Light-emitting device

Abstract

Light-emitting device, comprising: a light-emitting element configured to emit light having a peak wavelength in a range of 380 nm to 460 nm; and a phosphor group comprising a plurality of types of phosphors excited by the light emitted from the light-emitting element and having a continuous emission spectrum in a wavelength range of 400 nm to 780 nm, wherein the phosphor group comprises a phosphor having a peak wavelength in a range of 720 nm ± 5%, and in which the phosphor group includes two types of alkaline earth halophosphate phosphors, a β-sialon phosphor, a Ca solid solution α-sialon phosphor, and a CASON phosphor.

Description

The invention relates to a light emitting device.In recent years, an attempt has been made in many places to mimic bulb color, halogen lamp light and natural sunlight using LEDs (light emitting diode), and various phosphors have been developed to obtain light having high color rendering properties.For example, an LED module that emits light having a continuous emission spectrum distribution over a wavelength range of 380 nm to 780 nm is known for mimicking how a filament of an incandescent lamp emits light or for mimicking its color (see, e.g., JP 2016 / 76652 A). In the LED module disclosed in JP 2016 / 76652 A, at least four kinds of phosphors that are blue, green, yellow, and red phosphors are used.Meanwhile, a light emitting device having a general color rendering index Ra of more than 85 and a specific color rendering index R9 (red) of more than 50 is known (see, e.g., JP 2016 / 111190 A). In the light emitting device disclosed in JP 2016 / 111190 A, four kinds of phosphors having emission peaks in different wavelength ranges are used. US 2013 / 0 277 694 A1, WO 2010 / 053 341 A1 and U.S. Pat. No. 9,609,715 B1 disclose further light-emitting devices. Chen et al.: Ca-α-SiAlON:Eu Phosphors: Oxidation States, Energy Transfer, and Emission Enhancement by Incorporation-Animated Surface Engineering, Applied Materials & Interfaces, 2017, 9, 30982-30991, DOI: 10.1021 / acsami.7b05603 discloses properties of Ca-α-SiAlON:Eu Phosphor.However, in the known light emitting devices including the devices disclosed in JP 2016 / 76652 A and JP 2016 / 111190 A, since a phosphor having a peak wavelength at about 660 nm is used as a red phosphor forming the red region of the emission spectrum, the emission spectrum of the device is very different from the spectrum of sunlight or halogen light, particularly in a deep red region at not less than 700 nm. Therefore, lack of color in the deep red region is remarkable when attempting to mimic sunlight or halogen light.It is an object of the disclosure to provide a light emitting device whose emission spectrum intensity is relatively increased in the deep red region so that a decrease (deterioration) in color rendering properties is suppressed.According to an embodiment of the disclosure, a light emitting device defined below by [1] to [6] is provided.[1] A light emitting device, comprising:a light emitting element that emits light having a peak wavelength in a range from 380 nm to 460 nm; anda phosphor group (phosphor group) including a plurality of kinds of phosphors (phosphors) excited by the light emitted from the light emitting element and having a continuous emission spectrum in a wavelength range of 400 nm to 780 nm,wherein the phosphor group comprises a phosphor having a peak wavelength in a range of 720 nm±5%, andwherein the phosphor group comprises two kinds of alkaline earth halophosphate phosphors, a β-sialon phosphor, a Ca solid solution α-sialon phosphor and a CASON phosphor.[2] The light emitting device according to [1], wherein said phosphor having the peak wavelength in the range of 720 nm±5% comprises an oxide comprising Gd and Ga.[3] The light emitting device according to [2], wherein the phosphor comprises a Cr-activated Gd 3 Ga 5 O 12.[4] The light emitting device according to any one of [1] to [3], wherein a color rendering index Rf is not less than 95 when light having a color temperature of 3000K is used as a reference light, and a difference (deviation) of a color rendering index Rg of 100 is not more than 5 when light having a color temperature of 3000K is used as a reference light.[5] The light emitting device according to any one of [1] to [4], wherein a color rendering index Rf is not less than 95 when light having a color temperature of 6500K is used as a reference light, and a difference (deviation) of a color rendering index Rg of 100 is not more than 5 when light having a color temperature of 6500K is used as a reference light.