JP5370047B2 - Color rendering improvement method for white light emitting device and white light emitting device - Google Patents

Description

  The present invention is a white light emitting device such as a white light emitting diode (white LED) provided with a semiconductor light emitting element as an excitation source, in particular, using a blue phosphor as a source of blue light, which is a component of white light, and has a high color temperature. The present invention relates to a color rendering improvement method for a white light emitting device that generates white light. The present invention also relates to a white light emitting device that generates white light with improved color rendering.

  In recent years, the use of LED lamps using light emitting diode (LED) elements, in particular, white LEDs configured to emit white light by combining light emitting diode elements and phosphors, has expanded dramatically. Conventionally, the main application of the white LED has been a backlight of a liquid crystal panel for a mobile phone, but with the improvement of luminance, practical application in general lighting applications is becoming full-scale.

As is well known, an important evaluation item of a lighting device is color rendering.
Among white LEDs having a high correlated color temperature (4500 K or more), it is said that white light with good color rendering properties can be obtained by developing a high-performance nitride-based red phosphor. (Patent Document 1).

JP 2006-63233 A

  However, as shown in the experimental example described in Patent Document 1, in a white LED having a high correlated color temperature, the special color rendering index R12 indicating the appearance of blue tends to be low. Furthermore, it should be noted that even when a mixture containing four kinds of phosphors of blue, green, orange and red is emitted using ultraviolet light having a wavelength of 390 nm, special color rendering index is obtained for so-called daylight white light. That is, R12 exceeding 90 is not obtained.

  In order to improve the special color rendering index R12 in a white LED having a high correlated color temperature, the emission peak of a semiconductor light emitting element or blue phosphor used as a blue light source is lengthened (particularly, 470 nm or more). ) Is effective (Japanese Patent Laid-Open No. 2007-191680).

  In a white LED for illumination that requires high spatial color uniformity, the LED element is used exclusively as a phosphor excitation source, and the phosphor generates three primary color lights (RGB). It is desirable to adopt the method of making them. In this type of white LED, an InGaN-based violet light-emitting element (emission peak wavelength: 395 nm to 435 nm) can be suitably used as an excitation source. This is because the luminous efficiency of the InGaN-based LED element is maximized when the emission peak wavelength is in the range of 395 nm to 450 nm (G. Chen, et al., Phys. Stat. Sol. (A) 205, No. 5, 1086-1092 (2008)).

Many high-performance blue phosphors that can be excited by light having a wavelength of 395 nm or more have an emission peak wavelength of less than 460 nm. By using such a blue phosphor, it is possible to obtain a white LED for illumination with good emission luminance, while generating daylight white light or white light having a higher color temperature as described above. It is difficult to obtain a special color rendering index R12 exceeding 90.

  The present invention has been made in order to solve this problem. A blue light emitting device for generating white light having a high color temperature by using a blue phosphor as a source of blue light which is a component of white light. The main purpose is to provide a method for improving color rendering. Another object of the present invention is to provide a white light-emitting device that generates white light having a high color temperature and improved color rendering for blue.

In the present invention, the “blue phosphor” means that, when excited by a semiconductor light emitting device having an emission peak wavelength in the range of 360 nm to 435 nm, emits blue light having a main emission peak wavelength in the range of 440 nm to 490 nm. Refers to a phosphor. Blue light corresponds to “purple blue”, “blue”, “greenish blue” or “blue-green” in the CIE chromaticity diagram (see FIG. 2 of Japanese Patent Publication No. 48-22117). Includes tonal light.
In the present invention, the “blue wavelength region” refers to a wavelength region having a wavelength of 440 nm to 490 nm.

In order to solve the above problems, according to one aspect of the present invention, the following method is provided:
A method for improving color rendering for a white light emitting device that emits white light having a correlated color temperature of 4500 K or more,
The white light includes light emission from a blue phosphor excited by a semiconductor light emitting element as a component, and has a peak wavelength Λ _B (nm) in a blue wavelength region of the spectrum,
The blue phosphor has an emission peak wavelength of λ _B (nm), and a wavelength at which the emission intensity is half the value at the wavelength λ _B on the longer wavelength side than the wavelength λ _B is λ _B + Δλ _B (nm),
A method in which part of light emitted from the blue phosphor is absorbed by the first phosphor defined in (A) below so that λ _B <Λ _B <490.
(A) The first phosphor can absorb light of wavelength λ _B and convert it into visible light of a different wavelength, and the intensity of the excitation spectrum is in the range from wavelength λ _B -Δλ _B to λ _B Is 90% or more of the intensity at λ _B and decreases from the wavelength λ _B to λ _B + Δλ _B until it becomes less than half of the intensity at λ _B.

