KR100616690B1 - White light emitting device - Google Patents

Abstract

Provided is a white light emitting device having improved luminance and color rendering index. A white light emitting device according to the present invention includes an ultraviolet light source (UV light source) for emitting ultraviolet light; A first phosphor having a peak emission wavelength of 490 to 550 nm; A second phosphor having a peak emission wavelength of 420 to 480 nm; A third phosphor having a peak emission wavelength of 580-620 nm, wherein the first phosphor is excited by the ultraviolet light to emit green light, and the second phosphor is excited by the ultraviolet light to emit blue light, The three phosphors are excited by the ultraviolet light and the emission light of the second phosphor to emit red light.

Light Emitting Diode, LED, White Light Emitting Phosphor

Description

White light emitting device {WHITE LIGHT EMITTING DEVICE}

1 is a conceptual diagram schematically showing a conventional white light emitting device.

2 is a conceptual diagram schematically showing a white light emitting device of the present invention.

3 is a schematic diagram showing an operating principle of the white light emitting device of the present invention.

4 is a schematic diagram schematically showing energy transfer between a blue phosphor and a red phosphor used in the white light emitting device of one embodiment of the present invention.

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

6 is a graph showing an excitation spectrum of a red phosphor used in another embodiment of the present invention.

7A is a graph showing an excitation spectrum of a blue phosphor used in one embodiment of the present invention.

7B is a graph showing the emission spectrum of the blue phosphor used in one embodiment of the present invention.

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

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

9 is a side sectional view showing a white light emitting device according to an embodiment of the present invention.

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

1: UV light source 2: UV light

4: green light 5, 6: blue light

7, 8: red light 11: white light

12: observer 231, 232, 233: phosphor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white light emitting device, and more particularly, to a white light emitting device including ultraviolet light sources such as ultraviolet LEDs and fluorescent materials that emit light by converting ultraviolet light emitted therefrom.

White LED devices are used as backlights of liquid crystal displays instead of conventional small lamps or fluorescent lamps. 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.

In a typical representative white LED device, an LED having an InGaN single quantum well is used as a blue LED, and a yttrium aluminum garnet (YAG: Ce) doped with cerium as a phosphor, that is, Y ₃ Al ₅ O ₁₂ : Ce ³⁺ is used. do. The blue light emitted from the blue LED emits yellow light by exciting the phosphor. Some blue light emitted from the blue LED is transmitted through the phosphor and mixed with the yellow light emitted by the phosphor. Such a mixture of blue light and yellow light is perceived by the observer (viewer) as white light. Blue LEDs emit light (blue light) with a wavelength of about 420-480 nm. When such blue light is combined with a yellow phosphor, white light has a color temperature of about 6000-8000K and a color rendering index (CRI) of about 77.

In addition, the blue LED can generate white light by combining with a phosphor converting blue light into red light and a phosphor converting into green 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, green 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 consistent in color and uniformity. It does not give light having sex. In addition, the three LEDs require three current regulators, increasing the manufacturing cost of the device and making it difficult to miniaturize.

As another way to implement a white LED device, it is possible to combine an ultraviolet LED (UV LED) with phosphors that output white light by varying the ultraviolet light emitted from the UV LED. 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. In order to obtain white light using a UV LED, the phosphors combined with the UV LED must emit radiation energy in the visible region of the spectrum in response to absorption of radiant energy outside the visible region of the spectrum. Accordingly, the phosphors convert electromagnetic radiation that is not detected by the naked eye into electromagnetic radiation that is perceived by the naked eye.

However, in order to actually obtain white light, it is very difficult to find three suitable phosphors that are excited by ultraviolet (UV) light to emit red, green and blue light, 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 conceptual diagram schematically showing a conventional white LED device using a UV LED. Referring to FIG. 1, blue, green, and red phosphors are excited by ultraviolet rays (350 to 410 nm) emitted from a UV LED light source, respectively, and are respectively 420-480 nm (blue), 490-550 nm (green), and 580-620 nm (red). ) Emits visible light in the wavelength range. These visible rays are mixed and output as white light. However, according to this prior art white light emitting device, the quantum yield of the red phosphor is too low compared to the blue and green phosphors. Accordingly, it is difficult to obtain high quality output light because the overall luminance and color rendering index are low.

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 high brightness white light emitting device having high quantum yield of red phosphor and improved color rendering index.

