Abstract:
Disclosed is a semiconductor light-emitting device including a package having a light outlet, a semiconductor laser diode disposed in the package and radiating a light having a first wavelength falling within a range of ultraviolet ray to visible light, and a visible-light-emitter containing a phosphor which absorbs a light radiated from the semiconductor laser diode and emits a visible light having a second wavelength differing from the first wavelength, the visible-light-emitter being disposed on an optical path of the laser diode and a peripheral edge of the visible-light-emitter being in contact with the package.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2009-072478, filed Mar. 24, 2009, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a light-emitting device employing a semiconductor laser diode as a light source. 
     2. Description of the Related Art 
     Conventionally, there have been proposed various kinds of light source devices or light-emitting devices each having a combination of a semiconductor light-emitting element and a fluorescent material (see, for example, JP-A 2008-153617, 2007-158009 and 2006-73202). These light-emitting devices are designed such that an excitation light emitted from a semiconductor light-emitting element is absorbed by a fluorescent material, thereby enabling the fluorescent material to emit a light having a different wavelength from that of the excitation light. 
     In JP-A 2008-153617, there is proposed a semiconductor light-emitting device which includes a CAN type package and has a combination of a laser diode and a phosphor. Further, in JP-A 2007-158009, there is proposed a thin wall type semiconductor light-emitting device employing a light-emitting diode. Further, in JP-A 2006-73202, there is proposed a light-emitting device for lighting which is equipped with a semiconductor laser element radiating laser beam and with light-guiding plate having a phosphor coated on a light-retrieving face thereof, thereby enabling the light-emitting device to emit light from the surface thereof. 
     However, in the case of the light-emitting device disclosed in JP-A 2008-153617, although it is made possible to realize a high output because of the employment of a laser diode, the area of emission is circular and wide and there is not provided idea of increasing the luminance. Further, in the case of the light-emitting device disclosed in JP-A 2007-158009, although the light-emitting surface is made narrow to thereby allegedly make it possible to increase the luminance, it fails to create a light-emitting surface which is smaller than the size of the LED element. Further, if it is tried to increase the output of the light-emitting device, the emission area of the LED element per se is required to be increased, resulting in the limitation of any further increase in luminance. Further, in the case of the light-emitting device disclosed in JP-A 2006-73202, although it may be possible to create a linear light source by suitably selecting the configuration of the light-guiding plate, this light-emitting device essentially requires the employment of the light-guiding plate and a cylindrical lens in its structure, resulting in a large number of optical components, thus making the structure complicated and large in size. 
     Meanwhile, with respect to the installation of the laser diode, in the case of JP-A 2008-153617, the laser diode is fixed to a central portion of the CAN type package. Further, there is also proposed a light-emitting device wherein the laser diode is held inside a heat sink (see, for example, JP-A 2000-150991). 
     However, in the case of the light-emitting device of JP-A 2008-153617, the control of heat dissipation which requires for increasing the output of laser would become insufficient. Further, in the case of the light-emitting device disclosed in JP-A 2007-158991, although the heat dissipation is ensured by holding the laser diode inside the heat sink, it is impossible to control the spreading of light, thus making it difficult to efficiently utilize the light with the control of only a light source. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a semiconductor light-emitting device using a laser diode as a light source, which has a narrow emission area and emits a linear white light of high luminance, and to provide a semiconductor light-emitting device which makes it possible to realize both high heat dissipation and high light-retrieval efficiency. 
     According to a first aspect of the present invention, there is provided a semiconductor light-emitting device comprising: a package having a light outlet; a semiconductor laser diode disposed in the package and radiating a light having a first wavelength falling within the range of ultraviolet ray to visible light; and a visible-light-emitter containing a phosphor which absorbs a light radiated from the semiconductor laser diode and emits a visible light having a second wavelength differing from the first wavelength, the visible-light-emitter being disposed on an optical path of the laser diode and a peripheral edge of the visible-light-emitter being in contact with the package. 
