Light-emitting device and illumination apparatus

BACKGROUND OF THE INVENTION

Field of the Invention

0001The present invention relates to a light-emitting device such as a white light-emitting diode lamp mainly used in the field of lighting and an illumination apparatus using the same.

0002Priority is claimed on <patcit id="pcit0001" dnum="JP2005079059A"><text>Japanese Patent Application No. 2005-079059, filed March 18, 2005</text></patcit>, the content of which is incorporated herein by reference.

Description of Related Art

0003In the field of lighting, there is great expectation for solid state lighting, particularly in regard to white lighting using semiconductor light-emitting diodes, which are the target of extensive and aggressive research and development efforts. White light-emitting diode lamps have achieved light-emitting efficiency equal to or higher than incandescent lamps, and have the potential of further improvement It is anticipated that they will come to be used extensively as energy-saving illumination apparatuses in the near future. It is advantageous that white light-emitting diode lamps do not contain substances that impose environmental load, such as mercury. Because of their small size, white light-emitting diode lamps are incorporated in backlight of liquid crystal display devices and mobile phones and widely used.

0004The present invention relates to a light-emitting device such as a white lighti-emitting diode lamp used in the field of lighting and provides a light-emitting device having high efficiency, excellent long-term reliability, and various emission colors, such as daylight, neutral white, white, warm white, and incandescent lamp colors, for improved color rendering, and an illumination apparatus.

0005In the prior art, white light-emitting diode lamps (hereafter referred to as LEDs) are known which use an LED element that emits light of short wavelengths such as blue light and a fluorescent (phosphor) material that absorbs and is excited by all or a part of the light emitted by the LED element and emits fluorescence of longer wavelengths such as yellow fluorescence. For example, a white LED lamp including a compound semiconductor blue LED element and a cerium-activated yttrium-aluminum-garnet (hereafter referred to as YAG) fluorescent material that absorbs blue light and emits yellow, complementary color to blue, fluorescence is described in <patcit id="pcit0002" dnum="JP2900928B"><text>Japanese Patent Publication Nos. 2900928</text></patcit> and <patcit id="pcit0003" dnum="JP2927279B"><text>2927279</text></patcit> and <nplcit id="ncit0001" npl-type="s"><text>K. Bando, K. Sakano, Y Noguchi, and Y. Shimizu, "Development of High-bright and Pure-white LED Lamps," J. Light &amp; Vis. Env. Vol. 22, No.1 (1998), pp. 2-5</text></nplcit>.

0006Adding a red light-emitting material to compensate for the red constituent is a known technique. <patcit id="pcit0004" dnum="JP2008273409A"><text>Japanese Unexamined Patent Application, First Publication No. 2008-273409</text></patcit> discloses a technique in which a red fluorescent material such as (Sr_1-x-y-zBa_xCa_y)₂Si₅N₈ : Eu_z²⁺ or SrS : Eu, (Ca_xSr_1-x S : Eu²⁺ is added to a white LED including a blue LED element and a cerium-activated YAG fluorescent material. Similar techniques are disclosed in <patcit id="pcit0005" dnum="JP2003321675A"><text>Japanese Unexamined Patent Application, First Publication No. 2003-321675</text></patcit> and <nplcit id="ncit0002" npl-type="s"><text>M. YAMADA, T. NAITOU, K. IZUNO, H. TAMAKI, Y MURAZAKI, M. KAMESHIMA, and T. MUKAI, "Red-Enhanced White-Light-Emitting Diode Using a New Red Phosphor," Jpn. J. Appl. Phys. Vol. 42, (2003) pp. L20-L23</text></nplcit>.

0007Further, a technique to realize a white LED using a blue LED element, a fluorescent material excited by blue light and emitting green light, and a fluorescent material excited by blue light and emitting red light is known and disclosed for example in <patcit id="pcit0006" dnum="JPH10163535A"><text>Japanese Unexamined Patent Application, First Publication No. H10-163535</text></patcit>. Further, a white LED using SrGa₂S₄ : Eu²⁺, a fluorescent material excited by blue light and emitting green light, and SrS : Eu²⁺, a fluorescent material excited by blue light and emitting red light, is disclosed for example in <nplcit id="ncit0003" npl-type="s"><text>Paul S. Martin, "Performance, Thermal, Cost &amp; Reliability challenges for Solid State Lightning," OIDA Conference, May 30th, 2002</text></nplcit>.

0008Recently, there has been extensive research on oxynitride and nitride fluorescent materials. For example, europium (Eu)-activated calcium (Ca) doped α-SiAlON fluorescent material is known from <patcit id="pcit0007" dnum="JP2002363554A"><text>Japanese Unexamined Patent Application, First Publication No. 2002-363554</text></patcit>. This fluorescent material is excited by blue light and emits yellow light and, therefore, is preferably used as a white LED wavelength conversion material. This fluorescent material is described in detail for example by <nplcit id="ncit0004" npl-type="s"><text>R. J. Xie, N. Hirosaki. K. Sakuma, Y Tamamoto, M. Mitomo, "Eu2+-doped Ca-α SiAION: A yellow phosphor for white light-emitting diodes," Appl. Phys. Lett., Vol. 84, pp. 5404-5406 (2004)</text></nplcit>. A low color temperature white LED lamp using the fluoreseent material and having excellent color stability in the presence of temperature changes is described by <nplcit id="ncit0005" npl-type="s"><text>K. Sakuma, K. Omichi, N. Kimura, M. Ohashi, D. Tanaka, N. Hirosaki, Y Yamamoto, R.-J. Xie, T. Suehiro, "Warm-white light-emitting diode with yellowish orange SiAlON ceramic phosphor," Opt. Lett. Vol. 29, pp. 2001-2003 (2004)</text></nplcit>.

0009Conventionally, fluorescent materials are predominantly oxides or sulfides and must be further improved in terms of durability and their high-temperature properties. Recent efforts have been focused on developing oxynitride and nitride fluorescent materials having improved long-term reliability and high-temperature properties.

