Invented by Chul Soo Yoon, Jong Rak Sohn, Il Woo Park, Samsung Electronics Co Ltd
The Samsung Electronics Co Ltd invention works as followsA white light emitting apparatus capable of expanding the range of wavelengths of a blue led used to produce white light. The white light-emitting device of the present invention consists of a blue led and a mixture orange phosphor/green phosphor placed above the blue led.
Background for White light emitting devices
The present invention is a white-light emitting device that uses a Light Emitting Diode. It can, in particular, increase the range of peak wavelengths of a LED when using orange and green phosphor.
A white Light Emitting Diode device has been widely used in recent years as the backlight for a liquid-crystal display device, replacing a fluorescent or small lamp. A white LED device can be created by combining a yellow phosphor with a blue led. The LED emits blue light, which excites the phosphor. This yellow light is then produced. The combination of blue and yellow light is perceived by the observer as white. In this case, the yellow phosphor is typically made of YAG-Ce or TAG-Ce phosphors. These are garnet crystals activated by Ce3+. In addition, Eu2+-activated silicate phosphor is widely used for the yellow phosphor for the white LED device, including for example, phosphors having compositions expressed by formulae: (2?x?y)SrO.x(Ba,Ca)O. (1?a?b?c?d)SiO2.aP2O5bAl2O3.cB2O3.dGeO2:yEu2+, where 0
Each of the yellow phosphors mentioned above has a unique yellow peak wavelength. The wavelength of the LED used with yellow phosphors is very limited. This is because in order to achieve pure white in a range of x=0.27-0.33, y=0.25-0.35, in the CIE chromaticity of 1931, the wavelength of blue LEDs must be extremely short. To overcome these drawbacks, it has been suggested that Y can be substituted with Gd, Al or Ga in the YAG phosphor or Tb with Gd, Al or Ga in the TAG phosphor to obtain a shorter peak wavelength. In the case of silicate phosphors, Sr and Ca can be substituted together to change the wavelength of the yellow silicate phosphor.
The wavelength shift range is however limited by changing the composition in the manner described above. The shift range in wavelength is also limited in practice, because the phosphor wavelength changes result in reduced light emission in a particular wavelength region. The shift range for the yellow light emitting wavelength is also very small when using conventional Garnet or silicate-based yellow LEDs. This limits the light emission spectrum of the blue led used in conjunction to achieve white light. This, in turn, hinders the realization of high-quality white light.
The present invention was made to solve these problems in the prior art. Therefore, an aspect of this invention is a white LED emitting device that can expand the range of peak wavelengths of a blue led used to realize white light.
According to one aspect of the invention the invention provides: a white-light emitting device that includes a blue-light emitting phosphor; and a mixture orange phosphor, and green phosphor placed above the blue light emitting phosphor.
The white light emitting devices should include an encapsulant to encapsulate the blue light-emitting diode. The mixture of orange phosphor, and green phosphor, is then dispersed within the encapsulant.
According to the present invention the range for selecting the peak wavelengths of a blue LED that is applicable can be extended to a range between 420 and 480 nm. The orange phosphor emits light at a maximum of 560-590 nm. The green phosphor should have an emission peak between 510 and 550 nm.
According to an embodiment of the present invention, the orange phosphor may be a silicate phosphor having a composition expressed by a following formula: (3?x?y)SrO.x(Ba,Ca)O. (1?a?b?c?d)SiO2.aP2O5bAl2O3.cB2O3.dGeO2:yEu2+, where 0?x