Abstract:
A light emitting device includes a first light emitting element, a second light emitting element, a first phosphor sheet containing a first phosphor and a third phosphor, and covering a top face of the first light emitting element, and a second phosphor sheet containing a second phosphor and a fourth phosphor, and covering a top face of the second light emitting element, wherein a peak wavelength of light which is wavelength-converted by the first phosphor or the third phosphor is equal to or less than a peak wavelength of light which is wavelength-converted by the second phosphor or the fourth phosphor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority of prior Japanese Patent Application No. 2014-254411, filed on Dec. 16, 2014, the entire contents of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    Embodiments discussed in the present specification relate to a light emitting device including a semiconductor light emitting element. 
       BACKGROUND 
       [0003]    In recent years, a light emitting device obtaining white light by a combination of a semiconductor light emitting element such as a blue LED (Light-Emitting Diode) and a phosphor is in use. In particular, as such a light emitting device, a light emitting device including a semiconductor light emitting element of a blue LED and a plurality of phosphors to obtain white light of more natural tint (i.e., higher color rendering index) is known. 
         [0004]    For example, Japanese Laid-open Patent Publication No. 2007-243056 describes a light emitting device including two blue LED chips emitting blue light. The light emitting device includes: a first phosphor layer made of a first phosphor stacked on one of the LED chips and excited by light emitted from the LED chip to emit green light; and a second phosphor layer made of a second phosphor stacked on the other LED chip and excited by light emitted from the LED chip to emit red light. 
       SUMMARY 
       [0005]    The light emitting device described in Japanese Laid-open Patent Publication No. 2007-243056 can obtain white light from blue light emitted from one of the LED chips and output from the first phosphor layer, green light which is wavelength-converted by the first phosphor layer, blue light emitted from the other LED chip and output from the second phosphor layer, and red light which is wavelength-converted by the second phosphor layer. 
         [0006]    On the other hand, by combining the larger number of lights having different wavelengths, the intensity of the light becomes higher at all wavelengths, and white light of more natural tint (i.e., higher color rendering index) can be obtained. However, when the number of light emitting elements such as LED chips is increased in a light emitting device, the size and cost of the light emitting device increase. It is consequently desirable that a plurality of different types of phosphors be included in a phosphor layer stacked on a light emitting element so that light having the larger number of different wavelengths can be emitted on the basis of outgoing light from one light emitting element. 
         [0007]    However, when a plurality of different types of phosphors is included in a phosphor layer, there is the possibility that light which is wavelength-converted by a specific phosphor is absorbed by another phosphor and is again wavelength-converted. To obtain desired light, the amount of phosphors included in a phosphor layer is preferably adjusted in consideration of the fact that light which is wavelength-converted by a specific phosphor is absorbed by another phosphor. Depending on combinations of phosphors included in a phosphor layer, a large amount of phosphors is necessary. When the amount of the phosphors increases, light transmittance becomes lower, and the intensity of light to be emitted becomes lower. 
         [0008]    There is also the possibility that, depending on combinations of phosphors included in a phosphor layer, manufacturing variations in colors of lights emitted from respective phosphor layers become larger due to errors in manufacture in the amounts of the phosphors included in the phosphor layers. 
         [0009]    An object is to obtain white light having higher light intensity in a light emitting device using a plurality of light emitting elements and a plurality of phosphors and to reduce manufacturing variations of the light emitting device. 
         [0010]    A light emitting device according to an embodiment includes a first light emitting element, a second light emitting element, a first phosphor sheet containing a first phosphor and a third phosphor different from the first phosphor, and covering a top face of the first light emitting element, and a second phosphor sheet containing a second phosphor different from the first phosphor and a fourth phosphor different from the second phosphor, and covering a top face of the second light emitting element, wherein a peak wavelength of light which is wavelength-converted by the first phosphor is equal to or less than a peak wavelength of light which is wavelength-converted by the second phosphor and is equal to or less than a peak wavelength of light which is wavelength-converted by the fourth phosphor, and a peak wavelength of light which is wavelength-converted by the third phosphor is equal to or less than the peak wavelength of light which is wavelength-converted by the second phosphor and is equal to or less than a peak wavelength of light which is wavelength-converted by the fourth phosphor. 