0010Extensive research is taking place regarding solid state lighting devices using a combination of a semiconductor light-emitting element and a fluorescent material, where oxide or sulfide fluorescent materials are the primary materials. The inventors of the present application have realized a white LED lamp using a blue LED element and a europium (Eu)- activated calcium (Ca) doped α-SiAlON fluorescent material and emitting warm white light in the incandescent lamp color range. The α-SiAlON fluorescent material is a highly efficient oxynitride fluorescent material that is excited by blue light and emits yellow light and has excellent long-term reliability and high-temperature properties.

0011As light-emitting devices for higher color temperatures such as daylight, neutral white, white, and warm white colors other than the incandescent lamp color, the development of a light-emitting device using an oxynitride or nitride fluorescent material and having high emission efficiency and excellent long-term reliability and high-temperature properties is anticipated.

SUMMARY OF THE INVENTION

0012The present invention is made in view of the above circumstances and it is a preferred object of the present invention to provide a light-emitting device having high emission efficiency, excellent long-term reliability and high-temperature properties, improved color rendering, and an illumination apparatus.

0013The present invention offers a light-emitting device comprising: a semiconductor light-emitting element that emits blue-violet or blue light; and a fluorescent material that absorbs part or all of the light emitted by the semiconductor light-emitting element and emits fluorescence of wavelengths different from that of the light, the fluorescent material comprising a mixture of a first fluorescent material that emits green or yellow-green light, a second fluorescent material that has a longer emission wavelength than that of the first fluorescent material and emits yellow-green, yellow, or yellow-red light, and a third fluorescent material that has a longer emission wavelength than the second fluorescent material and emits yellow-red or red light. The first fluorescent material is a europium-activated β-SiAlON fluorescent material, the second fluorescent material is a europium-activated α-SiAlON fluorescent material, and the third fluorescent material is a nitride crystalline red fluorescent material expressed by the general formula of (Ca,Eu)AlSiN₃.

0014The present invention further provides a light-emitting device comprising: a semiconductor light-emitting element that emits blue-violet or blue light; and a fluorescent material that absorbs part or all of the light emitted by the semiconductor light-emitting element and emits fluorescence of wavelengths different from that of the light, the fluorescent material comprising a mixture of a first fluorescent material that emits green or yellow-green light, a second fluorescent material that has a longer emission wavelength than that of the first fluorescent material and emits yellow-green, yellow, or yellow-red light, and a third fluorescent material that has a longer emission wavelength than the second fluorescent material and emits yellow-red or red light. The first fluorescent material is a europium-activated β-SiAlON fluorescent material, the second fluorescent material is a europium-activated α-SiAlON fluorescent material, and the third fluorescent material is a nitride crystalline red fluorescent material expressed by the general formula of (Ca,Eu)AlSiN₃, and the α-SiAlON fluorescent material is expressed by the general formula of Ca_qEu_rSi,Al)₁₂(O,N)₁₆ in which q is between 0.75 and 1.0 and r is between 0.03 and 0.07 and has the primary phase of an α-SiAlON crystalline structure.

0015The present invention further provides a light-emitting device comprising: a semiconductor light-emitting element that emits blue-violet or blue light; and a fluorescent material that absorbs all or part of the light emitted by the semiconductor light-emitting element and emits fluorescence of wavelengths different from that of the light, the fluorescent material comprising a mixture of a first fluorescent material that emits green or yellow-green light, a second fluorescent material that has a longer emission wavelength than that of the first fluorescent material and emits yellow-green, yellow, or yellow-red light, and a third fluorescent material that has a longer emission wavelength than the second fluorescent material and emits yellow-red or red light. The first fluorescent material is a europium-activated β-SiAlON fluorescent material, the second fluorescent material is a europium-activated α-SiAlON fluorescent material, and the third fluorescent material is a nitride crystalline red fluorescent material expressed by the general formula of (Ca,Eu)AlSiN₃, and the β-SiAlON fluorescent material is expressed by the general formula Eu₃(Si,Al)_6-8 (O,N)₈ in which s is between 0.011 and 0.019 and has the primary phase of a β-SiAlON crystalline structure.

0016In the light-emitting device of the present invention, light obtained by mixing the light emitted by the semiconductor light-emitting element and the fluorescence emitted by the fluorescent material may have chromaticity within the daylight color range expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting a first point at the coordinates of x = 0.3274 and y = 0.3673, a second point at the coordinates of x = 0.3282 and y = 0.3297, a third point at the coordinates of x = 0.2998 and y = 0.3396, and a fourth point at the coordinates of x = 0.3064 and y = 0.3091.

0017In the light-emitting device of the present invention, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of (7.5 × C/A) : (1.3 × C/B) : 1 provided that the peak emission intensities of the first, second, and third fluorescent materials are A ; B : C when measured by a spectrum corrected fluorescence spectrophotometer.

0018In the light-emitting device of the present invention, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of 12 : 2: 1.

0019In the light-emitting device of the present invention, light resulting from the mixture of light emitted by the semiconductor light-emitting element and the fluorescence emitted by the fluorescent material may have chromaticity within the neutral white color range expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting a first point at the coordinates of x = 0.3616 and y = 0.3875, a second point at the coordinates of x = 0.3552 and y = 0,3476, a third point at the coordinates of x = 0.3353 and y = 0.3659, and a fourth point at the coordinates of x = 0.3345 and y = 0.3314.

0020In the light-emitting device of the present invention, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of (6.5 × C/A):(1.3 × GB) : 1 provided that the peak emission intensities of the first, second, and third fluorescent materials are A: B : C when measured by a spectrum corrected fluorescence spectrophotometer.

0021In the light-emitting device of the present invention, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of 10.3 : 2 : 1.

0022In the light-emitting device of the present invention, light obtained by mixing the light emitted by the semiconductor light-emitting element and the fluorescence emitted by the fluorescent material may have chromaticity within the white color range expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting a first point at the coordinates of x = 0.3938 and y = 0.4097, a second point at the coordinates of x = 0.3805 and y = 0.3642, a third point at the coordinates of x = 0.3656 and y = 0.3905, and a fourth point at the coordinates of x = 0.3584 and y = 0.3499.

