JP2007103512A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device which can emit white light excellent in color balance efficiently. <P>SOLUTION: The light emitting device comprises a light emitting element 3 formed on a substrate 2 and emitting excitation light in the wavelength range of 370-420 nm, and a wavelength conversion layer 4 formed to cover the light emitting element 3 in order to convert the excitation light into visible light and outputting the visible light. The wavelength conversion layer 4 includes a blue phosphor 5a emitting fluorescence of 430-490 nm, a green phosphor 5b emitting fluorescence of 500-560 nm, a yellow phosphor 5c emitting fluorescence of 540-600 nm, and red phosphor 5d emitting fluorescence of 590-700 nm wherein each phosphor has conversion efficiency of 60% or above and the difference of conversion efficiency of respective phosphors falls within 15%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  INDUSTRIAL APPLICABILITY The present invention is suitably used for a light-emitting device that converts the wavelength of light emitted from a light-emitting element such as an LED (Light Emitting Diode) and extracts it to the outside, in particular, a backlight power source for an electronic display, a fluorescent lamp, and the like. The present invention relates to a light emitting device.

  A light emitting element made of a semiconductor material (hereinafter sometimes referred to as “LED chip”) is small in size, has high power efficiency, and vividly develops color. LED chips have excellent characteristics such as long product life, strong on / off lighting repeatability, and low power consumption, so they are expected to be applied to backlight sources such as liquid crystals and lighting sources such as fluorescent lamps. Has been.

  The application of the LED chip to the light emitting device is that the wavelength of part of the light of the LED chip is converted with a phosphor, and the wavelength-converted light and the light of the LED that is not wavelength-converted are mixed and emitted, thereby It has already been manufactured as a light emitting device that emits a color different from that of light.

Specifically, in order to emit white light, a light emitting device in which a wavelength conversion layer containing a phosphor is provided on the surface of an LED chip has been proposed. For example, in a light emitting device in which a wavelength conversion layer containing a YAG phosphor expressed by a composition formula of (Y, Gd) ₃ (Al, Ga) ₅ O ₁₂ is formed on a blue LED chip using an nGaN-based material, Since blue light is emitted from the LED chip and a part of the blue light is changed to yellow light in the wavelength conversion layer, a light emitting device in which blue and yellow light are mixed and white is proposed (see Patent Document 1). ).

  An example of such a light emitting device is shown in FIG. 4, the light-emitting device includes a substrate 102 on which an electrode 101 is formed, a light-emitting element 103 including a semiconductor material that emits light having a central wavelength of 470 nm on the substrate 102, and a light-emitting element 103 on the substrate 102. The wavelength conversion layer 104 is provided so as to cover it, and the wavelength conversion layer 104 contains the phosphor 105. If desired, a reflector 106 that reflects light may be provided on the side surfaces of the light emitting element 103 and the wavelength conversion layer 104, and the light escaping to the side surfaces may be focused forward to increase the intensity of the output light.

  In this light emitting device, when the phosphor 105 is irradiated with light emitted from the light emitting element 103, the phosphor 105 is excited to emit visible light, and this visible light is used as an output. However, when the brightness of the light emitting element 103 is changed, the light quantity ratio between blue and yellow changes, so that there is a problem that the color tone of white changes and the color rendering property is inferior.

  Therefore, in order to solve such a problem, a purple LED chip having a peak of 400 nm or less is used as the light-emitting element 103 in FIG. 5, and three types of phosphors 115, 116, and 117 are formed on the wavelength conversion layer 104. It has been proposed to adopt a structure mixed in a molecular resin and convert white light by converting violet light into red, green, and blue wavelengths (see Patent Document 2). Thereby, a color rendering property can be improved.

However, in the light emitting device described in Patent Document 2, the luminous efficiency of a red component phosphor (for example, Y ₂ O ₃ S: Eu) in the ultraviolet region near 400 nm of excitation light is significantly higher than other phosphors. Due to the low level, there is a problem that white light with a good emission balance of red, green and blue cannot be obtained. Therefore, if the amount of the red phosphor with low luminous efficiency is increased, the fluorescence emitted from the green and blue phosphors is reabsorbed by the red phosphor, so that the emission amounts of the green and blue phosphors can be kept low. As a result, there is a problem that the luminous efficiency of the white light emitting device is not improved.

