White light-emitting diode

The invention relates to a light-emitting device for producing white light from a luminescence diode and a phosphor layer.

Luminescence diodes are used as signal lamps, indicator displays, control and warning lamps, as light transmitters in light barriers, optocouplers, IR remote control and optical fiber transmission systems. They offer a whole range of advantages over other light-emitting devices such as incandescent lamps. They have a long service life, high shock and vibration resistance, good modulability down to the MHZ range, high package densities, wide switching circuit compatibility and no inrush current peaks. They require a low operating voltage and low power consumption.

However, for a long time, a disadvantage of the luminescent diodes for visible light was that not all the colors of the visible light were available with the same luminous intensity. The efficiency of the luminescence diodes deteriorates with decreasing wavelength, ie from red over green to blue. While the brightness of red and green luminescence diodes was very good and was considerably increased by modern manufacturing methods, blue luminescence diodes had a comparatively low light intensity. Therefore, it was not possible to achieve color-neutral, white illumination by a combination of luminescence diodes by simple means.

Theoretically, any color of the visible light can be generated from shortwave light, ie, blue, violet, and ultraviolet light. For this purpose, the luminescence diode emitting shortwave light is combined with a suitable phosphor which converts the shortwave light into the desired color by absorbing the shortwave light and emitting light of the other color in the longer wavelength range.

For example, white light can be generated with a blue-emitting luminescence diode when combined with a phosphor that absorbs blue light, converts it, and emits it as light in the gel-borne region of the spectrum. The gel-borne light mixes with the remaining portion of the blue light from the luminescence diode, and blue white light is obtained from blue together with the complementary color.

For example, <patcit id="pcit0001" dnum="JP08007614A"><text>JP 08007614 A</text></patcit> (Patent Abstracts of Japan) discloses a planar light source for which a light emitting diode is used which emits blue light and which is combined with a fluorescent layer of an orange fluorescent pigment so that the blue light of the diode is observed as white light Can A disadvantage of this light source is that the color tone of the white light is strongly influenced by the small amount of the fluorescent pigment in the fluorescent layer and is therefore difficult to control. Only with a high color temperature between 8000 and 8600 K can a good color reproduction be obtained. If the color temperature is lowered, the color reproduction index CRI also drops considerably.

Furthermore, <nplcit id="ncit0001" npl-type="s"><text>Jpn.J. Appl. Phys. Vol.35 (1996) pp. L838 - L839</text></nplcit> (Blue), ZnS: Cu, Al (green), and ZnCdS: Ag (blue), a light source is known which comprises a blue light-emitting diode excited by a high injection current also for emitting UV light, Red).

In the unpublished <patcit id="pcit0002" dnum="WO9748138A"><text>WO 97/48138</text></patcit> A lamp is disclosed from an array of individual red, green, and blue phosphorescent UV LEDs that deliver individually controlled red green or blue light or collectively driven white mixed light.

Moreover, in <patcit id="pcit0003" dnum="EP0446846A"><text>EP 0446 846</text></patcit> Dye preparations containing fluorescent europium complexes, as well as their use in dye preparations for a thermal transfer color printing process.

It is the object of the present invention to provide a light emitting device for producing white light whose color tone reproduction is easy to regulate and whose color reproduction index is high.

According to the invention, the object is achieved by a light-emitting device with a UV diode with a primary emission of 300 nm ≤ λ≤ 370 nm and with a phosphor layer with a mixture of a blue-emitting phosphor with an emission band of 430 μm≤λ≤490 nm, A green-emitting phosphor which is a line emitter with an emission band with a wavelength maximum of 520 nm ≤ λ ≤ 570 nm and a red-emitting phosphor which is a line emitter with an emission band with a wavelength maximum of 605 nm ≤ λ ≤ 620 nm.

The light-emitting device exhibits high color reproduction and simultaneously high efficiency because the phosphors absorb the UV band with high efficiency, the quantum yield is high - over 90%, and the half-width of the emission line is small. The light output is high because no light is emitted in the region above 440 nm and below 650 nm, where the eye sensitivity is low. -

The white light emitted from the light emitting device is of high quality. The color rendering index CRI is 90 at a color temperature of 4000 K. The color reproduction depends only on the composition of the three phosphors, not on the relation of converted to nonconverted light and is therefore easy to control and regulate.

In the context of the present invention, it is preferred that the phosphors are lanthanide-activated phosphors, in particular that the phosphors are activated by Eu (III) or Tb (III).

It is also preferred that the blue-emitting phosphor is a line emitter with an emission band at 430 nm ≤ λ ≤ 490 nm.

