KR20070065486A - White light emitting device - Google Patents

Abstract

A white light emitting device is provided to obtain high-quality emission of white light having improved brightness, light emitting efficiency and a color rendering index by using UV(ultraviolet) LED(light emitting diode), a red fluorescent material, a green fluorescent material, a blue fluorescent material and a reflective medium. A UV LED is encapsulated by molding resin(107). Blue, green and red fluorescent materials emit blue, green and red light, excited by UV rays emitted from the UV LED. The UV rays emitted from the UV LED is reflected to the fluorescent material by a reflective medium. The reflective medium can include a UV reflection layer(108) which is formed on the molding resin to reflect UV rays and transmits visible rays.

Description

White light emitting device {WHITE LIGHT EMITTING DEVICE}

1 is a schematic cross-sectional view of a conventional white light emitting device.

2 is a cross-sectional view schematically showing a white light emitting device according to an embodiment of the present invention.

3 is a cross-sectional view schematically showing a white light emitting device according to another embodiment of the present invention.

4 is a cross-sectional view schematically showing a white light emitting device according to still another embodiment of the present invention.

5 is a schematic diagram showing an operating principle of a white light emitting device according to an embodiment of the present invention.

6 is a schematic diagram schematically showing energy transfer between phosphors used in the white light emitting device of one embodiment of the present invention.

7 is a graph showing an excitation spectrum and an emission spectrum of a red phosphor used in one embodiment of the present invention.

8A is a graph showing an excitation spectrum of a blue phosphor used in one embodiment of the present invention.

8B is a graph showing the emission spectrum of the blue phosphor used in one embodiment of the present invention.

9A is a graph showing excitation spectra of green phosphors used in one embodiment of the present invention.

9B is a graph showing the emission spectrum of the green phosphor used in one embodiment of the present invention.

10 to 12 are cross-sectional views schematically illustrating a light scattering layer according to various embodiments of the present disclosure.

<Description of the symbols for the main parts of the drawings>

100: white light emitting device 101: casing

102: UV LED (UV LED) 103: phosphor

104: reflective powder medium 105: reflective cup

106: reflecting surface 107: molding resin

108: ultraviolet reflecting film (UV reflecting film) 110: light scattering layer

The present invention relates to a white light emitting device, and more particularly, to a white light emitting device having an ultraviolet light emitting diode (also called an ultraviolet LED or a UV LED) and fluorescent materials.

The white LED device is used as a backlight of a liquid crystal display device instead of a conventional small lamp or a fluorescent lamp. S. Nakamura et al. "The Blue Laser", pp. As discussed in Chapter 10.4 of 216-221 (Springer 1997), white LED devices can be fabricated by forming a ceramic phosphor layer on the exit face of a blue LED.

Conventional representative white LED devices include a blue LED with InGaN quantum wells and a Y ₃ Al ₅ O ₁₂ : Ce ³⁺ (YAG: Ce) yellow phosphor. The blue light emitted from the blue LED emits yellow light by exciting the phosphor. The blue light from the blue LED and the yellow light from the yellow phosphor are mixed to be perceived by the viewer as white light.

In addition, blue LEDs can be combined with red phosphors and green phosphors to generate white light. Suitable phosphors should have high excitation efficiency and a wide chromatic zone in the range of about 420-480 nm.

White light can also be obtained by combining red LEDs, green LEDs, and blue LEDs. However, because different LEDs have different electro-optical characteristics (eg, lumens vs. lifetime profiles, power vs. input current curves of output light, and resistance vs. temperature curves), the combination of these LEDs is useful in the manufacture of white light emitting devices. It increases the cost and disadvantages the miniaturization of the device and does not produce light with consistent chromaticity and uniformity.

As another alternative for implementing white LED devices, blue, red and green phosphors can be combined with ultraviolet LEDs (UV LEDs). These phosphors are used to convert ultraviolet light emitted from UV LEDs into white light. Each phosphor used for this absorbs energy in a given region of the electromagnetic spectrum and emits radiant energy in another region. Typically, the energy of photons emitted is lower than the energy of photons that are absorbed. To obtain white light, phosphors combined with UV LEDs emit radiant energy (visible light) in the visible region of the spectrum in response to absorption of radiant energy (ultraviolet) outside the visible region.

However, to actually obtain white light, it is very difficult to find three suitable phosphors that are excited by ultraviolet light and emit light in the red, green, and blue regions, respectively. In general, the quantum yield of red phosphors is very low compared to green and blue phosphors. Therefore, high quality white light having an excellent color rendering index has not been obtained.