Further, the efficiency can be improved by increasing the mixing amount of the green and blue phosphors having high luminous efficiency, but there is a problem that it is impossible to obtain white light with a good emission balance of red, green and blue.
JP 11-261114 A JP 2002-314142 A

  An object of the present invention is to provide a light emitting device capable of efficiently emitting white light with excellent color balance.

  As a result of intensive studies to solve the above problems, the present inventor has blue phosphors, green phosphors, yellow phosphors and red phosphors having a conversion efficiency of a certain amount or more and a small variation (difference) in conversion efficiency. It has been found that when a phosphor is used, it is possible to efficiently emit excellent white light with good color balance, and the present invention has been completed.

That is, the light emitting device of the present invention has the following configuration.
(1) A light emitting element that emits excitation light in a wavelength range of 370 nm to 420 nm on a substrate, and a wavelength conversion layer that converts the excitation light formed so as to cover the light emitting element into visible light, the visible light In the wavelength conversion layer, a blue phosphor emitting fluorescence of 430 nm to 490 nm, a green phosphor emitting fluorescence of 500 nm to 560 nm, and fluorescence of 540 nm to 600 nm are emitted in the wavelength conversion layer. A yellow phosphor and a red phosphor emitting fluorescence from 590 nm to 700 nm, each phosphor has a conversion efficiency of 60% or more, and the difference in conversion efficiency of each phosphor is 15%. A light emitting device characterized by being within.
(2) The yellow phosphor and the red phosphor are contained in a portion close to the light emitting element, and the blue phosphor and the green phosphor are located farther from the light emitting element than the yellow phosphor and the red phosphor. The light emitting device according to (1), wherein the light emitting device is contained in a large amount.
(3) The light emitting device according to (2), wherein the wavelength conversion layer is composed of one layer.
(4) The wavelength conversion layer has a laminated structure of two or more layers, and a yellow phosphor and a red phosphor are contained in a layer closer to the light emitting element than a layer containing a blue phosphor and a green phosphor. The light-emitting device according to (1) or (2), wherein
(5) The light-emitting device according to any one of (1) to (4), wherein the phosphor is dispersed in a polymer resin mainly composed of a silicon-oxygen bond.
(6) The light emitting device according to any one of (1) to (5), wherein a peak wavelength of the output light is 400 to 750 nm. (7) A thickness of the wavelength conversion layer is 0.1. The light-emitting device according to any one of (1) to (6), which is ˜5 mm.
(8) The light emitting device according to any one of (1) to (7), wherein a reflective member that emits light emitted from the light emitting device forward is provided on side surfaces of the light emitting device and the wavelength conversion layer. apparatus.
(9) The light emitting device according to any one of (1) to (8), wherein an average particle size of the blue phosphor is 0.1 to 50 μm.
(10) The blue phosphor is [(M, Mg) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu] (M is at least one selected from Ca, Sr and Ba) or [BaMgAl ₁₀ O ₁₇ : Eu]. The light-emitting device according to any one of (1) to (9), wherein
(11) The light emitting device according to any one of (1) to (10), wherein the green phosphor has an average particle size of 0.1 to 50 μm.
(12) The green phosphor is [BaMgAl ₁₀ O ₁₇ : Eu, Mn], [ZnS: Cu, Al] or [MGa ₂ S ₄ : Eu] (1) to (11) The light emitting device according to any one of the above.
(13) The light-emitting device according to any one of (1) to (12), wherein the red phosphor is a semiconductor ultrafine particle having an average particle diameter of 10 nm or less.
(14) The red phosphor is a semiconductor composition comprising at least two elements belonging to Group I, Group II, Group III, Group IV, Group V, and Group VI of the Periodic Table The light-emitting device according to any one of (1) to (13).
(15) The light-emitting device according to any one of (1) to (14), wherein the yellow phosphor is a semiconductor ultrafine particle having an average particle diameter of 10 nm or less.
(16) The yellow phosphor is a semiconductor composition comprising at least two elements belonging to Group I, Group II, Group III, Group IV, Group V, and Group VI of the Periodic Table The light emitting device according to any one of (1) to (15).