It is further preferred that the UV diode is a GaN diode.

In the context of the present invention, it may be preferred that the phosphor layer contains a blue-emitting phosphor in an amount x1 of 0 &lt;x1≤30% by weight, a green-emitting phosphor in an amount x2 of 20≤x2≤50% % And a red-emitting phosphor in an amount x3 of 30≤x3≤70% by weight.

It may also be preferred that the phosphor layer is used as a blue-emitting phosphor BaMgAl₁₀O₁₇: Eu, as green-emitting phosphorus ZnS: Cu, and as red-emitting phosphorus Y₂O₂S: Eu.

In the context of the present invention, it is particularly preferred that the phosphorus layer as a red-emitting phosphor is a phosphorus of the composition [Eu (diketonate)_aX_b1X '_b2] Where X = pyridine or a monodentate pyridine derivative and X '= 2,2'-bipyridine or a 2,2'-bipyridyl derivative and 2a + b₁ + 2b₂ = 8.

The invention is further described below with reference to a figure and three exemplary embodiments. <ul><li><b>FIG. 1:</b> Light emitting device</li></ul>

A light emitting device according to the invention comprises a UV diode as excitation source for the UV radiation and a phosphor layer, with a mixture of three phosphors which convert the UV light of the UV diode into visible, white light. In the exemplary embodiment illustrated in the drawing, the device is constructed in such a way that the UV diode is poured into a hemispherical cup made of a polymer which is deposited on a transparent substrate (front plate)<b>1</b> Is arranged. The three phosphorus powders<b>2</b> Are finely divided into the polymer <b>3</b> embedded. The polymer dish, together with the phosphorus powders, forms the phosphor layer. The device according to the invention can furthermore comprise mirrors<b>4</b> For UV and visible light for improving the light output. For example, the cup itself can be designed as a reflector.

In the simplest case, the light-emitting device consists of a UV diode and a transparent coating applied to it, which contains the phosphors. The transparent coating may, for example, contain the phosphors in a solid solution in a transparent matrix of polyacrylate, polystyrene, epoxy resin or another polymer.

As mass products, LEDs are usually encapsulated in epoxy resin housings, wherein a cast-on dome-shaped lens made of epoxy resin serves to improve the coupling-out of the light from the diode. In this embodiment, the phosphors can be applied as a contact layer between the actual diode and the epoxy resin dome. They can also be applied as a coating on the outside of the epoxy resin dome.

Large two-dimensional light emitting devices can be easily fabricated by combining a diode array with the phosphor layer of the invention. For example, the diode array may be covered by a glass plate which is printed with the phosphors.

The UV diode is, in particular, a UV diode made of InGaN or GaN and has its emission maximum between 370 and 410 nm with a half-value width FWHM &lt;50 nm.

To maintain the light emission, means are provided for supplying electrical energy to the UV diode. These means comprise at least two electrodes.

The three phosphors are selected to be excited by the UV light of the UV diode, and the red phosphorus has a narrow emission line at 590 mm.ltoreq.λ.ltoreq.630 nm, the green phosphorus is a narrow emission line at 520 nm.ltoreq.λ.ltoreq.570 Nm and the blue phosphor has a narrow emission line at 430 nm ≤ λ ≤ 490 nm. For the blue phosphorus, a broadband emitter can also be used instead of a line emitter with a narrow emission line. The emission guidelines of the three phosphors can be coordinated very precisely, even if the emissions are not quite independent of each other, since emissions flanks partly overlap. Thus, the color coordinates of the white light can be precisely adjusted. The phosphors are preferably lanthanide-activated phosphors, for example Eu³⁺ - or Tb³⁺ Activated phosphors.

Phosphors of the composition [Eu (diketonate)_aX_b1X '_b2] Where X = pyridine or a monodentate pyridine derivative and X '= 2,2'-bipyridine or a 2,2'-bipyridyl derivative and 2a + b₁ + 2b₂ = 8 is preferred. These complex coordination compounds of Europium (III) contain Eu³⁺ As metal centers, diketonates as anionic chelate ligands and 2,2'-bipyridine or a 2,2'-bipyridyl derivative as neutral chelate ligands. Suitable diketonates are pentane-2,4-dithionate (acac), 2,2,6,6-tetramethyl-3,5-heptanedithionate (thd), 1- (2-thenoyl) -4,4,4-trifluoro-1 , 3-butanedithionate (ttfa), 7,7-dimethyl-1,1,1,2,2,3,3-heptafluoro-4,6-octanedithionate (fod), 4,4,4-trifluoro-1- 2-naphthyl) -1,3-butanedithionate (tfnb), 1,3-diphenyl-1,3-propanedithionate (dbm), neutral ligands X are pyridine, or the bidentate ligands are 2,2'-bipyridine (bpy), 1 , 10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (dpphene), 5-methyl-1,10-phenathroline (mphen), 4,7- 3,4-tetramethyl-1,10-phenanthroline (tmphene), 5-nitro-1,10-phenanthroline (NOphen), 5-chloro-1,10-phenanthroline (Clphen) or dipyridinephenazine (dppz) .