[6] The light emitting device according to any one of [1] to [5], wherein a specific color rendering index R9 is not less than 96.8 when light having a color temperature of 6500K is used as a reference light.According to an embodiment of the disclosure, a light emitting device can be provided whose emission spectrum intensity is relatively increased in the deep red region so that a decrease in color rendering properties is suppressed.Next, the present disclosure will be explained in more detail in conjunction with the accompanying drawings, of which: FIG. 1 is a vertical cross-sectional view showing a light emitting device in an embodiment; FIG. 2 is a graph showing emission spectra of light emitting devices when a combination of phosphors and a ratio between concentrations thereof are adjusted so that the emission spectrum has a shape close to that of evening sunlight having a color temperature of 3000 K; and FIG. 3 is a graph showing emission spectra of light emitting devices when a combination of phosphors and a ratio between concentrations thereof are adjusted so that the emission spectrum has a shape close to morning to afternoon sunlight with a color temperature of 6500K.FIG. 1 is a vertical cross-sectional view showing a light emitting device 1 in an embodiment. The light emitting device 1 includes a case 10 having a recessed portion 10 a, a lead frame 11 contained in the case 10 so as to be exposed on the bottom of the recessed portion 10 a, a light emitting element 12 mounted on the lead frame 11, connection wires (bonding wires) 13 electrically connecting the lead frame 11 to electrodes of the light emitting element 12, a sealing resin 14 filled in the recessed portion 10 afor sealing the light emitting element 12, and a specific phosphor (phosphor) 15 contained in the sealing resin 14.The housing 10 is formed by injection molding or transfer molding using, for example, a thermoplastic resin such as polyphtalamide resin, LCP (liquid crystal polymer), or PCT (polycyclohexylene dimethylene terephthalate), or a thermosetting resin such as silicone resin, modified silicone resin, epoxy resin, or modified epoxy resin. The housing 10 may contain light reflecting particles of titanium dioxide, etc. for improving light reflection.For example, the whole or the surface of the lead frame 11 is formed of a conductive material such as Ag, Cu, or Al.The light emitting element 12 is typically an LED element or a laser diode element. The light emitting element 12 is an upward-facing type element (front-up) connected to the lead frame 11 via the connection wires 13 in the example shown in FIG. 1, but may be a downward-facing type element (front-down) or may be connected to the lead frame via a connection member other than connection wires, e.g., via conductive dimples.The light emitting element 12 emits light having a peak wavelength (peak wavelength) in a range of 380 nm to 460 nm (the range of not less than 380 nm and not more than 460 nm). Since phosphors (phosphors) included in the phosphor 15 (described later) can be efficiently excited by light having a wavelength of not more than 460 nm, the peak wavelength of the light emitted from the light emitting element 12 is preferably not more than 460 nm.On the other hand, if the peak wavelength of the light emitted from the light emitting element 12 is too short, the emission spectrum of the light emitting device 1 is less likely to be close to that of sunlight due to too large a valley between the peak of the emission spectrum of the light emitting element 12 and that of the phosphor 15. Therefore, the peak wavelength of the light emitted from the light emitting element 12 is preferably not less than 380 nm.The sealing resin 14 is formed of, for example, a resin material such as silicone-based resin or epoxy-based resin.The phosphor 15 is a phosphor that is excited by light emitted from the light emitting element 12 and emits fluorescence. The phosphor 15 is a phosphor group consisting of a plurality of kinds of phosphors, has a continuous emission spectrum (never having zero intensity) over at least a wavelength range of 400 nm to 780 nm, and has a phosphor emitting deep red light (hereinafter referred to as "deep red phosphor") having a peak wavelength in a range of 720 nm±5%, so that the light emitting device 1 can have an emission spectrum close to that of sunlight.The deep red phosphor is formed of an oxide containing Gd and Ga, and is, for example, a Cr-activated Gd 3 Ga 5 O 12( Gd 3 Ga 5 O 12: Cr 3+) etc. The deep red phosphor can relatively increase an intensity in the deep red region of the emission spectrum of the light emitting device 1, thereby preventing the emission spectrum in the deep red region from being different from the spectrum of sunlight or halogen light.In addition, it is preferable