Lumninescent materials for illumination purposes

The invention relates to phosphors according to the preamble of claim 1, and to fluorescent lamps coated therewith according to the preamble of claim 21.

It is closely related to German patent application P 43 11 197.1, which discloses a new mode of operation for dielectrically impeded discharges. The teaching explained in more detail there enables, among other things, a significantly more efficient generation of UV or VUV radiation, in particular by means of excimers - for example Xe₂*, which emits a molecular band radiation in the range around 172 nm - than was previously possible. In the following, the term “VUV radiation” is to be used in particular to denote electromagnetic radiation with wavelengths in the range between approximately 145 nm and 185 nm.

The main area of ​​application for today's phosphors in lighting technology, ie for converting short-wave electromagnetic radiation into light, is the fluorescent lamp. This is based on the low-pressure mercury discharge, which emits energy mainly in the form of UV radiation. This is essentially the radiation of an atomic spectral line with a wavelength of approx. 254 nm.

In order to take increasing environmental awareness into account, mercury-free UV and VUV radiation sources have been developed increasingly recently. So far, however, only relatively low UV or VUV yields (approx. 10% to 20%, with technically relevant power densities) have been achieved compared to low-pressure mercury discharge (approx. 70%). Use of this mercury-free UV or. VUV spotlights designed as fluorescent lamps for general lighting were therefore uneconomical and have so far not been considered. Therefore, there has been no need to look for phosphors that are both excitable in the VUV area and suitable for general lighting in terms of their emission properties. With the in above The operation described in the patent application can now for the first time achieve efficiencies even in mercury-free discharges, in particular for the generation of VUV radiation of 65% and more. The high VUV yields are particularly due to the very efficient generation of Xe₂* - Excimers realized. The main part of the radiation power is emitted in the wavelength range between approx. 145 nm and 185 nm. With regard to efficient radiation generation, a real alternative has been found for conventional low-pressure mercury discharge. To use the new radiation source in general lighting, however, the conversion of the short-wave VUV radiation into light is required, ie in the visible range of the optical spectrum.

The invention is based on the object of specifying phosphors which, when irradiated with VUV radiation, in particular with wavelengths in the range between approximately 145 nm and 185 nm, efficiently luminesce in the visible region of the optical spectrum. This object is solved by claim 1. Further advantageous features can be found in claims 2 to 20.

Another object of the invention is to provide a fluorescent lamp with a fluorescent coating suitable for general lighting purposes, the fluorescent lamp being based on a VUV emitter which, in particular, generates wavelengths in the range between approximately 145 nm and 185 nm. This object is solved by claim 21. Further advantageous features can be found in claims 22 to 24.

A characteristic variable for the efficiency of the conversion of electromagnetic radiation by phosphors is their wavelength-dependent excitability. It is proportional to the product of absorption and quantum efficiency. The latter is the likelihood of a photon being generated by the phosphor after a shorter wavelength (higher energy) photon has been absorbed. Maximum excitability is therefore present if both the absorption and the quantum efficiency are 100%, ie each incident photon is absorbed and converted into a photon with a longer wavelength (lower energy).

In preliminary investigations, the excitability of a large number of phosphors customary for use in conventional fluorescent lamps with low-pressure mercury discharge using VUV radiation has been determined by measurement. It has been shown that with all phosphors the absorption increases substantially with decreasing wavelength of the incident radiation, but surprisingly the excitability decreases drastically when the wavelength falls below a limit. This behavior is shown as an example in FIGS. 1-3. The normalized excitability is shown as a function of the wavelength of one red (<i>Y</i>₂<i>O</i>₃:<i>Eu</i>³⁺), <i>Green (GdMgB</i>₅<i>O</i>₁₀<i>: Ce, Tb</i>) and blue fluorescent (<i>BaMgAl</i>₁₀<i>O</i>₁₇:<i>Eu</i>). As a result, some phosphors that are advantageously used in conventional fluorescent lamps have, for example, the green phosphor<i>CeMgAl</i>₁₁<i>O</i>₁₉:<i>Tb</i>³⁺, insufficient excitability due to VUV radiation. In this case, the drop in excitability already extends across the entire VUV range. Other phosphors, on the other hand, are better stimulated by VUV radiation, since the waste only starts at the short-wave end of the VUV range. An example of this is the blue fluorescent, which is also known<i>BaMgAl</i>₁₀<i>O</i>₁₇: <i>Eu</i>²⁺ (see Figure 3).