Table 1 shows blue-emitting, green-emitting and red-emitting phosphors with their wavelength maximum and their absorption at 370 nm.<tables id="tabl0001" num="0001"><table frame="all"><title><b>Table 1</b></title><tgroup cols="4"><colspec colnum="1" colname="col1" colwidth="36mm" /><colspec colnum="2" colname="col2" colwidth="15mm" /><colspec colnum="3" colname="col3" colwidth="40mm" /><colspec colnum="4" colname="col4" colwidth="24mm" /><thead><row><entry namest="col1" nameend="col4" align="left" valign="top">Blue-emitting phosphors</entry></row><row><entry valign="top">composition</entry><entry valign="top">Λ [max]</entry><entry valign="top">Absorption at 370 nm [%]</entry><entry valign="top">QE at 370 nm</entry></row></thead><tbody><row><entry>BaMgAl₁₀O₁₇: Eu</entry><entry>450</entry><entry>70</entry><entry>90</entry></row><row><entry>Sr₅(PO₄) "₃Cl: Eu</entry><entry>450</entry><entry>70</entry><entry>90</entry></row><row><entry>ZnS: Ag</entry><entry>450</entry><entry>75</entry><entry>75</entry></row></tbody></tgroup><tgroup cols="4"><colspec colnum="1" colname="col1" colwidth="36mm" /><colspec colnum="2" colname="col2" colwidth="15mm" /><colspec colnum="3" colname="col3" colwidth="40mm" /><colspec colnum="4" colname="col4" colwidth="24mm" /><thead><row><entry namest="col1" nameend="col4" align="left" valign="top">Green-emitting phosphors</entry></row><row><entry valign="top">composition</entry><entry valign="top">Λ [max]</entry><entry valign="top">Absorption at 370 nm [%]</entry><entry valign="top">QE at 370 nm</entry></row></thead><tbody><row><entry>ZnS: Cu</entry><entry>550</entry><entry>40</entry><entry>85</entry></row><row><entry>BaMgAl₁₀O₁₇: Eu, Mn</entry><entry>515</entry><entry>70</entry><entry>90</entry></row></tbody></tgroup><tgroup cols="4"><colspec colnum="1" colname="col1" colwidth="36mm" /><colspec colnum="2" colname="col2" colwidth="15mm" /><colspec colnum="3" colname="col3" colwidth="40mm" /><colspec colnum="4" colname="col4" colwidth="24mm" /><thead><row><entry namest="col1" nameend="col4" align="left" valign="top">Red-emitting phosphors</entry></row><row><entry valign="top">composition</entry><entry valign="top">Λ [max]</entry><entry valign="top">Absorption at 370 nm [%]</entry><entry valign="top">QE at 370 nm</entry></row></thead><tbody><row><entry>Y₂O₂S: Eu³⁺</entry><entry>628</entry><entry>30</entry><entry>90</entry></row><row><entry>YVO₄: Eu³⁺</entry><entry>620</entry><entry>25</entry><entry>85</entry></row><row><entry>Y (V, P, B) O₄: Eu³⁺</entry><entry>615</entry><entry>25</entry><entry>85</entry></row><row><entry>YNbO₄: Eu³⁺</entry><entry>615</entry><entry>20</entry><entry>90</entry></row><row><entry>YTaO₄: Eu³⁺</entry><entry>615</entry><entry>20</entry><entry>90</entry></row><row><entry>[Eu (acac)₃(Phen)]</entry><entry>611</entry><entry>97</entry><entry>70</entry></row></tbody></tgroup></table></tables>

The mixture according to the invention provides a good color rendering index and at the same time a good energy yield. The light-emitting device has a color reproduction index CRI &lt;90 at a color temperature ≥4000 K and is therefore suitable for interior lighting.