0023In the light-emitting device of the present invention, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of (6.3 × C/A) : (1.9 × C/B) : 1 provided that the peak emission intensities of the first, second, and third fluorescent materials are A : B : C when measured by a spectrum corrected fluorescence spectrophotometer.

0024In the light-emitting device of the present invention, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of 10 : 3 : 1.

0025In the light-emitting device of the present invention, light obtained by mixing the light emitted by the semiconductor light-emitting element and the fluorescence emitted by the fluorescent material may have chromaticity within the warm white color range expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting a first point at the coordinates of x = 0.4341 and y = 0.4233, a second point at the coordinates of x = 0.4171 and y = 0.3846, a third point at the coordinates of x = 0.4021 and y = 0,4076, and a fourth point at the coordinates of x = 0.3903 and y = 0.3719.

0026In the light-emitting device of the present invention, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of (5.1 × C/A): (1.9 × C/B) : 1 provided that the peak emission intensities of the first, second, and third fluorescent materials are A : B : C when measured by a spectrum corrected fluorescence, spectrophotometer.

0027In the light-emitting device of the present invention, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of 8:3:1.

0028In the light-emitting device of the present invention, light obtained by mixing the light emitted by the semiconductor light-emitting element and the fluorescence emitted by the fluorescent material may have chromaticity within the incandescent lamp color range expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting a first point at the coordinates of x = 0.4775 and y = 0.42183, a second point at the coordinates of x = 0.4594 and y = 0.3971, a third point at the coordinates of x = 0.4348 and y = 0.4185, and a fourth point at the coordinates of x = 0.4214 and y = 0.3887.

0029In the light-emitting device of the present invention, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of (5.1 × C/A): (1.6 × C/B) : 1 provided that the peak emission intensities of the first, second, and third fluorescent materials are A : B : C when measured by a spectrum corrected fluorescence spectrophotometer.

0030In the light-emitting device of the present invention, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of 8 : 2.5 : 1.

0031The present invention further provides an illumination apparatus having the light-emitting device described above as a light source.

0032The present invention provides a light-emitting device having high emission efficacy, excellent long-term reliability and high-temperature properties, and improved color rendering, and an illumination apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

0033<ul id="ul0001" list-style="none" compact="compact"><li>FIG 1 is a graphical representation showing the emission spectrum of a high color rendering white LED lamp of Example 1 of the present invention.</li><li>FIG 2 is a graphical representation showing the emission spectrum of a conventional white LED lamp of Comparative Example 1.</li><li>FIG 3 is a graphical representation showing the emission spectrum of a conventional white LED lamp of Comparative Example 2.</li><li>FIG. 4 is a graphical representation showing the emission spectrum of a high color rendering white LED lamp of example 2 of the present invention.</li><li>FIG 5 is a graphical representation showing the emission spectrum of a high color rendering white LED lamp of Example 3 of the present invention.</li><li>FIG. 6 is a graphical representation showing the emission spectrum of a high color rendering white LED lamp of Example 4 of the present invention.</li><li>FIG. 7 is a graphical representation showing the emission spectrum of a high color rendering white LED lamp of Example 5 of the present invention.</li><li>FIG 8 is a graphical representation showing the emission spectrum and the excitation spectrum of a β-SiAlON fluorescent material used as the first fluorescent material.</li><li>FIG 9 is a graphical representation showing the emission spectrum and the excitation spectrum of an α-SiAlON fluorescent material used as the second fluorescent material.</li><li>FIG. 10 is a graphical representation showing the emission spectrum and the excitation spectrum of a Ca_1-pAlSiN₃: Eu²⁺_p fluorescent material used as the third fluorescent material.</li><li>FIG 11 is a graphical representation showing the emission spectra of the β-SiAlON fluorescent material, α-SiAlON fluorescent material, and Ca_1-pAlSiN₃ : Eu²⁺_p fluorescent material.</li><li>FIG 12 is a cross-sectional view of a bullet type white LED lamp.</li><li>FIG 13 is a cross-sectional view of a chip type white LED lamp.</li><li>FIG 14 is a graphical representation showing a CIE 1931 XYZ colorimetricisystem chromaticity diagram.</li></ul>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

0034Examples of the light-emitting device of the present invention are described hereafter with reference to the drawings.

0035The light-emitting device of the present invention comprises a semiconductor light-emitting element that emits blue-violet or blue light and a fluorescent material that absorbs all or a part of the light emitted by the semiconductor light-emitting element and emits fluorescence of wavelengths different from that of the light, wherein the fluorescent material comprises a mixture of a first fluorescent material that emits green or yellow-green light, a second fluorescent material that has a longer emission wavelength than that of the first fluorescent material and emits yellow-green, yellow, or yellow-red light, and a third fluorescent material that has a longer emission wavelength than the second fluorescent material and emits yellow-red or red light, and the first fluorescent material is a europium-activated β-SiAlON fluorescent material, the second fluorescent material is a europium-activated α-SiAlON fluorescent material, and the third fluorescent material is a nitride crystalline red fluorescent material expressed by the general formula of (Ca,Eu)AlSiN₃. The α-SiAlON fluorescent material may be expressed by the general formula of Ca_qEu_r(Si,Al)₁₂(O,N)₁₆ in which q is between 0.75 and 1.0 and r is between 0.03 and 0.07 and has the primary phase of an α-SiAlON crystalline structure.

0036The β-SiAlON fluorescent material may be expressed by the general formula Eu₈(Si,Al)_6-8(O,N)₈ in which s is between 0.011 and 0.019 and has the primary phase of a β-SiAlON crystalline structure.

0037Light resulting from the mixture of the light emitted by the semiconductor light-emitting element and the fluorescence emitted by the fluorescent material may have chromaticity within the daylight color range expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting four points at the coordinates (x, y) of (0.3274, 0.3673), (0.3282, 0.3297), (0.2998, 0.3396), and (0.3064, 0.3091).