     According to a second aspect of the present invention, there is provided a semiconductor light-emitting device comprising: a package having a light outlet; a semiconductor laser diode disposed in the package and radiating a light having a first wavelength falling within the range of ultraviolet ray to visible light, the semiconductor laser diode being held, through its top and bottom surfaces, between a couple of heat sinks each having a tapered structure; and a visible-light-emitter containing a phosphor which absorbs a light radiated from the semiconductor laser diode and emits a visible light having a second wavelength differing from the first wavelength, the visible-light-emitter being disposed on an optical path of the semiconductor laser diode. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1A  is a planar cross-sectional view of a light-emitting device according to a first embodiment; 
         FIG. 1B  is a cross-sectional view, as viewed from the front side, of the light-emitting device according to the first embodiment; 
         FIG. 1C  is a perspective view of the light-emitting device according to the first embodiment; 
         FIG. 2A  is a diagram for illustrating the principle of emission in the light-emitting device shown in  FIGS. 1A-1C ; 
         FIG. 2B  is a cross-sectional view, as viewed from the front side, of the light-emitting device shown in  FIG. 2A ; 
         FIG. 3  is a planar cross-sectional view of a modified example of the light-emitting device according to the first embodiment; 
         FIG. 4  is a planar cross-sectional view of another modified example of the light-emitting device according to the first embodiment; 
         FIG. 5A  is a planar cross-sectional view of a light-emitting device according to a second embodiment of the present invention; 
         FIG. 5B  is a cross-sectional view, as viewed from the front side, of the light-emitting device according to the second embodiment; 
         FIG. 5C  is a perspective view of the light-emitting device according to the second embodiment; 
         FIG. 6A  is a diagram for illustrating the principle of emission in the light-emitting device shown in  FIGS. 5A-5C ; 
         FIG. 6B  is a cross-sectional view, as viewed from the front side, of the light-emitting device shown in  FIG. 6A ; 
         FIG. 7  is a planar cross-sectional view of a modified example of the light-emitting device according to the second embodiment; 
         FIG. 8  is a partial cross-sectional view of a visible-light-emitter; 
         FIG. 9  is a graph illustrating the relationship between the intensity of the light that cannot be absorbed by the phosphor and the product to be obtained by the thickness of a light-emitter and the concentration of a phosphor in the light-emitter; 
         FIG. 10  is a cross-sectional view showing an end-face emission type AlGaInN-based laser diode employed as a light-emitting element to be employed in a light emitting device according one embodiment of the present invention; 
         FIG. 11  is a cross-sectional view showing an end-face emission type MgZnO laser diode employed as a light-emitting element to be employed in a light emitting device according one embodiment of the present invention; 
         FIG. 12  is a cross-sectional view showing an end-face emission type MgZnO laser diode employed as a light-emitting element to be employed in a light emitting device according one embodiment of the present invention; and 
         FIGS. 13A ,  13 B,  13 C and  13 D show respectively a perspective view illustrating various configurations of a visible-light-emitter. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Various embodiments of the present invention will be explained with reference to drawings. In the description of the drawings, the same or similar components will be identified by the same or similar reference numbers or symbols. 
       FIGS. 1A-1C  show a light-emitting device according to a first embodiment of the present invention, wherein  FIG. 1A  is a planar cross-sectional view thereof,  FIG. 1B  is a cross-sectional view as viewed from the front side thereof, and  FIG. 10  is a perspective view thereof. As shown in  FIGS. 1A-1C , the light-emitting device according to the first embodiment of the present invention is constructed such that a light-emitting element  13  is contained in a package  10  which is constituted by a bottom part  11  and a top cover part  12 . The light-emitting element  13  is mounted on a heat sink  14  which is secured to the sidewall of the bottom part  11 . A couple of visible-light-emitters  15   a  and  15   b  are respectively disposed in each of the optical paths of the light-emitting element  13 , these optical paths being located on the opposite sides (front side and rear side) of package  10 . 
     The heat sink  14  is electrically insulated from the bottom part  11  and electrically connected with one of the electrodes of light-emitting element  13 . Further, the other electrode of light-emitting element  13  is connected, through a bonding wire  17 , with an interconnect layer  16  which is electrically insulated from the bottom part  11 . The bottom part  11  and the interconnect layer  16  are respectively electrically connected with an external power source. A mirror (not shown) which is capable of reflecting laser beam and visible light is disposed on each of the surfaces of the bottom part  11  and of the top cover part  12 , which face to the optical paths of laser beam. 
       FIGS. 2A and 2B  show respectively an optical path of the emission from the light-emitting element  13 . As shown in  FIG. 2B , a first mirror  18   a  is disposed on the bottom part  11  and under the optical path. Further, a second mirror  18   b  is disposed on the top cover part  12  and over the optical path. A space between the first mirror  18   a  and the second mirror  18   b  can be narrowed, at minimum, down to the ridge width of laser diode or to the laser-emitting width. Further, the maximum width of the space would be such that corresponds to the spreading angle of laser beam. 
     These visible-light-emitters  15   a  and  15   b  are disposed on the optical path of laser beam to be radiated from the light-emitting element  13  and are attached to the package  10 . Accordingly, these visible-light-emitters  15   a  and  15   b  are in contact with the package  10 . 
     The width of the longitudinal axis of each of the visible-light-emitters  15   a  and  15   b  can be determined by the spreading of the laser beam to be released from the light-emitting element  13 . On this occasion, this width of the longitudinal axis may preferably be almost the same as that of the spreading of laser beam. 
     In order to obtain an emission having a fine linear cross-section, the visible-light-emitter may desirably be constructed such that it has a contour of a rectangular configuration, a polygonal configuration or an oval configuration each having an aspect ratio of 2:1 or more and that the longer axis thereof is the same in direction as the longer axis of the emission configuration of light to be emitted from the laser diode. 
     Since the visible-light-emitters  15   a  and  15   b  are only required to be disposed on the optical path of laser beam to be emitted from the light-emitting element  13 , these visible-light-emitters  15   a  and  15   b  may not necessarily be required to be attached to the sidewall of package  10  as shown in  FIGS. 1A-1C . However, it is more preferable to attach these visible-light-emitters  15   a  and  15   b  respectively to the light outlets located on the opposite sides of the package  10 . 
     As shown in  FIGS. 2A and 2B , the light-emitting element  13  is designed such that the excitation light Le ranging from ultraviolet ray to visible light and emitted therefrom is irradiated to these visible-light-emitters  15   a  and  15   b . These visible-light-emitters  15   a  and  15   b  are enabled to absorb this excitation light Le and then emit a visible light. As a result, the visible light is emitted as a visible output light Lf having a fine linear cross-section from these visible-light-emitters  15   a  and  15   b  to the outside of the device. 