To produce the phosphor layer, the three phosphors can be applied as a coating with a binder on the diode surface. Suitable binders are, for example, film-forming acrylic polymers such as methyl acrylate and polystyrene. Alternatively, they can be added in micrograms to the epoxy resin of the epoxy resin dome and distributed uniformly throughout the epoxy resin dome. Instead of epoxy resin, another transparent thermosetting resin can also be used. This results in a more diffuse emission of the white light. Because of the high brightness of the light emitting device, it may be desirable for the light emission to be more diffuse for safety reasons.

In operation, UV light is generated by the UV diode with a wavelength λ ≤ 370 nm, which falls on the mixture of the phosphors in the phosphor layer. These absorb the radiation and emit a longer-wave radiation, ie the phosphors transform the invisible UV radiation into visible light which is converted into visible light by the phosphors. By mixing the three phosphors with different emission lines, the light of the desired composition is obtained.

Since the light of the light-emitting device according to the invention is not the light emitted by an incandescent body, but the excitation light of the phosphors in the phosphor layer, the light output is extraordinarily high. The light emitting device according to the invention provides a pleasant, color-accurate light. The visible emission lines of the phosphors lie so close together that a quasi-continuous spectrum results, which results in a good color reproduction.

EXAMPLE 1

A light emitting device made of a UV diode and a phosphor layer with a mixture of the three phosphors was prepared. An undoped GaN diode with transparent sapphire was used as the diode substrate. The dioctyl substrate was coated with a suspension of three phosphors in various proportions according to Table 2 in a 1% strength polyvinyl alcohol solution and baked at 200 ° C.<tables id="tabl0002" num="0002"><table frame="all"><title>Table 2</title><tgroup cols="6"><colspec colnum="1" colname="col1" colwidth="12mm" /><colspec colnum="2" colname="col2" colwidth="33mm" /><colspec colnum="3" colname="col3" colwidth="22mm" /><colspec colnum="4" colname="col4" colwidth="26mm" /><colspec colnum="5" colname="col5" colwidth="11mm" /><colspec colnum="6" colname="col6" colwidth="42mm" /><thead><row><entry valign="top">T_c[K]</entry><entry valign="top">x₁[BaMgAl₁₀O₁₇: Eu]</entry><entry valign="top">x₂[ZnS: Cu]</entry><entry valign="top">x₃[YVO₄: Eu³⁺]</entry><entry valign="top">Ra8</entry><entry valign="top">Phosphorus diode eff. [Lm / W]</entry></row></thead><tbody><row><entry align="center">2700</entry><entry align="char" char="." charoff="37">.04</entry><entry align="char" char="." charoff="30">.36</entry><entry align="char" char="." charoff="33">.60</entry><entry align="center">85</entry><entry align="char" char="." charoff="44">9.7</entry></row><row><entry align="center">3000</entry><entry align="char" char="." charoff="37">.08</entry><entry align="char" char="." charoff="30">.37</entry><entry align="char" char="." charoff="33">.56</entry><entry align="center">85</entry><entry align="char" char="." charoff="44">9.8</entry></row><row><entry align="center">4000</entry><entry align="char" char="." charoff="37">.16</entry><entry align="char" char="." charoff="30">.41</entry><entry align="char" char="." charoff="33">.43</entry><entry align="center">91</entry><entry align="char" char="." charoff="44">9.9</entry></row><row><entry align="center">5000</entry><entry align="char" char="." charoff="37">.22</entry><entry align="char" char="." charoff="30">.41</entry><entry align="char" char="." charoff="33">.36</entry><entry align="center">92</entry><entry align="char" char="." charoff="44">9.6</entry></row><row><entry align="center">6300</entry><entry align="char" char="." charoff="37">.28</entry><entry align="char" char="." charoff="30">.43</entry><entry align="char" char="." charoff="33">.30</entry><entry align="center">96</entry><entry align="char" char="." charoff="44">9.8</entry></row></tbody></tgroup></table></tables>