The physical processes underlying the observed behavior have not yet been fully clarified. It is currently believed that possible causes are due to fundamentally different absorption mechanisms for radiation with wavelengths below the cutoff wavelength. The radiation power of the spectral line most important for fluorescent excitation of the conventional mercury low-pressure discharge with the wavelength 254 nm mainly leads to an excitation of the activator atoms, which may also act as luminous centers, or any existing co-activators (sensitizers). In this case, the sensitizers transfer the excitation energy to the activator atoms. Below the cutoff wavelength, the absorption by the host grating increases abruptly (the absorption coefficient reaches values ​​of the order of 10⁵ cm^-1 and more). The cut-off wavelength can therefore be interpreted simply as the wavelength that a photon may have at most in order to be able to excite an electron from the valence band of the host lattice into the conduction band. The corresponding energy difference between the valence and conduction bands is referred to below as the optical band gap and the cut-off wavelength as the optical band edge.

If an electron in the host lattice is excited from the valence band into the conduction band by absorbing a photon of the appropriate energy, an "electron-hole pair" is created, whereby the electron and hole can be free or bound as an exciton (details can be found in: Charles Kittel, "Introduction to Solid State Physics", Oldenbourg Verlag, Munich, 5th edition, 1980, pp. 359 ff). An exciton is electrically neutral and can therefore move relatively freely within the grid and release its energy to a collision partner, for example an activator atom. This in turn can emit energy in the form of light. For increasing photon energies (decreasing wavelengths of the absorbed radiation) a significant decrease in excitability was determined experimentally as soon as the photon energies larger than the optical band gap (ie the wavelengths of the photons are smaller than the optical band edge). Without intending to be bound by any theoretical explanation, both surface and bulk defects are currently held responsible for this observation. The impurities "increasingly" capture the free electrons and holes or the excitons before the latter can release their energy to the activator atoms (ie luminous centers). From the defects - this can cause contamination, dislocations, etc. be - the energy goes into different loss channels without radiation and ultimately only leads to an undesirable heating of the phosphor.

This is where the teaching of the invention comes in, which specifically targets those phosphors for lighting purposes that can be excited efficiently with VUV radiation. On the basis of the findings described at the outset, these are luminescent materials whose optical band gap of the host lattice lies above the low-energy limit of the energy spectrum of the VUV radiation, in particular above 6.7 eV. Suitable host lattices are, for example, borates, phosphates, aluminates and silicates. The host lattice is doped with at least one additional substance, which functions as a luminous center and is usually referred to as an activator. The optical spectrum of the luminescence can be specifically influenced by a suitable choice of the activator. The color of the luminescence is used to identify the phosphor in question. The three primary colors red, green and blue are of outstanding interest for the lighting technology, because they can be used to create any mixed color, for example for effect or signal lighting as well as white light - particularly important for general lighting. For this purpose, the different phosphor components are suitably combined, for example mixed or arranged in an alternating sequence. Suitable activators are, for example, Eu³⁺ for red fluorescent substances, Tb³⁺ for green fluorescent and EU²⁺ for blue phosphors. In particular, it can be used to specifically activate those phosphors whose emission spectra are particularly well suited for a three-band phosphor. To optimize both the luminous efficacy and the color rendering of a three-band lamp for general lighting, the main emission of the red phosphor must be around 610 nm, the green phosphor at approx. 540 nm and the blue phosphor at around 450 nm (see, for example, AW Thornton, J. Opt. Soc. Am. 61 (1971) 1155).