0038In such a case, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of (7.5 × C/A) : (1.3 × CB) ; 1 provided that the peak emission intensities of the first, second, and third fluorescent materials are A : B : C when measured by a spectrum corrected fluorescence spectrophotometer.

0039In such a case, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of 12 : 2 : 1.

0040Further, light obtained by mixing the light emitted by the semiconductor light-emitting element and the fluorescence emitted by the fluorescent material may have chromaticity within the neutral white color range expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting four points at the coordinates (x, y) of (0.3616, 0.3875), (0.3552,0.3476), (0.3353, 0.3659), and (0.3345, 0.3314).

0041In such a case, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of (6.5 × C/A): (1.3 × C/B) : 1 provided that the peak emission intensities of the first, second, and third fluorescent materials are A : B : C when measured by a spectrum corrected fluorescence spectrophotometer.

0042In such a case, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of 10.3 : 2 : 1.

0043Further, light obtained by mixing the light emitted by the semiconductor light-emitting element and the fluorescence emitted by the fluorescent material may have chromaticity within the white color range expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting four points at the coordinates (x, y) of (0.3938,0.4097), (0.3805, 0.3642), (0.3656, 0.3905), and (03584, 0.3499).

0044In such a case, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of (6.3 × C/A) : (1.9 × C/B) : 1 provided that the peak emission intensities of the first, second, and third fluorescent materials are A : B : C when measured by a spectrum corrected fluorescence spectrophotometer.

0045In such a case, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of 10 : 3 : 1.

0046Further, light obtained by mixing the light emitted by the semiconductor light-emitting element and the fluorescence emitted by the fluorescent material may have chromaticity within the warm white color range expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting four points at the coordinates (x, y) of (0.4341, 0.4233), (0.4171, 0.3846), (0.4021, 0.4076), and (03903, 0.3719).

0047In such a case, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of (5.1 × C/A) : (1.9 × C/B) : 1 provided that the peak emission intensities of the first, second, and third fluorescent materials are A: B : C when measured by a spectrum corrected fluorescence spectrophotometer.

0048In such a case, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of 8 : 3 : 1.

0049Further, light obtained by mixing the light emitted by the semiconductor light-emitting element and the fluorescence emitted by the fluorescent material may have chromaticity within the incandescent lamp color range expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting four points at the coordinates (x, y) of (0.4775, 0.4283), (0.4594 ,0.3971), (0.4348, 0.4185), and (0.4214, 0.3887).

0050In such a case, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of (5.1 x C/A) : (1.6 x C/B) : 1 provided that the peak emission intensities of the first, second, and third fluorescent materials are A : B : C when measured by a spectrum corrected fluorescence spectrophotometer.

0051In such a case, the fluorescent material may comprise a mixture of the first, second, and third fluorescent materials with a mass ratio of 8 : 2.5 : 1.

0052Examples of the present invention are described hereafter.

Example 1

0053The present invention improves the color rendering of a highly reliable incandescent color LED lamp by adding small amounts of an oxynitride green fluorescent material and a nitride red fluorescent material to a white LED lamp that includes of a blue LED element and a europium (Eu)-activated calcium (Ca) doped α-SiAlON fluorescent material and emits white light in the incandescent color range, which is a low color temperature, warm white.

0054First, the synthesis of the first fluorescent material or a europium-activated β-SiAlON fluorescent material that emits green or yellow-green light is described. Generally, the β-SiAlON is expressed by the general formula Si_6-zAl_zO_zN_8-z. In the specification of this application, the β-SiAlON fluorescent material is a nitride or oxynitride fluorescent material that is expressed by the general formula Eu_s(Si,Al)_6-s(O,N)₈ and has a crystalline structure equivalent to the beta Si₃N₄ or the β-SiAlON.

0055Many samples containing Si₃N₄, AlN, and Eu₂O₃ at different ratios were prepared from the raw powders and their emission properties were compared. Particulariy excellent emission intensity was obtained using 89 mol % of Si₃N₄,10.7 mol % of AlN, and 0.3 mol % of Eu₂O₃. Table 1 shows the results of some of the experimental samples. <tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="5" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="21mm" colsep="1" /><colspec colnum="2" colname="col2" colwidth="24mm" colsep="1" /><colspec colnum="3" colname="col3" colwidth="20mm" colsep="1" /><colspec colnum="4" colname="col4" colwidth="24mm" colsep="1" /><colspec colnum="5" colname="col5" colwidth="30mm" colsep="1" /><thead><row><entry namest="col1" nameend="col1" align="center" valign="top" /><entry namest="col2" nameend="col2" align="center" valign="top">Si₃N₄[mol%]</entry><entry namest="col3" nameend="col3" align="center" valign="top">AlN[mol%]</entry><entry namest="col4" nameend="col4" align="center" valign="top">Eu₂O₃[mol%]</entry><entry namest="col5" nameend="col5" align="center" valign="top">emission intensity</entry></row></thead><tbody><row><entry namest="col1" nameend="col1" align="left" valign="top">Sample G1</entry><entry namest="col2" nameend="col2" valign="top" align="char" char="." charoff="43">89.0</entry><entry namest="col3" nameend="col3" valign="top" align="char" char="." charoff="42">11.0</entry><entry namest="col4" nameend="col4" valign="top" align="char" char="." charoff="40">0.0</entry><entry namest="col5" nameend="col5" align="center" valign="top">209</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Sample G2</entry><entry namest="col2" nameend="col2" valign="top" align="char" char="." charoff="43">89.0</entry><entry namest="col3" nameend="col3" valign="top" align="char" char="." charoff="42">10.9</entry><entry namest="col4" nameend="col4" valign="top" align="char" char="." charoff="40">0.1</entry><entry namest="col5" nameend="col5" align="center" valign="top">845</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Sample G3</entry><entry namest="col2" nameend="col2" valign="top" align="char" char="." charoff="43">89.0</entry><entry namest="col3" nameend="col3" valign="top" align="char" char="." charoff="42">10.8</entry><entry namest="col4" nameend="col4" valign="top" align="char" char="." charoff="40">0.2</entry><entry namest="col5" nameend="col5" align="center" valign="top">1323</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Sample G4</entry><entry namest="col2" nameend="col2" valign="top" align="char" char="." charoff="43">89.0</entry><entry namest="col3" nameend="col3" valign="top" align="char" char="." charoff="42">10.7</entry><entry namest="col4" nameend="col4" valign="top" align="char" char="." charoff="40">0.3</entry><entry namest="col5" nameend="col5" align="center" valign="top">2245</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Sample G5</entry><entry namest="col2" nameend="col2" valign="top" align="char" char="." charoff="43">89.0</entry><entry namest="col3" nameend="col3" valign="top" align="char" char="." charoff="42">10.6</entry><entry namest="col4" nameend="col4" valign="top" align="char" char="." charoff="40">0.4</entry><entry namest="col5" nameend="col5" align="center" valign="top">1897</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Sample G6</entry><entry namest="col2" nameend="col2" valign="top" align="char" char="." charoff="43">89.0</entry><entry namest="col3" nameend="col3" valign="top" align="char" char="." charoff="42">10.5</entry><entry namest="col4" nameend="col4" valign="top" align="char" char="." charoff="40">0.5</entry><entry namest="col5" nameend="col5" align="center" valign="top">1446</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Sample G7</entry><entry namest="col2" nameend="col2" valign="top" align="char" char="." charoff="43">89.0</entry><entry namest="col3" nameend="col3" valign="top" align="char" char="." charoff="42">10.4</entry><entry namest="col4" nameend="col4" valign="top" align="char" char="." charoff="40">0.6</entry><entry namest="col5" nameend="col5" align="center" valign="top">1537</entry></row><row><entry namest="col1" nameend="col1" align="left" valign="top">Sample G8</entry><entry namest="col2" nameend="col2" valign="top" align="char" char="." charoff="43">89.0</entry><entry namest="col3" nameend="col3" valign="top" align="char" char="." charoff="42">10.3</entry><entry namest="col4" nameend="col4" valign="top" align="char" char="." charoff="40">0.7</entry><entry namest="col5" nameend="col5" align="center" valign="top">1033</entry></row></tbody></tgroup></table></tables>

