Yi__x__aLu_x)B0₃:Pr_a, (Yi__x__aLu_x)P0₄:Pr_a, (Yi__x__aLu_x)P0₄:Bi_a, Lai_ _aP0₄:Pr_a, (Y_!__x__aLu_x)A10₃:Pr_a, (Ca₁__x__2aSr_x)₂P₂0₇:Pr_aNa_a, (C_ai__x__2aSr_x)Al₁₂0i₉:Ce_aNa_a, or (Laj. _x__aGd_x)P0₄:Ce_a with x >0 and <1 and a is >0 and <0.1 (for all materials) or mixtures thereof.

7. Use of A(Yi__x__a__yLu_xGd_y)F₄:Pr_a , whereby A is an alkali metal or a mixture thereof, x is >0 and <1, y is >0 and <1 (with x+y < 1-a) and a is >0 and <0.1 as an activator in UV-C emitting illumination systems.

8. A system comprising a discharge lamp according to any of the claims 1 to 6 and/or making use of Claim 7, the system being used in one or more of the following applications:

Equipment for medical therapy,

- Equipment for cosmetic skin treatment (e.g. tanning devices),

Water sterilization and/or purification applications, e.g. by the photochemical activation of Cl₂ or C10_2,

chemical reactors, e.g. for the photochemical synthesis of advanced chemical products, e.g. vitamin D₃.