1 is a schematic cross-sectional view of a conventional white light emitting device using a UV LED. Referring to FIG. 1, the white light emitting device 50 includes a casing 51 in which a reflective cup 55 is formed and a UV LED 52 mounted in the casing 51. The side of the reflective cup 55 forms a reflective surface 56. In the reflecting cup 55, a molding resin 57 for encapsulating the UV LEDs 52 is formed, and phosphors 53 are dispersed in the molding resin 57. The phosphor 53 may be composed of a blue phosphor, a green phosphor, and a red phosphor, which are excited by ultraviolet light emitted from the UV LED 52 to emit blue light, green light, and red light, respectively. The blue, green, and red light emitted from the phosphor 53 are mixed with each other to output white light.

However, according to such a conventional white light emitting device 50, the quantum yield of the phosphor 53 (particularly the red phosphor) is not sufficient and the light loss in the light emitting device 50 is considerable. Therefore, the overall luminance of the light emitting device 50 is low, and it is difficult to obtain sufficient luminous efficiency and excellent color rendering index.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a high quality white light emitting device having high luminous efficiency and color rendering index as a white light emitting device having UV LEDs.

In order to achieve the above technical problem, a white light emitting device according to the present invention, UV LED; A molding resin encapsulating the UV LED; Blue, green and red phosphors which are excited by ultraviolet rays emitted from the UV LEDs and emit blue, green and red light, respectively; And a reflective medium for reflecting the ultraviolet light emitted from the UV LED to the phosphor.

According to a preferred embodiment of the present invention, the reflecting medium includes an ultraviolet reflecting film (UV reflecting film) formed on the molding resin to reflect ultraviolet light but transmit visible light. Preferably, the UV reflecting film is made of a multilayer dielectric film. The multilayer dielectric film includes two or more dielectric films having different refractive indices. The multilayer dielectric film may include at least one of a group consisting of TiO ₂ , ZrO ₂ , MgF _2, and LiF ₂ . Preferably, the multilayer dielectric film is a multilayer film formed by alternately stacking a first dielectric film having a first refractive index and a second dielectric film having a second refractive index smaller than the first refractive index. Preferably, the first refractive index is 1.82 to 2.5, and the second refractive index is 1.35 to 1.45. The white light emitting device may further include a glass substrate disposed between the molding resin and the ultraviolet reflecting film.

According to an embodiment of the present invention, the reflective medium may include a reflective powder medium dispersed in the molding resin to reflect the ultraviolet light emitted from the UV LED. The reflective powder medium may be made of at least one material selected from the group consisting of MgO, BaSO ₄ , Al ₂ O ₃ , ZrO ₂ and TiO ₂ . Preferably, the particle size of the reflective powder medium is larger than the peak emission wavelength of the ultraviolet light.

In one embodiment of the present invention, the phosphor and the reflective powder medium may be uniformly mixed in the molding resin. According to another embodiment, the phosphor and the reflective powder medium may be separated from each other on the UV LED to form a discontinuous layer structure. In this case, preferably, the phosphor is disposed on the UV LED and the reflecting powder medium is disposed on the phosphor.

According to the embodiment of the present invention, the reflective medium may include the UV reflective film and the reflective powder medium together. In this case, the ultraviolet reflection effect by the reflection medium further increases.

According to a preferred embodiment, the white light emitting device further comprises a casing having a reflecting cup, wherein the UV LED is mounted in the reflecting cup. The reflective cup may have a reflective surface formed of, for example, pressed BaSO ₄ on its inner surface.

According to an embodiment of the present invention, the white light emitting device may further include a light scattering layer formed on the UV LED. Preferably, the average particle size of the upper surface portion of the light scattering layer is greater than or equal to the wavelength of the ultraviolet light. Preferably, the refractive index of the light scattering layer is equal to or greater than the refractive index of the constituent material of the UV LED. The light scattering layer may be made of a material selected from the group consisting of Al ₂ O ₃ , SiO ₂ and SiN _x .

The light scattering layer may include a subcoating portion (subcoating) at the bottom thereof, the average particle size of the sub-coating portion is smaller than the average particle size of the upper surface of the light scattering layer and less than the ultraviolet wavelength. Preferably, the refractive index of the sub-coating portion is equal to or greater than the refractive index of the constituent material of the UV LED. The sub-coating portion may be made of a phosphor material.

