Abstract:
A light emitting diode (LED). In one embodiment, the LED comprises a base including a cavity, an LED chip disposed on a bottom of the cavity and configured to generate a first light, and a light conversion layer. The light conversion layer includes an upper substrate, a lower substrate and a wavelength conversion particle. The light conversion layer is configured to convert a portion of the first light into a second light according to light emitted by the wavelength conversion particle. Furthermore, the light conversion layer is disposed on an upper surface of the base.

Description:
PRIORITY STATEMENT 
     This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 2008-105660, filed on Oct. 28, 2008 in the Korean Intellectual Property Office (KIPO), the contents of which are herein incorporated by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to light emitting diodes, and more particularly to light emitting diodes including a light conversion layer which converts received light to light with different wavelength. 
     2. Description of the Related Art 
     A white LED using a semiconductor, having advantages such as a long lifetime, capability of reduced size and operability at low voltage, is receiving attention as a next-generation LED. 
     There has been proposed a conventional technique of realizing white light by applying red, green and blue phosphors around a UV short wavelength LED. In this configuration, the red, green and blue phosphors are excited by the UV LED, and thus emit red, green and blue light, respectively. The red, green and blue light then mixes to produce white light. 
     However, there are a limited number of conventional phosphors that have sufficient light conversion efficiencies. The emission spectrum of these phosphors is not easily changed. Futhermore, the spectra are less than ideal in that the amount of light emitted varies as a function of wavelength. Hence, even by combining several phosphors, an optimum white light source is not obtained. 
     “Quantum dot” (QD) phosphors are phosphors whose emission spectra depends on the size of the particles, and hence can be used to convert light to a predetermined wavelength by utilizing the appropriate sized particles. Quantum dots are nanometer-sized semiconducting materials which exhibit quantum confinement effects. When the quantum dots are irradiated by light from an excitation source to reach energy excitation states, they emit energies corresponding to the respective energy band gaps. Since the control over the size of the quantum dots effectively controls the corresponding band gaps, energies of various wavelength regions can be obtained. QD phosphor is generally used in the form of resin mixture. Ligands are usually attached to the outer surface of the QD for high stability and high dispersion. 
     However, resin typically used for QD is optimized for inorganic phosphors. Since ligands conjugated with the outer surface of the QD are organic substances, resin interacts with the ligands, thereby hampering efficiency and durability of QD phosphors. 
     SUMMARY OF THE INVENTION 
     The present invention provides a light emitting diode (LED) including a base, a light conversion layer and an LED chip. Some embodiments of the invention are capable of achieving high efficiency and long durability of the light emitting diode. 
     The present invention also provides a backlight assembly including the light emitting diode. 
     These and other aspects of the present invention will be described in or be apparent from the following description of the exemplary embodiments. 
     According to an exemplary embodiment of the present invention, a light emitting diode (LED) comprises a base including a cavity, an LED chip disposed on a bottom of the cavity and configured to generate a first light, and a light conversion layer. The light conversion layer includes an upper substrate, a lower substrate and a wavelength conversion particle. The light conversion layer is configured to convert a portion of the first light into a second light according to light emitted by the wavelength conversion particle. Furthermore, the light conversion layer is disposed on an upper surface of the base. 
     In another exemplary embodiment, a light emitting diode (LED) comprises a base including a cavity, the cavity having a bottom and an opening, an LED chip disposed on the bottom and configured to generate a first light, and a light conversion layer. The light conversion layer includes an upper substrate, a middle substrate, a lower substrate, a sealing material and an organic solution with a wavelength conversion particle. The light conversion layer is disposed on an upper surface of the base. Additionally, the organic solution with the wavelength conversion particle fills gaps formed between the upper substrate and the middle substrate, and between the middle substrate and the lower substrate. 
     In still another exemplary embodiment of the present invention, a backlight assembly comprises a light emitting diode (LED) including a base including a cavity with a bottom and an opening, an LED chip disposed on the bottom and configured to generate a first light, and a light conversion layer. The light conversion layer includes an upper substrate, a lower substrate, and a wavelength conversion particle, and is configured to convert a portion of the first light into a second light. The assembly also includes an optical sheet disposed above the light emitting diode, and a receiving container receiving the light emitting diode and the optical sheet. The light conversion layer is disposed on an upper surface of the base, and comprises an organic solution filling a gap between the upper substrate and the lower substrate. The wavelength conversion particle is dispersed within the organic solution. 
     In still another exemplary embodiment, a backlight assembly comprises a light emitting diode (LED) including a base including a cavity with a bottom and an opening, an LED chip disposed on the bottom and configured to generate a first light, and a light conversion layer. The light conversion layer includes an upper substrate, a middle substrate, a lower substrate, and a wavelength conversion particle, and is configured to convert a portion of the first light into a second light. The assembly also includes an optical sheet disposed above the light emitting diode, and a receiving container receiving the light emitting diode and the optical sheet. The light conversion layer is disposed on an upper surface of the base, and the organic solution fills gaps formed between the upper substrate and the middle substrate, and between the middle substrate and the lower substrate. 
     In still another exemplary embodiment of the present invention, a method of manufacturing a light emitting diode comprises providing an upper substrate of a light conversion layer and a second substrate of the light conversion layer, each of which are transparent and comprise one or more of glass, plastic and resin. The method also includes filling a gap formed between the upper substrate and the second substrate with a wavelength conversion particle dispersed in an aqueous solution. A base is provided, the base including a cavity with a bottom and an opening, and an LED chip disposed on the bottom and configured to generate a first light. The light conversion layer is placed on an upper surface of the base. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of the present invention will become more apparent by describing in more detailed exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is an exploded perspective view of an exemplary embodiment of a liquid crystal display according to the present invention. 
         FIG. 2  is a cross-sectional view of a phosphor particle according to an exemplary embodiment of the present invention; 
         FIG. 3  is a cross-sectional view of an LED package according to the first exemplary embodiment of the present invention; 
         FIG. 4  is an enlarged view of a light conversion layer according to the first exemplary embodiment of the present invention; 
         FIG. 5  is a cross-sectional view of an LED package according to the second exemplary embodiment of the present invention; 
         FIG. 6  is an enlarged view of a light conversion layer according to the second exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout. 
       FIG. 1  is an exploded perspective view illustrating a first exemplary embodiment of a liquid crystal display  1000  according to the present invention. Referring to  FIG. 1 , a liquid crystal display may include a liquid crystal panel assembly  200 , a backlight assembly  300 , an upper receiving container  100 , and a plurality of LEDs  400 . 
     The liquid crystal panel assembly  200  may include a liquid crystal panel  210 , a gate PCB  230  and a data PCB  220 . The liquid crystal panel  210  may include a pair of glass substrates, and a liquid crystal layer provided therebetween (not shown). The gate PCB  230  and the data PCB  220  are attached to the liquid crystal panel. 
     The backlight assembly  300  may include a frame  310 , an optical sheet  320 , a reflective sheet  330  and a lower receiving container  340 . 
     The reflective sheet  330  is disposed below the LEDs  400  and, in the orientation shown, reflects light upward from below the LEDs  400 . 
     The optical sheets  320  are disposed on the LEDs  400  and serve to diffuse and focus light coming from the LEDs  400 . The optical sheet  320  may be an optical plate. 
     The frame  310  is disposed above optical sheet  320 . 
     The light emitting diodes (“LEDs”)  400  are disposed on the lower receiving container  340 . The LEDs  400  generate light using an LED driving voltage applied to the LEDs  400  from an external source (not shown). According to the present exemplary embodiment, a blue-green LED  400  and a blue-red LED  400  can be paired as an LED unit, generating white light. A single LED  400  can constitute an LED unit as well, creating white light by itself. Each LED  400  may include a light conversion layer  430  which contains a wavelength conversion particle such as a QD  500 . Each LED  400  is placed apart from each other at a predetermined distance, creating uniformity of the light. Specific structures of an LED  400  will be described in more detail below. 
     The lower receiving container  340  has sidewalls extending from the edges of a bottom surface. The lower receiving container  340  receives the optical sheet  320 , the LEDs  400 , the reflective sheet  330 , the frame  310 , and the liquid crystal panel assembly  200  in an area defined by its sidewalls. The lower receiving container  340  also serves to prevent bending of the optical sheets  320 . 
     The lower receiving container  340  is coupled to the upper receiving container  100  so that a periphery of an upper surface of the liquid crystal panel assembly  200  received in the lower receiving container  340  is covered. A window for exposing the liquid crystal panel assembly  200  to the outside is disposed on an upper surface of the upper receiving container  100 . 
       FIG. 1  describes a direct type of backlight assembly. However, the present invention is not limited thereto or thereby. The present invention may be applied to an edge type of backlight assembly. 
     Referring to  FIG. 2 , a QD phosphor  500  according to the exemplary invention may include a core nanocrystal  510  and at least two layers of shell nanocrystals  520 ,  530  having different compositions than those formed on the surface of the core nanocrystal  510 . 
     The QD phosphor  500  may include a core nanocrystal  510  and a plurality of shell nanocrystals  520 ,  530 . The QD phosphor  500  may have a structure wherein at least one shell layer  520 ,  530  of nanocrystals may be formed on a surface of a core nanocrystal  510  to shift the emission wavelength of the core nanocrystal  510  to a longer wavelength and at least one shell layer  520 ,  530  of nanocrystals may be formed thereon to increase the luminescence efficiency. 
     The QD phosphor  500  may include at least one material selected from among group II, III, V and VI compound semiconductors. Specifically, the core nanocrystal  510  may include CdSe or InGaP, and the shell nanocrystals  520 ,  530  may include ZnS or CuZnS. The size of QD phosphor  500  is generally between 1 nm and 10 nm. 
     Wavelengths of light emitted by the QD phosphor  500  may be controlled by either the size of QD phosphor  500  or molar ratio of a molecular cluster compound to nanoparticle precursors during the synthesis. Organic ligands  540  such as pyridine, mercapto alcohol, thiol, phosphine and phosphine oxide are used as stabilizers for QD phosphors  500  in an unstable state after synthesis. After syntheses, dangling bonds are created on outer surface of the QD phosphor  500  causing the QD phosphor  500  to be unstable. One end of ligands  540  include open bonds which can be conjugated with dangling bonds of QD phosphor  500 , making QD phosphor  500  stable. 
     Referring to  FIG. 3 , an LED  400  according to a first exemplary embodiment may include a base  410 , an LED chip  420 , and a light conversion layer  430 . The base  410  may include a cavity  412  formed as a substantially conical recess in the base  410 . The cavity  412  may include a bottom and an opening. An LED chip  420  may be die-mounted on the bottom of the cavity. The LED chip  420  generates a first light and may include a blue light-emitting source or a UV light-emitting source. The blue light-emitting source has a wavelength range of about 440 nm to about 500 nm. The UV light-emitting source has a wavelength range of about 350 nm to about 400 nm. A transparent resin  411  may fill the cavity  412  and cover the LED chip  420 , providing humidity protection around the LED chip  420 . The transparent resin  411  may include epoxy or silicon. The base  410  may be made of PPA (Poly Phthal Amide). The anode electrode (not shown) and the cathode electrode (not shown) are formed on the bottom of the base  410 , and serve to provide a power supply to the LED chip  420 . 
     Referring to  FIGS. 3 and 4 , the light conversion layer  430  converts the first light into a second light and may include an upper substrate  431 , a lower substrate  432  and a wavelength conversion particle  435 . The substrates are transparent and may be made of at least one material selected from among glass, plastic and resin. A generally constant gap d is formed between the two substrates, and an organic solution  434  containing wavelength conversion particles  435  fills the gap d. Joint portions between the upper substrate  431  and the lower substrate  432  are sealed with sealing materials  433  after the constant gap d is filled with the organic solution  432 . The sealing materials  433  make the light conversion layer  430  airtight. The wavelength conversion particles  435  are dispersed within the organic solution  434 . The organic solution  432  may include at least one of toluene, chloroform and ethanol. The light conversion layer  430  is disposed on an upper surface formed around the opening of the base  410 . An adhesive material (not shown) may be used to fix the light conversion layer  430  to the base  410  preventing any movement. 
     When using the blue light emitting source as an LED chip  420 , the wavelength conversion particles  435  may be either a green QD phosphor or a red QD phosphor. The green QD phosphor converts portions of blue light into green light having a wavelength range of about 520 nm to about 560 nm. The red QD phosphor converts portions of blue light into red light having a wavelength range of about 630 nm to about 660 nm. A white light can be generated when light from a blue light emitting source with a green QD phosphor, and a blue light emitting source with a red QD phosphor, are appropriately mixed. 
     When using the UV light-emitting source as an LED chip  420 , the wavelength conversion particles  435  may be one of a blue QD phosphor, a green QD phosphor and a red QD phosphor. The blue QD phosphor converts portions of UV light into blue light having a wave length range of about 430 nm to about 470 nm. A white light can be generated when light from a UV light-emitting source with the blue QD phosphor, a UV light-emitting source with a green QD phosphor, and a UV light-emitting source with a red QD phosphor are appropriately mixed. The color of each QD phosphor  435  is controlled by either the size of the QD phosphor or the molar ratio of a molecular cluster compound to nanoparticle precursors during the synthesis. 
     Referring to  FIGS. 5 and 6 , an LED  600  according to a second exemplary embodiment may include a base  610 , an LED chip  620 , and a light conversion layer  630 . One difference between the first exemplary embodiment and the second exemplary embodiment lies in the structure of the light conversion layer  630 . The light conversion layer  630  of the second exemplary embodiment may include an upper substrate  631 , a middle substrate  632 , a lower substrate  633 , and wavelength conversion particles  637 ,  638 . The light conversion layer  630  converts a portion of the first light into a second light and a portion of the first light into a third light. The light conversion layer  630  may include an organic solution  635 ,  634  with the wavelength conversion particles  637 ,  638  filling each generally constant gap d 1 , d 2  (where the gaps d 1 , d 2  are formed between the upper substrate  631  and middle substrate  632 , and between the middle substrate  632  and lower substrate  633 , respectively). The wavelength conversion particles  637 ,  638  are dispersed in the organic solution  635 ,  634 . The wavelength conversion particles  637 ,  638  may include QD phosphor. Sealing materials  636  seal each joint portion between the upper substrate  631  and middle substrate  632 , and between the middle substrate  632  and lower substrate  633 , respectively. The sealing materials  636  make the light conversion layer  630  airtight. 
     The LED chip  620  generating the first light may include a blue light emitting source. The blue light emitting source has a wavelength range of about 440 nm to about 500 nm. An upper portion  635  of the organic solution  635 ,  634  may then have red QD phosphor wavelength conversion particles  637 , while a lower portion  634  of the organic solution  635 ,  634  may have green QD phosphor wavelength conversion particles  638 . The red QD phosphor  637  converts the first light into a second light having a wavelength range of about 630 nm to about 660 nm. The green QD phosphor  638  converts the first light into a third light having a wavelength range of about 520 nm to about 560 nm. 
     This LED structure generates a white light by mixing blue, green and red light. Certain sequences of color QD phosphors may be preferred. For example, if the organic solution with red QD phosphor is disposed above the organic solution with green QD phosphor, interaction between red QD phosphor and green QD phosphor may occur, making the fabrication process difficult. That is, an additional process for preventing the interaction between the red QD phosphor and the green QD phosphor is omitted, so that the fabrication process may be simplified. 
     While the present invention has been particularly shown and described with reference to the exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. It is therefore desired that the present embodiments be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than the foregoing description to indicate the scope of the invention.