In a further embodiment, one or more further doping substances are added to the host lattice. These are also activators, ie lighting centers. In this way it is also possible to achieve any desired mixed colors in principle with a suitable choice of the various activators, even with only one phosphor. For example, yellow light is generated from a phosphor with a green and a red luminescent activator. For white light, at least a third, blue luminescent activator is also required.

Depending on the position of their optical band edge within the VUV area of ​​interest here, the VUV phosphors according to the invention - ie, efficiently excitable - can be roughly divided into two classes. In the first class, more than 50% of the incident VUV radiation power is absorbed by the host grid and transferred from there to the lighting centers. The rest of the VUV radiation power can be absorbed directly by the activator atoms, for example. An example of this is the red phosphor <i>(Y</i>_<i>x</i><i>DG</i>_<i>y</i><i>EU</i>_<i>e.g.</i><i>) BO</i>₃. It is a trivalent Europium Eu³⁺ activated mixed borate. Suitable values ​​for x, y and z are 0 ≤<i>x</i> ≤ 0,99, 0 ≤ <i>y</i> ≤ 0,99, 0,01 ≤ <i>e.g.</i> ≤ 0.2, preferably 0, 55 ≤ <i>x</i> ≤ 0,87, 0,1 ≤ <i>y</i> ≤ 0.3 and 0.03 ≤ <i>e.g.</i> ≤ 0.15, with the boundary condition in each case <i>x</i>+ <i>y</i>+ <i>e.g.</i>≈1 is fulfilled. An example of a blue fluorescent substance is that with divalent Europium Eu²⁺ activated mixed aluminate <i>(Ba</i>_<i>x</i><i>EU</i>_<i>y</i><i>) MgAl</i>₁₀<i>O</i>₁₇. Suitable values ​​for x and y are 0.6 ≤<i>x</i> ≤ 0,97, 0,03 ≤ <i>y</i> ≤ 0.4, preferably 0.8 ≤ <i>x</i> ≤ 0,95, 0,05 ≤ <i>y</i> ≤ 0.2, where each <i>x</i>+<i>y</i>≈1 applies. Examples of trivalent terbium Tb³⁺ Activated green phosphors are: 1.) the mixed aluminate <i>(Y</i>_<i>x</i><i>DG</i>_<i>y</i><i>Tb</i>_<i>e.g.</i><i>)</i>₃<i>Al</i>₅<i>O</i>₁₂, where: 0.1 ≤ <i>x</i> ≤ 0,99, 0 ≤ <i>y</i> ≤ 0,9, 0,03 ≤ <i>e.g.</i> ≤ 0.4 and <i>x + y + z</i> = 1, in particular <i>y</i> = 0, 0,8 ≤ <i>x</i> ≤ 0,99, 0,01 ≤ <i>e.g.</i> ≤ 0.2 and <i>x + z</i> = 1, 2.) the mixed silicate <i>(Y</i>_<i>x</i><i>Sc</i>_<i>y</i><i>Tb</i>_<i>e.g.</i><i>)</i>₂<i>SiO</i>₅, where: 0.6 ≤ <i>x</i> ≤ 0,99, 0 ≤ <i>y</i> ≤ 0,1, 0,01 ≤ <i>e.g.</i> ≤ 0.4 and <i>x + y + z</i>≈1, as well as 3.) the mixed borate <i>(Y</i>_<i>x</i><i>DG</i>_<i>y</i><i>Tb</i>_<i>e.g.</i><i>) BO</i>₃, where: 0 ≤ <i>x</i> ≤ 0,99, 0 ≤ <i>y</i> ≤ 0,99, 0,01 ≤ <i>e.g.</i> ≤ 0.4, preferably 0.55 ≤ <i>x</i> ≤ 0,8, 0,1 ≤ <i>y</i> ≤ 0,3, 0,03 ≤ <i>e.g.</i> ≤ 0.2 and <i>x + y + z</i>≈1. The closer the optical band edge is to the upper limit of the VUV wavelength range, the more the absorption of the VUV radiation by the host grating dominates. In extreme cases there is only host lattice absorption, ie the same absorption results with and without activator.