According to a preferred embodiment of the present invention, the blue phosphor has a peak emission wavelength of 420 to 480 nm, the green phosphor has a peak emission wavelength of 490 to 550 nm, and the red phosphor of 580 to 620 nm Has a peak emission wavelength. The blue phosphor is excited by the ultraviolet light to emit blue light, the green phosphor is excited by the ultraviolet light and the blue light to emit green light, and the red phosphor is excited by the ultraviolet light, the blue light and the green light. To emit red light. Preferably, the UV LED has a peak emission wavelength of 350 to 410 nm.

Preferably, the blue phosphor is (Sr, Ca) ₅ (PO ₄ ) ₃ Cl: Eu ²⁺ , La _2.99 Ce _0.01 (SiS ₄ ) ₂ I and Ce ₃ (SiS ₄ ) ₂ X (X is Cl, Br Or at least one phosphor selected from the group consisting of I). Preferably, the green phosphor comprises at least one phosphor selected from the group consisting of SrGa ₂ S ₄ : Eu ²⁺ and (Ba, Sr) ₂ SiO ₄ : Eu ²⁺ . Preferably, the red phosphor comprises Ca (Eu _0.5 La _0.5 ) Si ₃ O ₁₃ .

According to a preferred embodiment of the invention, the blue, green and red phosphors are each separated and form a discontinuous layer structure on the UV LED. Preferably, the red phosphor is on the UV LED, the green phosphor is on the red phosphor, and the blue phosphor is on the green phosphor. Preferably, the blue, green and red phosphors are dispersed in the molding resin.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

2 is a cross-sectional view schematically showing a white light emitting device of the present invention. Referring to FIG. 2, the white light emitting device 100 includes a casing 101 and a UV LED 102. The casing 101 is formed with a concave reflection cup 105, and the UV LED 102 is mounted on the bottom of the reflection cup 105. The reflective cup 105 has a reflective surface 106 on its inner side. The reflecting surface 106 may be formed of, for example, press-BaSO ₄ (pressed BaSO _4). The reflecting surface 106 serves to increase the luminance of the output light by reflecting light incident on the reflecting surface 106 in the upward direction. The reflective cup 105 is filled with a transparent molding resin 107 for encapsulating the UV LEDs 102.

The phosphor 103 for wavelength conversion is dispersed in the molding resin 107. The phosphor 103 consists of a blue phosphor, a green phosphor and a red phosphor, which are excited by ultraviolet rays emitted from the UV LEDs 102 to emit blue light, green light and red light, respectively. Blue light, green light, and red light are mixed with each other to output white light.

Referring to FIG. 2, the white light emitting device 100 includes a UV anti-desert 108 formed on the molding resin 107. The UV reflecting film 108 is a kind of reflecting medium, and has a kind of band pass filter characteristic that reflects ultraviolet rays and transmits visible light. Using such a UV reflecting film 108 improves the brightness and luminous efficiency of the white light emitting device 100 because the ultraviolet rays reflected by the UV reflecting film 108 excite the phosphor 103 again. That is, the phosphor 103 is excited not only by the ultraviolet rays directly incident from the UV LED 102 but also by the ultraviolet rays reflected by the UV reflecting film 108. A glass substrate (not shown) may be disposed between the molding resin 107 and the UV reflecting film 108.

The UV reflecting film 108 may be made of a multilayer dielectric film. In this case, the UV reflecting film 108 may be formed of two or more dielectric films having different refractive indices n. In particular, the UV reflecting film 108 may be a multilayer film formed by alternately stacking a high refractive index dielectric film (preferably n = 1.82 to 2.5) and a low refractive index dielectric film (preferably n = 1.35 to 1.45). The multilayer dielectric film constituting the UV reflecting film 108 comprises at least one selected from the group consisting of TiO ₂ (n = 2.38), ZrO ₂ (n = 1.99), MgF ₂ (n = 1.38) and LiF ₂ (n = 1.39). It may include. For example, the UV reflecting film 108 can be made by alternately stacking a TiO ₂ film (n = 2.38) and an MgF ₂ film (n = 1.38).

3 is a cross-sectional view schematically showing a white light emitting device according to another embodiment of the present invention. Referring to FIG. 3, the white light emitting device 200 further includes a reflective powder medium 104 together with the above-described UV reflecting film 108 as a reflective medium. This reflective powder medium 104 reflects some of the ultraviolet light emitted from the UV LEDs 102. The ultraviolet rays reflected by the reflective powder medium 104 further excite the phosphor 103 (which is a combination of blue phosphor, green phosphor and red phosphor). The additional excitation further generates blue light, green light and red light, thereby increasing the overall quantum efficiency of the phosphor 103. Accordingly, the overall luminance of the white light emitting device 100 is further increased, and the color rendering index of the output white light is further improved.