     Further, as shown in  FIG. 3 , optical filters  19   a  and  19   b  may be disposed on the opposite sidewalls of package  10  so as to be in contact with these visible-light-emitters  15   a  and  15   b . Further, as shown in  FIG. 4 , optical filters  20   a  and  20   b  or films which are capable of transmitting the wavelength of the excitation light and also capable of reflecting visible light or a light having a wavelength of at least not less than 430 nm may be interposed between the light-emitting element  13  and the visible-light-emitters  15   a  and  15   b . As for the optical filters  19  and  20 , it is possible to employ a metallic film or a multi-layered dielectric film DBR, each having a reflectance of not less than about 80%, preferably not less than about 90% to the excitation light. Especially, the multi-layered dielectric film DBR may be designed, for example, such that it selectively reflects only the excitation light and permit the transmission of visible light and vice versa, thereby make it conform with the wavelength of excitation light. 
     As for the metal for the metallic film, it is possible to employ Al, Au, Ag, Pd, etc. As for the dielectric material for the multi-layered dielectric film, it is possible to employ oxides and nitrides of Si, Zr, Hf, Al, Ta, Ti, etc. 
     Alternatively, it is also possible to dispose a transparent plate-like or lens-like structure composed of, glass, metal or resin on the outer side of and in contact with the visible-light-emitter. 
       FIGS. 5A-5C  show respectively the light-emitting device according to the second embodiment of the present invention, wherein  FIG. 5A  is a planar cross-sectional view thereof,  FIG. 5B  is a cross-sectional view thereof as it is viewed from the front side thereof, and  FIG. 5C  is a perspective view thereof. As shown in  FIGS. 5A-5C , the light-emitting device according to the second embodiment of the present invention includes a package  30  and a light-emitting element  33  contained in the package  30 . The package  30  has a bottom part  31  and a top cover part  32 . The light-emitting element  33  is interposed between a couple of heat sinks  34   a  and  34   b , both being secured to the sidewall of the bottom part  31 . 
     These heat sinks  34   a  and  34   b  are electrically insulated from the bottom part  31 . A couple of interconnect layers  36   a  and  36   b  are disposed in a manner to pass through the package  31  (these interconnect layers are omitted in  FIG. 5B ). Electrodes (not shown) disposed respectively on the upper and lower surfaces of the light-emitting element  33  are electrically connected with the interconnect layers through these heat sinks  34   a  and  34   b.    
     At least one of the heat sinks  34   a  and  34   b  may be connected with the light-emitting element through solder or conductive pastes. In this case, the other heat sink is secured by spring action of a spring-like spacer  39  disposed between this heat sink and the bottom part  31 . 
     Further, at least one of the heat sinks  34   a  and  34   b  is provided, on the contacting surface thereof to the light-emitting element  33 , with a thick metallic film, thereby adhering the light-emitting element  33  to and thermally connected with at least one of the heat sinks  34   a  and  34   b.    
     Furthermore, the heat sinks  34   a  and  34   b  may be sandwiched between the bottom part  31  and the top cover part  32 , each being made of ceramics or metal at least having an insulating surface. 
     The heat that has been generated from the light-emitting element  33  is conducted, through the heat sinks  34   a  and  34   b , to the package  30  and then dissipated out of the device. Because of the structure where heat is enabled to move from the opposite surfaces of light-emitting element  33  to the heat sinks  34   a  and  34   b  as described above, the heat resistance of light-emitting element  33  can be greatly lowered as compared with the conventional device, thereby making it possible to drive the light-emitting device at a higher output. 
       FIGS. 6A and 6B  show the optical path of the light emitted from the light-emitting element  33 . As shown in  FIGS. 6A and 6B , under the optical path, a first mirror  38   a  is disposed on the bottom part  31  and, above the optical path, a second mirror  38   b  is disposed on the top cover part  32 . A space between the first mirror  38   a  and the second mirror  38   b  can be narrowed, at minimum, down to the ridge width of laser diode or to the laser-releasing width. Further, the maximum width of the space would be such that corresponds to the spreading angle of laser beam. 
       FIG. 7  shows a modified example of the light-emitting device according to the second embodiment of the present invention shown in  FIGS. 5A-5C . The light-emitting device shown in  FIG. 7  differs from the light-emitting device shown in  FIGS. 5A-5C  in the respect that the visible-light-emitters  35   a  and  35   b  are respectively disposed in the optical path of the light emitted from the light-emitting element  33 , and are located on the sidewalls (front side and rear side) of the package  30 . 
     The width of the longitudinal axis of each of the visible-light-emitters  35   a  and  35   b  can be determined by the spreading of the laser beam to be released from the light-emitting element  33 . On this occasion, this width of the longitudinal axis may more preferably be almost the same as that of the spreading of laser beam. 
     Since the visible-light-emitters  35   a  and  35   b  are only required to be disposed on the optical path of laser beam to be emitted from the light-emitting element  13 , these visible-light-emitters  35   a  and  35   b  may not necessarily be required to be attached to the sidewall of package  30 . However, it is more preferable to create a structure where these visible-light-emitters  35   a  and  35   b  are attached respectively to the sidewall of the package  30 . 
     With respect to the features of the light-emitting device shown in  FIG. 7  such as the optical path of the light emitted therefrom, the installation of mirror to be disposed at the lower surface and the upper surface of the optical path, and the installation intervals of mirrors, they are substantially the same as those of the light-emitting device according to the first embodiment. 