that the phosphor 15 also includes at least one kind of blue phosphor having a peak wavelength in a range from 445 nm to 490 nm, at least one kind of yellow-green phosphor having a peak wavelength in a range from 491 nm to 600 nm, and at least one kind of red phosphor having a peak wavelength in a range from 601 nm to 670 nm, so that the light emitting device 1 has a continuous emission spectrum over a wavelength range from 400 nm to 780 nm.The usable blue phosphor having a peak wavelength in a range of 445 nm to 490 nm is, for example, an alkaline earth halophosphate phosphor. The main compositions of the alkaline earth halophosphate phosphor are shown below in Table 1. Table 1 Table 1Alkaline Earth Halophosphate Phosphor(Ba, Sr, Ca, Mg) 5( PO 4)3 Cl:Eu 2+(Ba,Sr,Ca,Mg ) 10( PO 4)6 Cl 2: Eu 2+The emission spectrum of the alkaline earth halophosphate phosphor can be changed by changing concentrations of Eu as an activator or Ba, Sr, Ca, Mg as alkaline earth metals.The usable yellow-green phosphors having a peak wavelength in a range of 491 nm to 600 nm are, for example, Ca solid solution α-sialon phosphor, β-sialon phosphor, silicate phosphor, nitride phosphor, LSN phosphor, YAG phosphor and LuAG phosphor. The main compositions of these phosphors are shown below in Table 2. Table 2 Table 2Ca solid solution α-sialon phosphorCa-Si 12-(m+n) Al m+n O n N 16-n: Eu 2+β-sialon phosphorSi 6-z Al z O z N 8-z: Eu 2+Silicate Phosphor(Ca,Sr,Ba) 3 SiO 5: Eu 2+(Ba,Sr,Ca) 2 SiO 4: Eu 2+Nitride phosphor(Ca,Sr,Ba) 2 Si 5 N 8: Eu 2+LSN phosphor(La,Ca) 3 Si 6 N 11: Ce 3+YAG phosphor(Y,Gd) 3( Al,Ga) 5 O 12: Ce3+LuAG phosphorLu3(Al,Ga) 5 O 12: Ce 3+The emission spectra of the YAG phosphor and the LuAG phosphor can be changed by changing concentrations of Ce as an activator or Gd, Ga.The usable red phosphors having a peak wavelength in a range of 601 nm to 670 nm are, for example, CASN phosphor, SCASN phosphor, and CASON phosphor. The main compositions of these phosphors are shown below in Table 3. Table 3 Table 3CASN phosphorCaAlSiN 3: Eu 2+SCASN phosphor(Sr,Ca)AlSiN 3: Eu 2+CASON phosphorCaAlSi(O,N) 3: Eu 2+The emission spectra of the CASN phosphor, the SCASN phosphor, and the CASON phosphor can be changed by changing concentrations of Eu as an activator or Sr, Ca as alkaline earth metals.A combination of the phosphors constituting the phosphor 15 and a ratio between concentrations thereof are adjusted so that the emission spectrum of the light emitting device 1 is close to that of sunlight, for example, so that color rendering indices Rf, Rg, a general color rendering index Ra, and a specific color rendering index Ri (i=9 to 15) are close to 100 when sunlight is used as a reference light.The general color rendering index Ra and the specific color rendering index Ri (i=9 to 15) are parameters for numerically evaluating color rendering properties used in methods for specifying color rendering properties of light sources ("Method of specifying color rendering properties of light sources", JIS Z 8726:1990) specified by Japanese Industrial Standard. The closer the numerical values are to 100, the closer they are to the reference light (sunlight, etc.).Meanwhile, the color rendering indices Rf and Rg are color rendering indices used in TM-30-15, which is a novel method for evaluating color rendering properties of a light source defined by the North America lighting engineering society (IES).Rf is a parameter indicating color fidelity, and is obtained by a test based on a comparison with 99 colors. Thus, evaluation of the color fidelity by Rf is more accurate than by the general color fidelity index Ra. The maximum Rf is 100. The closer the Rf is to 100, the closer the color of the test light is to the color of the reference light (sunlight, etc.).Rg is a parameter indicating color brightness (color clarity), and is not used in the conventional evaluation methods. The closer the Rg is to 100, the closer the color brightness (color clarity) of the test light is to the reference light (sunlight, etc.). The value of Rg may be less than or greater than 100.The configuration of the phosphor 15 provided in the light emitting device 1 is not particularly limited. For example, the phosphor 15 may be dispersed in the sealing resin 14 or may be deposited on the bottom of the sealing resin 14. In addition, the phosphor 15 may be contained in a phosphor layer coated on the light emitting element.In addition, the configuration of the light emitting device 1 is not limited to that shown in the present embodiment as long as the light emitting element 12 and the phosphor 15 are provided. For example, the light emitting device 1 may be a surface-mount device (SMD) as shown in FIG. 1, or may