         [0011]    Preferably, the light emitting device further includes a white reflection resin provided between the first phosphor sheet and the second phosphor sheet. 
         [0012]    Preferably, the white reflection resin is provided in a position interrupting a portion between a side face of the first phosphor sheet and a side face of the second phosphor sheet opposed to the side face of the first phosphor sheet. 
         [0013]    A light emitting device according to an embodiment includes a first light emitting element, a second light emitting element, a third light emitting element, a first phosphor sheet containing a first phosphor and covering a top face of the first light emitting element, a second phosphor sheet containing a second phosphor different from the first phosphor and covering a top face of the second light emitting element, and a third phosphor sheet containing a third phosphor and a fourth phosphor different from the third phosphor and covering a top face of the third light emitting element, and a second white reflection resin provided between the second phosphor sheet and third phosphor sheet, wherein a peak wavelength of light which is wavelength-converted by the first phosphor is equal to or less than a peak wavelength of light which is wavelength-converted by the second phosphor, and a peak wavelength of light which is wavelength-converted by the second phosphor is equal to or less than the peak wavelength of light which is wavelength-converted by the third phosphor and is equal to or less than a peak wavelength of light which is wavelength-converted by the fourth phosphor. 
         [0014]    Preferably, the light emitting device further includes a white reflection resin provided between the first phosphor sheet and the second phosphor sheet, and a second white reflection resin provided between the second phosphor sheet and the third phosphor sheet. 
         [0015]    Preferably, the white reflection resin is provided in a position interrupting a portion between a side face of the first phosphor sheet and a side face of the second phosphor sheet opposed to the side face of the first phosphor sheet, and the second white reflection resin is provided in a position interrupting a portion between a side face of the second phosphor sheet and a side face of the third phosphor sheet opposed to the side face of the second phosphor sheet. 
         [0016]    In a light emitting device using a plurality of light emitting elements and a plurality of phosphors, it is possible to obtain white light having higher light intensity and to reduce manufacturing variations of the light emitting device. 
         [0017]    Other features and advantages of the present light emitting device will be apparent from the ensuing description, taken in conjunction with the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1A  is a schematic top view of a light emitting device  10 ; 
           [0019]      FIG. 1B  is a schematic cross section of a light emitting device  10 ; 
           [0020]      FIG. 2A  is a graph schematically illustrating spectra of lights emitted from LEDs and phosphors; 
           [0021]      FIG. 2B  is a graph schematically illustrating spectra of lights emitted from LEDs and phosphors; 
           [0022]      FIG. 2C  is a graph schematically illustrating spectra of lights emitted from LEDs and phosphors; 
           [0023]      FIG. 2D  is a graph schematically illustrating spectra of lights emitted from LEDs and phosphors; 
           [0024]      FIG. 2E  is a graph schematically illustrating spectra of lights emitted from LEDs and phosphors; 
           [0025]      FIG. 3  is a graph schematically illustrating spectra of lights emitted by the light emitting device  10  and a phosphor sheet for comparison; 
           [0026]      FIG. 4  is a CIExy chromaticity diagram of phosphors; 
           [0027]      FIG. 5A  is a schematic top view of a light emitting device  20 ; and 
           [0028]      FIG. 5B  is a schematic cross section of a light emitting device  20 ; and 
           [0029]      FIG. 6A  is a schematic top view of a light emitting device  30 . 
           [0030]      FIG. 6B  is a schematic cross section of a light emitting device  30 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0031]    Hereinafter, light emitting devices according to an embodiment, will be described with reference to the drawings. However, it should be noted that the technical scope of the invention is not limited to these embodiments, and extends to the inventions described in the claims and their equivalents. 
         [0032]      FIG. 1A  is a schematic top view of a light emitting device  10 .  FIG. 1B  is a cross section taken along line  1 B- 1 B in  FIG. 1A . 
