Patent Publication Number: US-2015084075-A1

Title: Light-Emitting Module and Luminaire

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-197362, filed on Sep. 24, 2013; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a light-emitting module and a luminaire. 
     BACKGROUND 
     As a light source of a luminaire, a light-emitting module mounted with a semiconductor chip is being used. For example, there is a light-emitting module in which a semiconductor chip configured to emit blue light and a phosphor configured to emit yellow light are combined to obtain white light. In order to improve an average color rendering index Ra, it is conceivable to combine red and green phosphors. However, the red phosphor and the green phosphor have external quantum efficiency lower than external quantum efficiency of a yellow phosphor. Therefore, if the red phosphor and the green phosphor are used, light-emitting efficiency is deteriorated. 
     In order to improve the light-emitting efficiency, it is conceivable to incorporate, in a light-emitting module, instead of the red phosphor, a semiconductor chip configured to emit red color. The average color rendering index Ra is improved and the light-emitting efficiency is improved by mounting the red semiconductor chip on the light-emitting module mixedly with another color semiconductor chip. 
     However, if a blue semiconductor chip and the red semiconductor chip are mixedly mounted, the area of the light-emitting module increases. The red semiconductor chip has a light decrease ratio to temperature larger than a light decrease ratio of the blue semiconductor chip. Therefore, if an actual working temperature is taken into account, a large number of red semiconductor chips are necessary. Therefore, the area of the light-emitting module further increases and luminous excitance is deteriorated. Further, it is difficult to mix lights excited by the red semiconductor chip and the blue semiconductor chip. This causes color unevenness on an irradiation surface. 
     As a method of solving these problems, it is conceivable to use a line red phosphor having a specific light emission peak without using the red semiconductor chip. However, the line red phosphor includes fluorine. Therefore, it is likely that hydrofluoric acid is generated because of affinity of the fluorine and the water in the atmosphere and deterioration (e.g., a color shift) of the line red phosphor occurs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic sectional view of a light-emitting module according to a first embodiment, 
         FIG. 1B  is an enlarged schematic sectional view of a phosphor provided in the light-emitting module; 
         FIG. 2A  is a diagram showing a light emission spectrum of a red phosphor according to the first embodiment, 
         FIG. 2B  is a schematic sectional view showing a process of formation of a protection film on the surface of the red phosphor; 
         FIG. 3A  is a schematic sectional view of a light-emitting module according to a first variation of the first embodiment, 
         FIG. 3B  is a schematic sectional view of a light-emitting module according to a second variation of the first embodiment; and 
         FIG. 4  is a schematic sectional view of a luminaire according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, there is provided a light-emitting module including: a substrate; a light-emitting body provided on the substrate; and a phosphor containing layer provided on the substrate and the light-emitting body, the phosphor containing layer including a first phosphor excited by emitted light of the light-emitting body, having a light emission peak in a wavelength range equal to or greater than 610 nm and less than 655 nm, and having a surface covered with a protection film. 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. In the following explanation, the same members are denoted by the same reference numerals and signs. Explanation of members once explained is omitted as appropriate. 
     First Embodiment 
       FIG. 1A  is a schematic sectional view of a light-emitting module according to a first embodiment.  FIG. 1B  is an enlarged schematic sectional view of a phosphor provided in the light-emitting module according to the first embodiment. 
     As shown in  FIG. 1A , a light-emitting module  10 A includes a substrate  3 , a plurality of light-emitting bodies  5 , a phosphor containing layer  11 , and a bank  7 . The light-emitting module  10 A is a light-emitting module of a so-called COB (Chip On Board) type. 
     The plurality of light-emitting bodies  5  are provided on the substrate  3 . The substrate  3  is, for example, a ceramic substrate. The light-emitting body  5  emits light having a wavelength of 400 to 480 (nm) and excites a red phosphor  15  and a yellow phosphor  17 . The light-emitting body  5  is a light-emitting diode (LED) and emits, for example, blue light having a dominant wavelength of 440 to 465 nm. 
     The light-emitting body  5  is mounted on, for example, an upper surface  3   a  of the substrate  3  via an adhesive. The plurality of light-emitting bodies  5  are mounted on the substrate  3  and connected in series or in parallel using a metal wire. The bank  7  is provided to surround a region where the plurality of light-emitting bodies  5  are mounted. The bank  7  includes, for example, a white resin. 