be a chip-on-board (COB) device.According to the embodiment, it is possible to provide the light emitting device 1 having an emission spectrum in which an intensity in the deep red region is relatively increased to solve the problem of lack of color in the deep red region while suppressing a decrease (deterioration) in color reproduction characteristics.The light emitting device 1 in the embodiment having an emission spectrum closer to that of sunlight than conventional devices has high (good) color rendering properties and can present the true color in an interior environment (for example, in a building), and is therefore suitable for lighting / illuminating food / food or clothes / cloth. In addition, the light emitting device 1 is suitable for a color test and can be used for evaluating, for example, a paint / (paint) color of a vehicle, etc.Example 1FIG. 2 is a diagram showing emission spectra of the light emitting devices 1 ( 1 a, 1 b) and a light emitting device 2 when a combination of the phosphors constituting the phosphor 15 and a ratio between concentrations thereof are adjusted so that the emission spectrum has a shape close to that of evening sunlight having a color temperature of 3000 K. Each emission spectrum shown in FIG. 2 is normalized so that the respective spectral flux (density) (W / nm) has the maximum value of 1.The light emitting device 2 is a light emitting device provided as a comparative example and having no deep red phosphor in the phosphor 15, and the configuration of the light emitting device 2 excluding the phosphor 15 is the same as that of the light emitting devices 1 ( 1 a, 1 b).The light emitting devices 1 ( 1 a, 1 b) in FIG. 2 have the phosphor 15 made of two kinds of alkaline earth halophosphate phosphors as blue phosphors, a β-sialon phosphor as a yellow-green phosphor, a CASON phosphor as a red phosphor, and a Cr-activated Gd 3 Ga 5 O 12 as a deep red phosphor. The phosphor 15 of the light emitting device 2 includes these phosphors except for the Cr-activated Gd 3 Ga 5 O 12, which is contained in the phosphor 15 of the light emitting devices 1 ( 1 a, 1 b).Table 4 below shows characteristics of the above-listed phosphors representing the phosphors 15 of the light-emitting devices 1 ( 1 a, 1 b) and the light-emitting device 2 in FIG. 2. Table 4 Table 4Alkaline Earth Halophosphate Phosphor405455590,1650,177Alkaline Earth Halophosphate Phosphor405482830,1760,291β-sialon phosphor405544550,3640,615CASON phosphor4056391250,5760,417Cr-activated Gd 3 Ga 5 O 12450739900,4890,517Table 5 below shows a relationship between concentrations of the phosphors constituting the phosphor 15 of the light-emitting devices 1 ( 1 a, 1 b) and the light-emitting device 2 in FIG. 2. In Table 5, "phosphor concentration" is a value (wt %) of the ratio of the mass of the phosphors 15 to the total mass of the sealing resin 14 formed of a methyl-based silicone and the phosphors 15.In addition, "phosphor concentration ratio" in Table 5 is a value (wt %) of the ratio of the mass of each phosphor to the mass of the phosphors 15 (all the phosphors), and "SCA1", "SCA2", "β", "CASON", and "GGG" respectively denote an alkaline earth halophosphate phosphor (peak wavelength of 455 nm), another alkaline earth halophosphate phosphor (peak wavelength of 482 nm), a β-sialon phosphor, a CASON phosphor, and a Cr-activated Gd 3 Ga 5 O 12. Table 5 Table 5Light Emitting Device 25531,647,43,817,20Light Emitting Device 1 a56,729,544,23,516,07,5Light Emitting Device 1 b58,627,441,12,415,313,8Table 6 below shows the color rendering indices Rf, Rg, the color rendering indices R1 to R8, the general color rendering index Ra, and the specific color rendering index Ri (i=9 to 15) of the light emitting devices 1 (1a, 1b) and the light emitting device 2 in FIG. 2 when evening sunlight having a color temperature of 3000 K is used as a reference light. Here, the general color rendering index Ra is an average of the color rendering indices R 1 to R 8. Table 6 Table 6Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf96,797,498,2Rg101,2100,799,6RaRa97,998,398,6R198,599,399,8R299,899,598,8R396,096,396,4R496,697,498,3R598,499,199,8R698,699,499,5R798,598,899,5R897,197,097,0R992,091,490,7R1097,897,196,1R1194,996,097,0R1297,297,797,0R1398,699,599,6R1496,797,097,3R1599,098,698,0As shown in Table 6, the color rendering indices of the light emitting devices 1 ( 1 a, 1 b) are equivalent to or better than the color rendering indices of the light emitting device 2, which shows that when evening sunlight having a color temperature of 3000 K is used as a reference light, a decrease (deterioration) in color rendering properties of the emission spectrum of the light emitting device is