         [0033]    The light emitting device  10  includes a plurality of blue LEDs  11 A and  11 B, a plurality of phosphor sheets  12 A and  12 B, white reflection resins  13 A and  13 B, a diffusion resin  14 , and a substrate  15 . 
         [0034]    Each of the blue LEDs  11 A and  11 B is flip-chip bonded on the substrate  15  and connected to the substrate  15  via bumps  16 . The top face of the blue LED  11 A is covered with the phosphor sheet  12 A containing a specific phosphor, and the top face of the blue LED  11 B is covered with the phosphor sheet  12 B containing a phosphor different from the phosphor contained in the phosphor sheet  12 A. Consequently, the light emitting device  10  mixes light emitted from the blue LED  11 A and output from the phosphor sheet  12 A, light which is wavelength-converted by the phosphor sheet  12 A, light emitted from the blue LED  11 B and output from the phosphor sheet  12 B, and light which is wavelength-converted by the phosphor sheet  12 B to obtain white light. 
         [0035]    The blue LEDs  11 A and  11 B are semiconductor blue-light-emitting elements (blue elements). For the blue LEDs  11 A and  11 B, for example, an InGaN compound semiconductor having a light emission wavelength range of 440 to 455 nm is used. As the blue LEDs  11 A and  11 B, preferably, LEDs whose forward voltage (VF), temperature characteristics, life, and the like considered to be almost equal to each other, are used. Consequently, it is preferable to use LEDs using, as materials, compound semiconductors of the same series as the blue LEDs  11 A and  11 B. 
         [0036]    The phosphor sheet  12 A includes a colorless transparent resin such as epoxy resin or silicon resin and covers the top face of the blue LED  11 A. In the phosphor sheet  12 A, phosphors  17 A and  17 B are dispersedly mixed. The phosphor sheet  12 B includes a colorless transparent resin such as epoxy resin or silicon resin and covers the top face of the blue LED  11 B. In the phosphor sheet  12 B, phosphors  17 C and  17 D are dispersedly mixed. 
         [0037]    The phosphor  17 A is a particulate phosphor material that absorbs blue light emitted from the blue LED  11 A and wavelength-converts the light to cyan light. The range of the peak wavelength of the light which is wavelength-converted by the phosphor  17 A is 480 to 500 nm. As the phosphor  17 A, for example, a silicate phosphor which is activated by Eu 2+  (europium), a phosphor of barium silicon oxynitride, or the like is used. 
         [0038]    The phosphor  17 B is a phosphor different from the phosphor  17 A and is a particulate phosphor material that absorbs blue light emitted from the blue LED  11 A and wavelength-converts the light to yellow light. The range of the peak wavelength of the light which is wavelength-converted by the phosphor  17 B is 535 to 570 nm. As the phosphor  17 B, for example, a YAG (yttrium aluminum garnet) phosphor which is activated by cerium or the like is used. 
         [0039]    The phosphor  17 C is a phosphor different from the phosphors  17 A and  17 B and is a particulate phosphor material that absorbs blue light emitted from the blue LED  11 B and wavelength-converts the light to yellow light. The range of the peak wavelength of the light which is wavelength-converted by the phosphor  17 C is 535 to 570 nm. As the phosphor  17 C, for example, a YAG (yttrium aluminum garnet) phosphor which is activated by cerium or the like is used. The phosphor  17 C may be the same phosphor as the phosphor  17 B. 
         [0040]    The phosphor  17 D is a phosphor different from the phosphors  17 A,  17 B, and  17 C and is a particulate phosphor material that absorbs blue light emitted from the blue LED  11 B and wavelength-converts the light to red light. The range of the peak wavelength of the light which is wavelength-converted by the phosphor  17 C is 600 to 630 nm. As the phosphor  17 D, for example, a CaAlSiN 3  (calcium aluminum silicon oxynitride) phosphor in which Eu 2+  (europium) is dissolved or the like is used. 