In the second class, however, more than 50% of the incident VUV radiation power is absorbed directly by the activator (ie the lighting center). The remaining part of the VUV radiation power can be absorbed, for example, by the host lattice and possibly further doping substances. This situation exists when the optical band edge of the host grating is significantly smaller than the upper limit of the VUV wavelength range. Examples of this class of phosphors are with trivalent terbium Tb³⁺ activated mixed phosphates according to the general formula <i>(Ln</i>_<i>x</i><i>Ce</i>_<i>y</i><i>Sc</i>_<i>w</i><i>Tb</i>_<i>e.g.</i><i>) PO</i>_<i>4</i><i>,</i> where Ln denotes one of the elements Lanthan La, Yttrium Y or Gadolinium Gd or a mixture of these elements. Suitable values ​​for<i>x, y, w</i> and <i>e.g.</i> are 0.35 ≤ <i>x</i> ≤ 0,95, 0 ≤ <i>y</i> ≤ 0,5, 0 ≤ <i>w</i> ≤ 0,2, 0,05 ≤ <i>e.g.</i> ≤ 0.5, preferred <i>w</i> = 0, 0,45 ≤ <i>x</i> ≤ 0,8, 0,1 ≤ <i>y</i> ≤ 0,3, 0,1 ≤ <i>e.g.</i> ≤ 0.25, where each <i>w + x + y + z</i>≈1 applies. In these cases, the excitation power is almost exclusively by the activator Tb³⁺ self absorbed. The Ce necessary for excitation with radiation of wavelength 254 nm as a sensitizer³⁺ In the present case, the VUV excitation for the phosphors of this class is of subordinate importance and can possibly be omitted without changing the light output. Whether Ce³⁺ In this context, an improvement (even if only a small one) at all has not yet been finally clarified.

In a preferred embodiment, one or more of the phosphors described are processed to form a phosphor coating. The phosphors are selected so that VUV radiation is converted into particularly suitable spectral ranges. For this purpose, the phosphor coating is advantageously applied to the inner wall surface of a lamp bulb, VUV radiation being generated within the lamp bulb, in particular with wavelengths in the range between approximately 145 nm and 185 nm. This short-wave radiation is already strongly absorbed in air and most lamp vessel materials, which is why a coating on the outer wall of special and therefore expensive VUV-transparent materials - e.g. special quartz glasses such as SUPRASIL^® (Heraeus) - would require. In addition, in this case the lamp would have to have an additional outer bulb to protect the coating against contact.

A particularly preferred embodiment is a three-band phosphor coating for generating white light. It consists of the following phosphors according to the invention: a red component R, in particular<i>(Y, Gd) BO</i>₃:<i>Eu</i>³⁺, a green component G, in particular <i>LaPO</i>₄<i>: (Tb</i>³⁺<i>, Ce</i>³⁺) and a blue component B, in particular <i>BaMgAl</i>₁₀<i>O</i>₁₇<i>: Eu</i>²⁺, where the weight fraction of the mixture is: 0.2 &lt; <i>R</i> &lt; 0,5, 0,4 &lt; <i>G</i> &lt; 0,7, 0,05 &lt; <i>B</i> &lt;0.15 and <i>R + G + B = 1.</i> In addition to good VUV excitability, this phosphor coating is characterized by good color rendering, which is particularly important in lighting technology. In addition, it can be advantageous to provide the surface of the phosphors, ie the individual phosphor grains and / or the phosphor coating applied, with a protective layer which is sufficiently transparent in the VUV range, for example made of MgF₂.