  According to the above (1), a blue phosphor emitting fluorescence of 40 nm to 490 nm, a green phosphor emitting fluorescence of 500 nm to 560 nm, and a yellow fluorescence emitting fluorescence of 540 nm to 600 nm mixed in the wavelength conversion layer. And a red phosphor emitting fluorescence of 590 nm to 700 nm, the conversion efficiency (quantum yield) of each phosphor is 60% or more, and the difference in conversion efficiency of each phosphor is within 15% As a result, the color rendering properties of the output light can be improved, and excellent luminous efficiency can be realized.

  According to the above (2), the arrangement of the phosphors in the wavelength conversion layer is mostly blue phosphors and green phosphors in portions far from the light emitting elements, and yellow phosphors and red phosphors in portions near the light emitting elements. Is contained in large quantities. By setting it as such a structure, the fall of the luminous efficiency by the self absorption between fluorescent substance can be suppressed. Furthermore, when the wavelength conversion layer has a single-layer structure as in (3) above, the number of steps for forming the layer can be reduced compared to the case where a plurality of layers are provided.

According to the above (4), a layer in which the blue phosphor and the green phosphor are dispersed is formed in a portion far from the light emitting element, and a layer in which the yellow phosphor and the red phosphor are dispersed is formed near the light emitting element. Has been. By setting it as such a structure, the efficiency fall by the said self absorption can be suppressed further. It is effective because the wavelength conversion layer can be made into a laminated structure of two or more layers containing each phosphor, whereby the wavelength conversion layer can be simplified and the wavelength conversion layer excellent in reliability can be realized. .
The wavelength conversion layer may be either a single-layer structure or a multilayer structure, but the optimality varies depending on the phosphor composition to be employed, the average particle diameter, and the like, and any one may be employed depending on the purpose.

  According to the above (5), in the wavelength conversion layer, the phosphor is dispersed and mixed in a polymer resin mainly composed of silicon-oxygen bonds. As a result, the light resistance, heat resistance, and transparency of the wavelength conversion layer can be increased, and as a result, the long life of the light emitting device can be ensured.

According to (6) above, when the peak wavelength of the output light from the wavelength conversion layer is 400 to 750 nm, it is possible to realize a light emitting device that is further excellent in color rendering.
According to the above (7), since the wavelength conversion layer has a thickness of 0.1 to 5 mm, the conversion efficiency is high and light is sufficiently transmitted, so that more excellent light emission characteristics can be exhibited.

  According to the above (8), the lateral side or the substrate side is conventionally provided by having a structure including the side-surface reflecting member provided so as to emit light emitted from the light emitting element forward around the light emitting element. The light emitted from the light emitting element can be emitted from the front surface, and the light emission efficiency can be improved.

According to the above (9) and (10), high conversion efficiency can be obtained because the blue phosphor has a predetermined average particle diameter and composition.
According to the above (11) and (12), high conversion efficiency can be obtained because the green phosphor has a predetermined average particle diameter and composition.

According to the above (13) and (15), yellow phosphors and red phosphors, which are semiconductor ultrafine particles having an average particle diameter of 10 nm or less, have high excitation efficiency in the wavelength range of 370 nm to 420 nm, and thus excellent luminous efficiency. Can be obtained.
According to the above (14) and (16), higher conversion efficiency can be obtained.

  The light emitting device of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an embodiment of a light emitting device of the present invention. According to FIG. 1, the light emitting device of the present invention is formed so as to cover the light emitting element 3 on the substrate 2, the light emitting element 3 provided on the substrate 2, the substrate 2 on which the electrode 1 is formed. One wavelength conversion layer 4 and a reflecting member 6 that reflects light are provided.

  The electrode 1 has a function as a conductive path for electrically connecting the light emitting element 3 and is connected to the light emitting element 3 with a conductive bonding material. As the electrode 1, for example, a metallized layer containing metal powder such as W, Mo, Cu, or Ag can be used. When the substrate 1 is made of ceramic, the electrode 1 is formed by firing a metal paste made of tungsten (W), molybdenum (Mo) -manganese (Mn), etc. on the upper surface of the substrate 1 at a high temperature. , A lead terminal made of copper (Cu), iron (Fe) -nickel (Ni) alloy or the like is molded and fixed inside the substrate 1.