         [0041]    The peak wavelength of the cyan light which is wavelength-converted by the phosphor  17 A is set to be equal to or less than the peak wavelength of the yellow light which is wavelength-converted by the phosphor  17 B. The peak wavelength of the yellow light which is wavelength-converted by the phosphor  17 B is set to be equal to or less than the peak wavelength of the yellow light which is wavelength-converted by the phosphor  17 C. The peak wavelength of the yellow light which is wavelength-converted by the phosphor  17 C is set to be equal to or less than the peak wavelength of the red light which is wavelength-converted by the phosphor  17 D. 
         [0042]    The white reflection resin  13 A is, for example, obtained by kneading reflective particles of titanium oxide, alumina, or the like into silicon resin and thermo-setting the resultant. The white reflection resin  13 A is disposed on the substrate  15  so as to cover the side faces of the light emitting device  10 . The white reflection resin  13 A reflexes light output from the phosphor sheets  12 A and  12 B to the inside of the light emitting device  10 . 
         [0043]    The white reflection resin  13 B is, like the white reflection resin  13 A, for example, obtained by kneading reflective particles of titanium oxide, alumina, or the like into silicon resin and thermo-setting the resultant. The white reflection resin  13 B is disposed on the substrate  15  so as to be provided between the phosphor sheets  12 A and  12 B. The white reflection resin  13 B is provided in a position interrupting at least the portion between the side face of the phosphor sheet  12 A and the side face of the phosphor sheet  12 B opposed to the side face of the phosphor sheet  12 A. The white reflection resin  13 B reflexes light output from the phosphor sheet  12 A to the phosphor sheet  12 A side, and reflexes light output from the phosphor sheet  12 B to the phosphor sheet  12 B side. By the white reflection resin  13 B, light emitted from the phosphor sheet  12 A is prevented from being absorbed by the phosphors  17 C and  17 D contained in the phosphor sheet  12 B. 
         [0044]    The diffusion resin  14  is obtained by, for example, making a light diffusion agent of titanium oxide or the like contained in a transparent resin base material and is disposed so as to seal a region surrounded by the substrate  15  and the white reflection resin  13 A. The diffusion resin  14  seals and protects the blue LEDs  11 A and  11 B and the phosphor sheets  12 A and  12 B, and uniformly irradiates and diffuses light emitted from the phosphor sheets  12 A and  12 B. 
         [0045]    The substrate  15  is, for example, an insulating substrate such as a glass epoxy substrate, a BT resin substrate, a ceramic substrate, or a metal core substrate having a surface on which the blue LEDs  11 A and  11 B are mounted. On the substrate  15 , electrodes (not illustrated) for bonding the blue LEDs  11 A and  11 B and a circuit pattern (not illustrated) are formed. Each of the electrodes of the blue LEDs  11 A and  11 B is flip-chip bonded on the substrate  15  and electrically connected to bonding electrodes on the substrate  15  via the bump  16 . Each of the electrodes of the blue LEDs  11 A and  11 B may be bonded to bonding electrodes on the substrate  17  via a conductive adhesive material such as Ag paste, a wire by wire bonding, or the like. Further, the bonding electrodes on the substrate  17  are electrically connected to electrodes (not illustrated) for connection to a DC (Direct Current) power supply on the outside. 
         [0046]      FIGS. 2A to 2E  and  FIG. 3  are graphs schematically illustrating spectra of lights emitted from LEDs and the phosphor. The horizontal axis of each of  FIGS. 2A to 2E  and  FIG. 3  indicates wavelength which becomes longer to the right. The vertical axis of each of  FIGS. 2A to 2E  and  FIG. 3  indicates intensity of light which becomes higher to the upside. 
         [0047]    Graph  201  in  FIG. 2A  indicates spectrum of blue light emitted from the blue LED  11 A according to an example, graph  202  indicates spectrum of cyan light which is wavelength-converted by the phosphor  17 A according to an example, and graph  203  indicates spectrum of yellow light which is wavelength-converted by the phosphor  17 B according to an example. In  FIG. 2A , spectra of lights normalized are displayed. 