     Further, as in the case of the light-emitting device shown in  FIG. 3 , optical filters may be disposed on the both sidewalls of package  10  so as to join them to these visible-light-emitters  35   a  and  35   b . Further, as in the case of the light-emitting device shown in  FIG. 4 , optical filters or films which are capable of transmitting a light of the same wavelength as that of the excitation light and also capable of reflecting visible light may be interposed between the light-emitting element  33  and the visible-light-emitters  35   a  and  35   b . As for the optical filters, it is possible to employ a metallic film or a multi-layered dielectric film DBR, each having a reflectance of not less than about 80%, preferably not less than about 90% to the excitation light. Especially, the multi-layered dielectric film DBR may be designed such that, for example, it selectively reflects only the excitation light and permit the transmission of visible light and vice versa, thereby make it conform to the wavelength of excitation light as in the light-emitting devices shown in  FIGS. 3 and 4 . 
       FIG. 8  shows a cross-sectional view of a part of the visible-light-emitters  15   a ,  15   b ,  35   a  and  35   b  to be employed in the above embodiments. As shown in  FIG. 8 , the visible-light-emitters  15   a ,  15   b ,  35   a  and  35   b  respectively includes transparent base material  40  and phosphor particles  42  dispersed in the transparent base material  40 . The excitation light Le that has been transmitted into visible-light-emitters  15   a ,  15   b ,  35   a  and  35   b  is absorbed by the phosphor particles  42  and is converted into visible light having a different wavelength from that of the excitation light Le. 
     The content of phosphor particles  42  contained in the transparent base material  40  can be adjusted so as enable the excitation light from the light-emitting elements  13  and  33  to be effectively absorbed and transmitted. More specifically, the light-emitters  15   a ,  15   b ,  35   a  and  35   b  may preferably contains the phosphor particles  42  dispersed in the transparent base material  40  at a content of about 5-75% by weight, preferably 25% by weight. 
     When the content of phosphor particles  42  is less than 5% by weight, the thickness of the visible-light-emitter would be required to be increased for enabling the visible-light-emitter to sufficiently absorb the excitation light, thereby rendering them to become too large in thickness to enable them to be installed in the device (if the size thereof confined to a prescribed size, it may become impossible to sufficiently absorb the excitation light). When the content of phosphor particles  42  is larger than 75% by weight, the thickness of the visible-light-emitter is caused to reduce and the content of the transparent base material is also caused to reduce, thereby rendering the visible-light-emitter to become brittle. As a result, the handling of the visible-light-emitter may become difficult. 
     As for the particle size of the phosphor particles  42 , it may preferably be confined to 5-25 μm in particle diameter. It is especially desirable to employ those which are high in emission intensity and in emission efficiency and which contain large particles of as large as about 20 nm or more in particle diameter, for example. When the particle diameter of the phosphor particles  42  is less than 5 μm, the absorbency of the phosphor may become too low and the phosphor may be easily deteriorated, thus making them unsuitable for use. When the particle diameter of the phosphor particles  42  is larger than 25 μm, the molding of the visible-light-emitter may become difficult and discoloration may be more likely to be generated. 
     It has been found out through the experiments conducted by the present inventors that there is a predetermined relationship between the thickness of light-emitter and the concentration of the phosphor in the light-emitter (weight of phosphor/weight of light-emitter). Namely, the intensity I of the light that cannot be absorbed by the phosphor (the light that cannot be utilized as luminous light) among the excitation light emitted from the light-emitting elements  13  and  33  can be represented by the following equation.
 
I=I 0 e KCt  
 
     I 0 : Intensity of excitation light; 
     K: Coefficient 
     C: Concentration (weight) of the phosphor in the light-emitter; 
     t: Thickness (μm) of the light-emitter; 
       FIG. 9  shows a graph wherein ct is plotted on the abscissa and I is plotted on the ordinate. 
     It will be recognized from  FIG. 9  that if the ct when the light that cannot be absorbed by the phosphor (leakage light) is not more than 10%, is set to about 100, it requires the employment of a light-emitter having a thickness of 400 μm where the concentration of phosphor is set to 25% by weight, or it requires the employment of a light-emitter having a thickness of 200 μm where the concentration of phosphor is set to 50% by weight. 
     Alternatively, the light-emitter may be formed of a sintered phosphor. 
     The light-emitting elements  13  and  33  to be employed in the light-emitting device according to above embodiment of the present invention may preferably be selected from those having an emission peak wavelength ranging from blue to ultraviolet in a wavelength region of not more than about 430 nm. More specifically, it is possible to employ a semiconductor laser diode or a light-emitting diode, wherein a III-V group compound semiconductor such as aluminum/gallium/indium nitride (AlGaInN) or a II-VI group compound semiconductor such as magnesium/zinc oxide (MgZnO) is used as a light-emitting layer (active layer). 
     For example, the III-V group compound semiconductor to be used as a light-emitting layer may be a nitride semiconductor containing at least one metal selected from the group consisting of Al, Ga and In. This nitride semiconductor can be specifically represented by Al x Ga y In (1−x−y)  (0≦x≦1, 0≦y≦1, 0≦(x+y)≦1). 
     The nitride semiconductor of this kind includes a binary system such as AlN, GaN and InN; a ternary system such as Al x Ga (1−x) N (0&lt;x&lt;1), Al x In (1−x) N (0&lt;x&lt;1) and Ga y In (1−y) N (0&lt;y&lt;1); and a quaternary system containing all of these elements. Based on the compositions x, y and (1−x−y) of Al, Ga and In, the emission peak wavelength ranging from ultraviolet to blue can be determined. 