0056Sample G4 containing 0.3 mol % of Eu₂O₃ exhibited the largest emission intensity. It is concluded that excellent emission intensity can be obtained using 0.25 to 0.45 mol % of Eu₂O₃. This corresponds to the general formula Eu₄(Si,Al)_6-8(O,N)₈ yielding excellent properties when 0.011 ≤ s ≤ 0,019 and yielding particularly excellent properties when s = 0.013.

0057Based on the experimental results, the composition including 89 mol % of Si₃N₄, 10.7 mol % ofAIN, and 0.3 mol % of Eu₂O₃ was selected. The raw powders included silicon nitride, aluminum nitride, and europium oxide powders. In order to obtain the Above composition, 95.82 % by mass of silicon nitride powder, 3.37 % by mass of aluminum nitride powder, and 0.81 % by mass of europium oxide powder were weighed to a batch of 50 g and, with the addition of n-hexane, mixed in a wet planetary ball mill for two hours. Then, the raw powder mixture was dried in a rotary evaporator, sufficiently disintegrated in a mortar, granulated to an appropriate particle size using a nominal aperture 125 µm stainless test sieve compliant to JIS Z 8801, and stored in a boron nitride container with a lid. Subsequently, the covered container containing the raw powders was introduced in a gas pressurized sintering furnace, sintered under gas pressure at a sintering temperature of 2000 °C and in a nitrogen atmosphere of 1 MPa for two hours, and then sintered under gas pressure at a sintering temperature of 1700 °C and in a nitrogen atmosphere of 0.5 MPa for further 24 hours. The sintered raw powders had a mass form, which was crushed to a powder form with a small force to obtain fluorescent powder. The chart obtained by X-ray powder diffraction method using the Kα line of Cu confirmed the β-SiAlON crystalline phase.

0058The synthesis of the second fluorescent material or a europium-activated α-SiAlON fluorescent material that has a longer emission wavelength than that of the first fluorescent material and emits yellow-green, yellow, or yellow-red light is described. This α-SiAlON fluorescent material is a calcium (Ca) doped α-SiAlON fluorescent material activated by divalent europium (Eu) and has a composition expressed by the general formula of Ca_q(Si,Al)₁₂(O,N)₁₆: Eu²⁺, Many samples with varied q and r were:prepared by the inventors of the present application and their emission properties were compared. Among these, the compositions with 0,75 ≤ q ≤ 1.0 and 0.03 ≤ r ≤ 0.07 exhibited particularly high emission intensities and their luminescent chromaticity was suitable for a white LED lamp.

0059Based on the experimental results, a composition with q = 0.875 and r = 0.07 was selected. The raw powders included silicon nitride, aluminum nitride, calcium carbonate, and europium oxide powders. In order to obtain a composition formula of Ca_0.875Si_9.06Al_2.94O_0.98N_15.02 : EU²⁺_0.07, 65.78 % by mass of silicon nitride powder 18.71 % by mass of aluminum nitride powder, 13.59 % by mass of calcium carbonate powder, and 1.91 % by mass of europium oxide powder were weighed to a batch of 50 g and with the addition of n-hexane, mixed in a wet planetary ball mill for two hours. The raw powder mixture was then dried in a rotary evaporator, sufficiently disintegrated in a mortar, granulated to an appropriate particle size using a nominal aperture 125 µm stainless test sieve compliant to JIS Z 8801, and stored in a boron nitride container with a lid. Subsequently, the covered container containing the raw powders was introduced in a gas pressurized sintering furnace, sintered under gas pressure at a sintering temperature of 1700 °C and in a nitrogen atmosphere of 0.5 MPa for 24 hours. The sintered raw powders had a mass form, which was crushed to a powder form with a small force to obtain fluorescent powder. The chart obtained by X-ray powder diffraction method using the Kα line of Cu confirmed the calcium doped α-SiAlON crystalline phase.