Moreover, according to one aspect of the present invention, the following white light emitting device is provided:
A white light emitting device that emits white light having a correlated color temperature of 4500 K or more,
The white light includes light emission from a blue phosphor excited by a semiconductor light emitting element as a component, and has a peak wavelength Λ _B (nm) in a blue wavelength region of the spectrum,
The blue phosphor has an emission peak wavelength of λ _B (nm), and a wavelength at which the emission intensity is half the value at the wavelength λ _B on the longer wavelength side than the wavelength λ _B is λ _B + Δλ _B (nm),
The first phosphor defined in (A) below is arranged so as to absorb part of the light emitted from the blue phosphor,
A white light emitting device in which λ _B <Λ _B <490.
(A) The first phosphor can absorb light in the wavelength λ _B range and convert it into visible light having a different wavelength, and the intensity of the excitation spectrum ranges from the wavelength λ _B −Δλ _B to λ _B. within the scope and the intensity of 90% or more at lambda _B, and is reduced to less than half the intensity at the wavelength lambda lambda _B over the λ _{B +} Δλ _B from _B.

  In the above method or apparatus, the spectrum of light emitted from the blue phosphor is transformed using a kind of optical filter. As a result, the same action as when the emission wavelength of the blue phosphor itself is lengthened occurs, and the color rendering property of white light containing the light emission of the blue phosphor as a component is improved.

  The main feature of the method or apparatus is that a “first phosphor” that is a wavelength converting substance is used as a substance that functions as the optical filter. The blue light absorbed by the first phosphor is converted into visible light of a different color and used as part of the output light of the white light emitting device. Therefore, the loss due to the filter action exhibited by the first phosphor is smaller than the loss when using an optical filter of the type that converts all absorbed light into heat.

Another major feature of the method or apparatus is the limitation of (A) above regarding the excitation properties of the first phosphor.
In the above limitation (A), λ _B and Δλ _B are numerical values obtained from emission spectrum measurement of the blue phosphor alone. That is, λ _B is the emission peak wavelength of the blue phosphor. Δλ _B is defined by setting the wavelength at which the emission intensity of the blue phosphor is half the intensity at the wavelength λ _B on the longer wavelength side than the wavelength λ _B to be λ _B + Δλ _B. The excitation wavelength used in this emission spectrum measurement may be any wavelength within the range of λ _E ± 10 (nm) when the emission peak wavelength of the semiconductor light emitting element used as the excitation source in the white light emitting device is λ _E (nm). .

First phosphor satisfying the limitation of the (A), among the light emitted from the blue phosphor emits, lambda components shorter than _B, and compared with the component of wavelength longer than lambda _B, the property of absorbing significantly stronger Have. Therefore, if there is a sufficient amount of the first phosphor, the absorption causes the emission spectrum of the blue phosphor to be transformed as if the emission peak has a longer wavelength. In a light emitting device that emits white light having a high correlated color temperature of 4500K or higher, this leads to an improvement in the special color rendering index R12. When such a modification of the emission spectrum of the blue phosphor occurs, the peak wavelength Λ _B of the spectrum of the output light (white light) of the white light emitting device in the blue wavelength region is longer than λ _B.

According to the method of the present invention, it is possible to obtain a white light emitting device that generates white light having a good color rendering property regarding blue.
Further, the white light emitting device according to the present invention can generate white light having a good color rendering property for blue.

2 is a cross-sectional structure of a white LED according to an embodiment of the present invention. 2 is an excitation spectrum of the phosphor BSS used in Example 1. It is an emission spectrum of white LED concerning the embodiment of the present invention. It is an emission spectrum of white LED concerning the embodiment of the present invention. 6 is an excitation spectrum of the phosphor BSON used in Example 3. It is an emission spectrum of white LED concerning the embodiment of the present invention.