  As the substrate 2, a substrate having excellent thermal conductivity and a large total reflectance is used. As the substrate 2, for example, a polymer resin in which metal oxide fine particles are dispersed in addition to a ceramic material such as alumina and aluminum nitride is preferably used.

  As the light-emitting element 3, an element that emits excitation light in a wavelength range of 370 nm to 420 nm, preferably 380 nm to 410 nm can be used. The light emitting element 3 is not particularly limited as long as it emits a central wavelength of 370 nm to 420 nm, but has a structure (not shown) including a light emitting layer made of a semiconductor material on the surface of the light emitting element substrate of the light emitting element 3. It is preferable that it has a high external quantum efficiency. Examples of such a semiconductor material include various semiconductors such as ZnSe and nitride semiconductor (GaN, etc.), but the type of the semiconductor material is not particularly limited as long as the emission wavelength is in the above wavelength range. A stacked structure having a light-emitting layer made of a semiconductor material may be formed over the light-emitting element substrate by a crystal growth method such as a metal organic chemical vapor deposition method (MOCVD method) or a molecular beam epitaxial growth method. In the light-emitting device illustrated in FIG. 1, a light-emitting element including a semiconductor material that emits light having a central wavelength of 370 nm to 420 nm is formed as the light-emitting element 3.

  The wavelength conversion layer 4 has a blue phosphor 5a emitting fluorescence from 430 nm to 490 nm, a green phosphor 5b emitting fluorescence from 500 nm to 560 nm, a yellow phosphor 5c emitting fluorescence from 540 nm to 600 nm, and fluorescence from 590 nm to 700 nm. The emitted red phosphor 5d is contained. Further, in the wavelength conversion layer 4 shown in FIG. 1, the yellow phosphor 5c and the red phosphor 5d are unevenly distributed in a portion close to the light emitting element 3, and the light emitting element 3 is more distant than the yellow phosphor 5c and the red phosphor 5d. In the far part, the blue phosphor 5a and the green phosphor 5b are unevenly distributed.

  On the other hand, when the phosphors are randomly dispersed, for example, the fluorescent light emitted from the blue fluorescent material and the green fluorescent material that emits the short-wavelength fluorescence is converted into the yellow fluorescent material and the red fluorescent material that express the long-wavelength fluorescent light. It is reabsorbed by the body and the luminous efficiency of the blue phosphor and the green phosphor is reduced. As a result, the light emission efficiency of the output light emitted from the light emitting device is lowered, and the light emission efficiency of the light emitting device as a whole is not sufficiently increased. In addition, a part of the fluorescence emitted from the blue phosphor and the green phosphor is reabsorbed by the yellow phosphor and the red phosphor, and emits yellow and red fluorescence, thereby producing a color balance of the output light emitted from the light emitting device. Is greatly reduced, and the color rendering is greatly deteriorated.

  In the present invention, the yellow phosphor 5c and the red phosphor 5d are contained near the light emitting element 3, and the blue phosphor 5a and the green phosphor 5b are located farther from the light emitting element 3 than the yellow phosphor 5c and the red phosphor 5d. Is contained. As described above, the phosphors 5a to 5d are separated and unevenly distributed in one layer, whereby the excitation light from the light emitting element 3 is first converted into yellow or red by the yellow phosphor 5c and the red phosphor 5d, and then Since the excitation light that has passed between the yellow phosphor 5c and the red phosphor 5d can be converted into blue or green by the blue phosphor 5a and the green phosphor 5b, between the phosphors 5a, 5b, 5c, and 5d. It is possible to efficiently convert excitation light while suppressing a decrease in light emission efficiency due to self-absorption.

  In the light emitting device of the present invention, it is preferable that the conversion efficiency of each phosphor 5a, 5b, 5c and 5d is 60% or more, and the difference between the conversion efficiencies is 15% or less. Using the blue phosphor 5a, the green phosphor 5b, the yellow phosphor 5c and the red phosphor 5d having such conversion efficiency, a balanced emission spectrum is achieved (improves the color rendering of the output light), A light emitting device having very excellent luminous efficiency can be obtained.