In order to achieve the above technical problem, a white light emitting device according to the present invention, the ultraviolet light source (UV light source) for emitting ultraviolet light; A first phosphor having a peak emission wavelength of 490-550 nm; A second phosphor having a peak emission wavelength of 420 to 480 nm; A third phosphor having a peak emission wavelength of 580-620 nm, wherein the first phosphor is excited by the ultraviolet light to emit green light, and the second phosphor is excited by the ultraviolet light to emit blue light, Type 3 phosphors are excited by the ultraviolet light and the emitted light of the second phosphor to emit red light.

According to a preferred embodiment of the invention, the UV light source is an ultraviolet LED having a peak emission wavelength of 350 to 410 nm. In another embodiment, the UV light source may be a mercury gas or an inert gas selected from at least one group consisting of Ne, Ar, and Xe.

According to a preferred embodiment of the present invention, the third phosphor has a peak excitation wavelength in the wavelength range of 350 to 480 nm. More preferably, the third phosphor has a peak excitation wavelength in the range of 420 to 480 nm. Even more preferably, the third phosphor has a peak excitation wavelength in the range of 350 to 410 nm and the range of 420 to 480 nm, respectively.

According to a preferred embodiment of the present invention, the first phosphor is Sr ₂ Si ₃ O _{8 2} SrCl ₂ : Eu ²⁺ , Sr ₄ Al ₁₄ O ₂₅ : Eu ²⁺ , Y ₂ SiO ₅ : Ce ³⁺ , Tb ³⁺ And BaYSi ₄ N ₇ : Eu ²⁺ .

According to a preferred embodiment of the present invention, the second 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 ) At least one phosphor selected from the group consisting of ₂ X (X is Cl, Br or I).

According to a preferred embodiment of the present invention, the third phosphor is composed of K ₂ Eu _2.5 (WO ₄ ) _6.25 : Sm and Li (WO ₄ ) _1.25 : Eu, Sm and Ca _0.76 MoO ₄ : Eu _0.24 ³⁺ At least one phosphor selected from the group.

According to a preferred embodiment of the present invention, the first, second and third phosphors are separated from each other and are formed in a discontinuous layer structure on the ultraviolet light source. Preferably, said second phosphor is above said third phosphor.

According to an embodiment of the invention, said first, second and third phosphors are contained within a molding material. In this case, an epoxy resin or a silicone resin may be used as the molding material.

According to a preferred embodiment of the present invention, further comprising a molding material formed on the UV light source, wherein the first, second and third phosphors are dispersed and contained in the molding material, the first, second and third phosphors Disposed in the form of a layer in the molding material, wherein the second phosphor is above the three phosphors.

The present invention provides a combination of phosphors combined with a UV light source to generate white light. The combination of phosphors is composed of a green phosphor (first phosphor), a blue phosphor (second phosphor) and a red phosphor (third phosphor). These phosphors are excited by the ultraviolet light emitted by the UV light source. In addition, the red phosphor (third phosphor) of the phosphors is further excited by the emission light (having a peak emission wavelength of about 420 to 480 nm) of the blue phosphor (second phosphor) to emit red light. Accordingly, visible light is emitted in the wavelength range of about 420 to 770 nm to emit white light.

The red phosphor is excited not only by ultraviolet light but also by the emitted light of the blue phosphor, further increasing the emitted light of the red phosphor. Therefore, the red phosphor is double excited by the UV light source and the blue phosphor. Accordingly, the quantum yield of the red phosphor is further increased, and the overall luminance (or luminous efficiency) and color rendering index of the white LED device are improved.

Hereinafter, the present invention will be described in detail with reference to the drawings.

2 is a conceptual diagram schematically showing a light emitting device of the present invention. Referring to FIG. 2, ultraviolet light is emitted from a UV light source such as a UV LED. Green, blue and red phosphors are excited by ultraviolet light emitted from the UV light source to emit green, blue and red visible light, respectively. The emitted green, blue and red visible light is mixed to produce white light. The green phosphor has a peak emission wavelength of 490-550 nm, the blue phosphor has a peak emission wavelength of 420-480 nm, and the red phosphor has a peak emission wavelength of 580-620 nm. Preferably, the phosphors have a high photon efficiency at a particular emission wavelength of the UV light source. Also, preferably, each of the phosphors is transparent to visible light emitted by other phosphors.

The red phosphor is excited not only by the ultraviolet rays emitted by the UV light source but also by the emitted light (blue light) of the blue phosphor to emit red light. Preferably, the red phosphor has a peak excitation wavelength in the range of 420 to 480 nm so that it can be excited sufficiently by blue emission light. In particular, when the UV light source is a UV LED, the red phosphor preferably has a peak excitation wavelength in the range of 350 to 410 nm and the range of 420 to 480 nm, respectively.