  The white light-emitting device referred to in the present invention includes all light-emitting devices that include a semiconductor light-emitting element as an excitation source of a phosphor and a configuration that generates white light using luminescent light emitted from the phosphor as a component.

  In addition to LEDs, semiconductor light emitting elements include LDs (laser diodes) and the like. There is no limitation on the type of semiconductor constituting the main part of the light-emitting element, and a semiconductor capable of generating short-wavelength light suitable for excitation of a phosphor, such as a gallium nitride semiconductor or a zinc oxide semiconductor, is preferably exemplified. The semiconductor light emitting element may be fixed to a package such as a shell-type package or an SMD type package, or may be directly fixed on a substrate as in the case of a chip-on-board type light emitting device.

  There is no limitation on the form of optical coupling between the semiconductor light emitting element and the phosphor, and the gap between the two may be simply filled with a transparent medium (including air), or a lens, An optical element such as an optical fiber or a light guide plate may be interposed between the two.

  As the phosphor, those provided in the form of particles can be preferably used, and those provided in the form of a luminescent ceramic containing a phosphor phase can also be used. The phosphor provided as particles can be used by being dispersed in a transparent matrix, and can also be used after being formed into a layered form on a certain surface by electrophoresis or aerosol desorption. it can.

  A typical example of a white light emitting device is a white LED. In the most common white LED, an LED chip is mounted on a shell type or SMD type package, and a particulate phosphor is added in a translucent resin coating covering the surface of the LED chip. Lighting devices including white LEDs as components (including indoor lights, outdoor lights, flashlights, headlights, etc.) also fall within the category of white light emitting devices referred to in the present invention.

  The characteristic of color rendering is an item evaluated in a light emitting device for illumination. The correlated color temperature of white light for illumination is normally set in the range of 2500K to 8000K. The present invention can be preferably applied to a white light emitting device that generates white light having a correlated color temperature of 4500K or more and 8000K or less, and in particular, to a light emitting device that emits white light having a color temperature classified as daylight white or daylight color. It can be preferably applied.

  FIG. 1 shows a cross-sectional structure of a white LED according to an embodiment of the present invention. The white LED 1 shown in this figure is an SMD (surface mount) type LED, and an InGaN-based LED chip 20 is bonded onto the bottom surface of a cavity (cup-shaped portion) provided in the package 10 using an adhesive (not shown). It is fixed.

  The package 10 includes an insulating substrate 11 formed of ceramic (alumina, AlN, etc.), white resin (composition in which a white pigment is dispersed in a transparent resin such as silicone resin), two package electrodes 12, metal or And a reflector 13 formed of a white material (ceramic or resin). Although the insulating substrate 11 and the reflector 13 are shown as separate members in this figure, they can be formed integrally using the same material.

  The InGaN-based LED chip 20 includes a crystal substrate 21 made of sapphire, SiC, GaN, or the like, and a gallium nitride-based semiconductor film 22 formed thereon. The gallium nitride based semiconductor film 22 has a laminated structure (not shown) composed of an InGaN active layer and p-type and n-type gallium nitride based semiconductor layers sandwiching the InGaN active layer, and a positive electrode on the p-type semiconductor layer. The negative electrode 24 is formed on the n-type semiconductor layer 23 partially exposed. Preferably, a reflective film 25 made of metal or dielectric is formed on the lower surface of the crystal substrate 21. The positive electrode 23 and the negative electrode 24 are connected to the two package electrodes 12 by bonding wires 30 made of Au, Al, Cu, or the like.

  The InGaN-based LED chip 20 is covered with a translucent coating 40. The surface of the coating 40 can be formed as a convex surface or an uneven surface by a method such as molding. The base material of the coating 40 is a transparent resin or glass, and among these, a silicon-containing compound is preferable.

The silicon-containing compound refers to a compound having a silicon atom in a molecule, for example, an organic material (silicone material) such as polyorganosiloxane, an inorganic material such as silicon oxide, silicon nitride, silicon oxynitride, and borosilicate. And glass materials such as phosphosilicate and alkali silicate. Among these, silicone materials are preferable from the viewpoints of transparency, adhesiveness, ease of handling, and excellent mechanical / thermal stress relaxation characteristics. The silicone-based material usually refers to an organic polymer having a siloxane bond as a main chain, and there are types such as a condensation type, an addition type, a sol-gel type, and a photo-curing type depending on the curing mechanism.