The invention is explained in more detail below with the aid of a few exemplary embodiments. First of all, some lighting data of phosphors are listed, which are suggested by excitation<i>Xe</i><maths id="math0001" num=""><math display="inline"><mrow><mfrac linethickness="0"><mrow><mtext>*</mtext></mrow><mrow><mtext>2</mtext></mrow></mfrac></mrow></math><img file="EP1076084A2_D0001.tif" /></maths>-Excimer radiation were determined. The size<i>E</i>_<i>xe</i> indicates the excitability with VUV radiation (with the spectrum of the <i>Xe</i><maths id="math0002" num=""><math display="inline"><mrow><mfrac linethickness="0"><mrow><mtext>*</mtext></mrow><mrow><mtext>2</mtext></mrow></mfrac></mrow></math><img file="EP1076084A2_D0002.tif" /></maths>Excimer radiation in the wavelength range between 145 nm and 185 nm weighted mean) relative to the maximum excitability that is achieved at a certain discrete wavelength. <i>E</i>_<i>xe</i> is therefore the value to which the excitability of a phosphor is reduced if it is not irradiated with radiation of the wavelength of its excitation maximum but with the entire continuum of excimer radiation in the wavelength range between 145 nm and 185 nm. <i>Q</i><maths id="math0003" num=""><math display="inline"><mrow><mfrac linethickness="0"><mrow><mtext>*</mtext></mrow><mrow><mtext mathvariant="italic">Xe</mtext></mrow></mfrac></mrow></math><img file="EP1076084A2_D0003.tif" /></maths> denotes the approximate quantum efficiency (it is influenced by the preparation of the phosphor and was not optimized, so that the values ​​given are to be understood as lower limits). Show it<ul id="ul0001" list-style="none"><li>Fig. 1 shows the VUV excitation spectrum of the red phosphor <i>Y</i>₂<i>O</i>₃<i>: Eu</i>³⁺,</li><li>Fig. 2 shows the VUV excitation spectrum of the green phosphor <i>CeMgAl</i>₁₁<i>O</i>₁₉ :<i>Tb</i>³⁺,</li><li>Fig. 3 shows the VUV excitation spectrum of the blue phosphor <i>BaMgAl</i>₁₀<i>O</i>₁₇<i>: Eu</i>²⁺,</li><li>4 shows the VUV excitation spectrum of the red phosphor (<i>Y</i>_0,72<i>DG</i>_0,2<i>Eu</i>_0,08)<i>BO</i>₃,</li><li>5 shows the VUV excitation spectrum of the green phosphor (<i>La</i>_0,43<i>Ce</i>_0,39<i>Tb</i>_0,18) <i>PO</i>₄,</li><li>6a shows the side view of a novel fluorescent lamp with a three-band fluorescent coating according to the invention</li><li>6b shows the cross section along AA of the fluorescent lamp shown in Fig. 6a,</li><li>7 shows the emission spectrum of the three-band fluorescent lamp from FIGS. 6a, b.</li></ul>

example 1

The first embodiment describes red phosphor with well-suited emission spectra. These are rare earth mixed borates activated with trivalent europium. The following table shows phosphors with different compositions, the first composition containing both yttrium Y and gadolinium Gd, the following two only yttrium and only gadolinium. In Figure 4, the excitation spectrum of phosphor No. 1 is shown.<tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" align="center"><b>No.</b></entry><entry namest="col2" nameend="col2" align="left"><b>composition</b></entry><entry namest="col3" nameend="col3" align="center"><i>E</i>_<i>Xe</i></entry><entry namest="col4" nameend="col4" align="center">Q<maths id="math0004" num=""><math display="inline"><mrow><mfrac linethickness="0"><mrow><mtext>*</mtext></mrow><mrow><mtext mathvariant="italic">Xe</mtext></mrow></mfrac></mrow></math><img file="EP1076084A2_D0004.tif" /></maths></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="center"><b>1</b></entry><entry namest="col2" nameend="col2" align="left">(<i>Y</i>_0,72<i>DG</i>_0,2<i>Eu</i>_0,08)<i>BO</i>₃</entry><entry namest="col3" nameend="col3" align="char" char=",">0,89</entry><entry namest="col4" nameend="col4" align="char" char=",">0,69</entry></row><row><entry namest="col1" nameend="col1" align="center"><b>2</b></entry><entry namest="col2" nameend="col2" align="left">(<i>Y</i>_0,92<i>Eu</i>_0,08)<i>BO</i>₃</entry><entry namest="col3" nameend="col3" align="char" char=",">0,86</entry><entry namest="col4" nameend="col4" align="char" char=",">0,57</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="center"><b>3</b></entry><entry namest="col2" nameend="col2" align="left">(<i>DG</i>_0,92<i>Eu</i>_0,08)<i>BO</i>₃</entry><entry namest="col3" nameend="col3" align="char" char=",">0,84</entry><entry namest="col4" nameend="col4" align="char" char=",">0,57</entry></row></tbody></tgroup></table></tables>

