Abstract:
A white light light-emitting diode is provided. The white light light-emitting diode includes a substrate including an anode and a cathode or a circuit, an ultraviolet light-emitting diode emitting ultraviolet with a peak wavelength between 320-400 nm disposed on the substrate, and a phosphor layer formed by blending blue, yellow and red phosphor grains with transparent resin pervious to ultraviolet and visible light applied on the ultraviolet light-emitting diode, wherein the yellow phosphor grains are excited by blue light with an emission band between about 400-530 nm.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a white light light-emitting diode, and in particular to a white light light-emitting diode with a layer comprising blue, yellow and red phosphor grains. 
         [0003]    2. Description of the Related Art 
         [0004]    A white light light-emitting diode (LED) is a point light source and packaged into matrix LED for illumination. When combined with different color LEDs, variety of mixing color light can be achieved. 
         [0005]    Combining at least two chromatic lights with various wavelengths produces white light. For example, combining blue and yellow light or blue, green and red light. Because light sources closer to sunlight are desirable, a white light LED with a specific spectrum, color rendering and correlated color temperature (CCT) similar to sunlight has been developed. The color rendering index (CRI) represents a real color exhibition of a subject while a light source irradiate thereon, which is compared to sunlight. Additionally, illumination demands for the home and factory are different. In the home, warm white source with low color temperature is required, for example, similar to the color of conventional tungsten-filament bulb. To the contrary, an illumination with high color temperature is required in the factory. Additionally, for LCD panels, a sufficient gamut of backlight (a light source) is required. Thus, various light sources have various illumination demands, and are designed to meet those demands. 
         [0006]    White light LEDs comprise of organic LEDs and inorganic LEDs. There are three main methods of forming the white light source of the inorganic LED. One is by a white light LED module composed of red, blue and green LEDs, with high luminous efficiency and high color rendering. However, various epitaxial materials (red, blue and green LED) exhibit different voltage properties, resulting in high cost and complicated control circuit design for implementation. Also, mixing trichromatic light to form white light is difficult. The second method uses blue LED to excite yellow phosphor grains to produce white light (Nichia Corporation). The blue LED is covered by an optical resin mixed with yellow phosphor grains. The blue LED emits blue light with a wavelength of 400-530 nm. The yellow phosphor grains are excited by the blue light emitted from the blue LED to produce yellow light, and combined with a proper amount of emitted blue light to finally produce the white light. 
         [0007]    However, the white light LED using the blue LED to excite the yellow phosphor grains suffers from some drawbacks. First, high color temperature and non-uniform light source are generated since the blue light dominated in the emitting spectrum. Also, an increasing in interaction between the blue light and the yellow phosphor grains is required to reduce the blue light intensity or increase yellow light intensity. However, the wavelength of blue light is shifted with increasing temperature, resulting in color shift of the white light emission. Finally, red light intensity is lacked, resulting in insufficient color rendering. Although red phosphor grains can be added to improve color rendering, color shift issue exist eventually. 
         [0008]    Another method uses ultraviolet LED to excite blue, green and red phosphor grains mixed in a transparent optical resin with a specific ratio, similar to white light generated from the fluorescent lamps. The white light source is uniform and high color rendering, without color shift. However, the luminous efficiency thereof is low. For example, Y. Narukawa utilizes 400 nm ultraviolet to excite blue and yellow phosphor grains under 20 mA to form a white light with color temperature of 5800K and color rendering index of 85.3. T. Nishida utilizes 350 nm ultraviolet to excite red, blue and green phosphor grains to form a white light with color rendering index of 86 and CIE color coordinates (x, y) of (0.411-0.416, 0.397-0.401). In order to improve color rendering, S. Nayama utilizes 375-380 nm ultraviolet to excite red, blue, green and yellow phosphor grains to form a white light with color rendering index of 94.2 and color temperature of 5800K. Y. Narukawa utilizes ultraviolet to excite blue-green, yellow and red phosphor grains under 20 mA to form a white light with color rendering index of 97 and color temperature of 5000K. The color shift, which results in using ultraviolet to excite various phosphor grains, is smaller than that of using blue light to excite yellow phosphor grains under 5 mA to 60 mA. U.S. Pat. No. 6,685,852 disclosed using 315-480 nm light sources to excite seven phosphor grains to form white light. Although the color rendering thereof achieved 95, at least four phosphor grains were required. US 2006/0022582 disclosed using 250-500 nm near ultraviolet or visible light to excite at least three phosphor grains, for example, green, orange and red phosphor grains to form white light. Light sources with high color rendering can be achieved by adjusting the concentration of the phosphor grains. However, its color was warm white. US 2007/0235751 disclosed using 405 nm ultraviolet to excite five phosphor grains to form a white light with color rendering index of 97.4. US 2007/0221938 disclosed using 400-405 nm light sources to excite red, yellow and blue or green or blue-green phosphor grains to form white light. Warm-white light sources with color rendering index of 90-99 can be achieved by adjusting the weight ratios among the phosphor grains. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    One embodiment of the invention provides a white light light-emitting diode comprising a substrate comprising an anode and a cathode or a circuit, an ultraviolet light-emitting diode with a peak wavelength between 320-400 nm disposed on the substrate, and a phosphor layer formed by blending blue, yellow and red phosphor grains with optically transparent resin, wherein the yellow phosphor grains are excited by blue light with wavelength of 400-530 nm. The phosphor layer is applied onto the ultraviolet light-emitting diode. 