  Particulate blue phosphor, green phosphor and red phosphor are dispersed in the coating 40 (phosphor not shown). In addition to these phosphors, or in place of the green phosphor, a yellow phosphor can be dispersed. Each phosphor can be uniformly distributed throughout the interior of the coating 40. In one example, the coating 40 may be multi-layered to provide a layer containing phosphor and a layer not containing phosphor, or the type and / or amount of phosphor contained in each layer may be different.

  The emission peak wavelength of the InGaN-based LED chip 20 is 360 nm or more and 435 nm so that the blue phosphor is sufficiently excited. Considering the luminous efficiency of the LED element, the emission peak wavelength of the InGaN-based LED chip 20 is preferably 395 nm to 435 nm, more preferably 405 nm to 430 nm. Furthermore, when the emission peak wavelength of the LED chip is 420 nm or less, the visibility of the light emitted from the LED chip is sufficiently low, so that the uniformity of the spatial color tone of the light emitted from the white LED 1 is particularly good.

Table 1 shows blue phosphors that can be used by being added to the coating 40. As the half-value width of the emission peak of the blue phosphor used is larger, the difference between Λ _B and λ _B can be increased, that is, the effect of improving the blue color rendering (R12) due to the above mechanism becomes more prominent. Specifically, this is a case where a blue phosphor having a half-value width of the emission peak of 50 nm or more, particularly 60 nm or more is used.
A typical example of a blue phosphor having good emission efficiency despite a relatively large half-value width of the emission peak is called Eu-activated aluminate-based phosphor, particularly BAM (Ca, Sr, Ba). MgAl ₁₀ O ₁₇ : Eu.

At least a part of the phosphor other than blue dispersed together with the blue phosphor in the coating 40 is a phosphor satisfying the above-mentioned definition (A), that is, a phosphor corresponding to the “first phosphor”. . Although it depends on the light emission characteristics of the blue phosphor, in general, the phosphor satisfying the above (A) has an excitation spectrum intensity rapidly decreasing with the wavelength within a wavelength range from 440 nm to 500 nm. It is a phosphor having a wavelength region.

  Accordingly, Eu-activated alkaline earth silicate phosphors, Eu-activated alkaline earth halosilicate phosphors, and Eu-activated BSON phosphors are preferably exemplified as candidates for the “first phosphor”.

The Eu-activated alkaline earth silicate phosphor is represented by the general formula (Ba, Sr, Ca, Mg) ₂ SiO ₄ : Eu. Japanese Patent Application Laid-Open No. 2006-124422 discloses production of an Eu-activated alkali metal earth silicate phosphor based on a silicate (silicate) of at least one alkaline earth metal selected from calcium, strontium and barium. Examples are disclosed, and according to FIGS. 4, 6, and 7, when the emission color is green, yellow, or yellow-green, the intensity of the excitation spectrum with the wavelength is within a wavelength range from 440 nm to 500 nm. The thing containing the wavelength range which falls rapidly is obtained.

JP 2006-1111829 discloses Eu-activated alkaline earth metal silicate-based yellow phosphors (Sr _0.915 La _0.06 Eu _0.025 ) ₂ SiO ₄ and (Sr _0.915 Ba _0.06 E).
An example of the production of u _0.025 ) ₂ SiO ₄ and the excitation spectrum (FIG. 2) are disclosed. The excitation spectrum includes a wavelength region in which the intensity rapidly decreases with the wavelength within a wavelength range from 440 nm to 500 nm.

Regarding the Eu-activated alkaline earth halosilicate phosphor, for example, Japanese Patent Publication No. 2003-535478 and Japanese Patent Publication No. 2009-515525 can be referred to. Japanese Patent Publication No. 2003-535478 discloses a production example and an excitation spectrum (FIG. 1) of a green phosphor Ca ₈ Mg (SiO ₄ ) ₄ Cl ₂ : Eu having a Ca—Mg-chlorosilicate skeleton.
JP 2009-517525 A discloses a production example and excitation spectrum (FIG. 5) of green phosphor (Ca, Sr) ₃ SiO ₄ Cl ₂ : Eu, and green phosphor (Ca, Sr) ₈ Mg (SiO 2). _{4) 4} Cl _2: preparation of Eu with the excitation spectrum (FIG. 7) is disclosed.
Each excitation spectrum includes a wavelength region in which the intensity rapidly decreases with the wavelength within a wavelength range from 440 nm to 500 nm.