Preferably, the reflective powder medium 104 is made of at least one material selected from the group consisting of MgO, BaSO ₄ , Al ₂ O ₃ , ZrO ₂ and TiO ₂ . For example, the reflective powder medium can be made using a sapphire (Al ₂ O ₃ ) material. In addition, the reflective powder medium 104 may be made of a metal or an inorganic material having high reflectance. In order to sufficiently reflect ultraviolet light, the particle size of the reflective powder medium 104 is preferably larger than the peak emission wavelength of the ultraviolet light. The reflective surface 106 can be made of the same powder material as the reflective powder medium 104.

The phosphor 103 and the reflecting powder medium 104 may be uniformly mixed in the molding resin 107. Alternatively, the phosphor 103 and the reflective powder medium 104 may be separated from each other on the UV LED 102 to form a discontinuous layer structure. In this case, the phosphor 103 is preferably disposed on the UV LED 102 and the reflective powder medium 104 is disposed on the phosphor 103. By arranging the phosphor layer and the reflecting powder medium layer in this order, the ultraviolet rays reflected by the reflecting powder medium can more easily excite the phosphor located rearward.

4 is a cross-sectional view of a white light emitting device according to still another embodiment. Referring to FIG. 4, the white light emitting device 300 includes a light scattering layer 110 together with a UV reflecting film 108, which is a reflecting medium, and a reflecting powder medium 104. This light scattering layer 110 serves to modify the symmetry of ray paths and the total internal reflection mechanism from the UV LEDs 102. By this light scattering layer 110, the light extraction efficiency from the UV LED 102 is improved.

10 is a cross-sectional view schematically showing a light scattering layer according to an embodiment of the present invention. Referring to FIG. 10, the light scattering layer 110 is formed on the light exit surface of the UV LED 102 to tunnel ultraviolet rays at the interface with the UV LED 102. Accordingly, the symmetry of the ultraviolet rays emitted from the UV LEDs 102 is changed and the total reflection mechanism at the interface with the UV LEDs 102 is changed. In addition, the upper surface portion of the light scattering layer 110 scatters ultraviolet rays passing through the light scattering layer 110. This tunneling phenomenon and scattering characteristics of the ultraviolet light, it is easy to extract the ultraviolet light toward the molding resin.

A portion 30 of the ultraviolet light 27 generated in the active region 26 of the UV LED 102 is tunneled at the interface between the light scattering layer 110 and the LED 102 and the other portion 29 of the ultraviolet light 27. ) Is reflected at its interface. This tunneling phenomenon occurs even when the ultraviolet ray 27 is incident at an incident angle larger than the critical angle. That is, when the distance between the surface of the UV LED 102 and the surface of the particles 111 of the light scattering layer 110 is equivalent to or smaller than the wavelength of the ultraviolet light 27, the light scattering layer 110 from the UV LED 102. Tunneling phenomenon of ultraviolet light is generated. The tunneled ultraviolet rays pass through the light scattering layer 110 and are scattered at the upper surface of the light scattering layer 110, thereby easily exiting to the outside (toward the molding resin).

The scattering characteristics of the light scattering layer 110 are affected by the size of the particles constituting the light scattering layer 110, in particular, the particle size at the upper surface of the light scattering layer 110. In order to effectively scatter the ultraviolet rays from the surface of the light scattering layer 110, the average particle size of the upper surface portion of the light scattering layer 110 is equal to or larger than the wavelength of the ultraviolet light.

Preferably, the refractive index of the light scattering layer 110 is equal to or greater than the refractive index of the constituents of the UV LEDs 102. As such, by using the light scattering layer 110 having a refractive index equal to or higher than the refractive index of the UV LED 102, the total reflection phenomenon at the interface between the light scattering layer 110 and the UV LED 102 can be further reduced.

Preferably, the number of particle monolayers in the light scattering layer 110 is 1-5. When the number of particle monolayers of the light scattering layer 110 is too large, the amount of light absorbed in the light scattering layer 110 increases, so that the number of the particle monolayers does not exceed five.

The light scattering layer 110 may be made of, for example, a material selected from the group consisting of Al ₂ O ₃ , SiO _2, and SiN _x . Alternatively, the light scattering layer may be made of an insulating polymer. As shown in FIG. 10, the light scattering layer 110 may be made of a single material having a uniform particle size. For example, the light scattering layer 110 may be made of sapphire (Al ₂ O ₃ ) particles having an average particle size of about 1㎛. However, the light scattering layer may be made of a single material having different particle sizes, or may be made of different materials having different particle sizes.

