KR20090004344A - White LED device - Google Patents

Abstract

Provided is a white LED device having excellent color rendering and high color reproducibility and good white uniformity. The white LED device of the present invention comprises: a blue LED chip emitting blue light at a peak wavelength of 450 to 470 nm; A green phosphor disposed on the blue LED chip and excited by the blue LED chip to emit green light at a peak wavelength of 525 to 535 nm; And an orange phosphor disposed on the blue LED chip and excited by the blue LED chip to emit orange light at a peak wavelength of 605 to 610 nm.

Description

White LED Device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to white light emitting diode devices used in backlight units, lighting, etc. of LCD displays, and more particularly, to high quality white LED devices exhibiting high color rendering index and stability by using a mixture of phosphors and blue LED chips of a specific wavelength band.

Recently, a white light emitting device (hereinafter referred to as a white LED device) using a semiconductor light emitting element called a light emitting diode (LED) has attracted attention as a white light source for illumination or a white light source of a backlight unit (BLU). Cold cathode fluorescent lamps (CCFLs) have conventionally been used as BLU white light sources for LCD displays used in notebooks, mobile phones, navigation systems, etc., but in recent years, there is a demand for more advantageous white LED devices in terms of excellent driving characteristics, small size, and environment. It is increasing.

The conventional white LED device for BLU is implemented by separately providing blue, green, and red LEDs and mounting a plurality of them on a PCB substrate. A white LED device using these three primary LEDs has excellent monochromatic peak wavelength, but lacks color rendering. That is, in the emission spectrum of the white LED device using the conventional RBG trichromatic LEDs, a valley portion having a relatively small light intensity exists widely in the wavelength region between the blue region and the green region, and between the green region and the red region, in particular, green Between the region and the red region, the valley is wide and the light intensity is also very low. Thus, because of the very low color rendering index in these valley regions, the overall color rendering (average color rendering index) is considerably lower than 50. In addition, the color mixing of the three primary LEDs may not be well done, causing color spots.

In order to improve the problem of the white LED device using the three primary LEDs, a white LED device using a combination of a blue LED chip and a yellow phosphor has been proposed. 1 shows an example of a conventional LED device using such an LED chip and phosphor combination. Referring to FIG. 1, the white LED device 10 includes a package body 12 having a reflection cup 12a formed thereon, and a blue LED chip 15 mounted on the bottom of the reflection cup 12a. An encapsulant resin 16 is disposed inside the reflecting cup 12a to apply the blue LED chip 15. In the resin packaging 16, for example, a YAG-based yellow phosphor 13 is dispersed. It is. During operation, part of the blue light emitted from the blue LED chip 15 excites the yellow phosphor 13 to emit yellow light from the phosphor 13, and the yellow light of the phosphor 13 and the blue light of the LED chip 15 are mixed. The white light is emitted.

However, the white LED device 10 using a combination of a blue LED chip and a yellow phosphor also does not exhibit sufficient color rendering near natural color light. For example, the white LED device 10 using the YAG-based yellow phosphor has a low intensity in the red region having a long wavelength, so that the color reproducibility of the red region is poor. In order to further improve this, a white LED device using a combination of a blue LED chip and a sulfide-based green and red phosphor has been proposed, but a sulfide-based phosphor has a lower luminance (IV) than the yellow phosphor, and particularly has a low humidity and temperature. Vulnerable to external environment

2 is a graph showing an emission spectrum of a conventional white LED device. As shown in Fig. 2, the emission spectrum of a white LED device using a blue LED chip and a yellow phosphor is particularly low in intensity in the red region of 600 nm or more. The emission spectrum of a white LED device using a blue LED chip, a sulfide-based green phosphor (SrGaS-based), and a red phosphor (CaS-based or SrS-based) shows higher color rendering than when yellow phosphors are used. However, the white LED device using such sulfide-based green and red phosphors has a low overall luminance (about 50% of the luminance compared to the case of using yellow phosphors) and easily damages the sulfide-based phosphor material in a high temperature or high humidity atmosphere. There are many problems in reliability and lifespan.

The present invention has been made to solve the above problems, and an object thereof is to provide a white LED device having high color rendering and color uniformity and excellent in reliability.

In order to achieve the above technical problem, the white LED device of the present invention, a blue LED chip for emitting blue light at a peak wavelength of 450 to 470nm; A green phosphor disposed on the blue LED chip and excited by the blue LED chip to emit green light at a peak wavelength of 515 to 540 nm; And an orange phosphor disposed on the blue LED chip and excited by the blue LED chip to emit orange light at a peak wavelength of 600 to 620 nm.

The white LED device outputs white light by mixing blue light emitted from the blue LED chip, green light emitted from the green phosphor, and orange light emitted from the orange phosphor.

According to an embodiment of the present invention, the peak wavelength of the blue LED chip may be 460 to 465 nm, the peak wavelength of the green phosphor may be 525 to 530 nm, and the peak wavelength of the orange phosphor may be 600 to 605 nm.