The Eu-activated BSON phosphor is a phosphor according to the invention disclosed in Japanese Patent Application Laid-Open No. 2008-138156, and is typically a composite oxynitride containing a “BSON phase” defined in the same document System phosphor. For specific examples of preferable chemical compositions of Eu-activated BSON phosphors, refer to paragraph [0056] of JP-A-2008-138156. For example, (Mg, Ca, Sr, Ba) Si ₂ O ₂ N ₂ : Eu, (Ba, Sr, Ca) ₃ Si ₆ O ₁₂ N ₂ : Eu, (Ba, Sr, Ca) ₃ Si ₆ O ₉ N ₄ : Eu, and the like.

Japanese Patent Application Laid-Open No. 2008-138156 discloses a synthesis example of an Eu-activated BSON green phosphor using a charged composition of Ba _1.88 Eu _0.12 Si ₆ O ₈ N ₄ and its excitation spectrum (FIG. 43). Is disclosed.
WO2009 / 017206 discloses a synthesis example of an Eu-activated BSON-based green phosphor having a Ba-Si-complex oxynitride skeleton with various amounts of added Eu and an excitation spectrum (FIG. 6). ing. In addition, a synthesis example and excitation spectrum (FIG. 27) of green phosphor Ba _2.7 (Pr _0.063 Eu _0.937 ) _0.3 Si ₆ O ₁₂ N ₂ are disclosed.
In any of these examples, the excitation spectrum includes a wavelength region in which the intensity rapidly decreases with the wavelength in the wavelength range from 440 nm to 500 nm.

In addition to the above phosphors, Mn-activated fluoride complex phosphors can also be cited as candidates for the “first phosphor”. This phosphor is a red phosphor having a base crystal of a fluoride complex salt of alkali metal, amine or alkaline earth metal. Fluoride complexes that form host crystals include those whose coordination center is a trivalent metal (B, Al, Ga, In, Y, Sc, lanthanoid), and tetravalent metal (Si, Ge, Sn, Ti, Zr, Re, Hf) and pentavalent metals (V, P, Nb, Ta), and the number of fluorine atoms coordinated around them is 5-7. As a specific example, A ₂ [MF ₆ ]: Mn (A is one or more selected from Li, Na, K, Rb, Cs and NH ₄ ; M is one or more selected from Ge, Si, Sn, Ti and Zr) ), E [MF ₆ ]: Mn (E is one or more selected from Mg, Ca, Sr, Ba, Zn; M is one or more selected from Ge, Si, Sn, Ti, Zr), Ba _0.65 , Zr _0.35 F _2.70 : Mn, A ₃ [ZrF ₇ ]: Mn (A is one or more selected from Li, Na, K, Rb, Cs, NH ₄ ), A ₂ [MF ₅ ]: Mn ( A is one or more selected from Li, Na, K, Rb, Cs, and NH ₄ ; M is one or more selected from Al, Ga, and In; A ₃ [MF ₆ ]: Mn (A is Li, Na, K) , Rb, Cs, NH ₄ or more; M is selected from Al, Ga, In Zn ₂ [MF ₇ ]: Mn (M is one or more selected from Al, Ga, In), A [In ₂ F ₇ ]: Mn (A is Li, Na, K, Rb, Cs, And one or more selected from NH ₄ ).

It can be seen from the excitation spectrum of K ₂ TiF ₆ : Mn disclosed in FIG. 1 of US Pat. No. 3,576,756 and the excitation spectrum of K ₃ AlF ₆ : Mn disclosed in FIG. 11 of JP-T-2009-528429. As described above, the Mn-activated fluoride complex phosphor has a wavelength region in which the intensity of the excitation spectrum rapidly decreases with the wavelength in the wavelength range from 440 nm to 500 nm.

