KR100654539B1 - Thiogallate phosphor and white light emitting device employing the same - Google Patents

Abstract

Disclosed are thiogallate phosphors which are excited by ultraviolet or blue light and emit light having a relatively longer wavelength, and a white light emitting element employing the same. This phosphor is represented by the general formula (A _1-xy Eu _x M ^III _y ) (B _2-y M ^II _y ) S ₄ (where 0.005 <x <0.9, 0 <y <0.995, x + y <1) do. Wherein A is at least one element selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca), and B is from the group consisting of aluminum (Al), gallium (Ga) and indium (In) At least one element selected, M ^III is at least one rare earth element selected from the group consisting of scandium (Sc), lanthanum (La), gadolinium (Gd) and lutetium (Lu), and M ^II is Mg, Zn and Be At least one element selected from the group consisting of Accordingly, it is possible to increase the luminous efficiency compared to the thiogallate phosphor having a general formula of AB ₂ S ₄ : Eu.

Thiogallate, phosphor, light emitting diode, white light emitting device

Description

Thiogallate phosphor and white light emitting device employing the same

1 is a cross-sectional view illustrating a white light emitting device according to an embodiment of the present invention.

2 is a graph for explaining excitation spectra of conventional phosphors.

3 is a graph for explaining emission spectra of conventional phosphors.

4 is a graph illustrating the excitation spectrum of a conventional thiogallate phosphor and a thiogallate phosphor according to embodiments of the present invention.

5 is a graph illustrating an emission spectrum of a conventional thiogallate phosphor and a thiogallate phosphor according to embodiments of the present invention.

Explanation of reference numerals for the main parts of the drawing

1: white light emitting element, 3: light emitting diode,

5: molding member, 7: phosphor,

9: reflective cup

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to phosphors and light emitting devices employing the same, and more particularly to thiogallate phosphors having improved light efficiency and white light emitting devices employing the same.

In general, the white light emitting device is a part of the blue light emitted from the gallium nitride (GaN) series of light emitting blue light, especially the aluminum _x in _y Ga _z N series of light emitting diodes and light emitting diodes It includes a phosphor that absorbs to emit yellow light. Since the white light emitting device uses a single wavelength light source as a light source, the structure of the white light emitting device is very simple and inexpensive compared to the white light emitting device using light sources of various wavelengths.

Examples of phosphors used in white light emitting devices include yttrium-aluminum-garnet (YAG: Ce) and europium ions (Eu ²⁺ ) using cerium ions (Ce ³⁺ ) as activators. Orthosilicate represented by Sr ₂ SiO ₄ : Eu, and thiogallate phosphors such as CaGa ₂ S ₄ : Eu and the like.

YAG: Ce and orthosilicate phosphors have relatively wide bandwidths of emission spectra and have a large color rendering index. However, in order to synthesize these phosphors, raw materials having a very high purity and strict chemical quantification are required, and high temperature heat treatment of 1300 ° C. or higher is required. This increases the cost of the phosphor and consequently increases the manufacturing cost of the white light emitting device.

On the other hand, the thiographite phosphor is represented by the general formula AB ₂ S ₄ : D, where A is at least one element of calcium (Ca), strontium (Sr) and barium (Ba), B is aluminum (Al). , Gallium (Ga) and indium (In) is at least one element, D is Eu ²⁺ or Ce ³⁺ is mainly used as the active ion. Thiogallate phosphors can obtain a variety of emission colors by adjusting the type and concentration of these elements and active ions. See, for example, US Pat. No. 3,639,254, entitled "alkaline earth thiogallate phosphors," by Peters, US Pat. No. 6,417,019, "phosphor converted light emitting diodes." ) By Mueller et al. And by Ellens et al. In US Pat. No. 6,695,982 entitled "highly efficient flourescent materials." Synthesis methods and luminescent properties of thiogallate phosphors have been disclosed. As disclosed in the above U.S. Patents, by varying the type of the A or B element in the general formula, it is possible to obtain the emission color of various wavelengths.

However, there is a continuing need for thiogallate phosphors having higher luminous efficiency, and research on this continues. In particular, in lighting white light emitting devices, there is a need for thioglate phosphors having higher luminous efficiency that can replace YAG: Ce or orthosilicate phosphors.