In this manner, the red phosphor emits red light by being excited not only by the UV light source but also by the blue phosphor. Thus, the low quantum yield of the red phosphor, which has been a conventional problem, can be overcome or alleviated according to the present invention. Furthermore, if conventionally discarded blue (e.g., blue emission light exiting behind the exit surface) is used to excite the red phosphor, the overall luminous efficiency becomes even greater.

As such, the red phosphor is double excited by the UV light source and the blue phosphor, thereby greatly increasing the quantum yield of the red phosphor. Accordingly, the white light output with improved luminous efficiency, luminance and color rendering index as compared with the conventional one is output.

3 is a schematic view for explaining the operation principle of the white light emitting device of the present invention. Referring to FIG. 3, a UV light source 1 such as a UV LED emits ultraviolet light 2 and emits three kinds of phosphors 230, that is, phosphor I 231, phosphor II 232, and phosphor III 233. To enter. The phosphors 230 preferably form a layer structure separated from each other. This is because it is more suitable to use the discarded emission light emitted behind the exit surface more efficiently than using the mixture of phosphors, respectively.

The ultraviolet rays emitted from the UV light source 1 are not visually sensed and have a wavelength of less than 420 nm. Preferably, the UV light source 1 is a UV LED having a peak emission wavelength of 350 to 410 nm.

Phosphor I 231 absorbs the ultraviolet rays 2 and then emits green light 4 having a peak emission wavelength of 490 to 550 nm. Phosphor II (232) absorbs the ultraviolet (2) and then emits blue light (5, 6) having a peak emission wavelength of 420 to 480 nm.

In addition, the phosphor III 233 absorbs the emitted light (blue light 6) of the ultraviolet ray 2 and the phosphor II 232, and then emits red light 7 and 8 having a peak emission wavelength of 580 to 620 nm. do. In particular, when the phosphor III 233 has a peak excitation wavelength in the range of 420 to 480 nm, the blue light 6 can be effectively absorbed (that is, can be effectively excited by the blue light 6). The red light 7 is the red light emitted by the phosphor III 233 due to the absorption of the emitted light 6 of the phosphor II 232. The red light 8 is red light emitted by the phosphor III 233 due to absorption of the emitted light (ultraviolet rays) of the ultraviolet light source. The observer 12 detects the combination of the green light 4, the blue light 5, and the red light 7, 8 as the white light 11.

As described above, the phosphor III 233 is double excited by the UV light source 1 and the phosphor II 232 to emit red light. Thus, the photon yield of the red phosphor (phosphor III (233)) is improved. Accordingly, an increase in overall luminance and an improvement in color rendering index can be expected. Specifically, the quantum yield of the red phosphor, the luminance and the color rendering index of the entire light emitting device are expected to increase by about 10-15%, respectively.

The UV light source 1 can be any light source capable of emitting ultraviolet rays to excite the phosphors I, II and III. Preferably, the UV light source 1 is a UV LED having a peak emission wavelength of 350 to 410 nm. However, besides, as the light source 1, for example, a mercury gas used for a fluorescent lamp or a high pressure mercury vapor lamp or the like, or an inert gas such as Ne, Ar, and / or Xe used in a plasma display may be used. .

The phosphor I 231 may be any phosphor that emits green light having a peak emission wavelength of 490 to 550 nm in response to the emission light 2 of the UV light source 1. In the case of using a UV LED having a peak emission wavelength of 350 to 410 nm as the UV light source 1, the phosphor I 231 has a peak emission wavelength of 490 to 550 nm, and with respect to the emission light (ultraviolet ray) of the UV LED. Phosphors with high photon efficiency can be used. For example, as phosphor I 231, Sr ₂ Si ₃ O _{8 2} SrCl ₂ : Eu ²⁺ , Sr ₄ Al ₁₄ O ₂₅ : Eu ²⁺ , Y ₂ SiO ₅ : Ce ³⁺ , Tb ³⁺ and , BaYSi ₄ N ₇ : Eu ²⁺ One or more phosphors selected from the group consisting of can be used. These phosphors are known to have peak emission wavelengths in the range of about 490-530 nm. Of these phosphors, in particular Sr ₂ Si ₃ O ₈ 2SrCl ₂ : Eu ²⁺ is preferred. This is because Sr ₂ Si ₃ O ₈ 2SrCl ₂ : Eu ²⁺ has a quantum efficiency of 90% or more for incident light having a wavelength of 340 to 440 nm and little selective absorption of visible light.