Due to the action of the “first phosphor”, the peak wavelength Λ _B of the spectrum of the output light (white light) of the white LED 1 in the blue wavelength region is longer than the emission peak wavelength λ _B of the blue phosphor alone. . Hereinafter, the difference (Λ _B −λ _B ) between Λ _B and λ _B is referred to as “blue region wavelength shift”.
Since the wavelength shift in the blue region is caused by the “first phosphor” absorbing part of the light emission of the blue phosphor, the quantitative ratio between the blue phosphor and the “first phosphor” included in the coating 40 is changed. It is possible to control by this.

In order to improve the improvement degree of the special color rendering index R12 (index of color rendering properties regarding blue) of the output light of the white LED 1, the wavelength shift in the blue region is preferably 5 nm or more, more preferably 10 nm or more. However, it should be noted that if Λ _B exceeds 490 nm, the color rendering may be degraded. Λ _B after the wavelength shift in the blue region is preferably 460 nm or more, more preferably 470 nm or more.
In order to adjust the color temperature of the white LED 1, in addition to the “first phosphor”, a green phosphor, an orange phosphor, a red phosphor, or the like can be appropriately contained in the coating 40.

[Experiment 1]
A transparent binder mainly composed of silicone resin, Eu-activated aluminate-based blue phosphor BaMgAl ₁₀ O ₁₇ : Eu (abbreviation: BAM), Eu-activated alkaline earth silicate-based green phosphor (Ba, Sr) ) ₂ SiO ₄ : Eu (abbreviation: BSS) and Eu-activated oxynitride red phosphor (Mg, Ca, Sr, Ba) AlSi (N, O) ₃ : Eu (abbreviation: CASON) A phosphor paste was prepared by mixing at the blending amount shown in 2.

When the emission spectrum of the BAM used in the phosphor paste was measured at an excitation wavelength of 400 nm, the emission peak wavelength λ _B was 455 nm, and the half width was 53 nm. Furthermore, the longer wavelength side than the wavelength lambda _B, the emission intensity half become wavelength λ _B + Δλ _B values at the wavelength lambda _B was 487 nm. Therefore, Δλ _B is calculated as 32 nm.
On the other hand, in the excitation spectrum measured for the BSS used for the phosphor paste, the intensity between the wavelength 423 nm (λ _B −Δλ _B ) and the wavelength 455 nm when the intensity at the wavelength 455 nm (λ _B ) is 100%. Was 100% to 112%, and the intensity at a wavelength of 487 nm (λ _B + Δλ _B ) was 45%. From the wavelength 455 nm to 487 nm, the intensity of the excitation spectrum decreased monotonously. An excitation spectrum of the phosphor BSS used is shown in FIG.

  Next, an InGaN-based LED chip having a 350 μm square and an emission peak wavelength of 403 nm formed using a sapphire substrate was mounted on an SMD type package, and the surface of the mounted LED chip was covered with the phosphor paste. Subsequently, the phosphor paste was cured by heat treatment to obtain a white LED.

The emission characteristics when a current of 36 mA per LED chip was applied to the obtained white LED were examined. Table 3 shows the evaluation results for the CIE chromaticity coordinate value, the correlated color temperature, the average color rendering index Ra, and the special color rendering index R12. The emission spectrum is as shown in FIG. 3, and the wavelength Λ _B of the emission peak existing in the blue region was 468 nm.

[Experiment 2]
When expressed as a weight ratio with respect to the total amount of the phosphor added to the phosphor paste, BAM was reduced by 2%, BSS and CASON were each increased by 1%, and in addition, the emission peak wavelength was 410 nm. A white LED was fabricated and the light emission characteristics were examined in the same manner as in Experimental Example 1 except that an InGaN-based LED chip was used. Table 3 shows the evaluation results for CIE chromaticity coordinate values, correlated color temperature, Ra (average color rendering index), and R12 (special color rendering index). The emission spectrum is as shown in FIG. 4, and the wavelength Λ _B of the emission peak existing in the blue region was 478 nm.

[Experiment 3]
Phosphor paste in the same manner as in Experimental Example 1, except that Eu-activated BSON green phosphor (abbreviation: BSON) was used instead of BSS, and the blending amounts of the binder and each phosphor were as shown in Table 2. Was made.
In the excitation spectrum of the BSON used in the phosphor paste, when the intensity at the wavelength 455nm (lambda _B) as 100%, the intensity between the wavelengths 423nm (λ _B -Δλ _B) the wavelength 455nm 100% The intensity at a wavelength of 487 nm (λ _B + Δλ _B ) was 42%. From the wavelength 455 nm to 487 nm, the intensity of the excitation spectrum decreased monotonously. An excitation spectrum of the phosphor BSON used is shown in FIG.