     The phosphor containing layer  11  is provided on the substrate  3  and on the light-emitting bodies  5 . The phosphor containing layer  11  includes a translucent resin  14  such as silicone, the red phosphor  15  (a first phosphor), and the yellow phosphor  17  (a second phosphor). For example, the red phosphor  15  and the yellow phosphor  17  are dispersed in the translucent resin  14  in the phosphor containing layer  11 . 
     The red phosphor  15  is excited by emitted light of the light-emitting body  5  and has a light emission peak in a wavelength range equal to or greater than 610 nm and less than 655 nm. The red phosphor  15  includes, for example, a phosphor represented by a chemical formula K 2 SiF 6 :Mn. The surface of the red phosphor  15  is covered with a protection film  18  ( FIG. 1B ). The protection film  18  includes, for example, an oxide. 
     The yellow phosphor  17  is excited by emitted light of the light-emitting body  5  and has a light emission peak in a wavelength range between a peak wavelength of a light emission spectrum of the light-emitting body  5  and a peak wavelength of a light emission spectrum of the red phosphor  15 . The yellow phosphor  17  is, for example, a YAG phosphor. 
     In the phosphor containing layer  11 , a green phosphor may be used instead of the yellow phosphor  17  or the green phosphor may be dispersed besides the red phosphor  15  and the yellow phosphor  17 . 
     In the light-emitting module  10 A, for example, the translucent resin  14 , in which the red phosphor  15  and the yellow phosphor  17  are dispersed, is poured into the inner side of the bank  7  and hardened. Consequently, the phosphor containing layer  11  configured to cover the light-emitting bodies  5  is provided. The correlated color temperature of the light-emitting module  10 A is, for example, 2700 to 5500 K. An average color rendering index of the light-emitting module  10 A is, for example, equal to or higher than  85 . 
     The red phosphor  15  according to the first embodiment is described more in detail. 
       FIG. 2A  is a diagram showing a light emission spectrum of the red phosphor according to the first embodiment.  FIG. 2B  is a schematic sectional view showing a process of formation of the protection film on the surface of the red phosphor according to the first embodiment. 
     The abscissa of  FIG. 2A  indicates a light emission wavelength λ and the ordinate of  FIG. 2A  indicates light emission intensity I L  (an arbitrary value). A line A in the figure represents a light emission spectrum of the K 2 SiF 6 :Mn phosphor included in the red phosphor  15 . A line B in the figure represents a light emission spectrum of a CASN phosphor according to a comparative example. 
     As represented by the line A, the K 2 SiF 6 :Mn phosphor has light mission peaks P 1  (λ: near 610 nm), P 2  (λ: near 630), and P 3  (λ: near 650) having half width equal to or smaller than 20 nm in a wavelength region equal to or greater than 610 nm and less than 655 nm. The light emission intensity I L  in a wavelength region equal to or greater than 655 nm is equal to or smaller than a half of the light emission peaks P 1  and P 2 . 
     On the other hand, as represented by the line B, the CASN phosphor has a broad light emission peak in a wavelength range of 500 to 700 nm. Half width of the light emission peak reaches about 170 nm. Light emission intensity at a wavelength of 650 nm is about 80% of light emission intensity at the peak wavelength. 
     In the K 2 SiF 6 :Mn phosphor, the intensity of a light emission spectrum in a wavelength band equal to or greater than 650 nm, where relative visibility falls, is lower than the intensity of the CASN phosphor. Therefore, if a correlated color temperature and an average color rendering index are the same, a luminous flux is larger in the light-emitting module in which the K 2 SiF 6 :Mn phosphor is used than in the CASN phosphor. That is, the light-emitting module having higher light-emitting efficiency is obtained. 
     The red phosphor  15 , the surface of which is covered with the protection film  18 , is formed by, for example, a method shown in  FIG. 2B . First, as shown in the left diagram of  FIG. 2B , after the red phosphor  15  including K 2 SiF 6 :Mn is prepared, a K 2 SiF 6  layer  18   a,  in which Mn (manganese) is not substituted, is formed on a surface  15   s  of the red phosphor  15 . Subsequently, the K 2 SiF 6  layer  18   a  is oxidized, whereby, as shown in the right drawing of  FIG. 2B , the K 2 SiF 6  layer  18   a  is changed to an oxide (e.g., SiO 2 ) of silicon (Si) included in the K 2 SiF 6  layer  18   a.  In a process in which the silicon oxide is preferentially formed, K (potassium) and F (fluorine) are removed. 