On the other hand, thiogallate phosphors have a relatively narrow bandwidth, that is, the bandwidth of the emission spectrum measured at 1/2 peak intensity. Therefore, the white light emitting device employing the thiogallate phosphor may have a low color rendering index (CRI). The color rendering index is a numerical value representing the degree to which the perception of the object color illuminated by the light source matches the perception when illuminated with a reference light source (for example, sunlight), and is related to the wavelength distribution of light emitted to the outside. Therefore, in order to implement illumination similar to sunlight while adopting a narrow bandwidth thiogallate phosphor, a white light emitting device capable of improving the color rendering index is required.

An object of the present invention is to provide a thiogallate phosphor that can replace the YAG: Ce or orosilicate phosphor.

Another object of the present invention is to provide a thiogallate phosphor with improved luminous efficiency.

Another object of the present invention is to provide a white light emitting device employing the thiogallate phosphor.

Another object of the present invention is to provide a white light emitting device capable of improving the color rendering index while adopting the thiogallate phosphor.

In order to achieve the above technical problem, the present invention provides a thiogallate phosphor which is excited by ultraviolet light or blue light, and emits light having a relatively long wavelength. Phosphor according to an aspect of the present invention is a general formula (A _1-xy Eu _x M ^III _y ) (B _2-y M ^II _y ) S ₄ (where, 0.005 <x <0.9, 0 <y <0.995, x + y <1). Wherein A is at least one element selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca), and B is selected from the group consisting of aluminum (Al), gallium (Ga) and indium (In) At least one element, M ^III is at least one rare earth element selected from the group consisting of scandium (Sc), lanthanum (La), gadolinium (Gd) and lutetium (Lu), and M ^II is magnesium (Mg), zinc At least one selected from the group consisting of (Zn) and beryllium (Be). M ^III represents a trivalent cation and M ^II represents a divalent cation. M ^III and M ^II charge balance because the same amount replaces A and B sites, respectively. In particular, since M ^III and M ^II each have an ion radius of the same size as the elements of the A site and the B site, they do not change the crystal field size of the active ions, and thus maintain the emission wavelength. Increase luminous efficiency.

In particular, the phosphor according to an embodiment of the present invention is a general formula (Ca _1-xy Eu _x M ^III _y ) (Ga _2-y M ^II _y ) S ₄ (where, 0.005 <x <0.9, 0 <y <0.995) , x + y <1). M ^III is at least one rare earth element selected from the group consisting of scandium (Sc), lanthanum (La), gadolinium (Gd) and lutetium (Lu), and M ^II is magnesium (Mg) and zinc (Zn) At least one element selected from the group consisting of: Meanwhile, the M ^III may be specified as scandium (Sc).

Meanwhile, in some embodiments of the present invention, the range of x and y may be 0.01 to 0.9 and 0.2 to 0.8, respectively.

According to another aspect of the present invention, a white light emitting device includes a light emitting diode emitting ultraviolet or blue light, and the thiogallate positioned on the light emitting diode to convert a portion of the light emitted from the light emitting diode into light having a relatively longer wavelength. Phosphors. In particular, the light emitting diode may be a light emitting diode emitting blue light, and the phosphor may be a thiogallate phosphor that absorbs blue light and emits yellow light.

The white light emitting device may further include an orthosilicate phosphor represented by (Ca, Sr, Ba) ₂ SiO ₄ : Eu. The orthosilicate phosphor has a wider emission wavelength, thereby improving the color rendering index of white light.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention;

1 is a schematic cross-sectional view for describing a white light emitting device 1 according to an embodiment of the present invention.

Referring to FIG. 1, the white light emitting device 1 includes a light emitting diode 3 and a phosphor 7. The light emitting diode 3 is an Al _x In _y Ga _z N (where x + y + z = 1, 0 ≦ x, y, z ≦ 1) light emitting diode emitting ultraviolet or blue light. In particular, the light emitting diodes 3 may be light emitting diodes emitting blue light in the range of 420 to 480 nm.