     Further, a part of the III group elements may be replaced by boron (B), thallium (Tl), etc. Further, a part of N of the V group elements may be replaced by phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), etc. 
     Likewise, the II-VI group compound semiconductor to be used as a light-emitting layer is an oxide semiconductor containing at least one metal selected from Mg and Zn. More specifically, this oxide semiconductor may be represented by Mg z Zn (1−z)  (0≦z≦1) and the emission peak wavelength of ultraviolet region can be determined based on the compositions z and (1−z) of Mg and Zn, respectively. 
       FIG. 10  is a cross-sectional view showing one example of an end face emission type AlGaInN-based laser diode which can be employed as the light-emitting elements  13  and  33 . As shown in  FIG. 10 , this AlGaInN-based laser diode has a laminated structure including an n-type GaN substrate  100 , on which an n-type GaN buffer layer  101 , an n-type AlGaN clad layer  102 , an n-type GaN optical guide layer  103 , a GaInN light-emitting layer  104 , a p-type GaN optical guide layer  105 , a p-type AlGaN clad layer  106  and a p-type GaN contact layer  107  are successively laminated. An insulating film  108  is formed on the ridge sidewall of the p-type GaN contact layer  107  and on the surface of the p-type AlGaN clad layer  106 . A p-type electrode  109  is formed on the surfaces of the p-type GaN contact layer  107  and of the insulating film  108 . An n-side electrode  110  is formed on the back surface of the n-type GaN substrate  100 . 
       FIGS. 11 and 12  illustrate respectively one example of the end face emission type MgZnO-based laser diode which can be employed as the light-emitting elements  13  and  33 . 
     In the case of the MgZnO-based laser diode shown in  FIG. 11 , a silicon (Si) substrate  130  is employed. On the other hand, in case of the MgZnO-based laser diode shown in  FIG. 12 , a sapphire substrate  140  is employed. 
     The MgZnO-based laser diode shown in  FIG. 11  has a laminated structure including a Si substrate  130 , on which a metallic reflection layer  131 , a p-type MgZnO clad layer  132 , an i-type MgZnO light-emitting layer  133 , an n-type MgZnO clad layer  134  and an n-type MgZnO contact layer  135  are successively laminated. An n-side electrode  136  is formed on the n-type contact layer  135 . A p-side electrode  137  is formed on the substrate  130 . 
     The MgZnO-based laser diode shown in  FIG. 12  has a laminated structure including a sapphire substrate  140 , on which a ZnO buffer layer  141 , a p-type MgZnO clad layer  142 , an MgZnO light-emitting layer  143  and an n-type MgZnO clad layer  144  are successively laminated. An n-side electrode  146  is formed, through an indium/tin oxide (ITO) electrode layer  145 , on the n-type clad layer  144 . A p-side electrode  148  is formed, through an ITO electrode layer  147 , on the p-type MgZnO clad layer  142 . 
     As for the materials for the transparent base material  40  of the light-emitters  15   a ,  15   b ,  35   a  and  35   b , it is possible to employ any kind of material which can be easily permeated by the excitation light and is high in heat resistance. Specific examples of such materials include, for example, silicone resin, epoxy resin, urea resin, fluorinated resin, acrylic resin, polyimide resin, etc. Especially, in viewpoints of availability, easiness in handling and low cost, the employment of epoxy resin and silicone resin is more preferable. It is also possible, other than the aforementioned materials, to employ glass, a sintered body, and a ceramic structure formed of a combination of yttrium/aluminum/garnet (YAG) and alumina (Al 2 O 3 ). 
     As for specific examples of the phosphor particles  42 , it is possible to employ a material which is capable of absorbing the light of wavelength region ranging from ultraviolet to blue and also capable of radiating visible light. For example, it is possible to employ a fluorescent material such as a silicate-based fluorescent material, an aluminate fluorescent material, a nitride-based fluorescent material, a sulfide-based fluorescent material, an oxysulfide-based fluorescent material, a YAG-based fluorescent material, a borate-based fluorescent material, a phosphate/borate-based fluorescent material, a phosphate-based fluorescent material, a halo-phosphate-based fluorescent material, etc. The following are the compositions of each of these fluorescent materials. 
     (1) Silicate-based fluorescent material: (Sr (1−x−y−z) Ba x Ca y Eu z ) 2 Si w O (2+2w)  (0≦x&lt;1, 0≦y&lt;1, 0.05≦z≦0.2, 0.90≦w≦1.10) 
     Among the silicate-based fluorescent materials represented by the aforementioned formula, it is more preferable to employ those having a composition where x=0.19, y=0, z=0.05, w=1.0. In order to stabilize the crystal structure and to enhance the emission intensity, a part of strontium (Sr), barium (Ba) and calcium (Ca) may be replaced by Ma and/or Zn. 
     It is also possible to employ other kinds of silicate-based fluorescent materials having a different composition ratio from those described above. For example, it is possible to employ MSiO 3 , MSiO 4 , M 2 SiO 3 , M 2 SiO 5  and M 4 Si 2 O 8  (M is at least one element selected from the group consisting of Sr, Ba, Ca, Mg, Be, Zn and Y). Incidentally, for the purpose of controlling the luminescent color, a part of Si may be replaced by germanium (Ge) (for example, Sr (1−x−y−z) Ba x Ca y Eu z ) 2 (Si (1−u) Ge u ) 2 O 4 ). Further, at least one of the elements selected from the group consisting of Ti, Pb, Mn, As, Al, Pr, Tb and Ce may be contained therein as an activating agent. 