  When the conversion efficiency of some phosphors is less than 60%, the fluorescence intensity of the corresponding phosphors decreases for the optimal white light spectrum, resulting in a decrease in color rendering of the output light emitted from the light emitting device. At the same time, the luminous efficiency of the output light is reduced. On the other hand, even when the conversion efficiency of all the phosphors exceeds 60%, if the difference (deviation) in the conversion efficiency between the phosphors is large, the color balance of the output light is greatly reduced and the color rendering properties are greatly reduced. A decrease occurs. For this reason, it is not possible to obtain white light with a good emission balance of red, green, and blue.

  The conversion efficiency of the phosphor is defined by a numerical value obtained by dividing the number of photons emitted from the phosphor by the number of photons absorbed by the phosphor. Since it is very difficult to measure the number of photons, the conversion efficiency of the phosphor is generally obtained using the following method. A reference substance with a known conversion efficiency is prepared, and first, the solution concentration is adjusted with a solvent such as toluene or ethanol in order to show the absorbance of the reference substance and the phosphor. The conversion efficiency can be obtained by obtaining the fluorescence spectrum area ratio after combining the absorbance of the reference substance and the phosphor, and comparing the relative ratio with the reference substance. Moreover, the difference in the conversion efficiency of each phosphor can be obtained by a deviation (difference) from the average value of the conversion efficiency of the phosphors used.

The blue phosphor 5a and the green phosphor 5b included in the wavelength conversion layer 4 are materials that emit fluorescence when excited by light in a wavelength range of 370 nm to 420 nm, and the blue phosphor 5a emits fluorescence of 430 nm to 490 nm, The green phosphor 5b is not particularly limited as long as it is a material emitting fluorescence of 500 nm to 560 nm. As the blue phosphor 5a and the green phosphor 5b, commonly used phosphors can be adopted. Examples of the blue phosphor 5a and the green phosphor 5b having a conversion efficiency of 60% or more include (Sr, Ca, Ba, Mg) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu, BaMgAl ₁₀ O ₁₇ : Eu, Mn, BaMgAl ₁₀ O ₁₇ : Eu, (Ba, Eu) MgAl ₁₀ O ₁₇ , (Sr, Ca, Ba, Mg) ₁₀ (PO ₄ ) ₆ Cl ₁₇ : Eu, Sr ₁₀ (PO ₄ ) ₆ Cl ₁₂ : Eu, Ba, Sr, Eu) (Mg , Mn) Al 10 O 17, 10 (Sr, Ca, Ba, Eu) · 6PO 4 · Cl 2, BaMg 2 Al 16 O 25: Eu, Y 3 Al 5 O 12: Tb _{, Y3 (Al, Ga) 5} O 12: Tb, Y 2 SiO 5: Tb, Zn 2 SiO 4: Mn, ZnS: Cu + Zn 2 SiO 4: Mn, Gd 2 O 2 S: Tb, (Zn, Cd) S : Ag, Y ₂ O ₂ S: Tb, ZnS: Cu, Al + In ₂ O ₃ , (Z n, Cd) S: Ag + In ₂ O ₃ , (Zn, Mn) ₂ SiO ₄ , BaAl ₁₂ O ₁₉ : Mn, (Ba, Sr, Mg) O · aAl ₂ O ₃ : Mn, LaPO ₄ : Ce, Tb, 3 (Ba, Mg, Eu, Mn) O.8Al ₂ O ₃ , La ₂ O ₃ .0.2SiO ₂ .0.9P ₂ O ₅ : Ce, Tb, CeMgAl ₁₁ O ₁₉ : Tb, Y ₂ O ₂ S : Eu, Y ₂ O ₃ : Eu, Zn ₃ (PO ₄ ) ₂ : Mn, (Zn, Cd) S: Ag + In ₂ O ₃ , (Y, Gd, Eu) BO ₃ , (Y, Gd, Eu) ₂ O ₃ , YVO ₄ : Eu, La ₂ O ₂ S: Eu, Sm, YAG: Ce, etc. are used. The blue phosphor 5a is made of [(M, Mg) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu] (M is at least one of Ca, Sr and Ba) or [BaMgAl ₁₀ O ₁₇ : Eu]. The green phosphor 5b is preferably [BaMgAl ₁₀ O ₁₇ : Eu, Mn], [ZnS: Cu, Al] or [MGa ₂ S ₄ : Eu].