In general, the light emitting diode 3 has two electrodes for connection to an external power source. The electrodes may be located on the same side or opposite sides of the light emitting diode 3. The electrodes may be electrically connected to a lead terminal (not shown) through an adhesive, or may be connected to the lead terminal through a bonding wire (not shown).

The light emitting diode 3 may be disposed in the reflecting cup 9. The reflecting cup 9 reflects the light emitted from the light emitting diode 3 into the required viewing angle, thereby increasing the luminance within a certain viewing angle. Thus, the reflecting cup 9 has a constant inclined surface according to the required viewing angle.

On the other hand, the phosphor 7 is located above the light emitting diode 3, and converts a part of the light emitted from the light emitting diode 3 into light having a relatively longer wavelength. In this case, the phosphor 7 may be dispersed and positioned in the transparent material 5. The transparent material 5 covers the light emitting diode 3 to protect the light emitting diode 3 from an external environment such as moisture or external force. The transparent material 5 may be epoxy or silicon and may be located in the reflective cup 9 as shown.

On the other hand, when the light emitting diode (3) emits blue light, the phosphor 7 may include a thiogallate phosphor emitting yellow light. Accordingly, the blue light emitted from the light emitting diode 3 and the yellow light emitted from the phosphor 7 are mixed to emit white light to the outside. Alternatively, the phosphor 7 may include both phosphors emitting green light and red light. At this time, the phosphor 7 includes a thiogallate phosphor that is excited by blue light and emits green light and / or a thiogallate phosphor that emits red light. When the light emitting diodes 3 emit ultraviolet rays, the phosphors 7 include other phosphors which are excited by the ultraviolet rays and emit blue light. The other phosphor may also be a thiogallate phosphor.

The thiogallate phosphor according to embodiments of the present invention is a general formula (A _1-xy Eu _x M ^III _y ) (B _2-y M ^II _y ) S ₄ (but 0.005 <x <0.9, 0 <y <0.995, x + y <1). Where A is at least one element of barium (Ba), strontium (Sr) and calcium (Ca), B is at least one element of aluminum (Al), gallium (Ga) and indium (In), M ^III Is a rare earth element of at least one of scandium (Sc), lanthanum (La), gadolinium (Gd) and lutetium (Lu), and M ^II is at least one of magnesium (Mg), zinc (Zn) and beryllium (Be) Element. M ^III and M ^II charge balance because the same amount replaces A and B sites, respectively. In particular, M ^III and M ^II may be selected to have ion radii of similar size as the elements of A site and B element, respectively. Therefore, since the crystal field size of the active ion is not changed, the luminous efficiency can be increased while maintaining the emission wavelength of the phosphor having the composition before substitution.

In some embodiments of the present invention, the range of x and y may be 0.01 to 0.9 and 0.2 to 0.8, respectively.

In particular, the thiogallate phosphor emitting yellow light of the present invention is a general formula (Ca _1-xy Eu _x M ^III _y ) (Ga _2-y M ^II _y ) S ₄ (where 0.005 <x <0.9, 0 < y <0.995, x + y <1). That is, in the general formula, A and B are specified as calcium (Ca) and gallium (Ga), respectively. Here, M ^III is at least one rare earth element of scandium (Sc), lanthanum (La), gadolinium (Gd) and lutetium (Lu), and M ^II is at least one element of magnesium (Mg) and zinc (Zn) to be. Since M ^III has an ion radius of a size similar to that of calcium (Ca), it is located at a calcium site in the phosphor crystal, and M ^II is located at a gallium site because of an ion radius of a size similar to that of gallium (Ga). . According to the aforementioned US Pat. No. 6,417,019, the CaGa ₂ S ₄ : Eu phosphor emits yellow light at a wavelength of about 560 nm. Accordingly, the thiogallate phosphor according to the embodiment of the present invention emits yellow light having a wavelength substantially similar to that of the CaGa ₂ S ₄ : Eu phosphor. In addition, the phosphor according to the embodiment of the present invention increases the luminous efficiency compared to CaGa ₂ S ₄ : Eu.