11 is a schematic cross-sectional view of a light scattering layer according to another embodiment of the present invention. Referring to FIG. 11, the light scattering layer 110 includes a sub-coating portion 121 formed at the bottom thereof. The average particle size of the sub-coating portion 121 is smaller than the average particle size of the upper surface portion 111 ′ of the light scattering layer 110 and is less than or equal to the wavelength of ultraviolet rays emitted from the UV LEDs 102. The sub-coating portion 121 constitutes a part of the light scattering layer 110 and may be made of the same material as the light scattering layer 110.

The sub-coating unit 121 greatly promotes the tunneling phenomenon of light at the interface of the UV LED 102 and the light scattering layer 110. Specifically, since the particle size of the sub-coating portion 121 is less than or equal to the wavelength of ultraviolet light, the distance between the surface of the UV LED 102 and the particle surface of the sub-coating portion 121 is equivalent to or smaller than the blue light wavelength. do. Therefore, the light incident on the surface of the UV LED 102 is mostly tunneled. That is, the majority 30 of the blue light 27 is tunneled at the interface between the sub-coating portion 121 and the LED 102, and only a very small portion 29 is reflected.

Preferably, the refractive index of the subcoat 121 is equal to or greater than the refractive index of the constituent material of the UV LED 102. For example, when ultraviolet rays are emitted toward the sapphire substrate of the LED 102, the refractive index of the sub-coating portion 121 may correspond to or greater than the refractive index of the sapphire substrate.

12 is a cross-sectional view schematically showing a light scattering layer according to still another embodiment of the present invention. Referring to FIG. 12, the sub-coating portion 131 disposed at the bottom of the light scattering layer 110 is made of a material different from that of the top surface of the light scattering layer 110. For example, the upper surface portion of the light scattering layer 110 may be made of sapphire particles, the sub-coating portion 131 may be made of a phosphor material. The phosphor material forming the subcoat 131 may be the same material as the phosphor 103 dispersed in the molding resin 107.

In the above-described embodiments, only the UV reflecting film is provided as the reflecting medium, or the UV reflecting film and the reflecting powder medium are provided together. However, the present invention is not limited thereto, and for example, only the reflective powder medium may be provided as the reflective medium.

Preferably, ultraviolet light emitted from UV LED 102 has a peak emission wavelength in the range of 350-410 nm. Preferably, the blue phosphor has a peak emission wavelength of 420-480 nm, the green phosphor has a peak emission wavelength of 490-550 nm, and the red phosphor has a peak emission wavelength of 580-620 m. Preferably, the phosphors have high photon efficiency at the emission wavelength of UV LED 102. In addition, each of the phosphors has a significant light transmission to visible light emitted by the other phosphors.

Preferably, the green phosphor is double excited by the UV LED 102 and the blue phosphor, and the red phosphor is triple excited by the UV LED 102 and the blue phosphor and the green phosphor. Accordingly, the quantum yield of the red phosphor and the green phosphor is further increased. As a result, the overall luminance (or luminous efficiency) and color rendering index of the white light emitting device are improved.

Specifically, the green phosphor is excited not only by the ultraviolet rays emitted from the UV LED 102 but also by the emitted light (blue light) of the blue phosphor. As a result, the quantum yield of the green phosphor is increased. In particular, if the conventionally used blue emission light (e.g., blue emission light exiting to the rear of the exit surface) is used to excite the green phosphor, the overall luminous efficiency becomes even greater. Preferably, the green phosphor has a peak excitation wavelength in the range of 350-480 nm so that it can be excited sufficiently by ultraviolet and blue light.

In addition, the red phosphor is excited not only by the ultraviolet rays emitted from the UV LED 102 but also by the emitted light (blue light) of the blue phosphor and the emitted light (green light) of the green phosphor. As a result, the quantum yield of the red phosphor is increased. In particular, the low quantum yield of the red phosphor, which is a problem in the related art (the resultant deterioration of the color rendering index of white light) can be overcome or reduced. Moreover, if the conventionally discarded blue light and green light (eg, blue emission light and green emission light exiting to the rear of the exit surface) are used to excite the red phosphor, the overall luminous efficiency becomes even greater. Preferably, the red phosphor has a peak excitation wavelength in the range of 420 to 480 nm and the range of 490 to 550 nm, respectively, so as to be sufficiently efficiently excited by the blue and green light. More preferably, each has a peak excitation wavelength in the range of 350 to 410 nm, the range of 420 to 480 nm and the range of 490 to 550 nm.