Example 2

The second embodiment describes green fluorescent materials with very suitable emission spectra. These are rare earth mixed phosphates activated with trivalent terbium. The following table shows phosphors with different compositions, some of which are additionally doped with trivalent cerium or scandium as a co-activator. The first four phosphors contain Lanthan La. In the following four phosphors, the lanthanum has been replaced by yttrium Y, with phosphor 8 being added to scandium Sc. In the last three phosphors, the lanthanum is replaced by Gadolinium Gd, with Scandium Sc also being added to the last phosphor. FIG. 5 shows the excitation spectrum of the phosphor (<i>La</i>_0,44<i>Ce</i>_0,43<i>Tb</i>_0,13)<i>PO</i>₄. <tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" align="center"><b>No.</b></entry><entry namest="col2" nameend="col2" align="left"><b>composition</b></entry><entry namest="col3" nameend="col3" align="center"><i>E</i>_<i>Xe</i></entry><entry namest="col4" nameend="col4" align="center"><i>Q</i><maths id="math0005" num=""><math display="inline"><mrow><mfrac linethickness="0"><mrow><mtext mathvariant="italic">*</mtext></mrow><mrow><mtext mathvariant="italic">Xe</mtext></mrow></mfrac></mrow></math><img file="EP1076084A2_D0005.tif" /></maths></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="center"><b>1</b></entry><entry namest="col2" nameend="col2" align="left">(<i>La</i>_0,43<i>Ce</i>_0,39<i>Tb</i>_0,18)<i>PO</i>₄</entry><entry namest="col3" nameend="col3" align="char" char=",">0,89</entry><entry namest="col4" nameend="col4" align="char" char=",">0,80</entry></row><row><entry namest="col1" nameend="col1" align="center"><b>2</b></entry><entry namest="col2" nameend="col2" align="left">(<i>La</i>_0,57<i>Ce</i>_0,29<i>Tb</i>_0,14)<i>PO</i>_<i>4</i></entry><entry namest="col3" nameend="col3" align="char" char=",">0,88</entry><entry namest="col4" nameend="col4" align="char" char=",">0,78</entry></row><row><entry namest="col1" nameend="col1" align="center"><b>3</b></entry><entry namest="col2" nameend="col2" align="left">(<i>La</i>_0,65<i>Ce</i>_0,20<i>Tb</i>_0,15)<i>PO</i>₄</entry><entry namest="col3" nameend="col3" align="char" char=",">0,87</entry><entry namest="col4" nameend="col4" align="char" char=",">0,76</entry></row><row><entry namest="col1" nameend="col1" align="center"><b>4</b></entry><entry namest="col2" nameend="col2" align="left"><i>(La</i>_0,828<i>Tb</i>_<i>0,172</i><i>) PO</i>₄</entry><entry namest="col3" nameend="col3" align="char" char=",">0,86</entry><entry namest="col4" nameend="col4" align="char" char=",">0,74</entry></row><row><entry namest="col1" nameend="col1" align="center"><b>5</b></entry><entry namest="col2" nameend="col2" align="left">(<i>Y</i>_0,434<i>Ce</i>_0,394<i>Tb</i>_0,172)<i>PO</i>₄</entry><entry namest="col3" nameend="col3" align="char" char=",">0,89</entry><entry namest="col4" nameend="col4" align="char" char=",">0,75</entry></row><row><entry namest="col1" nameend="col1" align="center"><b>6</b></entry><entry namest="col2" nameend="col2" align="left"><i>(Y</i>_0,65<i>Ce</i>_0,2<i>Tb</i>_0,15<i>) PO</i>₄</entry><entry namest="col3" nameend="col3" align="char" char=",">0,91</entry><entry namest="col4" nameend="col4" align="char" char=",">0,72</entry></row><row><entry namest="col1" nameend="col1" align="center"><b>7</b></entry><entry namest="col2" nameend="col2" align="left"><i>(Y</i>_0,828<i>Tb</i>_0,172<i>) PO</i>₄</entry><entry namest="col3" nameend="col3" align="char" char=",">0,82</entry><entry namest="col4" nameend="col4" align="char" char=",">0,65</entry></row><row><entry namest="col1" nameend="col1" align="center"><b>8</b></entry><entry namest="col2" nameend="col2" align="left">(<i>Y</i>_0,818<i>SC</i>_0,01<i>Tb</i>_0,172)<i>PO</i>₄</entry><entry namest="col3" nameend="col3" align="char" char=",">0,89</entry><entry namest="col4" nameend="col4" align="char" char=",">0,73</entry></row><row><entry namest="col1" nameend="col1" align="center"><b>9</b></entry><entry namest="col2" nameend="col2" align="left">(<i>DG</i>_0,434<i>Ce</i>_0,394<i>Tb</i>_0,172)<i>PO</i>₄</entry><entry namest="col3" nameend="col3" align="char" char=",">0,89</entry><entry namest="col4" nameend="col4" align="char" char=",">0,82</entry></row><row><entry namest="col1" nameend="col1" align="center"><b>10</b></entry><entry namest="col2" nameend="col2" align="left">(<i>DG</i>_0,828<i>Tb</i>_0,172)<i>PO</i>₄</entry><entry namest="col3" nameend="col3" align="char" char=",">0,84</entry><entry namest="col4" nameend="col4" align="char" char=",">0,71</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="center"><b>11</b></entry><entry namest="col2" nameend="col2" align="left">(<i>DG</i>_0,821<i>SC</i>_0,0067<i>Tb</i>_0,172)<i>PO</i>₄</entry><entry namest="col3" nameend="col3" align="char" char=",">0,89</entry><entry namest="col4" nameend="col4" align="char" char=",">0,8</entry></row></tbody></tgroup></table></tables>