         [0048]    Graph  211  in  FIG. 2B  indicates spectrum of light emitted from the phosphor sheet  12 A. In the spectrum illustrated in  FIG. 2B , respective peaks of intensities exist around peak wavelength λ 1  of the blue light and peak wavelength λ 2  of the cyan light. In the phosphor sheet  12 A, the amount of the phosphors  17 A and  17 B contained in the phosphor sheet  12 A is adjusted so that the intensity of the blue light is not too low. Consequently, the intensity in the peak wavelength λ 2  of the cyan light is lower than the peak in the peak wavelength λ 1  of the blue light and, in a region where the wavelength is longer than the peak wavelength λ 2 , the wave shape base becomes broader and the intensity gently decreases as the wavelength becomes longer. 
         [0049]    Graph  221  in  FIG. 2C  indicates spectrum of blue light emitted from the blue LED  11 B according to an example, graph  222  indicates spectrum of yellow light which is wavelength-converted by the phosphor  17 C according to an example, and graph  223  indicates spectrum of red light which is wavelength-converted by the phosphor  17 D according to an example. In  FIG. 2C , spectra of lights normalized are displayed. 
         [0050]    Graph  231  in  FIG. 2D  indicates spectrum of light emitted from the phosphor sheet  12 B. In the spectrum illustrated in  FIG. 2D , respective peaks of intensities exist around peak wavelength λ 3  of the blue light and peak wavelength λ 4  of the red light. In the phosphor sheet  12 B, blue light emitted from the blue LED  11 B is absorbed by the phosphors  17 C and  17 D, and the yellow light which is wavelength-converted by the phosphor  17 C is absorbed by the phosphor  17 D. Consequently, the intensity of the blue light and the yellow light is low. However, the wave shape base whose peak is wavelength λ 4  becomes broader and the intensity gently decreases. 
         [0051]    Graph  241  in  FIG. 2E  indicates spectrum of the entire light output from the light emitting device  10 . Since the white reflection region  13 B is provided between the phosphor sheets  12 A and  12 B in the light emitting device  10 , the light emitted from the phosphor sheet  12 A is not absorbed by the phosphors  17 C and  17 D. Therefore, as illustrated in  FIG. 2E , the spectrum of the light emitted from the light emitting device  10  almost matches a spectrum obtained by adding the intensities illustrated in graph  231  in  FIG. 2D  to the intensities illustrated in graph  211  in  FIG. 2B  at the respective wavelengths. 
         [0052]    In the spectrum illustrated in  FIG. 2E , a wavelength of low intensity does not exist, and the intensity is high in the entire wavelength. Therefore, the light emission spectrum of the entire light emitting device  10  is close to the spectrum of solar light, and white light emitted from the light emitting device  10  is white light of more natural tint (i.e., higher color rendering index). 
         [0053]    Graph  301  in  FIG. 3  indicates spectrum of light emitted from the light emitting device  10  and graph  302  indicates spectrum of light emitted in the case of eliminating the white reflection resin  13 B in the light emitting device  10 . In the case of eliminating the white reflection resin  13 B, the blue light emitted from the blue LED  11 A and the cyan light which is wavelength-converted by the phosphor  17 A are absorbed by the phosphors  17 C and  17 D, respectively. The yellow light which is wavelength-converted by the phosphor  17 A is absorbed by the phosphor  17 D. Therefore, in the spectrum illustrated by graph  302 , the intensity of light having short wavelength (particularly, around peak wavelength λ 5  of the blue light and peak wavelength λ 6  of the cyan light) is low as compared with the spectrum illustrated by graph  301 . Consequently, in the case of eliminating the white reflection resin  13 B, total luminous flux of light emitted from the light emitting device  10  is low. 
         [0054]    Since the white reflection resin  13 B reflects light emitted from the side faces of the LEDs and the phosphors in the light-outgoing direction of the light emitting device  10 , total luminous flux of the light emitted from the light emitting device  10  is high. By the white reflection resin  13 B, the directivity of the light can be narrowed. In the case of further adding optical parts such as a lens and a reflection frame to the light emitting device  10 , efficiency of light incidence to the optical parts can be increased, and optical design for the optical parts can be facilitated. 