By using multiexcitation of the green phosphor and the red phosphor as described above, the quantum yield of these phosphors can be increased. Accordingly, the overall luminous efficiency, luminance, and color rendering index are outputted with high quality white light, which is improved compared to the conventional art.

5 is a schematic view for explaining the operation principle of the white light emitting device according to the preferred embodiment of the present invention. Referring to FIG. 5, the UV LED 102 emits ultraviolet light 2 and injects it into the blue phosphor, the green phosphor, and the red phosphor. The blue phosphor absorbs ultraviolet light 2 (excited by the ultraviolet light 2) and emits blue light 4, 5, 6 having a peak emission wavelength of 420 to 480 nm.

The green phosphor absorbs the ultraviolet light 2 and the emitted light (blue light 5) of the blue phosphor, and then emits green light 7, 8, 9 having a peak emission wavelength of 490-550 nm. The green light 7 is green light emitted by the green phosphor due to absorption of the emission light of the blue phosphor (blue light 5). The green light 9 is green light emitted by the green phosphor due to absorption of the emitted light (ultraviolet ray 2) of the UV LED 102.

The red phosphor absorbs the ultraviolet (2), the emitted light of the blue phosphor (blue light 6) and the emitted light of the green phosphor (green light 8), and then the red light (10, 11) having a peak emission wavelength of 580 to 620 nm. 12). In particular, when the red phosphor has a peak excitation wavelength in the range of 420 to 480 nm and the range of 490 to 550 nm, respectively, the blue light 6 and the green light 8 can be effectively absorbed. The red light 10 is red light emitted by the red phosphor due to absorption of the emission light 6 of the blue phosphor. The red light 11 is red light emitted by the red phosphor due to absorption of the emission light 8 of the green phosphor. The red light 12 is red light emitted by the red phosphor due to absorption of the emitted light (ultraviolet ray 2) of the UV LED 102. In this way, the multiple excitation of the phosphors makes it possible to use light more efficiently and to further improve the color rendering index.

Referring to FIG. 5, phosphors are additionally excited by ultraviolet rays reflected by the reflection medium R. As shown in FIG. The aforementioned UV reflecting film 108 and / or reflecting powder medium 104 correspond to the reflecting medium R. The reflecting medium R reflects the ultraviolet light 2, and blue, green and red phosphors may be additionally excited by the reflected ultraviolet light. Accordingly, the blue, green and red phosphors additionally generate blue light 14, green light 17 and red light 20, respectively. Further excitation by the reflecting medium R results in higher photon efficiency of the phosphors.

By the interaction between the UV LED 102, the phosphor and the reflecting medium described above, the observer can combine the combination of blue light (4, 14), green light (7, 9, 17) and red light (10, 11, 12, 20) with white light. 40 is detected. It is apparent that this white light 40 shows better luminance and color rendering index as already explained.

Preferably, the blue phosphor is (Sr, Ca) ₅ (PO ₄ ) ₃ Cl: Eu ²⁺ , La _2.99 Ce _0.01 (SiS ₄ ) ₂ I and Ce ₃ (SiS ₄ ) ₂ X (X is Cl, Br Or at least one selected from the group consisting of I). These phosphors are known to have peak emission wavelengths in the range of about 450 to 480 nm.

Preferably, the green phosphor may be at least one selected from the group consisting of SrGa ₂ S ₄ : Eu ²⁺ and (Ba, Sr) ₂ SiO ₄ : Eu ²⁺ . These phosphors are known to have peak emission wavelengths in the range of about 490-530 nm. In particular, SrGa ₂ S ₄ : Eu ²⁺ phosphors are preferred. Since the SrGa ₂ S ₄ : Eu ²⁺ phosphor has a quantum efficiency of at least 90% for incident light having a wavelength of 350 to 500 nm, double excitation of the green phosphor is very easy.

Preferably, Ca (Eu _0.5 La _0.5 ) Si ₃ O ₁₃ may be used as the red phosphor. This phosphor has peak excitation wavelengths in the ultraviolet region (350-410 nm), blue region (420-480 nm), and green region (490-550 nm), respectively. Thus, it is a potent candidate for triple excited phosphors.

6 is a schematic diagram schematically showing energy transfer between phosphors used in the white light emitting device of one embodiment of the present invention. Referring to FIG. 6, the blue phosphor absorbs ultraviolet light of about 400 nm (ie, is excited by ultraviolet light) and emits blue light of about 465 nm. The green phosphor absorbs some of the emitted light of the blue phosphor as well as ultraviolet light of about 400 nm to emit green light of about 530 nm. The red phosphor absorbs ultraviolet rays, emitted light of the blue phosphor, and emitted light of the green phosphor to emit red light of about 613 nm. As described above, the white light emitting device of the present embodiment can operate based on multiple absorption or multiple excitation to output white light.