Example 3

The third embodiment also describes green fluorescent materials with very suitable emission spectra. As the following table shows, there are two yttrium borates activated with trivalent terbium, where No. 2 additionally contains gadolinium.<tables id="tabl0003" num="0003"><table frame="all"><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" align="center"><b>No.</b></entry><entry namest="col2" nameend="col2" align="left"><b>composition</b></entry><entry namest="col3" nameend="col3" align="center"><i>E</i>_<i>xe</i></entry><entry namest="col4" nameend="col4" align="center"><i>Q</i><maths id="math0006" num=""><math display="inline"><mrow><mfrac linethickness="0"><mrow><mtext mathvariant="italic">*</mtext></mrow><mrow><mtext mathvariant="italic">Xe</mtext></mrow></mfrac></mrow></math><img file="EP1076084A2_D0006.tif" /></maths></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="center"><b>1</b></entry><entry namest="col2" nameend="col2" align="left">(<i>Y</i>₀_<i>,</i>₉<i>Tb</i>_0,1)<i>BO</i>₃</entry><entry namest="col3" nameend="col3" align="char" char=",">0,84</entry><entry namest="col4" nameend="col4" align="char" char=",">0,62</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="center"><b>2</b></entry><entry namest="col2" nameend="col2" align="left">(<i>Y</i>_0,7<i>DG</i>_0,2<i>Tb</i>_0,1)<i>BO</i>₃</entry><entry namest="col3" nameend="col3" align="char" char=",">0,86</entry><entry namest="col4" nameend="col4" align="char" char=",">0,65</entry></row></tbody></tgroup></table></tables>

Example 4

The fourth embodiment describes a further green phosphor. It is a rare earth mixed silicate activated with trivalent terbium, which contains yttrium and scandium according to the composition (<i>Y</i>_0,924<i>Sc</i>_0,002<i>Tb</i>_0,074)₂<i>SiO</i>₅. The following values ​​were determined:<i>E</i>_<i>Xe</i> = 0,94, <i>Q</i><maths id="math0007" num=""><math display="inline"><mrow><mfrac linethickness="0"><mrow><mtext mathvariant="italic">*</mtext></mrow><mrow><mtext mathvariant="italic">Xe</mtext></mrow></mfrac></mrow></math><img file="EP1076084A2_D0007.tif" /></maths> = 0,8.