         [0055]      FIG. 4  is a CIE (Commission Internationale de l&#39;Eclairage) xy chromaticity diagram of the phosphors  17 A,  17 B,  17 C, and  17 D used in the light emitting device  10 . The horizontal axis of  FIG. 4  indicates CIEx, and the vertical axis indicates CIEy. 
         [0056]    A region  401  is a region corresponding to the cyan light which is wavelength-converted by the phosphor  17 A, a region  402  is a region corresponding to the yellow light which is wavelength-converted by the phosphor  17 B, and a region  403  is a region corresponding to light emitted from the phosphor sheet  12 A. A region  404  is a region corresponding to the yellow light wavelength-converted by the phosphor  17 C, a region  405  is a region corresponding to the red light wavelength-converted by the phosphor  17 D, and a region  406  is a region corresponding to light emitted by the phosphor sheet  12 B. 
         [0057]    A region  407  is a region corresponding to light emission color of the entire light emitting device  10 . The region  407  is positioned near a black-body locus  408 , thereby indicating that light emitted from the light emitting device  10  is white light having high color rendering index. 
         [0058]    White light can be also obtained from a phosphor sheet obtained by combining the phosphors  17 A and  17 D and a phosphor sheet obtained by combining the phosphors  17 B and  17 C. However, generally, a phosphor has characteristics of absorbing light having a shorter wavelength than the wavelength of light to be wavelength-converted and, the larger the difference between the wavelength of light to be absorbed and the wavelength of the light to be wavelength-converted is, absorbing larger amount of light. Consequently, when a phosphor sheet is manufactured by combining phosphors in which the wavelengths of light to be converted are largely different from each other such as the phosphors  17 A and  17 D, much of light which is wavelength-converted by the phosphor  17 A is absorbed by the phosphor  17 D and is again wavelength-converted. Therefore, to obtain desired light, a large amount of the phosphor  17 A is preferably included in a phosphor sheet in consideration of the fact that the light which is wavelength-converted by the phosphor  17 A is absorbed by the phosphor  17 D. When the amount of the phosphors contained in the phosphor sheet is large, light transmittance is low, and the intensity of light emitted is low. 
         [0059]    When wavelengths of lights which are wavelength-converted by phosphors are largely different, there is also the possibility that manufacturing variations for the colors of lights emitted from respective phosphor sheets become larger due to manufacture errors in the ratio of amounts of the phosphors included in the phosphor sheets. 
         [0060]    As described above, the peak wavelength of light which is wavelength-converted by the phosphor  17 A is equal to or less than the peak wavelength of light which is wavelength-converted by the phosphor  17 C and is equal to or less than the peak wavelength of light which is wavelength-converted by the phosphor  17 D. The peak wavelength of light which is wavelength-converted by the phosphor  17 B is also equal to or less than the peak wavelength of light which is wavelength-converted by the phosphor  17 C and is equal to or less than the peak wavelength of light which is wavelength-converted by the phosphor  17 D. 
         [0061]    In other words, the phosphor sheets of the light emitting device  10  are configured by a combination of the phosphors  17 A and  17 B and a combination of the phosphors  17 C and  17 D, whose wavelengths of lights converted are close to each other. Therefore, in the light emitting device  10 , the amount of the phosphors contained in each phosphor sheet can be made small and the intensity of outgoing light can be made high. Since the wavelengths of lights which are wavelength-converted by the phosphors included in the phosphor sheet are close, variations occurring in the colors of lights emitted from the respective phosphor sheets can be suppressed even when an error occurs in the ratio of the amounts of the phosphors. 
         [0062]      FIG. 5A  is a schematic top view of a light emitting device  20 .  FIG. 5B  is a cross section taken along line  5 B- 5 B in  FIG. 5A . The light emitting device  20  includes, in addition to the components of the light emitting device  10 , a blue LED  21 C, a phosphor sheet  22 C, and a white reflection resin  23 C. 