A white LED was produced in the same manner as in Experimental Example 1 except that the phosphor paste was changed as described above, and the light emission characteristics were examined. Table 3 shows the evaluation results for the CIE chromaticity coordinate value, the correlated color temperature, the average color rendering index Ra, and the special color rendering index R12. The emission spectrum is as shown in FIG. 6, and the wavelength Λ _B of the emission peak existing in the blue region was 468 nm.

Claims (16)

A method for improving color rendering for a white light emitting device that emits white light having a correlated color temperature of 4500 K or more,
The white light includes light emission from a blue phosphor excited by a semiconductor light emitting element as a component, and has a peak wavelength Λ _B (nm) in a blue wavelength region of the spectrum,
The blue phosphor has an emission peak wavelength of λ _B (nm), and a wavelength at which the emission intensity is half the value at the wavelength λ _B on the longer wavelength side than the wavelength λ _B is λ _B + Δλ _B (nm),
A method in which part of light emitted from the blue phosphor is absorbed by the first phosphor defined in (A) below so that λ _B <Λ _B <490.
(A) The first phosphor is an Eu-activated alkaline earth silicate green phosphor, an Eu-activated alkaline earth halosilicate green phosphor, or an Eu-activated BSON green phosphor, and has a wavelength λ _B. And the intensity of the excitation spectrum is 90% or more of the intensity at λ _B within the wavelength λ _B −Δλ _B to λ _B , and
From the wavelength λ _B to λ _B + Δλ _B , the intensity decreases to less than half of the intensity at λ _B. The method of claim 1, wherein Λ _B −λ _B ≧ 5. The method of claim 2, wherein λ _B <460, 460 <Λ _B. 470 <a lambda _B, Method according to claim 2 or 3. The method according to any one of claims 1 to 4, wherein the special color rendering index R12 of white light exceeds 90. The method according to any one of claims 1 to 5, wherein a half-value width of an emission peak of the blue phosphor is 50 nm or more. The blue phosphor is a blue phosphor Eu-activated aluminate A method according to any one of claims 1-6. The method according to claim 1, wherein the blue phosphor and the first phosphor are dispersed in a silicon-containing compound. A white light emitting device that emits white light having a correlated color temperature of 4500 K or more,
The white light includes light emission from a blue phosphor excited by a semiconductor light emitting element as a component, and has a peak wavelength Λ _B (nm) in a blue wavelength region of the spectrum,
The blue phosphor has an emission peak wavelength of λ _B (nm), and a wavelength at which the emission intensity is half the value at the wavelength λ _B on the longer wavelength side than the wavelength λ _B is λ _B + Δλ _B (nm),
A first phosphor as defined in (A) below, arranged to absorb part of the light emitted from the blue phosphor,
An apparatus wherein λ _B <Λ _B <490.
(A) The first phosphor is an Eu-activated alkaline earth silicate green phosphor, an Eu-activated alkaline earth halosilicate green phosphor, or an Eu-activated BSON green phosphor, and has a wavelength λ _B. by absorbing can be converted to a different wavelength visible light, the intensity of the excitation spectrum is within a wavelength range of from lambda _B -.DELTA..lambda _B to lambda _B is a strength of 90% or more at lambda _B, and, From the wavelength λ _B to λ _B + Δλ _B , the intensity decreases to less than half of the intensity at λ _B. The apparatus of claim 9 , wherein Λ _B −λ _B ≧ 5. The apparatus of claim 10 , wherein λ _B <460, 460 <Λ _B. 470 <a lambda _B, according to claim 10 or 11. The apparatus according to any one of claims 9 to 12, wherein the special color rendering index R12 of white light exceeds 90. The device according to any one of claims 9 to 13 , wherein a half width of an emission peak of the blue phosphor is 50 nm or more. The device according to claim 9, wherein the blue phosphor is an Eu-activated aluminate-based blue phosphor. The device according to any one of claims 9 to 15, wherein the blue phosphor and the first phosphor are dispersed in a silicon-containing compound.

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