EXAMPLE 2

A light emitting device made of a UV diode and a phosphor layer with a mixture of the three phosphors was prepared. An undoped GaN diode with transparent sapphire was used as the diode substrate. The dioctyl substrate was coated with a suspension of three phosphors in various proportions according to Table 2 in a 1% strength polyvinyl alcohol solution and baked at 200 ° C.<tables id="tabl0003" num="0003"><table frame="all"><title>Table 3</title><tgroup cols="6"><colspec colnum="1" colname="col1" colwidth="12mm" /><colspec colnum="2" colname="col2" colwidth="18mm" /><colspec colnum="3" colname="col3" colwidth="22mm" /><colspec colnum="4" colname="col4" colwidth="33mm" /><colspec colnum="5" colname="col5" colwidth="11mm" /><colspec colnum="6" colname="col6" colwidth="42mm" /><thead><row><entry valign="top">T_c[K]</entry><entry valign="top">x₁[BAM]</entry><entry valign="top">x₂[ZnS: Cu]</entry><entry valign="top">x₃[Eu (acac)₃(Phen)]</entry><entry valign="top">Ra8</entry><entry valign="top">Phosphorus diode eff. [Lm / W]</entry></row></thead><tbody><row><entry align="center">2700</entry><entry align="char" char="." charoff="25">.06</entry><entry align="char" char="." charoff="30">.36</entry><entry align="char" char="." charoff="37">.54</entry><entry align="center">82</entry><entry align="char" char="." charoff="46">12.0</entry></row><row><entry align="center">3000</entry><entry align="char" char="." charoff="25">.1</entry><entry align="char" char="." charoff="30">.37</entry><entry align="char" char="." charoff="37">.49</entry><entry align="center">83</entry><entry align="char" char="." charoff="46">11.9</entry></row><row><entry align="center">4000</entry><entry align="char" char="." charoff="25">.18</entry><entry align="char" char="." charoff="30">.41</entry><entry align="char" char="." charoff="37">.37</entry><entry align="center">89</entry><entry align="char" char="." charoff="46">11.8</entry></row><row><entry align="center">5000</entry><entry align="char" char="." charoff="25">.25</entry><entry align="char" char="." charoff="30">.41</entry><entry align="char" char="." charoff="37">.31</entry><entry align="center">91</entry><entry align="char" char="." charoff="46">11.4</entry></row><row><entry align="center">6300</entry><entry align="char" char="." charoff="25">.30</entry><entry align="char" char="." charoff="30">.43</entry><entry align="char" char="." charoff="37">.25</entry><entry align="center">95</entry><entry align="char" char="." charoff="46">11.3</entry></row></tbody></tgroup></table></tables>

EXAMPLE 3

A light emitting device made of a UV diode and a phosphor layer with a mixture of the three phosphors was prepared. An undoped GaN diode with transparent sapphire was used as a diode substrate. The dioctyl substrate was coated with a suspension of three phosphors in various proportions according to Table 2 in a 1% strength polyvinyl alcohol solution and baked at 200 ° C.<tables id="tabl0004" num="0004"><table frame="all"><title>Table 4</title><tgroup cols="6"><colspec colnum="1" colname="col1" colwidth="12mm" /><colspec colnum="2" colname="col2" colwidth="18mm" /><colspec colnum="3" colname="col3" colwidth="22mm" /><colspec colnum="4" colname="col4" colwidth="27mm" /><colspec colnum="5" colname="col5" colwidth="11mm" /><colspec colnum="6" colname="col6" colwidth="42mm" /><thead><row><entry valign="top">T_c[K]</entry><entry valign="top">x₁[BAM]</entry><entry valign="top">x₂[ZnS: Cu]</entry><entry valign="top">x₃[Y₂O₂S: Eu³⁺]</entry><entry valign="top">Ra8</entry><entry valign="top">Phosphorus diode eff. [Im / W]</entry></row></thead><tbody><row><entry align="center">2700</entry><entry align="char" char="." charoff="30">0.05</entry><entry align="char" char="." charoff="34">0.31</entry><entry align="char" char="." charoff="38">0.63</entry><entry align="center">85</entry><entry align="char" char="." charoff="46">12.2</entry></row><row><entry align="center">3000</entry><entry align="char" char="." charoff="30">0.09</entry><entry align="char" char="." charoff="34">0.32</entry><entry align="char" char="." charoff="38">0.59</entry><entry align="center">85</entry><entry align="char" char="." charoff="46">12.2</entry></row><row><entry align="center">4000</entry><entry align="char" char="." charoff="30">0.16</entry><entry align="char" char="." charoff="34">0.38</entry><entry align="char" char="." charoff="38">0.46</entry><entry align="center">89</entry><entry align="char" char="." charoff="46">12.7</entry></row><row><entry align="center">5000</entry><entry align="char" char="." charoff="30">0.23</entry><entry align="char" char="." charoff="34">0.38</entry><entry align="char" char="." charoff="38">0.39</entry><entry align="center">90</entry><entry align="char" char="." charoff="46">12.5</entry></row><row><entry align="center">6300</entry><entry align="char" char="." charoff="30">0.28</entry><entry align="char" char="." charoff="34">0.40</entry><entry align="char" char="." charoff="38">0.32</entry><entry align="center">95</entry><entry align="char" char="." charoff="46">12.5</entry></row></tbody></tgroup></table></tables>