     A component of the protection film  18  is not limited to the silicon oxide and only has to be a material having a refractive index equal to or higher than the refractive index of a silicone resin and having light transmittance at a wavelength equal to or greater than 400 nm. For example, the component of the protection film  18  may be aluminum oxide (Al 2 O 3 ), titanium oxide (TiO 2 ), or the like. As a method of forming the protection film  18  on the surface of the red phosphor  15 , a complex method, a sol-gel method, or the like is adopted. 
     An effect of the light-emitting module  10 A according to the first embodiment is described below. 
     For example, as light-emitting modules of a COB type, a first light-emitting module for comparison A, a second light-emitting module for comparison B, and the light-emitting module  10 A according to the first embodiment were prepared. In the light-emitting modules, on the substrate  3 , seven light-emitting bodies  5  are mounted in series and twenty-four rows of the seven light-emitting bodies  5  are mounted in parallel. A dimension of a light-emitting section of each of the light-emitting modules is 13 mm×17 mm. 
     On the inner side of the bank  7  of the light-emitting module A, the translucent resin  14  in which a yellow phosphor (YAG), a green phosphor (G-YAG), and a red phosphor (CASN) are dispersed is arranged as a phosphor containing layer. The translucent resin  14  is, for example, a methyl silicone resin. The average color rendering index Ra of the light-emitting module A is  89  and the correlated color temperature of the light-emitting module A is 2900 K. 
     In the light-emitting module B, the red phosphor  15  (K 2 SiF 6 :Mn) not provided with the protection film  18  is used instead of the red phosphor (CASN) of the light-emitting module A. Components other than the red phosphor  15  are the same as the components of the light-emitting module A. 
     In the light-emitting module  10 A, the red phosphor  15  (K 2 SiF 6 :Mn) provided with the protection film  18  is used instead of the red phosphor (CASN) of the light-emitting module A. Components other than the red phosphor  15  are the same as the components of the light-emitting module A. 
     Among the light-emitting modules, the light-emitting efficiency of the light-emitting module B and the light-emitting module  10 A rose to “115” compared with the light-emitting efficiency of the light-emitting module A assumed to be “100”. In the light-emitting module B and the light-emitting module  10 A, K 2 SiF 6 :Mn is used as the red phosphor. Therefore, the light-emitting efficiency of the light-emitting module B and the light-emitting module  10 A rises more than the light-emitting efficiency of the light-emitting module A. 
     In the light-emitting module B, compared with a correlated color temperature after 100 hours elapsed from the start of lighting, a correlated color temperature after 1000 hours elapsed from the start of lighting rose Δ110 K. However, in the light-emitting module  10 A, compared with the correlated color temperature after 100 hours elapsed from the start of lighting, the correlated color temperature after 1000 hours elapsed from the start of lighting only rose Δ30 K. 
     In the light-emitting module B, the surface of the red phosphor  15  is not covered with the protection film  18 . The red phosphor  15  includes fluorine having affinity with water. Therefore, the water in the atmosphere diffuses in the translucent resin  14  and directly comes into contact with the red phosphor  15 . As a result, if the light-emitting module B is continuously used for a long time, deterioration of the red phosphor  15  sometimes occurs in the light-emitting module B. 
     On the other hand, in the light-emitting module  10 A, the surface of the red phosphor  15  is covered with the protection film  18 . Therefore, even if the light-emitting module  10 A is continuously used for a long time, in the light-emitting module  10 A, the red phosphor  15  is protected by the protection film  18 . Deterioration of the red phosphor  15  is suppressed compared with the light-emitting module B. 
     As explained above, the light-emitting module  10 A has the high color rendering index and the high light-emitting efficiency. Deterioration of the red phosphor  15  is suppressed. That is, in the first embodiment, the light-emitting module  10 A is realized that has the high color rendering index and the high light-emitting efficiency and in which a color shift less easily occurs. 
     Variation of the First Embodiment 
       FIG. 3A  is a schematic sectional view of a light-emitting module according to a first variation of the first embodiment.  FIG. 3B  is a schematic sectional view of a light-emitting module according to a second variation of the first embodiment. 
     In a light-emitting module  10 B shown in  FIG. 3A , in addition to the components of the light-emitting module  10 A, the phosphor containing layer  11  further includes oxide particles  19 . The oxide particles  19  are, for example, oxide particles having a refractive index higher than the refractive index of the translucent resin  14 . The oxide is, for example, a titanium oxide (TiO 2 ). In the light-emitting module  10 B, as in the light-emitting module  10 A, the surface of the red phosphor  15  is covered with the protection film  18 . 