According to an embodiment of the present invention, the green phosphor and the orange phosphor are silicate-based phosphors. In particular, the green body may be a silicate-based phosphor including at least one of Ba, Sr, and Ca, and the orange phosphor may be a silicate-based phosphor including Sr. The silicate-based phosphor may be coated by a nano coating layer.

According to an embodiment of the present invention, the white LED device further comprises a package main body for accommodating the LED chip, the package main body is formed with a concave reflective cup on the top, the blue LED chip is It is mounted.

The white LED device may further include a translucent resin for coating the blue LED chip in the reflective cup, and the green and orange phosphors may be dispersed in the translucent resin.

As described above, according to the present invention, high-quality white light having a high color rendering index close to natural light can be obtained by using a blue LED chip having a specific range of peak wavelengths, a green phosphor, and an orange phosphor. In addition, by using the silicate-based phosphors as the phosphors, it is possible to implement excellent reliability compared to the conventional sulfide-based phosphors. Furthermore, by coating the silicate-based phosphor with a nano-coating may further improve the resistance to humidity. When the white LED device of the present invention is used as a BLU light source of an LCD display, color reproducibility is improved due to an improvement in color rendering index (CRI) and white uniformity is increased. As a result, a high color reproducibility and white uniformity BLU using a white LED, which can replace the conventional CCFL, can be realized. In addition, the white LED device of the present invention can be usefully used as a white light source of a lighting device that emits white light close to natural light.

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. In the drawings, the shape and size of each component may be exaggerated for clarity.

3 is a side cross-sectional view schematically showing a white LED device according to an embodiment of the present invention. Referring to FIG. 3, the white LED device 100 includes a blue LED chip 105 and a green phosphor 104 and an orange phosphor 108 disposed on the LED chip 105. These phosphors 104 and 108 combinations or phosphor mixtures are dispersedly disposed in the translucent resin 106 for packaging (or applying) the blue LED chip 105. However, the present invention is not limited thereto, and for example, the green phosphor 104 and the orange phosphor 108 may be present in a layered structure.

The white LED device 100 may also further include a package body 102 that houses the LED chip 105 and the phosphors 104, 108. On the upper portion of the package body 102, a concave reflection cup 102a may be formed to reflect light in the emission direction (and also to improve light extraction efficiency through such light reflection). As shown in FIG. 3, the blue LED chip 105 and the phosphors 104 and 108 are located inside the reflecting cup 102a. For convenience, an electrode pattern, a lead frame, and the like in the package body electrically connected to the LED chip are omitted.

During operation, when blue light comes from the blue LED chip 105, part of it is absorbed by the green and orange phosphors 104 and 108. By the light energy of the absorbed blue light, the phosphors 104 and 108 are excited to emit green light and orange light, respectively. A portion of the blue light emitted from the blue LED chip 105 (the blue light portion not absorbed by the phosphor) and the green light and the orange light emitted from the phosphors 104 and 108 are mixed with each other to output white light.

In order to realize superior color rendering and high color reproducibility as compared with the related art, each peak wavelength of the blue LED chip, the green phosphor, and the orange phosphor is limited to a specific range. Specifically, as a result of many experiments, blue LED chips (especially 450-470 nm) having emission peaks (peak wavelengths) of 450 nm or more, green phosphors having peak wavelengths of 515-540 nm, and peak wavelengths of 600-620 nm It was confirmed that by combining the orange phosphor having it can exhibit a markedly improved color rendering and color reform compared to the conventional (see Fig. 4).

When white light is output using an LED chip having such peak wavelengths and green and orange phosphors, high color rendering property of 85 or more of an average color rendering index (CRI) can be achieved. In particular, when the peak wavelength of the blue LED chip is set to 460 to 470 nm, a high color rendering index close to 90 is obtained, thereby allowing the output of white light close to natural light.

A blue LED chip having the above-described peak wavelength range, for example, _{In x Ga y Al 1 -x- y} N -based Group III nitride semiconductor LED can be used. By adjusting the bandgap material (eg, InGaN) of the active layer (single quantum well or multiple quantum well structure) of the nitride semiconductor LED, a blue LED having a specific range of peak wavelengths can be obtained. In addition, as the green phosphor and the orange phosphor having the peak wavelength range, a silicate-based phosphor may be used. For example, a silicate-based phosphor including at least one of Ba, Sr, and Ca, such as (Ba, Sr, Ca) ₂ SiO ₄ : Eu, may be used as the silicate-based green phosphor. As the silicate orange phosphor, a silicate phosphor containing Sr such as Sr ₃ SiO ₅ : Eu can be used.

As described above, when silicate-based green and orange phosphors limited to the peak wavelengths are used instead of the conventional sulfide-based green and red phosphors, not only the color rendering property is excellent but also the phosphor resistance at room temperature and high temperature is excellent. The silicate-based green and orange phosphors are more resistant to humidity and better than sulfide-based phosphors, but in order to improve the reliability and lifespan, especially in a high humidity atmosphere, the above-mentioned silicate-based phosphors are coated with nano-scale protective coating layers (eg, silica coating layers). Can be formed.