0060The third fluorescent material is a nitride crystalline red fluorescent material that has a longer emission wavelength than the second fluorescent material and emits yellow-red or red light and is expressed by the general formula of (Ca,Eu)AlSiN₃. The synthesis of the third fluorescent material is described hereafter. The raw powders were siliconnitride powder, aluminum nitride powder, calcium nitride powder, and europium nitride obtained by nitridation of metal europium in ammonium. In order to obtain a composition formula of Eu_0.005Ca_0.9995AlSiN₃, 34.0735 % by mass of silicon nitride powder, 29.8705 % by mass of aluminum nitride powder, 35.9956 % by mass of calciummitride powder, and 0.06048 % by mass of europium nitride powder were weighed and mixed for 30 minutes using an agate mortar and a pestle. The obtained mixture was molded using a metal mold under a pressure of 20 MPa to yield a molded piece of 12 mm in diameter and 5 mm in thickness. Weighing, mixing, and molding the powders were conducted in a glove box where an atmosphere of nitrogen with moisture of 1 ppm or less and oxygen of 1 ppm or less was maintained. The molded piece was placed in a boron nitride crucible and introduced in a graphite resistance heating type electric furnace. For firing a vacuum firing atmosphere was created using a diffusion pump and heated from the room temperature to 800 °C at a rate of 500 °C per hour. At the temperature of 800 °C, 99.999 % by volume pure nitrogen was introduced to a pressure of 1 MPa, heated to 1800 °C at a rate of 500 °C per hour, and maintained at 1800 °C for two hours. Afterfirings, the sintered piece was disintegrated to a powder form using an agate mortar and a pestle to obtain fluorescent powder. The chart obtained by X-ray powder diffraction method using the Kα line of Cu confirmed the CaAlSiN₃ crystalline phase.

0061Optical properties of the first, second, and third fluorescent materials prepared as described above are described hereafter. Measurements were obtained using a fluorescence spectrophotometer F-4500 manufactured by Hitachi, Ltd. The spectrophotometer was calibrated by the rhodamine B method and a standard light source for spectral correction.

0062FIG 8 is a graphical representation showing the emission spectrum and the excitation spectrum of the β-SiAlON fluorescent material used as the first fluorescent material.

0063FIG 9 is a graphical representation showing the emission spectrum and the excitation spectrum of the a-SiAlON fluorescent material used as the second fluorescent material.

0064FIG 10 is a graphical representation showing the emission spectrum and the excitation spectrum of the Ca_1-pAlSiN₃ : Eu²⁺_p fluorescent material used as the third fluorescent material.

0065Assuming excitation by a blue LED, an excitation wavelength of 450 nm was used to measure emission spectra. The peak emission wavelength of each fluorescent material was used as a monitoring wavelength to measure excitation spectra. In FIGs. 8 to 10, the emission intensity on the vertical axis was normalized as the peak emission intensity of a reference fluorescent material being 1. The reference fluorescent material was a commercially available (Y,Gd)₃Al₃O₁₂ : Ce³⁺ fluorescent powder (a YAG fluorescent material), which was used in Comparative Example 1 above.

0066For the excitation wavelength of 450 nm, the first fluorescent material or a β-SiAlON fluorescent material had a central emission wavelength of 539 nm; the second fluorescent material or an α-SiAlON fluorescent material, 585 nm; and the third fluorescent material or a Ca_1-pAlSiN₃ : Eu²⁺p fluorescent material, 655 nm.

0067As for the excitation spectrum, all of the fluorescent materials had a significantly wide excitation range from the blue to ultraviolet light range. It was found that the second fluorescent material or an α-SiAlON fluorescent material and the third fluorescent material or a Ca_1-pAlSiN₃ : Eu²⁺p fluorescent material may be highly efficiently excited particularly by blue light of wavelengths around 450 nm. The first fluorescent material or a β-SiAlON fluorescent material exhibited a sufficiently high excitation efficiency for a wavelength of 450 nm. However, it was found that further shorter wavelengths are preferably used for higher excitation efficiency.

0068Assuming that the peak emission intensity of the reference material to be 100 %, the first fluorescent material or a β-SiAlON fluorescent material had a peak emission intensity of 117 %; the second fluorescent material or an α-SiAlON fluorescent material, 116 %; and the third fluorescent material or a Ca_1-pAlSiN₃: Eu²⁺p fluorescent material, 184 %. FIG. 11 is a graphical representation showing the emission spectra of the first to third fluorescent materials for comparison.

0069As the light-emitting device of Example 1, the structure of a white LED lamp using a mixture of the first to third fluorescent materials is described hereafter. FIG 13 shows a chip type light-emitting diode lamp 11. A white resin package 19 clamps two lead wires 12 and 13 and has a recess in the center. In the recess, the ends of the lead wires 12 and 13 are exposed and a blue LED element 14 having a peak emission wavelength of 450 nm is placed. The bottom electrode of the blue LED element 14 and the end of one lead wire 12 are electrically connected by conductive paste. The top electrode of the blues LED element 14 and the other lead wire 13 are electrically connected by a bonding wire 15 made of a thin gold wire. Fluorescent powder 16 obtained by mixing the first, second, and third fluorescent materials is dispersed in a transparent resin 17 and the resin 17 with the fluorescent powder 16 dispersed therein entirely covers the blue LED element 14 and seals the whole recess including the lead wires 12 and 13.

0070The blue LED element preferably has a central emission wavelength of 400 to 480 nm, particularly a central emission wavelength of 450 nm for efficiently exciting the second fluorescent material or an α-SiAlON fluorescent material and the third fluorescent material or a Ca_1-pAlSiN₃ : Eu²⁺p fluorescent material.

0071The production process of the light-emitting device of Example 1 is described hereafter.

0072In the first step, the first, second, and third fluorescent materials were weighed and mixed.

0073In the second step, the blue LED element 14 having a peak emission wavelength of 450 nm was die bonded to the end of one lead wire 12 using conductive paste.

0074In the third step, the top electrode of the blue LED element 14 and the other lead wire 13 were wire-bonded by a thin gold wire.