The white light emitting device 1 may further include an orthosilicate phosphor represented by (Ca, Sr, Ba) SiO ₄ : Eu. The orthosilicate phosphor may be distributed in the transparent material 5 together with the thioglate phosphor. The orthosilicate phosphor has a wider emission wavelength, which improves the color rendering index of white light.

The thiogallate phosphor can be synthesized using a solid phase reaction method. Hereinafter, a method of synthesizing a (Ca _1-xy Eu _x Sc _y ) (Ga _2-y Zn _y ) S ₄ thiogallate phosphor using the solid phase reaction method will be described.

First, prepare raw materials. Ca raw material is calcium carbonate (CaCO ₃ ) or calcium sulfide (CaS), Eu raw material is europium oxide (Eu ₂ O ₃ ) or europium sulfide (Eu ₂ S ₃ ), Sc raw material For example, scandium oxide (Sc ₂ O ₃ ) or scandium nitrate (Sc (NO ₃ ) ₂ ) is used as a raw material of Ga, and gallium oxide (Ga ₂ O ₃ ) or gallium sulfide (Ga ₂ S ₃ ) is used. Zinc oxide (ZnO) or zinc sulfide (ZnS) may be used as a raw material of Zn. The raw material used to synthesize the thiogallate phosphor may be of lower purity than the raw material used to synthesize the YAG: Ce phosphor.

Generally, a raw material having a high purity of 99.999% is used to synthesize a YAG: Ce phosphor, but a raw material having a purity of about 99.9% may be used for a thiogallate phosphor according to embodiments of the present invention.

The raw materials are mixed in the required composition ratio. Raw materials may be mixed dry or wet, and ethanol may be used in wet mixing. In addition, the raw materials may be mixed using ball milling so that the raw materials are uniformly mixed.

The mixed raw materials are calcined by heat treatment in a H ₂ S atmosphere at a temperature in the range of 800 to 1100 ° C. Before the heat treatment, the mixed raw materials may be heated at low temperature to evaporate ethanol. In the synthesis of YAG: Ce or orosilicate phosphors, heat treatment on the order of about 1600 ° C is required, and flux is added to lower the temperature. However, the thiogallate phosphor according to embodiments of the present invention can be fired at a relatively low temperature. As a result, phosphors of a desired composition are synthesized.

In addition, after the heat treatment is completed, the synthesized phosphors may be pulverized and remixed to perform secondary heat treatment. Secondary heat treatment may be carried out under the same conditions as the previous heat treatment. Accordingly, a phosphor having a more uniform composition can be synthesized.

Experimental Examples

Hereinafter, the excitation spectrum and the emission spectrum of the phosphors according to the prior art and the phosphors according to the embodiments of the present invention will be described. 2 and 3 are graphs for explaining the excitation spectrum and the emission spectrum of various phosphors according to the prior art, respectively, and FIGS. 4 and 5 are thiogallate phosphors according to the prior art and thiogal according to an embodiment of the present invention, respectively. It is a graph for explaining the excitation spectrum and emission spectrum of the latent phosphor. Here, the excitation spectrum and emission spectrum were measured using a fluorescence spectrometer model FP-6200 manufactured by Jasco, Inc., and a xenon (Xe) lamp was used as the excitation light source. The excitation spectrum was measured based on the wavelength of the emission spectrum 550 nm, the emission spectrum was measured using an excitation light source of 460 nm. On the other hand, as the thiogallate phosphor 15 of the prior art, a phosphor of Ca _0.96 Ga ₂ S ₄ : Eu _0.04 was used, and as the thiogallate phosphor 23 according to the embodiment of the present invention, the composition (Ca _{0.36) was used.} A phosphor having Sc _0.6 ) (Ga _1.4 Zn _0.6 ) S ₄ : Eu _0.04 was used.

Referring to FIG. 2, the thiogallate phosphor 15 of the prior art has a stronger relative intensity of the excitation spectrum than most of the YAG: Ce phosphor 11 in most wavelength regions. In addition, the thiogallate phosphor 15 of the prior art has a stronger intensity of the excitation spectrum than the orthosilicate (Sr, Ba) ₂ SiO ₄ : Eu phosphor 13 in the wavelength region of 440 nm or more, 420 to 440 In the wavelength range of nm, the relative intensity was almost similar to that of the (Sr, Ba) ₂ SiO ₄ : Eu phosphor 13.