  The average particle diameter of the blue phosphor 5a and the green phosphor 5b is 0.1 to 50 μm, preferably 0.1 to 20 μm, more preferably 1 to 20 μm. When the average particle diameter is larger than 50 μm, the light transmittance of the wavelength conversion layer is remarkably lowered, so that the light emitted by the phosphor is not emitted from the wavelength conversion layer, and as a result, the luminous efficiency of the light emitting device is remarkably lowered. . On the other hand, when the average particle diameter is smaller than 0.1 μm, the light emission characteristics deteriorate due to surface defects, and as a result, the light emission efficiency of the light emitting device decreases.

The yellow phosphor 5c and the red phosphor 5d included in the wavelength conversion layer 4 are preferably composed of semiconductor ultrafine particles. Examples of the yellow phosphor 5c and the red phosphor 5d having a conversion efficiency of 60% or more include, for example, a periodic rule. More preferably, the semiconductor ultrafine particles are composed of at least two kinds of elements belonging to Tables I, II, III, IV, V, VI. For example, III-V group compound semiconductors such as BN, BP, BAs, AlN, AlP, AlSb, GaN, GaP, GaSb, InN, InP, and InSb, II-VI group compound semiconductors such as ZnO and ZnS, CuInS ₂ , CuGaS ₂ , CuAlS ₂ , Cu (In _1-x Al _x ) S ₂ , CuInS ₂ , Cu (In _1-x Ga _x ) S ₂ (x and y are 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, respectively. AgInS ₂ , AgGaS ₂ , AgAlS ₂ , Ag (In _1-x Al _x ) S ₂ , AgInS ₂ , Ag (In _1-x Ga _x ) S ₂ , ZnAgInS ₂ (x and y are respectively (Values represented by 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) are preferably used.

  In the present invention, the average particle diameter of the yellow phosphor 5c and the red phosphor 5d is preferably 10 nm or less, particularly preferably 2 nm to 5 nm. The conventional yellow phosphor has a very low excitation efficiency in the wavelength range of 370 nm to 420 nm, and has a structure in which the yellow phosphor is excited and emitted by absorbing the fluorescence emitted from the blue phosphor. There has been a problem that the luminous efficiency of the phosphor is lowered, but by adopting semiconductor ultrafine particles having an average particle diameter of 10 nm or less that exhibits yellow fluorescence, the above problems can be solved and excellent luminous efficiency can be realized.

  Even with ordinary red phosphors, there is a problem that the excitation efficiency in the wavelength range of 370 nm to 420 nm is very small, but semiconductor ultrafine particles having an average particle diameter of 10 nm or less that exhibit red fluorescence realize very high luminous efficiency. Therefore, it is excellent in luminous efficiency and color rendering.

  Further, in the yellow phosphor 5c and the red phosphor 5d, the band gap energy of the compound semiconductor in the bulk state of the semiconductor composition constituting it is preferably in the range of 1.5 to 2.5 eV at a temperature of 300K. .

  The yellow phosphor 5c and the red phosphor 5d according to the present invention may have a so-called core-shell structure including an inner core (core) and an outer shell (shell). A core-shell type semiconductor may be suitable for an application utilizing an exciton absorption / emission band. In this case, it is generally effective to form an energy barrier by using a shell semiconductor particle having a forbidden band width (band gap) larger than that of the core. This is presumed to be due to a mechanism that suppresses the influence of an undesirable surface level or the like due to the influence of the outside world or crystal lattice defects on the crystal surface.

  The composition of the semiconductor material suitably used for the shell depends on the band gap of the core semiconductor crystal, but the band gap in the bulk state is 2.5 eV or more at a temperature of 300 K, such as BN, BAs, GaN, GaP, etc. III-V group compound semiconductors, II-VI group compound semiconductors such as ZnO and ZnS, and compounds of Group 2 elements of the periodic table and Group 16 elements of the periodic table such as MgS and MgSe are preferably used.