     (2) Aluminate-based fluorescent material: M 4 Al 10 O 17  (M is at least one element selected from the group consisting of Ba, Sr, Mg, Zn and Ca) 
     Eu and/or Mn may be contained as an activating agent. 
     It is also possible to employ other kinds of aluminate-based fluorescent materials having a different composition ratio from those described above. For example, it is possible to employ MAl 2 O 4 , MAl 4 O 17 , MAl 8 O 13 , MAl 12 O 19 , M 2 Al 19 O 17 , M 2 Al 11 O 19 , M 3 Al 5 O 12 , M 3 Al 16 O 27  and M 4 Al 5 O 12  (M is at least one element selected from the group consisting of Ba, Sr, Ca, Mg, Be and Zn). Further, at least one of the elements selected from the group consisting of Mn, Dy, Tb, Nd and Ce may be contained therein as an activating agent. 
     (3) Nitride-based fluorescent material (mainly, silicon nitride-based fluorescent material): L x Si y N (2x/3+4y/3) :Eu or L x Si y O z N (2x/3+4y/3−2z/3) :Eu (L is at least one element selected from the group consisting of Sr, Ca, Sr and Ca) 
     Among the aforementioned compositions, it is more preferable to employ those having a composition where x=2 and y=5 or x=1 and y=7. However, the values of these x and y may be optionally selected. 
     With respect to specific examples of the nitride-based fluorescent material which is represented by the above formula, it is preferable to employ fluorescent materials wherein Eu is added as an activating agent such as (Sr x Ca (1−x) ) 2 Si 5 N 8 :Eu, Sr 2 Si 5 N 8 :Eu, Ca 2 Si 5 N 8 :Eu, Sr x Ca (1−x) Si 7 N 10 :Eu, SrSi 7 N 10 :Eu, CaSi 7 N 10 :Eu, etc. These fluorescent materials may contain at least one element selected from the group consisting of Mg, Sr, Ca, Ba, Zn, B, Al, Cu, Mn, Cr and Ni. These fluorescent materials may further contain, as an activating agent, at least one element selected from the group consisting of Ce, Pr, Tb, Nd and La. 
     (4) Sulfide-based fluorescent material: (Zn (1−x) Cd x )S:M (M is at least one element selected from the group consisting of Cu, Cl, Ag, Al, Fe, Cu, Ni and Zn; x is a number satisfying 0≦x≦1) 
     Incidentally, S may be replaced by Se and/or Te. 
     (5) Oxysulfide-based fluorescent material: (Ln (1−x) Eu x )O 2 S (Ln is at least one element selected from the group consisting of Sc, Y, La, Gd and Lu; x is a number satisfying 0≦x≦1) 
     Incidentally, at least one element selected from the group consisting of Tb, Pr, Mg, Ti, Nb, Ta, Ga, Sm and Tm may be contained therein as an activating agent. 
     (6) YAG-based fluorescent material: (Y (1−x−y−z) Gd x La y Sm z ) 3 (Al (1−v) Ga v ) 5 O 12 :Ce,Eu (0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦v≦1,) 
     Incidentally, at least one element selected from Cr and Tb may be contained therein as an activating agent. 
     (7) Borate-based fluorescent material: MBO 3 :Eu (M is at least one element selected from the group consisting of Y, La, Gd, Lu and In) 
     Incidentally, Tb may be contained therein as an activating agent. 
     It is also possible to employ other kinds of borate-based fluorescent materials having a different composition ratio from those described above, specific examples of which including Cd 2 B 2 O 5 :Mn, (Ce, Gd, Tb)MgB 5 O 10 :M, GdMgB 5 O 10 :Ce,Tb, etc. 
     (8) Phosphate/borate-based fluorescent material: 2(M (1−x) M′ x )O·aP 2 O 5 ·bB 2 O 3  (M is at least one element selected from the group consisting of Mg, Ca, Sr, Ba and Zn; M′ is at least one element selected from the group consisting of Eu, Mn, Sn, Fe and Cr; and x, a and b respectively represent a number satisfying 0.001≦x≦0.5, 0≦a≦2, 0≦b≦3, 0.3&lt;(a+b)) 
     (9) Phosphate-based fluorescent material: (Sr (1−x) Ba x ) 3 (PO 4 ) 2 :Eu or (Sr (1−x) Ba x ) 3 P 2 O 7 :Eu, Sn 
     Incidentally, Ti and/or Cu may be contained therein as an activating agent. 
     (10) Halo-phosphate-based fluorescent material: (M (1−x) Eu x ) 10 (PO 4 ) 6 Cl 2  or (M (1−x) Eu x ) 5 (PO 4 ) 3 Cl (M is at least one element selected from the group consisting of Ba, Sr, Ca, Mg and Cd; and x is a number satisfying 0≦x≦1) 
     Incidentally, at least part of Cl may be replaced by fluorine (F). Further Sb and/or Mn may be contained therein as an activating agent. 