         [0063]    The blue LEDs  21 A,  21 B, and  21 C are semiconductor light emitting elements (blue elements) similar to the blue LEDs  11 A and  11 B, flip-chip bonded on a substrate  25 , and connected to the substrate  25  via bumps  26 . 
         [0064]    The phosphor sheets  22 A,  22 B, and  22 C cover the top faces of blue LEDs  21 A,  21 B, and  21 C, respectively. In the phosphor sheet  22 A, a phosphor  27 A similar to the phosphor  17 A is dispersedly mixed. In the phosphor sheet  22 B, a phosphor  27 B similar to the phosphor  17 B is dispersedly mixed. In the phosphor sheet  22 C, a phosphor  27 C similar to the phosphor  17 C and a phosphor  27 D similar to the phosphor  17 D are dispersedly mixed. 
         [0065]    The white reflection resin  23 C is disposed on the substrate  25  so as to be provided between the phosphor sheets  22 B and  22 C. The white reflection resin  23 C is provided in a position interrupting at least a portion between the side face of the phosphor sheet  22 B and the side face of the phosphor sheet  22 C opposed to the side face of the phosphor sheet  22 B. The white reflection resin  23 C reflects light emitted from the phosphor sheet  22 B to the phosphor sheet  22 B side and reflects light emitted from the phosphor sheet  22 C to the phosphor sheet  22 C side. 
         [0066]    Except for the above point, the configuration of the light emitting device  20  is the same as that of the light emitting device  10 . 
         [0067]    As described above, the peak wavelength of the light which is wavelength-converted by the phosphor  27 A is equal to or less than the peak wavelength of the light which is wavelength-converted by the phosphor  27 B, and the peak wavelength of the light which is wavelength-converted by the phosphor  27 B is equal to or less than the peak wavelength of the light which is wavelength-converted by the phosphor  27 C and is equal to or less than the peak wavelength of the light which is wavelength-converted by the phosphor  27 D. 
         [0068]    In other words, the phosphor sheet  22 C is configured by combining the phosphors  27 C and  27 D whose wavelengths of lights converted are close to each other. Therefore, in the light emitting device  20 , the amount of the phosphor contained in the phosphor sheet  22 C can be made small and the intensity of light emitted can be made high. In addition, manufacturing variations of the phosphor sheets can be also suppressed. 
         [0069]      FIG. 6A  is a schematic top view of a light emitting device  30 .  FIG. 6B  is a cross section taken along line A-A′ in  FIG. 6A . In the light emitting device  30 , a white reflection resin  33  is disposed in the whole of the light emitting device  30  to the height of the top faces of phosphor sheets  32 A and  32 B, and top faces of the phosphor sheets  32 A and  32 B and the white reflection resin  33  are covered with a diffusion resin  34 . Except for the above point, the configuration of the light emitting device  30  is the same as the light emitting device  10 . 
         [0070]    As described above, in the light emitting devices  10  to  30 , by configuring each of the phosphor sheets by combining phosphors having close wavelengths which are to be converted, the amount of the phosphors included in each of the phosphor sheets can be reduced and the intensity of light to be emitted can be increased. In addition, manufacturing variations in respective phosphor sheets can be suppressed. 
         [0071]    Further, in the light emitting devices  10  to  30 , a plurality of kinds of phosphors are separately disposed to a plurality of phosphor sheets, and the white reflection resin is provided between the phosphor sheets. Thereby, light which is wavelength-converted by a specific phosphor is absorbed by another phosphor and wavelength-converted to light having a longer wavelength is suppressed. Therefore, white light having higher color rendering index can be obtained. 
         [0072]    Each of the light emitting devices  10  to  30  can be used, for example, as a light source such as a back light in a liquid crystal display of a large area. Each of the light emitting devices  10  to  30  can be also used as various illuminating light sources such as a light guide plate lighting in a liquid crystal display of a small area in a cellular phone and a back light unit of meters or indicators. 
         [0073]    The preceding description has been presented only to illustrate and describe exemplary embodiments of the present invention. It is not intended to be exhaustive or to limit the invention to any precise form disclosed. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. The invention may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope.