Wavelength conversion plate and light emitting device using the same

Provided is a wavelength conversion plate having excellent luminous efficiency of a wavelength-converted light. The wavelength conversion plate includes a dielectric layer with nano pattern, a metal layer formed inside the nano pattern, and a wavelength conversion layer formed on the metal layer and having quantum dot or phosphor which wavelength-converts an excitation light to generate a wavelength-converted light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No. 2008-0086983 filed on Sep. 3, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device and a method for manufacturing the same, and more particularly, to a wavelength conversion plate having excellent luminous efficiency of a wavelength-converted light, and a light emitting device using the same.

2. Description of the Related Art

Light emitting diode (LED) is characterized in that it emits light substantially identical to monochromatic light, while light from other light emitting devices such as an incandescent lamp has a wide light emission spectrum. Since LEDs have different energies according to their electron-hole recombination, they emit a red light, a green light, a blue light, a reddish yellow light, or a yellow light according to their characteristics.

Recently, there have been developed LEDs which can emit a white light or reproduce a plurality of colors. A white LED is manufactured by combination of several color LED chips, or combination of LED chips emitting specific color light and phosphors emitting specific color fluorescence. The currently commercialized white LED generally employs the latter method.

For example, a white LED package can be obtained by encapsulating a blue LED chip with a molding resin where a yellow phosphor is dispersed. If light having a wavelength of 460 nm is generated from the blue LED chip, the yellow phosphor absorbs the light and generates light having a wavelength of 545 nm. The two lights having the different wavelengths are mixed to output a white light. Therefore, a desired color light can be obtained by combining different kinds of phosphors.

Although the desired color can be obtained using the phosphors, the increase of the luminous efficiency is still required in view of the emission of the LED.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a wavelength conversion plate having excellent luminous efficiency of a wavelength-converted light, and a light emitting device using the same.

According to an aspect of the present invention, there is provided a wavelength conversion plate including: a dielectric layer with nano pattern; a metal layer formed inside the nano pattern; and a wavelength conversion layer formed on the metal layer and comprising quantum dot or phosphor which wavelength-converts an excitation light to generate a wavelength-converted light.

The dielectric layer may include polymer resin or metal oxide. The polymer resin may include poly methyl methacrylate (PMMA), poly lauryl methacrylate (PLMA), or polystyrene. The metal oxide may include SiO2or TiO2. The metal layer may include any one of Au, Ag, Al, Cu, Pt, Pd, and alloy thereof.

According to another aspect of the present invention, there is provided a light emitting device including: a light emitting element; a groove part having a bottom surface where the light emitting element is mounted, and a side surface where a reflection part is formed; a support part supporting the groove part and having an electrode part electrically connected to the light emitting element; and a wavelength conversion plate disposed in at least one of the bottom surface and the side surface of the groove part, wherein the wavelength conversion plate includes: a dielectric layer with nano pattern; a metal layer formed inside the nano pattern; and a wavelength conversion layer formed on the metal layer and comprising quantum dot or phosphor which wavelength-converts an excitation light to generate a wavelength-converted light.

The light emitting device may further include a wavelength conversion unit disposed on the light emitting element and having quantum dot or phosphor which wavelength-converts light from the light emitting element. The wavelength conversion unit may be implemented with a plurality of layers. In this case, the wavelength conversion unit may be formed inside the groove part where the light emitting element is mounted.

When the wavelength conversion unit is implemented with a plurality of layers, at least two wavelength conversion units among the plurality of wavelength conversion units may include quantum dots or phosphors which convert the light emitted from the light emitting element into light having different wavelengths. Therefore, the light emitting element may emit an infrared light; the wavelength conversion plate may emit a blue light; a first wavelength conversion unit among the plurality of wavelength conversion units may emit a red light; and a second wavelength conversion unit different from the first wavelength conversion unit among the plurality of wavelength conversion units may emit a green light. In this way, the light emitting device can emit a white light.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1illustrates a wavelength conversion plate according to an embodiment of the present invention. The wavelength conversion plate10according to the embodiment of the present invention includes a dielectric layer11with nano pattern12, a metal layer13formed inside the nano pattern12, and a wavelength conversion layer14formed on the metal layer13and having quantum dot or phosphor wavelength-converting an excitation light to generate a wavelength-converted light.

Since the wavelength conversion plate10according to the embodiment of the present invention includes the dielectric layer11with the nano pattern12and the film-type metal layer13inside the nano pattern12, that is, the patterned metal layer13, incident light is amplified by surface plasmon phenomenon generated at an interface of the dielectric layer11and the metal layer13.

The surface plasmon phenomenon is a collective charge density oscillation generated at the surface of the metal film, and a surface plasmon wave generated by the collective charge density oscillation is a surface electromagnetic wave which propagates along the interface of the metal and the dielectric. Such a phenomenon is generated in metals, such as gold (Au), silver (Ag), copper (Cu) or aluminum (Al), which are easily subject to emission of electrons by external stimulation and have a negative dielectric constant. Among those metals, silver (Ag) exhibiting the sharpest surface plasmon resonance (SPR) peak and gold (Au) exhibiting excellent surface stability are usually used.

The excitation of the surface Plasmon refers to the phenomenon that, when an electric field is applied from the outside to the interface of two media (i.e., metal and dielectric) having a different dielectric constant, surface charges are induced because of the discontinuity of vertical components of the electric field at the interface of the two media, and oscillation of those surface charges is exhibited as the surface plasmon wave.

Recently, the emission increase phenomenon derived from the surface plasmon phenomenon has been reported (Nano Letters, Vol. 5, No. 8, 1557-1561, 2005). According to this document, after patterning a polymer resin with constant sizes and intervals, an Ag layer was formed and a visible ray was irradiated thereon. In this case, the luminous efficiency was rapidly increased more than 10 times.

In the wavelength conversion plate10according to the embodiment of the present invention, if the quantum dot or phosphor included in the wavelength conversion layer14wavelength-converts the excitation light, the surface plasmon phenomenon is generated in the metal layer13and thus the wavelength-converted light is amplified.

The dielectric layer11may include a material having a different dielectric function from the metal layer13in order to generate the surface plasmon phenomenon in the metal layer13. For example, the dielectric layer11may include polymer resin or metal oxide. The polymer resin used herein may be, but is not limited to, poly methyl methacrylate (PMMA), poly lauryl methacrylate (PLMA), or polystyrene. Also, the metal oxide used herein may be, but is not limited to, SiO2or TiO2.

The nano pattern12is formed in the dielectric layer11. Referring toFIG. 1, the nano pattern12may be formed in a cylindrical shape with a curved bottom. However, there is no special limitation in the shape of the nano pattern12only if the pattern itself is nano-sized.

As a method of forming the nano pattern12in the dielectric layer11, an Anodic Aluminum Oxide template (AAO template) formed by oxidizing aluminum may be used. In the method using the AAO template, aluminum is used because of its unique characteristic in that aluminum forms a pore arrangement in itself in an oxidation process for forming aluminum oxide. In this case, the pore is several ten to several hundred nanometers in diameter and is several micrometers in length according to voltage and concentration of an acid solution in the aluminum oxidation process.

Therefore, if the dielectric layer is formed and its upper surface is etched using the AAO template, the nano pattern12is formed in the same shape as the pore formed in the AAO template.

The metal layer13patterned along the pattern inside the nano pattern12is formed on the dielectric layer11. As described above, the metal layer13may be formed using a metal where the surface Plasmon phenomenon is easily generated, that is, a metal which is easily subject to emission of electrons by external stimulation and has a negative dielectric constant. The metal may include, but is not limited to, Au, Ag, Al, Cu, Pt, or Pd. There are many methods of forming the metal layer13. As one method, the metal layer13may be formed by sputtering a metal onto the dielectric layer11where the nano pattern12is formed.

The wavelength conversion layer14is formed on the metal layer13. The wavelength conversion layer14includes quantum dot or phosphor which wavelength-converts the excitation light to generate the wavelength-converted light. The wavelength conversion layer14is formed while filling the inside of the pattern of the metal layer13.

The quantum dot is a nano-sized light emitting body which has a diameter of 10 nm or less and exhibits a quantum confinement effect. The quantum dot generates stronger light than a typical phosphor in a narrow wavelength. The emission of the quantum dot is generated when excited electrons move from a conduction band to a valence band. Even the same material exhibits different wavelengths according to the particle size. As the size of the quantum dot is smaller, light having a shorter wavelength is emitted. Thus, light having a desired wavelength range can be obtained by adjusting the size of the quantum dot.

The quantum dot emits light even at an arbitrary excitation wavelength. Thus, when several kinds of quantum dots exist, several color light can be observed at a time even though the quantum dot is excited at a single wavelength. Furthermore, since the quantum dot moves from the ground oscillation state of the conduction band to the ground oscillation state of the valence band, it is advantageous that the emission wavelength is almost the monochromatic light.

The quantum dot may be a semiconductor nanocrystal. Examples of the quantum dot may include Si nanocrystal, group II-VI compound semiconductor nanocrystal, group III-V compound semiconductor nanocrystal, or group IV-VI compound semiconductor nanocrystal. In the current embodiment, the quantum dots may be used solely or in mixture thereof.

Moreover, the group IV-VI compound semiconductor nanocrystal may include, but is not limited to, SbTe.

As a method of synthesizing the nanocrystal as the quantum dot, the quantum dot is formed by a vapor deposition method, such as a metal organic chemical vapor deposition (MOCVD) or a molecular beam epitaxy (MBE), or a chemical wet method of growing a crystal by putting a precursor material into an organic solvent.

The phosphor may be selected from an oxide phosphor, a sulfide phosphor, and a nitride phosphor according to the conversion wavelength. For example, the phosphor may include a yellow emission phosphor based on β-SiAlON:Eu,Re, a silicate-based green emission phosphor such as (Ba,Sr,Ca,Mg)2SiO4:Eu,Re, or a sulfide-based green emission phosphor such as (Ba,Sr,Ca,Mg) (Ga,Al,In)2(S,Se,Te)4:Eu,Re, a nitride-based red emission phosphor such as (Sr,Ca,Ba,Mg)AlSiNx:Eu,Re (1≦x≦5), or a sulfide-based red emission phosphor such as (Sr,Ca,Ba,Mg)(S,Se,Te):Eu,Re. Herein, Re may be any one of Nd, Pm, Sm, Tb, Dy, Ho, Er, Tm, Yb, F, Cl, Br, and I.

The wavelength conversion layer14may be used by dispersing the quantum dot in a dispersive medium. The dispersive medium may be a resin such as epoxy resin or silicon. The wavelength conversion layer14may be formed by dispersing the quantum dot or phosphor in the dispersive medium and coating the dispersive medium on the metal layer13. The wavelength conversion performance of the wavelength conversion layer14may be selected by adjusting the concentration of the quantum dot or phosphor dispersed in the dispersive medium.

In the wavelength conversion plate10, the quantum dot or phosphor included in the wavelength conversion layer14absorbs the incident light and emits the wavelength-converted light. Thus, in addition to the wavelength conversion function, the wavelength conversion plate10can amplify the emission of the wavelength-converted light due to the surface plasmon phenomenon generated in the metal layer13formed inside the nano pattern12.

Therefore, the wavelength conversion plate10can be variously used when it is necessary to receive an excitation light from a light source, wavelength-convert the received excitation light and then amplify the wavelength-converted light. For example, the wavelength conversion plate10may be used as a reflection plate of a light guide panel in an LED package or backlight unit, but it is not limited thereto. Hereinafter, a light emitting device using the wavelength conversion plate10will be described in detail with reference toFIGS. 2 to 5.

FIG. 2illustrates a light emitting device including a wavelength conversion plate according to an embodiment of the present invention. Herein, duplicate description about the dielectric layer, the nano pattern, the metal layer, and the wavelength conversion layer in the light emitting device100ofFIG. 2will be omitted, except when necessary.

The light emitting device100according to the embodiment of the present invention includes a light emitting element140, a groove part, a support part110, and a wavelength conversion plate160. The groove part has a bottom surface where the light emitting element140is mounted, and a side surface where a reflection part120is formed. The support part110supports the groove part and includes an electrode part130electrically connected to the light emitting element140. The wavelength conversion plate160is disposed in at least one of the bottom surface and the side surface of the groove part. The wavelength conversion plate160includes a dielectric layer with nano pattern, a metal layer formed inside the nano pattern, and a wavelength conversion layer formed on the metal layer and including quantum dot or phosphor which wavelength-converts an excitation light to generate a wavelength-converted light. The electrode part130is formed with two sections which are electrically separated.

The light emitting element140may be one of a light emitting diode and a laser diode. A blue LED may be used as the light emitting element140. The blue LED may be a GaN-based LED emitting a blue light of 420-480 nm. The electrode part130is formed on the support part110and is electrically connected to the light emitting element140through a wire.

An encapsulation part150is formed of an encapsulation material on the light emitting element140in order to encapsulate the light emitting element140. The encapsulation part150is formed by filling the groove part with an encapsulation material, such as epoxy, silicon, acryl-based polymer, glass, carbonate-based polymer, or a mixture thereof.

The reflection part120formed in the side surface of the groove part reflects light generated from the light emitting element140toward the outside of the groove part. InFIG. 2, the wavelength conversion plate160is formed in the reflection part120.

The wavelength conversion plate160includes the dielectric layer with the nano pattern, the metal layer formed on the dielectric layer, and the wavelength conversion layer formed on the metal layer and including the quantum dot or phosphor which wavelength-converts the light generated from the light emitting element140to generate the wavelength-converted light. As described above with reference toFIG. 1, the wavelength conversion layer may be used by dispersing the quantum dot or phosphor in the dispersive medium. Since the dispersive medium may be a resin such as epoxy resin or silicon, it may be an identical or similar material to the encapsulation material.

Since the wavelength conversion plate160wavelength-converts and amplifies the light from the light emitting element140, the quantum dot or phosphor inside the wavelength conversion plate160may be selected considering color and intensity of light desired to be obtained from the light emitting device100. For example, when the light emitting element140emits a blue light, the light emitting device100can emit a white color by selecting the quantum dot or phosphor inside the wavelength conversion plate160such that it emits a yellow color.

Although the wavelength conversion plate160shown inFIG. 2is disposed at the reflection part120located on the side surface of the groove part, it can also be disposed on the bottom surface of the groove part.FIG. 3illustrates a light emitting device according to another embodiment of the present invention, in which a wavelength conversion plate is disposed on a bottom surface of a groove part. Regarding a dielectric layer, a nano pattern, a metal layer, and a wavelength conversion layer in the light emitting device200ofFIG. 3, the description of the same parts as described with reference toFIGS. 1 and 2will be omitted, except when necessary. Also, regarding a support part210, a reflection part220, an electrode part230, a light emitting element240, an encapsulation part250, and a wavelength conversion plate260, the description of the same parts as described with reference toFIG. 2will be omitted.

Unlike inFIG. 2, the wavelength conversion plate260is disposed on the bottom surface of the groove part where the light emitting element240is mounted. The wavelength conversion plate260is formed in a region other than the region where the light emitting element240is formed. The case where the wavelength conversion plate260is formed on the bottom surface of the groove part is related to the shape of the light emitting device200. In order for the wavelength conversion plate260to effectively wavelength-convert and amplify the light from the light emitting element240, the quantity of light reaching the wavelength conversion plate260should be large. However, if the width of the light emitting device200is wide, the case where the excitation light reaches the bottom surface may be much more than the case where the excitation light reaches the reflection part220. Therefore, in such a case, the wavelength conversion plate260is formed on the bottom surface of the groove part.

According to another embodiment of the present invention, in addition to the wavelength conversion plate formed in at least one of the side surface and the bottom surface of the groove part, a light emitting device further includes a wavelength conversion unit which wavelength-converts light from the light emitting element.FIG. 4illustrates the light emitting device which further includes the wave conversion unit according to the embodiment of the present invention. Regarding a dielectric layer, a nano pattern, a metal layer, and a wavelength conversion layer in the light emitting device300ofFIG. 4, the description of the same parts as described with reference toFIGS. 1 to 3will be omitted, except when necessary. Also, regarding a support part310, a reflection part320, an electrode part330, a light emitting element340, an encapsulation part350, and a wavelength conversion plate360, the description of the same parts as described with reference toFIGS. 2 and 3will be omitted.

In the current embodiment, the wavelength conversion unit370further included in the light emitting device300includes a wavelength conversion body371and a dispersive medium372. The wavelength conversion body371may be a typical quantum dot or phosphor. The dispersive medium372may be a medium which properly disperses polymer resin and the wavelength conversion body371. The dispersive medium372may be an identical or similar material to an encapsulation material of the encapsulation part350.

After mounting the light emitting element340, the wavelength conversion unit370may be formed on the light emitting element340before the groove part is filled with the encapsulation material350. The wavelength conversion unit370can include an appropriate quantum dot or phosphor according to the wavelength of light desired to be obtained from the light emitting device300, the color of the light emitted from the light emitting device300can be controlled together with the quantum dot or phosphor included in the wavelength conversion plate360. Although the wavelength conversion unit370shown inFIG. 4is formed in a layer type, it can also be formed to cover the surface of the light emitting device340. Also, the wavelength conversion unit370may be disposed in any shape only if the light incident from the light emitting element340can be wavelength-converted at the wavelength conversion unit370.

At this point, the light emitting device300can emit a white light, when the light emitting element340emits a blue light, the quantum dot or phosphor of the wavelength conversion unit370emits a red light, and the quantum dot or phosphor of the wavelength conversion plate360emits a green light. Furthermore, the light emitting element340can be made to emit a blue light, and the quantum dot or phosphor of the wavelength conversion unit370can be made to emit a yellow light. In this case, the quantum dot of the wavelength conversion plate360can be selected to emit a blue light or a yellow light. The color rendering of the light emitted from the light emitting device300can be controlled by making the quantum dot of the wavelength conversion plate360emit the light having the lower intensity of the blue light and the yellow light.

According to another embodiment of the present invention, a light emitting device may further include a plurality of wavelength conversion units.FIG. 5illustrates the light emitting device which further includes the plurality of wave conversion units according to the embodiment of the present invention. Regarding a dielectric layer, a nano pattern, a metal layer, and a wavelength conversion layer in the light emitting device400ofFIG. 5, the description of the same parts as described with reference toFIGS. 1 to 4will be omitted, except when necessary. Also, regarding a support part410, a reflection part420, an electrode part430, a light emitting element440, an encapsulation part450, and a wavelength conversion plate460, the description of the same parts as described with reference toFIGS. 2 and 4will be omitted.

In the current embodiment, the wavelength conversion units further included in the light emitting device400include a first wavelength conversion unit470and a second wavelength conversion unit480. InFIG. 5, a wavelength conversion unit nearer to the light emitting element440is referred to as the first wavelength conversion unit470, and another is referred to as the second wavelength conversion unit480. The first wavelength conversion unit470includes a first wavelength conversion body471and a first dispersive medium472, and the second wavelength conversion unit480includes a second wavelength conversion body481and a second dispersive medium482. The first and second wavelength conversion bodies471and481may be typical quantum dots or phosphors. The first and second dispersive media472and482may be media which properly disperse polymer resin and the first and second wavelength conversion bodies471and481. The first and second dispersive media472and482may be an identical or similar material to an encapsulation material of the encapsulation part450.

When the wavelength conversion unit is implemented with a plurality of layers, at least two wavelength conversion units may include quantum dots or phosphors which can convert the light emitted from the light emitting element into light having different wavelengths. Therefore, the light emitting element440emits a blue light, any one of the wavelength conversion units emits a red light, and the second wavelength conversion unit480different from the first wavelength conversion unit emits a green light. In this way, the light emitting device can emit a white light. Furthermore, the wavelength conversion plate460can select quantum dots to emit light by appropriately selecting the wavelength of the light required to be amplified among the blue light, the red light, and the green light.

Alternatively, the light emitting device can emit a white light, when the light emitting element440emits an infrared ray, and the wavelength conversion plate460, the first wavelength conversion unit470and the second wavelength conversion unit480emit a blue light, a green light and a red light, respectively.

The light emitting devices are shown in a package type inFIGS. 2 to 5, but they are not limited thereto. For example, the light emitting devices may be lamp-type light emitting devices.

The wavelength conversion plates according to the embodiments of the present invention can use the surface plasmon phenomenon by forming the metal layer on the dielectric layer with the nano pattern. Therefore, the wavelength-converted light generated by the wavelength conversion of the excitation light at the quantum dot, or the light emitted from the light emitting source can be amplified by the surface plasmon phenomenon.

Furthermore, if the wavelength conversion plate capable of amplifying the light by using the surface plasmon phenomenon is used on the side surface of the light emitting package, the luminous efficiency of the light emitting package can be increased. In addition, if the wavelength conversion plate is used as the reflection plate or wavelength conversion plate of the light emitting source, the light of the light emitting source can be amplified. Thus, the light emitting device having excellent efficiency can be manufactured.