0075In the fourth step, an appropriate amount of the resin 17 in which the fluorescent powder mixture 16 was dispersed to 17 % by mass was applied and cured in the recess to cover the blue LED element 14. Here, the appropriate application amount was previously determined by experiments. The resin was an epoxy resin.

0076Example 1 used the first, second, and third fluorescent materials with a mixing ratio of 8 : 2.5 : 1, achieving luminescent chromaticity of incandescent lamp color. The incandescent lamp color range is expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting four points at the coordinates (x, y) of (0.4775, 0.4283), (0.4594, 0,3971), (0.4348, 0.4185), and (0.4214, 0.3887).

0077The incandescent lamp color LED lamp of Example 1 exhibited an incandescent lamp color of which the coordinates (x, y) on the CIE 1931 XYZ colorimetric system chromaticity diagram shown in FIG 14 were (0.460, 0.409) and had a correlated color temperature of 2690 K. The emission efficacy to input power was 20.5 lm/W and the general color rendering index Ra was 89, FIG. 1 shows the emission spectrum of the incandescent lamp color LED lamp of Example 1.

0078The first to third fluorescent materials used in Example 1 are still in the process of review for improved optical properties and their emission intensities can be further improved in the future. The fluorescent materials used in Example 1 described above had the emission spectra having the relationships shown in FIG 11. If any of the fluorescent materials is improved in emission intensity and their proportions are changed, the mixing ratio of the first to third fluorescent materials have to be reviewed so that the white LED lamp yields luminescent chromaticity of incandescent color. For example, the mixing ratio can be (5.1 × C/A) : (1.6 × CB) : 1 provided that the peak emission intensities of the first to third fluorescent materials are A : B : C when measured by a spectrum corrected fluorescence spectrophotometer.

Example 2

0079Example 2 used the first, second, and third fluorescent materials with a mixing ratio of 12 : 2 : 1, achieving luminescent chromaticity of daylight color. The daylight color range is expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting four points at the coordinates (x, y) of (0.3274, 0.3673), (0.3282, 0.3297), (0.2998, 0.3396), and (0.3064, 0.3091). A white LED lamp was produced in the same manner as Example 1 except that the fluorescent materials were mixed at the changed mixing ratio and the measurements were obtained in the same manner as in Example 1.

0080The white LED lamp of Example 2 exhibited a daylight color of which the coordinates (x, y) on the CIE 1931 XYZ colorimetric system chromaticity diagram shown in FIG. 14 were (0.311, 0.333) and had a correlated color temperature of 6580 K. The emission efficacy to input power was 28.0 lm/W and the general color rendering index Ra was 81. FIG. 4 shows the emission spectrum of the white LED lamp of Example 2.

0081The first to third fluorescent materials used in Example 2 are still in the process of review for improved optical properties and their emission intensities can be further improved in the future. The fluorescent materials used in Example 2 described above had the emission spectra having the relationships shown in FIG 11. If any of the fluorescent materials is improved in emission intensity and their proportions are changed, the mixing ratio of the first to third fluorescent materials have to be reviewed so that the white LED lamp yields luminescent chromaticity of daylight color. For example, the mixing ratio can be (7.5 × C/A) : (1.3 × C/B) : 1 provided that the peak emission intensities of the first to third fluorescent materials are A : B : C when measured by a spectrum corrected fluorescence spectrophotometer.

Example 3

0082Example 3 used the first, second, and third fluorescent materials with a mixing ratio of 10.3 : 2 : 1, achieving luminescent chromaticity of neutral white color. The neutral white color range is expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting four points at the coordinates (x, y) of (0.3616, 0,3875), (0.3552, 0.3476), (0.3353, 0.3659), and (0.3345, 0.3314). A white LED lamp was produced in the same manner as Example 1 except that the fluorescent materials were mixed at the changed mixing ratio and the measurements were obtained in the same manner as Example 1.

0083The white LED lamp of Example 3 exhibited a neutral white color of which the coordinates (x, y) on the CIE 1931 XYZ colorimetric system chromaticity diagram shown in FIG. 14 were (0.345, 0,358) and had a correlated color temperature of 5010 K. The emission efficacy to input power was 25.3 lm/W and the general color rendering index Ra was 82. FIG 5 shows the emission spectrum of the white LED lamp of Example 3.

0084The first to third fluorescent materials used in Example 3 are still in the process of review for improved optical properties and their emission intensities can be further improved in the future. The fluorescent materials used in Example 3 described above had the emission spectra having the relationships shown in FIG 11. If any of the fluorescent materials is improved in emission intensity and their proportions are changed, the mixing ratio of the first to third fluorescent materials have to be reviewed so that the white LED lamp yields luminescent chromaticity of neutral white color. For example, the mixing ratio can be (6.5 × C/A) : (1.3 × C/B) : 1 provided that the peak emission intensities of the first to third fluorescent materials are A: B : C when measured by a spectrum corrected fluorescence spectrophotometer.

Example 4

0085Example 4 used the first, second, and third fluorescent materials with a mixing ratio of 10 : 3 : 1, achieving luminescent chromaticity of white color. The white color range is expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting four points at the coordinates (x, y) of (0.3938,0.4097), 0.3805, 0.3642), (0.3656, 0.3905), and (0.3584, 0.3499). A white LED lamp was produced in the same manner as Example 1 except that the fluorescent materials were mixed at the changed mixing ratio and the measurements were obtained in the same manner as Example 1.

0086The white LED lamp of Example 4 exhibited a white color of which the coordinates (x, y) on the CIE 1931 XYZ colorimetric system chromaticity diagram shown in FIG 14 were (0.373, 0.370) and had a correlated color temperature of 4160 K. The emission efficacy to input power was 27.1 Im/W and the general color rendering index Ra was 83. FIG 6 shows the emission spectrum of the white LED lamp of Example 4.

0087The first to third fluorescent materials used in Example 4 are still in the process of review for improved optical properties and their emission intensities can be further improved in the future. The fluorescent materials used in Example 4 described above had the emission spectra having the relationships shown in FIG. 11. If any of the fluorescent materials is improved in emission intensity and their proportions are changed, the mixing ratio of the first to third fluorescent materials have to be reviewed so that the white LED lamp yields luminescent chromaticity of white color. For example, the mixing ratio can be (6.3 × C/A) : (1.9 × C/B) : 1 provided that the peak emission, intensities of the first to third fluorescent materials are A : B : C when measured by a spectrum corrected fluorescence spectrophotometer.