suppressed even when a deep red phosphor is added to the phosphor 15 to increase a red component.For example, as shown in Table 6, the color rendering indices of the light emitting devices 1 when evening sunlight having a color temperature of 3000 K is used as a reference light may be such that Rf is not less than 97.4, a difference (deviation) of 100 from Rg is not more than 0.7, and Ra is not less than 98.3. Note that, as compared with evening sunlight having a color temperature of 3000 K, the desirable Rf is not less than 95, and the desirable difference (deviation) from 100 of Rg is not more than 5.In addition, as shown in FIG. 2, an intensity in the red region of the emission spectrum, particularly in the deep red region at not less than 700 nm, is stronger in the light emitting devices 1 ( 1 a, 1 b) than in the light emitting device 2.In the case of the light emitting device 2, simply adding a Cr-activated Gd 3 Ga 5 O 12 to the phosphor 15 causes a relative decrease in a blue component and a resultant decrease in color rendering properties. In such a case, a mixing ratio of phosphors needs to be adjusted in the same manner as in the light emitting devices 1 ( 1 a, 1 b) so as to improve the color rendering index.Example 2FIG. 3 is a diagram showing emission spectra of the light emitting devices 1 ( 1 c, 1 d) and a light emitting device 3 when a combination of the phosphors constituting the phosphor 15 and a ratio between concentrations thereof are adjusted so that the emission spectrum has a shape close to morning to afternoon sunlight having a color temperature of 6500K. Each emission spectrum shown in FIG. 3 is normalized such that the respective spectral radiation flux (spectral radiation density) (W / nm) has the maximum value of 1.The light emitting device 3 is a light emitting device provided as a comparative example and having no deep red phosphor in the phosphor 15, and the configuration of the light emitting device 3 excluding the phosphor 15 is the same as that of the light emitting devices 1 ( 1 c, 1 d).The light emitting devices 1 ( 1 c, 1 d) in FIG. 3 have the phosphor 15 consisting of two kinds of alkaline earth halophosphate phosphors as blue phosphors, a β-sialon phosphor and a Ca solid solution α-sialon phosphor as yellow-green phosphors, a CASON phosphor as a red phosphor, and a Cr-activated Gd 3 Ga 5 O 12 as a deep red phosphor. The phosphor 15 of the light emitting device 3 includes these phosphors except for the Cr-activated Gd 3 Ga 5 O 12, which is contained in the phosphor 15 of the light emitting devices 1 ( 1 c, 1 d).Table 7 below shows characteristics of the Ca solid solution α-sialon phosphor constituting the phosphor 15 of the light emitting devices 1 ( 1 c, 1 d) and the light emitting device 3 in FIG. 3. The characteristics of the other phosphors are the same as those shown in Table 4. Table 7 Table 7Ca solid solution α-sialon phosphor405594840,5460,444Table 8 below shows a relationship between concentrations of the phosphors representing the phosphors 15 of the light-emitting devices 1 ( 1 c, 1 d) and the light-emitting device 3 in FIG. 3. In Table 8, "phosphor concentration" is a value (wt %) of the ratio of the mass of the phosphors 15 to the total mass of the sealing resin 14 formed of a methyl-based silicone and the phosphors 15.In addition, "phosphor concentration ratio" in Table 8 is a value (wt %) of the ratio of the mass of each phosphor to the mass of the phosphors 15 (all the phosphors), and "α" denotes the Ca solid solution α-sialon phosphor. The abbreviated names of the other phosphors are the same as shown in Table 5. Table 8 Table 8Light Emitting Device 33363,229,80,92,14,00Light Emitting Device 1 c31,958,417,50,71,25,316,9Light Emitting Device 1 d36,265,57,30,41,24,720,8Table 9 below shows the color rendering indices Rf, Rg, the color rendering indices R1 to R8, the general color rendering index Ra, and the specific color rendering index Ri (i=9 to 15) of the light emitting devices 1 (1c, 1d) and the light emitting device 3 in FIG. 3 when morning to afternoon sunlight having a color temperature of 6500K is used as a reference light. Table 9 Table 9Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf Rf94,796,295,4Rg99,6100,7100,3RaRa94,896,396,1R196,695,596,4R295,696,196,0R394,196,494,6R497,296,097,2R596,295,696,6R692,794,694,6R793,997,896,4R892,298,997,1R983,697,896,8R1090,090,989,9R1195,093,395,1R1291,393,593,6R1396,095,195,7R1496,997,996,8R1599,396,998,2As shown in Table 9, the color rendering indices of the light emitting devices 1 ( 1 c, 1 d) are equivalent to or better than the color rendering indices of the light emitting device 3.For example, according to Table 9, the color rendering indices of the