     The aforementioned fluorescent materials may be optionally selected to employ them as a blue light-emitter, a yellow light-emitter, a green light-emitter, a red light-emitter or a white light-emitter. Further, it is also possible to suitably combine plural kinds of fluorescent materials to create a light-emitter emitting an intermediate color. If it is desired to create a white light-emitter, three kinds of fluorescent materials each corresponding to three primary colors, i.e. red/green/blue (RGB), may be combined or alternatively additive complementary colors such as blue and yellow may be suitably combined to create a white light-emitter. 
     Further, although these combinations of colors are performed by a light-emitter including a mixture of a plurality of fluorescent material, it is also possible to create a multi-layered structure consisting of a plurality of layers each representing one kind of phosphor or to create a plurality of partitioned regions each representing one kind of fluorescent material. For example, a multi-layered structure consisting of a plurality of layers each representing each of RGB, is formed in a light-emitter. In this case, a layer of a fluorescent material emitting a light having a longer wavelength is disposed more close to the laser diode, thereby making it possible to obtain a light-emitting device which is capable of effectively radiating white light. 
     Further, when fluorescent materials corresponding to RGB are mixed in the same transparent base material, a light-emitting device where visible-light-emitters  15   a ,  15   b ,  35   a  and  35   b  are enabled to radiate individual white light can be obtained. If it is desired to secure the stability in terms of light-retrieving efficiency and tint, it is preferable to incorporate one kind of phosphor into each of the layers or regions of light-emitter, thereby creating the light of white color as a whole in the light-emitting device. On the other hand, if it is desired to attach importance to the easiness in the manufacture of light-emitter, it is preferable to create a structure where fluorescent materials are mixed together. 
     As for a material of the packages  10  and  30 , it is preferable to employ a material which is excellent in heat conductivity. For example, it is possible to employ AlN, Al 2 O 3 , Cu, Cu alloys, BN, plastics, ceramics, diamond, etc. Further, as for a material of the heat sinks  14 ,  34   a  and  34   b , it is preferable to employ a material which is excellent not only in electric conductivity but also in heat conductivity. For example, where the packages  10  and  30  and the heat sinks  14 ,  34   a  and  34   b  are made of materials such as Cu and Cu alloys, it is possible to effectively release the heat that may be generated during the operation of the light-emitting element  13  or  33 . 
     With respect to a material of the interconnect layers  16 ,  36   a  and  36   b , it is preferable to employ a material which is low in electric resistance and also low in absorption coefficient of visible light. For example, these interconnect layers may be formed of a metallic material such as Au, Ag, Cu, Cu alloys, W, etc. The interconnect layers  16 ,  36   a  and  36   b  may be constituted by a thin film or a thick film. In order to enhance the bondability, the interconnect layers  16 ,  36   a  and  36   b  may be covered with an Au-plated layer, an Ag-plated layer, a Pd-plated layer or a solder-plated layer. 
     With respect to a material of the boding wire  17 , it is preferable to employ a material which is low in electric resistance and also low in absorption coefficient of visible light. For example, it is possible to employ an Au wire. Alternatively, a wire formed of a combination of a noble metal such as Pt and Au may be employed. Furthermore, by applying the plating of Au, etc., to the entire surface of the heat sink  12 , the interconnects may be substantially integrated with the heat sink. 
     EXAMPLES 
     Next, various examples of the light-emitting device according to the embodiments of the present invention discussed above will be explained as follows. 
     Example 1 
     This example relates to the semiconductor light-emitting device shown in  FIGS. 1A-1C . 
     First of all, the light-emitters  15   a  and  15   b  of the semiconductor light-emitting device shown in  FIGS. 1A-1C ,  2 A and  2 B were formed. As for a transparent base material for the visible-light-emitter, silicone resin was used. Light-emitters containing two kinds of fluorescent materials with each content of 50 wt %, which are dispersed in the transparent base material, are prepared. The two kinds of fluorescent materials have a relation of complementary colors enabling them to create white color. 
     As the two kinds of fluorescent materials, a blue color-emitting material containing a blue fluorescent material was employed, and a yellow color-emitting material containing a yellow fluorescent material was employed. More specifically, (Sr, Ca, Ba) 10 (PO 4 ) 6 Cl 2 :Eu was employed as the blue fluorescent material and (Sr, Ca, Ba) 2 Si 2 O 4 :Eu was employed as the yellow fluorescent material. 
     The printed circuit board  10  made of aluminum was constructed such that the surface thereof in contact with the heat sink was treated to make it electrically insulative and that facing the optical path thereof was worked to have a mirror-like surface. As for the material of the heat sink  14  functioning also as an interconnect, an Au-plated copper was employed. Further, the heat sink  14  was in contact with a copper wire, thereby enabling the heat sink  14  to electrically connect with an external power source (omitted in the drawing). A metallic film formed of Au, etc., was formed on the surface of the bottom part  11 . Then, the metallic film thus formed was subjected to a patterning process by making use of photolithography, etching, etc., to thereby form interconnect layer  16  on the surface of the bottom part  11 . 
     A semiconductor laser diode having an AlGaInN light-emitting layer generating bluish violet light was mounted, as a light-emitting element  13 , on the surface of the heat sink  14 . Subsequently, the interconnect layer  16  was electrically connected with the electrode (not shown) of the light-emitting element  13  by making use of a bonding wire  17 . 