         [0010]    Another embodiment of the invention provides a white light light-emitting diode comprising a substrate comprising an anode and a cathode or a circuit, an ultraviolet light-emitting diode emitting ultraviolet with a peak wavelength between 320-400 nm disposed on the substrate, a transparent resin layer pervious to ultraviolet and visible light overlying the ultraviolet light-emitting diode, and a phosphor layer formed by blending blue, yellow and red phosphor grains with transparent resin, wherein the yellow phosphor grains are excited by blue light with wavelength of 400-530 nm. The phosphor layer is applied onto the transparent resin layer. 
         [0011]    Yet another embodiment of the invention provides a white light light-emitting diode comprising a substrate comprising an anode and a cathode or a circuit, an ultraviolet light-emitting diode emitting ultraviolet with a peak wavelength between 320-400 nm disposed on the substrate, a transparent layer pervious to ultraviolet and visible light overlying the ultraviolet light-emitting diode, and a plurality of phosphor layers comprising blue, yellow and red phosphor layers respectively formed by blending blue, yellow or red phosphor grains with optical resin, wherein the yellow phosphor grains are excited by blue light with wavelength of 400-530 nm. 
         [0012]    In the invention, the blue, yellow and red phosphor grains are excited and their emitting lights are mixed to form white light. The red and blue phosphor grains are first excited by the ultraviolet light-emitting diode with a wavelength of 320-400 nm to emit red and blue light. The yellow phosphor grains are then excited by the emitting blue light to emit yellow light. The yellow light is formed through secondary excitation, rather than primary excitation. The remaining blue light is then combined with the yellow and red light to form white light with color rendering exceeding 90. 
         [0013]    In the white light light-emitting diode, the blue, yellow and red phosphor grains mixed in the phosphor layer with a proper ratio are excited by the ultraviolet light-emitting diode, achieving CIE color coordinates of (0.33, 0.33), color temperature of 3000-8000K and color rendering exceeding 90. 
         [0014]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawing, wherein: 
           [0016]      FIG. 1  is a cross-sectional view of a white light light-emitting diode in an embodiment of the invention. 
           [0017]      FIG. 2  is a cross-sectional view of a white light light-emitting diode in an embodiment of the invention. 
           [0018]      FIG. 3  is a cross-sectional view of a white light light-emitting diode in an embodiment of the invention. 
           [0019]      FIG. 4  is a spectrum of a white light light-emitting diode in an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0021]    An embodiment of a white light light-emitting diode of the invention is shown in  FIG. 1 . The white light light-emitting diode  10  comprises a substrate  12 , an ultraviolet light-emitting diode  14  and a phosphor layer  16 . The substrate  12  comprises an anode and a cathode (not shown) or a circuit (not shown). The ultraviolet light-emitting diode  14  is disposed on the substrate  12 . The phosphor layer  16  is applied on the ultraviolet light-emitting diode  14 . The phosphor layer  16  comprises blue, yellow and red phosphor grains  16 ′ and a transparent resin  18 . The yellow phosphor grains may comprise one of YAG, TAG and BOS phosphor grains. 
         [0022]    The ultraviolet light-emitting diode  14  may comprise Ill-V photosemiconductor, for example, GaN, InGaAlN or AlGaN. The ultraviolet light-emitting diode  14  emitted ultraviolet with a wavelength of 320-400 nm to excite the blue and red phosphor grains in the phosphor layer  16  to emit blue and red light. The yellow phosphor grains are excited by blue light with a wavelength of about 400-530 nm emitted from the blue phosphor grains to emit yellow light. The remaining blue light is then combined with the yellow and red light to form white light. 
         [0023]    In the phosphor layer  16 , the blue phosphor grains have a weight percent of about 15-50%. The yellow phosphor grains have a weight percent of about 10-70%. The red phosphor grains has a weight percent of about 15-40%. The transparent resin  18  is pervious to ultraviolet and visible light. The transparent resin  18  may comprise epoxy or silicon resin. The white light light-emitting diode  10  is a surface mount device (SMD) type white light light-emitting diode. 
         [0024]    Another embodiment of a white light light-emitting diode of the invention is shown in  FIG. 2 . The white light light-emitting diode  20  comprises a substrate  22 , an ultraviolet light-emitting diode  24 , a transparent layer  26  and a phosphor layer  28 . The substrate  22  comprises an anode and a cathode (not shown) or a circuit (not shown). The ultraviolet light-emitting diode  24  is disposed on the substrate  22 . The transparent layer  26  overlies the ultraviolet light-emitting diode  24 . The phosphor layer  28  is applied on the transparent layer  26 . The phosphor layer  28  comprises blue, yellow and red phosphor grains  16 ′ and a transparent resin  28 ′. The yellow phosphor grains may comprise one of the YAG, TAG and BOS phosphor grains. 