The phosphor II 232 may be any phosphor that emits blue light having a peak emission wavelength of 420 to 480 nm in response to the emission light 2 of the UV light source 1. When using a UV LED having a peak emission wavelength of 350 to 410 nm as the UV light source (1), the phosphor II (232), with a peak emission wavelength of 420 to 480 nm, with respect to the emitted light (ultraviolet) of the UV LED Phosphors with high photon efficiency can be used. For example, as phosphor II (232), (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 It is possible to use at least one phosphor selected from the group consisting of Cl, Br or I). These phosphors are known to have peak emission wavelengths in the range of 450 to 480 nm.

As the phosphor I 231 and the phosphor II 232, not only the above-mentioned phosphors but also other phosphors may be used. For example, when using a light source other than a UV LED as the UV light source 1, a phosphor having high quantum efficiency for incident light having a peak wavelength of 254 nm or 147 nm can be used for fluorescent lamp or plasma display applications. . Mercury gas emissions in fluorescent lamps have a peak emission wavelength of 254 nm and Xe plasma discharges in plasma displays have a peak emission wavelength of 147 nm.

The phosphor III 233 may be any phosphor that emits red light having a peak emission wavelength of 580 to 620 nm in response to the emission light 2 of the UV light source 1 and the phosphor II 232. Preferably, the phosphor III 233 may emit red light of 580-620 nm by absorbing not only the emission light of the UV LED of 350 to 410 nm but also the emission light of the phosphor II 232 of 420 to 480 nm. For example, as phosphor III (233), at least one selected from the group consisting of K ₂ Eu _2.5 (WO ₄ ) _6.25 : Sm and Li (WO ₄ ) _1.25 : Eu, Sm and Ca _0.76 MoO ₄ : Eu _0.24 ³⁺ Phosphors can be used. These phosphors can be double excited by the emission light 2 of the UV light source 1 and the emission light 6 of the phosphor II 232. As a result, the quantum efficiency of the red phosphor (phosphor III 233) is increased and the overall luminous efficiency, luminance and color rendering index are improved.

4 is a schematic diagram schematically showing energy transfer between a blue phosphor (phosphor II) and a red phosphor (phosphor III) used in the white light emitting device of one embodiment of the present invention. Referring to FIG. 4, phosphor II is excited by ultraviolet light of about 400 nm and emits blue light of about 460 nm. In addition, the phosphor III absorbs not only about 400 nm of ultraviolet light but also a part of the emitted light of the phosphor II to emit red light of about 611 nm.

5 is a graph showing an excitation spectrum of a red phosphor (phosphor III) used in one embodiment of the present invention. In particular, FIG. 5 shows an excitation spectrum of Ca _0.76 MoO ₄ : Eu _0.24 ³⁺ . As shown in FIG. 5, Ca _0.76 MoO ₄ : Eu _0.24 ³⁺ has a peak excitation wavelength at about 395 nm as well as around about 460 nm. Therefore, Ca _0.76 MoO ₄ : Eu _0.24 ³⁺ corresponds to the red phosphor (phosphor III) capable of double excitation as described above. 6 shows an excitation spectrum of another red phosphor that can be used in the present invention. In particular, FIG. 6 shows an excitation spectrum of K ₂ Eu _2.5 (WO ₄ ) _6.25 : Sm. K ₂ Eu _2.5 (WO ₄ ) _6.25 : Sm also has a peak excitation wavelength near about 395 nm and around 460 nm to enable double excitation.

7A and 7B are graphs showing the excitation spectrum and the emission spectrum of the blue phosphor (phosphor II) used in one embodiment of the present invention, respectively. In particular, FIG. 7A 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. 7B shows its emission spectrum. In these graphs, the emission wavelength of the excitation spectrum is around 500 nm (blue region), and the excitation light wavelength of the emission spectrum is around 372 nm (ultraviolet region).

8A and 8B are graphs showing the excitation spectrum and the emission spectrum of the green phosphor (phosphor I) used in one embodiment of the present invention, respectively. In particular, FIGS. 8A and 8B show excitation spectra and release spectra of Sr ₂ Si ₃ O ₈ 2SrCl ₂ : Eu ²⁺ , respectively.

According to a preferred embodiment of the present invention, the phosphors I 231, II 232 and III 233 are each separately arranged to form a discontinuous layer structure on the ultraviolet LED 1. Preferably, phosphor II 232 is on phosphor III 233. That is, phosphor III 233 is disposed on UV light source 1 such as a UV LED, and phosphor II 232 is disposed on phosphor III 233.