light emitting devices 1 when morning to night sunlight having a color temperature of 6500K is used as a reference light may be such that Rf is not less than 95.4, a difference (deviation) of 100 from Rg is not more (greater) than 0.7, Ra is not less than 96.1, and R9 (red) is not less (less) than 96.8. Note that, as compared with morning to afternoon sunlight having a color temperature of 6500K, the desirable Rf is not less than 95 and the desirable difference (deviation) from 100 of Rg is not more than 5.In addition, as shown in FIG. 3, an intensity in the red region of the emission spectrum, particularly in the deep red region at not less than 700 nm, is stronger in the light emitting devices 1 ( 1 c, 1 d) than in the light emitting device 3.In the case of the light emitting device 3, simply adding a Cr-activated Gd 3 Ga 5 O 12 to the phosphor 15 causes a relative decrease in a blue component and a resultant decrease in color rendering properties. In such a case, a mixing ratio of phosphors needs to be adjusted in the same manner as in the light emitting devices 1 ( 1 c, 1 d) so as to improve the color rendering index.Although the embodiment and examples of the disclosure have been described, the invention is not intended to be limited to the embodiment and the examples, and the various kinds of modifications can be made without departing from the spirit of the invention.For example, although in the examples, evening sunlight having a color temperature of 3000 K and morning to night sunlight having a color temperature of 6500 K are used as the reference, light to be used as the reference is not limited thereto. For example, using, for example, sunlight having a given color temperature in a range of 2000 to 9000K or light of a halogen lamp as a reference, an intensity in the deep red region of the emission spectrum can be relatively increased while suppressing a decrease (deterioration) in color rendering properties.In addition, the invention according to the claims is not limited to the embodiment and the examples. Further, it should be noted that all combinations of the features described in the embodiment and the examples are not necessary for solving the problem of the invention.It is explicitly stated that all features disclosed in the specification and / or the claims are intended to be disclosed separately and independently of each other both for the purpose of original disclosure and for the purpose of limiting the claimed invention, independently of the compilation of features in the embodiments and / or the claims. It is explicitly explained that all value ranges or indications of groups of objects disclose each possible intermediate value or any possible intermediate object both for the purpose of the original disclosure and for the purpose of limiting the claimed invention, in particular for determining the limits of value ranges.

Claims

A light emitting device comprising: a light emitting element configured to emit light having a peak wavelength in a range of 380 nm to 460 nm; and a phosphor group including a plurality of kinds of phosphors excited by the light emitted from the light emitting element and having a continuous emission spectrum in a wavelength range of 400 nm to 780 nm, wherein the phosphor group includes a phosphor having a peak wavelength in a range of 720 nm±5%, and wherein the phosphor group includes two kinds of alkaline earth halophosphate phosphors, a β-sialon phosphor, a Ca solid solution α-sialon phosphor, and a CASON phosphor.The light emitting device of claim 1, wherein said phosphor having the peak wavelength in the range of 720 nm±5% comprises an oxide comprising Gd and Ga.The light emitting device of claim 2, wherein the phosphor comprises a Cr-activated Gd 3 Ga 5 O 12.The light emitting device according to any one of claims 1 to 3, wherein a color rendering index Rf is not less than 95 when light having a color temperature of 3000K is used as a reference light, and a difference of a color rendering index Rg of 100 is not more than 5 when light having a color temperature of 3000K is used as a reference light.The light emitting device according to any one of claims 1 to 4, wherein a color rendering index Rf is not less than 95 when light having a color temperature of 6500K is used as a reference light, and a difference of a color rendering index Rg of 100 is not more than 5 when light having a color temperature of 6500K is used as a reference light.The light emitting device according to any one of claims 1 to 5, wherein a specific color rendering index R9 is not less than 96.8 when light having a color temperature of 6500K is used as a reference light.

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