     It is known that, among red phosphors, K 2 SiF 6 :Mn has a low refractive index compared with the other red phosphors. Therefore, if the light-emitting body  5  is covered with the phosphor containing layer  11  including the red phosphor  15 , it is likely that efficiency of extracting light from the light-emitting body  5  is deteriorated in a light-emitting module. 
     On the other hand, in the light-emitting module  10 B, the decrease in the refractive index of the phosphor containing layer  11  due to the mixing of the red phosphor  15  is suppressed by mixing the oxide particles  19  having the high refractive index in the phosphor containing layer  11 . Consequently, in the light-emitting module  10 B, the deterioration in the light-emitting efficiency is suppressed. For example, it is known that, if the light-emitting efficiency of the light-emitting module  10 A is assumed to “100”, the light-emitting efficiency of the light-emitting module  10 B, in which the titanium oxide particles are dispersed in the phosphor containing layer  11 , rises to “107”. 
     The phosphor containing layer does not need to be a single layer and may be formed by, for example, a plurality of layers. 
     For example, as shown in  FIG. 3B , a light-emitting module  10 C includes the phosphor containing layer  11  and a phosphor containing layer  13 . The phosphor containing layer  11  includes the red phosphor  15  and the translucent resin  14 . The phosphor containing layer  13  includes the yellow phosphor  17  and a translucent resin  16 . The phosphor containing layer  13  is provided between the light-emitting bodies  5  and the phosphor containing layer  11 . That is, on the substrate  3 , the yellow phosphor  17  is arranged between the red phosphor  15  and the light-emitting bodies  5 . As the phosphor  17 , a green phosphor may be used or a phosphor obtained by mixing a yellow phosphor and a green phosphor may be used. The oxide particles  19  may be mixed in the phosphor containing layer  11 . 
     Second Embodiment 
       FIG. 4  is a schematic sectional view of a luminaire according to a second embodiment. 
     Any one of the light-emitting modules  10 A to  10 C is incorporated in a luminaire  100  as a light source. The luminaire  100  is, for example, a bulb-type lamp. The luminaire  100  includes any one of the light-emitting modules  10 A to  10 C, a housing  21  mounted with any one of the light-emitting modules  10 A to  10 C, and a cover  30  configured to cover any one of the light-emitting modules  10 A to  10 C. The luminaire  100  is one example. The embodiments are not limited to the luminaire  100 . 
     On the inside of the housing  21 , a power converting section  40  configured to supply electric power to any one of the light-emitting modules  10 A to  10 C is provided. The power converting section  40  is electrically connected to any one of the light-emitting modules  10 A to  10 C and a cap  50  via lead wires  41  and  42 . The power converting section  40  is housed in an insulating case  23  provided on the inside of the housing  21 . The power converting section  40  receives the supply of alternating-current power from a not-shown commercial power supply via the cap  50 , converts the alternating-current power into, for example, direct-current power, and supplies the direct-current power to any one of the light-emitting modules  10 A to  10 C. 
     Any one of the light-emitting modules  10 A to  10 C receives the supply of electric power from the power converting section  40  and emits white light. That is, the light-emitting module emits white light obtained by mixing blue light emitted from the light-emitting body  5 , red light emitted from the red phosphor  15 , and yellow light emitted from the yellow phosphor  17 . 
     As the light-emitting module, the light-emitting module of the COB type is illustrated. However, a light-emitting module of an SMD (Surface Mount Device) type may be used. 
     In the embodiments, “a part A is provided on a part B” means that the part A is provided on the part B in contact with the part B and also sometimes means that the part A is provided above the part B not in contact with the part B. 
     Although the embodiments are described above with reference to the specific examples, the embodiments are not limited to these specific examples. That is, design modification appropriately made by a person skilled in the art in regard to the embodiments is within the scope of the embodiments to the extent that the features of the embodiments are included. Components and the disposition, the material, the condition, the shape, and the size or the like included in the specific examples are not limited to illustrations and can be changed appropriately. 
     The components included in the embodiments described above can be combined to the extent of technical feasibility and the combinations are included in the scope of the embodiments to the extent that the feature of the embodiments is included. Various other variations and modifications can be conceived by those skilled in the art within the spirit of the invention, and it is understood that such variations and modifications are also encompassed within the scope of the invention. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.