7 is a graph showing an excitation spectrum and an emission spectrum of a red phosphor used in one embodiment of the present invention. In particular, FIG. 7 shows an excitation spectrum and an emission spectrum of Ca (Eu _0.5 La _0.5 ) Si ₃ O ₁₃ . In Fig. 7, the excitation spectrum is an excitation spectrum measured at an emission wavelength of 613 nm, and the emission spectrum is an emission spectrum obtained using an excitation light wavelength of 395 nm. As shown in FIG. 7, Ca (Eu _0.5 La _0.5 ) Si ₃ O ₁₃ has a peak excitation wavelength at about 395 nm as well as at about 460 nm and about 530 nm. The peak emission wavelength is about 613 nm. Therefore, Ca (Eu _0.5 La _0.5 ) Si ₃ O ₁₃ corresponds to the 'red phosphor capable of triple excitation' as described above.

8A and 8B are graphs each showing an excitation spectrum and an emission spectrum of a blue phosphor used in one embodiment of the present invention. In particular, FIG. 8A shows an excitation spectrum of La _2.99 Ce _0.01 (SiS ₄ ) ₂ I and Ce ₃ (SiS ₄ ) ₂ X (X is Cl, Br or I), and FIG. 8B shows its emission spectrum. As can be seen in Figures 8a and 8b, La _2.99 Ce _0.01 (SiS ₄ ) ₂ I and Ce ₃ (SiS ₄ ) ₂ X (X is Cl, Br or I) is efficiently by UV light of 350 to 410nm It is excited and can emit blue light of 420-480 nm.

9A and 9B are graphs showing excitation spectra and emission spectra of the green phosphors used in one embodiment of the present invention, respectively. In particular, FIGS. 9A and 9B show excitation spectra and emission spectra of SrGa ₂ S ₄ : Eu ²⁺ , respectively. As shown in FIG. 9A, SrGa ₂ S ₄ : Eu ²⁺ can generate sufficient excitation in the range of 350 to 410 nm as well as in the range of 420 to 480 nm to emit a considerable intensity of green light. Therefore, SrGa ₂ S ₄ : Eu ²⁺ corresponds to the 'green phosphor capable of double excitation' as described above.

In the case of using the multiple excitation of the above-described phosphor, it is preferable that the blue, green and red phosphors form a layer structure separated from each other. This is because it is more suitable to efficiently use the discarded emission light emitted behind the emission surface rather than using a mixture of phosphors, respectively, rather than using a mixture of phosphors. In this case, preferably, the green phosphor is disposed more rearward (i.e. closer to the UV LED 102) than the blue phosphor, and the red phosphor is disposed more rearward than the green phosphor. By this arrangement, the light 5, 6 emitted backward from the blue phosphor is easily absorbed by the green phosphor and the red phosphor, and the light 8 emitted backward from the green phosphor is easily absorbed by the red phosphor. (See FIG. 5).

The present invention is not limited by the above-described embodiment and the accompanying drawings, but is intended to be limited by the appended claims, and various forms of substitution, modification, and within the scope not departing from the technical spirit of the present invention described in the claims. It will be apparent to those skilled in the art that changes are possible.

As described above, according to the present invention, by using the UV LED, the red phosphor, the green phosphor, the blue phosphor, and the reflecting medium, high-quality white light emission with improved luminance, luminous efficiency and color rendering index can be obtained. In addition, by providing a light scattering layer additionally, light extraction efficiency can be increased, and by using green and blue phosphors of multiple excitations, the light emission efficiency can be further increased.

Claims (31)