In this way, the light 6 emitted backward from the phosphor II 232 is easily absorbed by the phosphor III 233 to emit the red light 7. Accordingly, the additional emitted light 7 of phosphor III 233 further increases the overall brightness of the light emitting device and further improves the color rendering index. In addition, it effectively utilizes the light 6 to be emitted to the rear. Phosphor placement of such a layer structure can be easily realized by forming a layer of molding resin in which each phosphor is dispersed.

9 is a side sectional view showing a white light emitting device according to an embodiment of the present invention. Referring to FIG. 9, in the white light emitting device 100, an ultraviolet LED 104 is disposed in a recess of the casing 101. The terminal electrode 103 provided in the casing 101 is electrically connected to the LED 104 through the bonding wire 105. On the LED 104, a molding layer 130 in which phosphor III is dispersed, a molding layer 120 in which phosphor II is dispersed, and a molding layer 110 in which phosphor I is dispersed are sequentially stacked. By the white light emitting device 100, the quantum yield of the red phosphor (phosphor III) is increased, and high-quality white light with improved overall luminance and color rendering index can be obtained.

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 a red phosphor which is double excited by ultraviolet rays and green light, it is possible to increase the quantum yield of the red phosphor, to improve the overall luminance, and to improve the color rendering index. As a result, white light emission of high quality and high brightness is obtained.

Claims (15)

An ultraviolet light source emitting ultraviolet light; A first phosphor having a peak emission wavelength of 490 to 550 nm; A second phosphor having a peak emission wavelength of 420 to 480 nm; A third phosphor having a peak emission wavelength of 580-620 nm, The first phosphor is excited by the ultraviolet light to emit green light, the second phosphor is excited by the ultraviolet light to emit blue light, and the third phosphor is excited by the emitted light of the ultraviolet light and the second phosphor. And emit red light. The method of claim 1, The ultraviolet light source is a white light emitting device, characterized in that the ultraviolet LED having a peak emission wavelength of 350 to 410nm. The method of claim 1, The ultraviolet light source is a white light emitting device, characterized in that the mercury gas. The method of claim 1, The ultraviolet light source is a white light emitting device, characterized in that at least one selected from the group consisting of Ne, Ar and Xe. The method of claim 1, And the third phosphor has a peak excitation wavelength in a wavelength range of 350 to 480 nm. The method of claim 1, The third phosphor has a peak excitation wavelength in a range of 420 to 480 nm. The method of claim 1, The third phosphor has a peak excitation wavelength in the range of 350 to 410 nm and the range of 420 to 480 nm, respectively. The method of claim 1, The first phosphor is Sr ₂ Si ₃ O _{8 2} SrCl ₂ : Eu ²⁺ , Sr ₄ Al ₁₄ O ₂₅ : E ²⁺ , Y ₂ SiO ₅ : Ce ³⁺ , Tb ³⁺ and BaYSi ₄ N ₇ : Eu ²⁺ A white light emitting device, characterized in that it comprises at least one phosphor selected from the group consisting of. The method of claim 1, The second 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, characterized in that it comprises at least one phosphor selected from the group consisting of. The method of claim 1, The third phosphor comprises at least one phosphor selected from the group consisting of K ₂ Eu _2.5 (WO ₄ ) _6.25 : Sm and Li (WO ₄ ) _1.25 : Eu, Sm and Ca _0.76 MoO ₄ : Eu _0.24 ³⁺ White light emitting device. The method of claim 1, The first phosphor is Sr ₂ Si ₃ O _{8 2} SrCl ₂ : Eu ²⁺ , Sr ₄ Al ₁₄ O ₂₅ : E ²⁺ , Y ₂ SiO ₅ : Ce ³⁺ , Tb ³⁺ and BaYSi ₄ N ₇ : Eu ²⁺ At least one phosphor selected from the group consisting of, The second 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) At least one phosphor selected from the group consisting of, The third phosphor comprises at least one phosphor selected from the group consisting of K ₂ Eu _2.5 (WO ₄ ) _6.25 : Sm and Li (WO ₄ ) _1.25 : Eu, Sm and Ca _0.76 MoO ₄ : Eu _0.24 ³⁺ White light emitting device. The method of claim 1, The first, second and third phosphors are separated from each other and are formed in a discontinuous layer structure on the ultraviolet light source. The method of claim 12, And said second phosphor is on said third phosphor. The method of claim 1, And the first, second and third phosphors are contained in a molding material. The method of claim 1, Further comprising a molding material formed on the ultraviolet light source, The first, second and third phosphors are dispersed and contained in the molding material, The first, second and third phosphors are arranged in layers in the molding material, And said second phosphor is on said third phosphor.

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