Example 5

0088Example 5 used the first, second, and third fluorescent materials with a mixing ratio of 8 : 3 : 1, achieving luminescent chromaticity of warm white color. The warm white color range is expressed by a rectangular formed on the CIE 1931 XYZ colorimetric system chromaticity diagram by connecting four points at the coordinates (x, y) of (0.4341, 0.4233), (0.4171, 0.3846), (0.4021, 0.4076), and (0.3903, 0.3719). A white LED lamp was produced in the same manner as Example 1 except that the fluorescent materials were mixed at the changed mixing ratio and the measurements were obtained in the same manner as Example 1.

0089The white LED lamp of Example 5 exhibited a warm white color of which the coordinates (x, y) on the CIE 1931 XYZ colorimetric system chromaticity diagram shown in FIG 14 were (0.407, 0.392) and had a correlated color temperature of 3470 K. The emission efficacy to input power was 23.7 lm/W and the general color rendering index Ra was 86. FIG. 7 shows the emission spectrum of the white LED lamp of Example 5.

0090The first to third fluorescent materials used in Example 5 are still in the process of review for improved optical properties and their emission intensities can be further improved in the future. The fluorescent materials used in Example 5 described above had the emission spectra having the relationships shown in FIG 11. If any of the fluorescent materials is improved in emission intensity and their proportions are changed, the mixing ratio of the first to third fluorescent materials have to be reviewed so that the white LED lamp yields luminescent chromaticity of white color. For example, the mixing ratio can be (5.1 × C/A) : (1.9 x C/B) : 1 provided that the peak emission; intensities of the first to third fluorescent materials are A : B : C when measured by a spectrum corrected fluorescence spectrophotometer.

0091The white LED lamps (light-emitting devices) produced in Examples 1 to 5 described above were of a chip type white LED lamp. However, they can be of other types of light-emitting devices such as a bullet type white LED lamp shown in FIG. 12.

0092The light-emitting device of the present is suitable for constituting an illumination apparatus by itself or by mounting many of them on a substrate. The illumination apparatus using the light-emitting device of the present invention as a light source has advantages such as small size, energy-saving, high luminance, long life, and high color rendering.

Comparative Example 1

0093For comparison, a bullet type LED lamp shown in FIG 12 was produced as a conventional white LED lamp using a commercially available YAG fluorescent material as the fluorescent material.

0094A bullet type LED lamp 1 has a approximately cylinder shape with the rounded top, in other words a bullet-like shape and comprises two lead wires 2 and 3, a blue LED element 4 emitting blue light, a bonding wire 5, a fluorescent material 7, a first resin 6 mixed with the fluorescent material 7, and a second, transparent resin 8. A recess is formed at the top end of one lead wire 2 and the blue LED element 4 is placed in the recess. The bottom electrode of the blue LED element 4 is electrically connected to the one lead wire 2 for example by die bonding using conductive paste. The top electrode of the blue LED element 4 is electrically connected to the other lead wire 3 for example by wire bonding using the bonding wire 5. The blue LED element 4 and bonding wire 5 within the recess are embedded in the first resin mixed with the fluorescent material 7. These components are sealed in the transparent resin 8 molded in a bullet shape except for the lower parts of both lead wires 2 and 3.

0095In Comparative Example 1, the fluorescent material 7 used was a commercially available (Y,Gd)₃Al₅O₁₂ : Ce³⁺ fluorescent powder (YAG fluorescent material). FIG. 2 shows the emission spectrum of the white LED lamp of Comparative Example 1 The emission color had chromaticity coordinates (x, y) = (0.34,0.36) on the CIE 1931 XYZ colorimetric system chromaticity diagram and a correlated color temperature of 5070 K. The general color rendering index Ra was 73 and the luminous efficacy to input power was 40 lm/W (lumen per watt). The white LED lamp of Comparative Example 1 is an excellent light-emitting device that efficiently emits white light. However, it is difficult to shift the emission wavelength for longer wavelengths by using the YAG fluorescent material. Therefore, a white LED lamp that emits low color temperature white flight in the light source color chromaticity range of incandescent lamp color defined by BIS Z 9112-1990 cannot be realized. It is known that the YAG fluorescent material has lowered emission intensity at high temperatures. Color changes due to environmental temperature changes are also problematic. Further improvement in color rendering is also required.

Comparative Example 2

0096Comparative Example 2 was different from Comparative Example 1 in that the fluorescent material 7 was an α-SiAION fluorescent material. FIG. 3 shows the emission spectrum of a white LED lamp of Comparative Example 2 using an α-SiAlON fluorescent material having a composition formula of Ca_0.875(Si,Al)₁₂(O,N)₁₆Eu²⁺_0.07.

0097The emission color had chromaticity coordinates (x, y) = (0.46, 0.41) on the CIE 1931 XYZ colorimetric system chromaticity diagram and a correlated color temperature of 2780 K. The general color rendering index was 56 and the luminous efficacy to input power was 36 lm/W (lumen per watt). The white LED lamp of Comparative Example 2 using an alpha SiAlON fluorescent material, or an oxynitride fluorescent material, is an excellent light-emitting device that efficiently emits low color temperature white light in the light source color chromaticity range of incandescent lamp color. It is also excellent in color stability over temperature changes as disclosed in <nplcit id="ncit0006" npl-type="s"><text>K. Sakuma, K. Omichi, N. Kimura, M. Ohashi, D. Tanaka, N. Hirosaki, Y. Yamamoto, R,-J. Xie, T. Suebiro "Warm-white light-emitting diode with yellowish orange SiAlON ceramic phosphor," Opt. Lett., Vol. 29, pp. 2001-2003 (2004)</text></nplcit>. However, it is slightly behind general fluorescent lamps in color rendering and improvement is required.

0098While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.