Example 5

The fifth exemplary embodiment describes two further green phosphors. These are rare earth mixed aluminates activated with trivalent terbium. The first phosphor is an yttrium aluminate with the following composition (<i>Y</i>_0,9<i>Tb</i>_0,1<i>)</i>₃<i>Al</i>₅<i>O</i>₁₂. The following values ​​were determined:<i>E</i>_<i>xe</i> = 0,94, <i>Q</i><maths id="math0008" num=""><math display="inline"><mrow><mfrac><mrow><mtext mathvariant="italic">*</mtext></mrow><mrow><mtext mathvariant="italic">Xe</mtext></mrow></mfrac></mrow></math><img file="EP1076084A2_D0008.tif" /></maths> = 0.76. In the second phosphor - with the same properties - yttrium is 20% substituted by gadolinium:<i>(Y</i>_0,7<i>DG</i>_0.2<i>Tb</i>_0.l<i>)</i>₃<i>Al</i>₅<i>O</i>_l2

Example 6

The sixth embodiment describes a blue phosphor. It is a mixed aluminate activated with divalent europium according to the composition (<i>Ba</i>_0,94<i>Eu</i>_0,06)<i>MgAl</i>₁₀<i>O</i>₁₇. The following values ​​were determined:<i>E</i>_<i>Xe</i><i> = 0,96,</i> Q<maths id="math0009" num=""><math display="inline"><mrow><mfrac linethickness="0"><mrow><mtext>*</mtext></mrow><mrow><mtext mathvariant="italic">Xe</mtext></mrow></mfrac></mrow></math><img file="EP1076084A2_D0009.tif" /></maths> = 0,86.

Example 7

6a shows the side view and in FIG. 6b the cross section of a fluorescent lamp 1, which is particularly suitable for lighting purposes. The circular cylindrical discharge vessel 2 consists of 0.7 mm thick DURAN^®Glass (Schott), has a diameter of approx. 50 mm and is filled with xenon at a pressure of 173 hPa. An inner electrode 3 consisting of a stainless steel rod with a circular cross section and a diameter of 2 mm is arranged centrally axially within the discharge vessel 2. On the outer wall of the discharge vessel 2, twelve 1 mm wide and 8 cm long conductive silver strips are arranged as outer electrodes 4, axially parallel and evenly distributed. The inner wall of the discharge vessel 2 is coated with a phosphor layer 6. It is a three-band phosphor mixture with the blue component B: (<i>Ba</i>_0,94<i>Eu</i>_0,06)<i>MgAl</i>₁₀<i>O</i>₁₇, the green component G: <i>(La</i>_0,43<i>Ce</i>_0,39<i>Tb</i>_0,18<i>) PO</i>₄ and the red component R: <i>(Y</i>_0,72<i>DG</i>_0,2<i>Eu</i>_0,08)<i>BO</i>₃. The components are mixed in the ratio B: G: R = 0.085: 0.555: 0.36. A pulsed periodic voltage is applied to the inner electrode 3 by means of Edison base 7, which is approximately 4 kV with respect to the outer electrode, with an average pulse duration of approximately 1.2 µs and a pulse frequency of approximately 25 kHz. A luminous efficacy of 40lm / W is thus achieved. The color temperature is 4000 K and the color location according to the CIE color standard table has the coordinates<i>x</i> = 0.38 and <i>y</i> = 0.377. The emission spectrum of this lamp is shown in Figure 6.