Referring to FIG. 3, the peak intensity of the thiogallate phosphor 15 is relatively stronger than that of the YAG: Ce phosphor 11 and the (Sr, Ba) ₂ SiO ₄ : Eu phosphor 13, but the bandwidth is higher than that of the phosphor. Narrow.

As a result, the overall emission amount of the thiogallate phosphor 15 in the yellow light region is almost similar to that of the YAG: Ce phosphor 11 and (Sr, Ba) ₂ SiO ₄ : Eu phosphor 13 for the same excitation light source, It appears to be weaker than these.

Referring to FIG. 4, thiogallate (Ca _0.36 Sc _0.6 ) (Ga _1.4 Zn _0.6 ) S ₄ : Eu _0.04 phosphor 23 according to an embodiment of the present invention is measured in all wavelength ranges, in particular in the ultraviolet region and the blue light region. The relative intensity of the excitation spectrum was stronger than that of the thiogallate phosphor 15 of the prior art.

Referring to FIG. 5, the thiogallate phosphor 23 according to the embodiment of the present invention showed a relatively very strong peak intensity at the wavelength of about 550 nm compared with the conventional thiogallate phosphor 15. Meanwhile, the bandwidths of the thiogallate phosphors 15 and 23, that is, the bandwidths at positions 1/2 of the peak intensity, showed similar values.

As a result, the thiogallate phosphor 23 according to the embodiment of the present invention has improved luminous intensity compared to the conventional thiogallate phosphor 15 for the same excitation light source, from which it can be seen that the luminous efficiency increased. have.

According to the present invention, it is possible to provide a thiogallate phosphor with improved luminous efficiency. The thiogallate phosphor can be economically synthesized, and the luminous efficiency is improved compared to the conventional thiogallate phosphor, thereby replacing YAG: Ce or orthosilicate phosphor. In addition, it is possible to provide a white light emitting device by adopting a thiogallate phosphor according to the present invention, it is possible to provide a white light emitting device that can improve the color rendering index by additionally adopting an orthosilicate phosphor.

Claims (7)

The general formula is (A _1-xy Eu _x M ^III _y ) (B _2-y M ^II _y ) S ₄ , wherein A is at least one selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca) Is an element of, B is at least one element selected from the group consisting of aluminum (Al), gallium (Ga) and indium (In), M ^III is scandium (Sc), lanthanum (La), gadolinium (Gd) And at least one rare earth element selected from the group consisting of lutetium (Lu), M ^II is at least one element selected from the group consisting of Mg, Zn and Be, and 0.005 <x <0.9, 0 <y <0.995, x + phosphor with y <1. The general formula is (Ca _1-xy Eu _x M ^III _y ) (Ga _2-y M ^II _y ) S ₄ , where M ^III is scandium (Sc), lanthanum (La), gadolinium (Gd), and lutetium (Lu) At least one rare earth element selected from the group consisting of M ^II is at least one element selected from the group consisting of Mg, Zn and Be and a phosphor having 0.005 <x <0.9, 0 <y <0.995, x + y <1 . The general formula is (Ca _1-xy Eu _x M ^III _y ) (Ga _2-y M ^II _y ) S ₄ , M ^III is scandium (Sc), M ^II is composed of magnesium (Mg) and zinc (Zn) One phosphor selected from the group, wherein 0.005 <x <0.9, 0 <y <0.995, x + y <1. The phosphor according to any one of claims 1 to 3, wherein 0.01≤x <0.9 and 0.2≤y≤0.8. Light emitting diodes emitting ultraviolet or blue light; And a phosphor according to any one of claims 1 to 3, positioned above the light emitting diode and converting a part of the light emitted from the light emitting diode into light having a relatively longer wavelength. The white light emitting device of claim 5, wherein the light emitting diode emits blue light having a wavelength in a range of 420 nm to 480 nm, and the phosphor converts a part of the blue light into yellow light. The white light emitting device of claim 5, further comprising an orthosilicate-based phosphor positioned on the light emitting diode to convert a part of the light emitted from the light emitting diode into light having a relatively longer wavelength.

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