4 is a graph showing emission spectra of the white LED device of Examples and Comparative Examples. In FIG. 4, the white LED device (solid line) of Comparative Example 1 emits white light by using a blue LED chip having a peak wavelength of 440 nm and a YAG-based yellow phosphor having a peak wavelength of 565 nm. The white LED device (dotted chain line) of Comparative Example 2 emits white light by using a blue LED chip having a peak wavelength of 440 nm and the above-described silicate green and orange phosphors. In Comparative Example 3 (dotted line), white light is emitted using a blue LED chip having a peak wavelength of 460 nm and a YAG-based yellow phosphor having a peak wavelength of 565 nm. The white LED device (two dashed line) of the embodiment shown in FIG. 4 emits white light using a blue LED chip having a peak wavelength in the range of 460 to 465 nm and the above-described silicate green and orange phosphors. The silicate-based green phosphor of the above example has a peak wavelength in the range of 525 to 530 nm, and the orange phosphor of the example has a peak wavelength in the range of 600 to 605 nm.

As shown in the emission spectrum of FIG. 4, when the yellow phosphor is used as in the conventional white LED device (Comparative Examples 1 and 3), the light intensity of the long wavelength region of 600 nm or more is considerably low and the overall color rendering is low. Therefore, it is difficult to realize high color reproducibility close to natural color. In addition, even when the green and orange silicate-based phosphors are used, when the peak wavelength of the blue LED chip is less than 450 nm (Comparative Example 2), the light intensity is very low in the wavelength region of 470 to 480 nm, so that the effect of improving the color rendering index hardly occurs ( For Comparative Example 2, the CRI is only about 75).

In contrast, when using green LEDs (515-540 nm) and orange phosphors (600-620 nm) in the specified peak wavelength range with blue LED chips of 450 nm or more and less than 470 nm, an average color rendering index (CRI) of 85 or more. It was confirmed that it can be represented). In particular, as shown in the embodiment of Figure 4, when using a blue LED chip of 460 to 465 nm, a green phosphor of 525 to 530 nm, and an orange phosphor of 600 to 605 nm, a high average color rendering index close to 90 can be obtained. have. As the color rendering index rises, when the white LED device of the present invention is used as a BLU of the LCD, color reproducibility is improved and it is more suitable to realize an LCD display closer to the full color.

In addition, the white LED device of the embodiment not only improves the color rendering properties, but also has excellent material stability due to temperature rise compared to the conventional sulfide-based phosphors, thereby improving reliability and lifespan. To improve further resistance to humidity in high humidity environments, transparent coatings such as silica may be coated on the phosphor particles. In addition, by using 'combination of blue LEDs and green and orange phosphors disposed thereon' basically, white uniformity can be increased (particularly compared to white LED devices using conventional RGB tri-color LEDs).

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. For example, unlike the embodiment of FIG. 3, a blue LED chip may be directly mounted on a PCB substrate without a separate package body, and the mounted LED chip may be coated with a transparent resin using a mold.

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

2 is a graph showing emission spectra of conventional white LED devices.

3 is a schematic cross-sectional view of a white LED device according to an embodiment of the present invention.

4 is a graph showing emission spectra of the white LED device of Examples and Comparative Examples.

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

100: white LED device 102: package body

102a: reflection cup 104: green phosphor

105: blue LED chip 106: translucent resin

108: orange phosphor

Claims (7)

A blue LED chip emitting blue light at a peak wavelength of 450 to 470 nm; A green phosphor disposed on the blue LED chip and excited by the blue LED chip to emit green light at a peak wavelength of 515 to 540 nm; An orange phosphor disposed on the blue LED chip and excited by the blue LED chip to emit orange light at a peak wavelength of 600 to 620 nm, White LED device. The method of claim 1, The white LED device is a white LED device, characterized in that for mixing the blue light emitted from the blue LED chip, the green light emitted from the green phosphor, and the orange light emitted from the orange phosphor to output white light. The method of claim 1, The peak wavelength of the blue LED chip is 460 to 465 nm, the peak wavelength of the green phosphor is 525 to 530 nm, the peak wavelength of the orange phosphor is 600 to 605 nm. The method of claim 1, The green phosphor and the orange phosphor is a white LED device, characterized in that the silicate-based phosphor. The method of claim 4, wherein Wherein said green phosphor is a silicate-based phosphor comprising at least one of Ba, Sr, and Ca, and said orange phosphor is a silicate-based phosphor comprising Sr. The method of claim 1, Further comprising a package body for receiving the LED chip, The package body is a white LED device, characterized in that the concave reflection cup is formed on the upper portion, the blue LED chip is mounted in the reflection cup. The method of claim 6, Further comprising a translucent resin for coating the blue LED chip in the reflection cup, Wherein the green and orange phosphors are dispersed in the light transmitting resin.

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