Ultraviolet LED; A molding resin encapsulating the ultraviolet LED; Blue, green, and red phosphors excited by ultraviolet rays emitted from the ultraviolet LEDs to emit blue, green, and red light, respectively; And And a reflective medium for reflecting the ultraviolet rays emitted from the ultraviolet LED to the phosphor. The method of claim 1, And the reflective medium includes an ultraviolet reflective film formed on the molding resin to reflect ultraviolet light and transmit visible light. The method of claim 2, The ultraviolet reflecting film is a white light emitting device, characterized in that consisting of a multilayer dielectric film. The method of claim 3, And said multilayer dielectric film comprises two or more dielectric films having different refractive indices. The method of claim 3, And said multilayer dielectric film comprises at least one selected from the group consisting of TiO ₂ , ZrO ₂ , MgF ₂ and LiF ₂ . The method of claim 3, And wherein the multilayer dielectric film is a multilayer film formed by alternately stacking a first dielectric film having a first refractive index and a second dielectric film having a second refractive index smaller than the first refractive index. The method of claim 6, The first refractive index is 1.82 to 2.5, the second refractive index is a white light emitting device, characterized in that 1.35 to 1.45. The method of claim 2, The white light emitting device further comprises a glass substrate disposed between the molding resin and the ultraviolet reflecting film. The method of claim 1, And the reflecting medium comprises a reflecting powder medium dispersed in the molding resin to reflect the ultraviolet light emitted from the ultraviolet LED. The method of claim 9, Wherein said reflective powder medium is comprised of at least one material selected from the group consisting of MgO, BaSO ₄ , Al ₂ O ₃ , ZrO ₂ and TiO ₂ . The method of claim 9, And the particle size of the reflective powder medium is larger than the peak emission wavelength of the ultraviolet light. The method of claim 9, And said phosphor and said reflective powder medium are uniformly mixed in said molding resin. The method of claim 9, And the phosphor and the reflective powder medium are separated from each other on the ultraviolet LED to form a discontinuous layer structure. The method of claim 13, And the phosphor is disposed on the ultraviolet LED and the reflective powder medium is disposed on the phosphor. The method of claim 1, The reflective medium, An ultraviolet reflecting film formed on the molding resin to reflect ultraviolet light and transmit visible light; And And a reflecting powder medium dispersed in the molding resin to reflect ultraviolet rays emitted from the ultraviolet LED. The method of claim 1, The white light emitting device further includes a casing having a reflective cup, The ultraviolet LED is mounted in the reflective cup, wherein the reflective cup has a reflective surface formed on its inner surface. The method of claim 16, The reflective cup has a reflective surface formed of pressed BaSO ₄ . The method of claim 1, White light emitting device further comprises a light scattering layer formed on the ultraviolet LED. The method of claim 18, And an average particle size of the upper surface portion of the light scattering layer is equal to or larger than the wavelength of the ultraviolet light. The method of claim 18, The refractive index of the light scattering layer, the white light emitting device, characterized in that greater than or equal to the refractive index of the constituent material of the ultraviolet LED. The method of claim 18, The light scattering layer is a white light emitting device, characterized in that made of a material selected from the group consisting of Al ₂ O ₃ , SiO ₂ and SiN _x . The method of claim 18, The light scattering layer includes a sub-coating formed on the bottom portion, The average particle size of the sub-coating portion is smaller than the average particle size of the upper surface portion of the light scattering layer, And the average particle size of the sub-coating portion is less than or equal to the wavelength of the blue light. The method of claim 22, The refractive index of the sub-coating unit, the white light emitting device, characterized in that greater than or equal to the refractive index of the component of the blue LED. The method of claim 22, And the sub-coating unit is made of a phosphor material. The method of claim 1, The ultraviolet LED has a white light emitting device having a peak emission wavelength of 350 to 410nm. The method of claim 1, The blue phosphor has a peak emission wavelength of 420 to 480 nm, the green phosphor has a peak emission wavelength of 490 to 550 nm, the red phosphor has a peak emission wavelength of 580 to 620 nm, The blue phosphor is excited by the ultraviolet light to emit blue light, the green phosphor is excited by the ultraviolet light and the blue light to emit green light, and the red phosphor is excited by the ultraviolet light, the blue light and the green light to emit red light. White light emitting device, characterized in that for emitting. The method of claim 1, The blue phosphor is (Sr, Ca) ₅ (PO ₄ ) ₃ Cl: Eu ²⁺ , La _2.99 Ce _0.01 (SiS ₄ ) ₂ I and Ce ₃ (SiS ₄ ) ₂ X (X is Cl, Br or I) A white light emitting device comprising at least one phosphor selected from the group consisting of. The method of claim 1, Wherein said green phosphor comprises at least one phosphor selected from the group consisting of SrGa ₂ S ₄ : Eu ²⁺ and (Ba, Sr) ₂ SiO ₄ : Eu ²⁺ . The method of claim 1, The red phosphor comprises a Ca (Eu _0.5 La _0.5 ) Si ₃ O ₁₃ White light emitting device characterized in that. The method of claim 1, The blue, green, and red phosphors are separated from each other, and form a discontinuous layer structure on the ultraviolet LED. The method of claim 30, And the red phosphor is on the ultraviolet LED, the green phosphor is on the red phosphor, and the blue phosphor is on the green phosphor.

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