     The visible-light-emitters  15   a  and  15   b  were respectively disposed at each of the light outlets positioned respectively at an end portion of the package so as to make these visible-light-emitters face the light-emitting element  13 . Further, these visible-light-emitters  15   a  and  15   b  were respectively fixed between the bottom part  11  and the top cover part  12 , thereby bonding these visible-light-emitters to these components. 
     The space between mirror faces and the width of the shorter axis of each of the visible-light-emitters  15   a  and  15   b  were set to 0.4 mm which was equal to that of the light-emitting element  13 . Further, the width of the longer axis of each of the visible-light-emitters  15   a  and  15   b  were set to 4 mm in conformity with the spreading of laser. 
     A couple of optical filters  20   a  and  20   b  for reflecting the light having a wavelength of not more than 420 nm were respectively disposed on the outside of the bottom part  11  and of the top cover part  12 , thus contacting these optical filters with the visible-light-emitters  15   a  and  15   b.    
     In the operation of the light-emitting device manufactured as described above, an operating voltage was applied between the electrodes of the light-emitting element  13  to oscillate a laser beam. The excitation light that was radiated from the light-emitting element  13  and directed toward the visible-light-emitters  15   a  and  15   b  was absorbed by each of these visible-light-emitters  15   a  and  15   b  and then white light was enabled to emit outside from the package  10 . In this case, the light-emitting part of the light-emitting device was a linear light source having an aspect ratio of 1:10, and the emitted light was high brightness white light of 1000. 
     Example 2 
     This example relates to the semiconductor light-emitting device shown in  FIGS. 5A-5C . 
     This semiconductor light-emitting device differs from the semiconductor light-emitting device of Example 1 in the respect that the light-emitting element  13  was sandwiched and fixed between a couple of heat sinks  34   a  and  34   b . Namely, a laser diode  33  having an AlGaInN light-emitting layer emitting bluish violet light was mounted on the heat sink  34   a  by means of solder. Then, the other heat sink  34   b  having a thick gold film was disposed to face the surface of the laser diode, and was pressed and secured by spring-like spacers  39 . 
     In the operation of the light-emitting device manufactured as described above, an operating voltage was applied between the electrodes of the light-emitting element  33  to drive the device. At this time, the heat resistance was 9K/W, thus obtaining a value which was lower by 50% as compared with the conventional package and the conventional mounting method. As a result, the rise in temperature of the light-emitting element  33  was suppressed, thereby making it possible to drive the laser diode at a higher current injection and a higher output. 
     Example 3 
     This example relates to the semiconductor light-emitting device shown in  FIG. 7 . 
     Silicone resin was used as the transparent base material for the light-emitter. Two kinds of fluorescent materials of 50 wt % respectively, having a complementary color relation and enabling to create white color, are dispersed in the transparent base material to form visible-light-emitters  35   a  and  35   b  containing these fluorescent materials. 
     As the two kinds of fluorescent materials, a blue color-emitting material containing a blue fluorescent material was employed, and a yellow color-emitting material containing a yellow fluorescent material was employed. More specifically, (Sr, Ca, Ba) 10 (PO 4 ) 6 Cl 2 :Eu was employed as the blue fluorescent material and (Sr, Ca, Ba) 2 Si 2 O 4 :Eu was employed as the yellow fluorescent material. 
     As shown in  FIG. 7 , the visible-light-emitters  35   a  and  35   b  thus obtained were respectively disposed at each of the light outlets positioned respectively at an end portion of the package  30  so as to make these visible-light-emitters face the light-emitting element  33 . Further, these visible-light-emitters  15   a  and  15   b  were respectively interposed between the bottom part  31  and the top cover part  32 , thereby fixing these visible-light-emitters to these components. 
     In the operation of the light-emitting device manufactured as described above, an operating voltage was applied between the electrodes of the light-emitting element  33  to drive the device. As a result, the excitation light emitted from the light-emitting element  33  and directed toward the visible-light-emitters  35   a  and  35   b  was absorbed by each of these visible-light-emitters  35   a  and  35   b  and then white light was enabled to output outside from the package  30 , thus obtaining a linear white light source which was high in luminance and in output. 
     In the embodiments and examples of the present invention described above, the light-emitting devices each employing a visible-light-emitter which is capable of radiating white light have been explained. However, the present invention is not limited to the light-emitting devices employing a visible-light-emitter which is capable of radiating white light but can be also applied to light-emitting devices using a visible-light-emitter wherein visible light of other colors can be radiated. For example, a light-emitter which is capable of radiating red, orange, yellow, yellowish green, green, bluish green, blue, violet or white visible light may be also utilized depending on the end-use. 
     In the embodiments and examples of the present invention described above, the visible-light-emitters have been explained as having a contour of a rectangular configuration. However, the present invention is not limited to such a configuration but can be modified into various configurations. Examples of such various configurations are shown in  FIGS. 13A-13D  for instance. 
     As for the end-use of the light-emitting device according to the present invention, it includes ordinary lighting equipments, lighting equipments for business use, back-light for a liquid crystal display apparatus of televisions or personal computers, the lighting system of motor cars, motor bicycles or bicycles, etc. 
     Further, the present invention is not applied to the above-described embodiments per se but constituent elements of these embodiments may be variously modified in actual use thereof without departing from the spirit of the present invention. Further, the constituent elements described in these various embodiments may be suitably combined to create various inventions. For example, some of the constituent elements described in these embodiments may be deleted. Further, the constituent elements described in different embodiments may be optionally combined with each other.