         [0025]    The ultraviolet light-emitting diode  24  may comprise Ill-V photosemiconductor, for example, GaN, InGaAlN or AlGaN. The ultraviolet light-emitting diode  24  may emit ultraviolet with a wavelength of 320-400 nm to excite the blue and red phosphor grains in the phosphor layer  28  to emit blue and red light. The yellow phosphor grains are excited by the emitting blue light from the blue phosphor grains to emit yellow light. The remaining blue light is then combined with the yellow and red light to form white light. The transparent layer  26  may be pervious to ultraviolet and visible light and comprise epoxy or silicon resin. 
         [0026]    In the phosphor layer  28 , the blue phosphor grains have a weight percent of about 15-50%. The yellow phosphor grains have a weight percent of about 10-70%. The red phosphor grains have a weight percent of about 15-40%. The transparent resin  28 ′ may be pervious to ultraviolet and visible light and comprise epoxy or silicon resin. 
         [0027]    Yet another embodiment of a white light light-emitting diode of the invention is shown in  FIG. 3 . The white light light-emitting diode  30  comprises a substrate  32 , an ultraviolet light-emitting diode  34 , a transparent layer  36  and a plurality of phosphor layers  38 . The substrate  32  comprises an anode and a cathode (not shown) or a circuit (not shown). The ultraviolet light-emitting diode  34  is disposed on the substrate  32 . The transparent layer  36  overlies the ultraviolet light-emitting diode  34 . The phosphor layers  38  were applied on the transparent layer  36 . The phosphor layers  38  comprises a blue phosphor layer  39 , a yellow phosphor layer  40 , a red phosphor layer  41  with transparent resin  39 ′,  40 ′ and  41 ′ dispersed in each phosphor layer. The blue phosphor grains have a weight percent of about 5-40% in the blue phosphor layer  39 . The yellow phosphor grains have a weight percent of about 10-50% in the yellow phosphor layer  40 . The red phosphor grains have a weight percent of about 5-40% in the red phosphor layer  41 . The transparent resin  39 ′,  40 ′ and  41 ′ may be pervious to ultraviolet and visible light and comprise epoxy or silicon resin. 
         [0028]    In this embodiment, the phosphor layers  48  comprise the blue phosphor layer  39 , the yellow phosphor layer  40  and the red phosphor layer  41  from bottom to top. However, the invention is not limited thereto, as any combination of the phosphor layers may be appropriate. However, the blue phosphor layer underlying the yellow phosphor layer is required to excite yellow phosphor grains. The yellow phosphor grains may comprise YAG, TAG or BOS phosphor grains. 
         [0029]    The ultraviolet light-emitting diode  34  may comprise GaN, InGaAlN or AlGaN. The ultraviolet light-emitting diode  34  may emit ultraviolet with a wavelength of 320-400 nm to excite the blue and red phosphor grains in the phosphor layers  38  to emit blue and red light. The yellow phosphor grains are excited by the emitting blue light from the blue phosphor grains to emit yellow light. The remaining blue light is then combined with the yellow and red light to form white light. The transparent layer  36  may be pervious to ultraviolet and visible light and comprise epoxy or silicon resin. 
         [0030]    In the invention, the blue, yellow and red phosphor grains are excited and their emitting lights are mixed to form white light. The red and blue phosphor grains are first excited by the ultraviolet light-emitting diode emitting ultraviolet with a wavelength of 320-400 nm to emit red and blue light. The yellow phosphor grains are then excited by the emitting blue light to emit yellow light. The yellow light is formed through secondary excitation, rather than primary excitation. The remaining blue light is then combined with the yellow and red light to form white light with color rendering exceeding 90. 
         [0031]    In the white light light-emitting diode, the blue, yellow and red phosphor grains mixed in the phosphor layer with a proper ratio are excited by the ultraviolet light-emitting diode, achieving Commission Internationale de l&#39;Eclairage (CIE) chromaticity coordinate of (0.33, 0.33), color temperature of 3000-8000K and color rendering exceeding 90. 
       EXAMPLE 1 
       [0032]    In accordance with the white light light-emitting diode shown in  FIG. 1 , blue phosphor grains had a weight percent of 35-40% in the total weight of phosphor grains. Yellow phosphor grains had a weight percent of 30-35% in the total weight of phosphor grains. Red phosphor grains had a weight percent of 25-35% in the total weight of phosphor grains. The white light light-emitting diode possessed improved luminescence performance, with color temperature of 6188K under 20 mA, color rendering of 93.69, and color coordinate of (0.33, 0.33). 
         [0033]      FIG. 4  shows spectrums of the abovementioned white light light-emitting diode and a CIE standard illuminates (D65) (CCT=6500K). In  FIG. 4 , the spectrum of the abovementioned white light light-emitting diode is similar to that of the CIE standard illuminates (D65). Thus, the quality of the the abovementioned white light light-emitting diode is similar to that of the standard light source (D65), achieving color coordinate (0.33, 0.33), color temperature less than 6500K and color rendering exceeding 90. 
         [0034]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.