  Further, the yellow phosphor 5c and the red phosphor 5d in the present invention may be covered with a surface modifying molecule made of an organic ligand. By covering the surface modification molecules, aggregation of the semiconductor ultrafine particles can be suppressed, and the function of the semiconductor ultrafine particles can be expressed to the maximum. Surface modifying molecules are n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, octyl, decyl, dodecyl, hexadecyl, octadecyl Examples include molecules having an alkyl group having about 3 to 20 carbon atoms, such as a group, and a hydrocarbon group containing an aromatic hydrocarbon group such as a phenyl group, a benzyl group, a naphthyl group, or a naphthylmethyl group. Molecules having a linear alkyl group having about 6 to 16 carbon atoms such as a hexyl group, octyl group, decyl group, dodecyl group, hexadecyl group and the like are more preferable. Also, sulfur atom-containing functional groups such as mercapto group, disulfide group, thiophene ring, nitrogen atom-containing functional groups such as amino group, pyridine ring, amide bond, nitrile group, carboxyl group, sulfonic acid group, phosphonic acid group, phosphinic acid Using molecules having acidic functional groups such as groups, phosphorus atom-containing functional groups such as phosphine groups and phosphine oxide groups, or oxygen atom-containing functional groups such as hydroxyl groups, carbonyl groups, ester bonds, ether bonds, polyethylene glycol chains, etc. Also good.

The yellow phosphor 5c and the red phosphor 5d can be manufactured by a general manufacturing method. Manufacturing methods include, for example, gas phase chemical reaction methods such as flame process, plasma process, electric heating process, laser process, physical cooling method, sol-gel method, alkoxide method, coprecipitation method, hot soap method, hydrothermal synthesis method, Examples include liquid phase methods such as spray pyrolysis, mechanochemical bonding, microreactor methods, and microwave heating methods.
The average particle diameter of the synthesized semiconductor ultrafine particles can be measured using the method of measuring the average particle diameter of the phosphor in the examples described later.

Among the phosphors having a conversion efficiency of 60% or more, as a combination in which the difference in conversion efficiency between the phosphors is within 15%, (1) Blue phosphor 5a [(Ca, Mg) ₁₀ (PO ₄ ) ₆ Cl _2: the Eu], as a green phosphor 5b [BaMgAl ₁₀ O _17: Eu, Mn,], the ZnAgInS ₂ as a yellow phosphor 5c, the combination of using ZnAgInS ₂ as a red phosphor 5d, (2) blue phosphor as 5a,: a [BaMgAl ₁₀ O ₁₇ Eu], as a green phosphor 5b [ZnS: Cu, Al] and the ZnCuInS ₂ as a yellow phosphor 5c, using ZnCuInS ₂ as a red phosphor 5d combination, (3) [(Sr, Ca, Ba, Mg) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu] is used as the blue phosphor 5a, and [BaMgAl ₁₀ O ₁₇ : Eu, Mn is used as the green phosphor 5b. ], A combination using [ZnAgInS ₂ ] as the yellow phosphor 5c and [ZnAgInS ₂ ] as the red phosphor 5d.

  In order to produce the wavelength conversion layer 4, first, the blue phosphor 5a, the green phosphor 5b, the yellow phosphor 5c, and the red phosphor 5d are mixed with an uncured matrix resin. As the matrix resin, for example, an epoxy resin, a polycarbonate resin, an acrylic resin, or a polymer resin (silicone resin or the like) mainly composed of a silicon-oxygen bond is preferable in terms of transmittance.

  In particular, a polymer resin mainly composed of a silicon-oxygen bond has an excellent heat resistance and light resistance because it has a very large silicon-oxygen bond energy and does not deteriorate by absorbing light at around 400 nm. . As a result, by dispersing and mixing phosphors in a polymer resin mainly composed of silicon-oxygen bonds, the light conversion, heat resistance and transparency of the wavelength conversion layer can be improved, and the long life of the light emitting device is ensured. can do. Therefore, a silicone resin is most preferable because it has both transmittance and heat resistance. In addition, it is desirable to use a dispersant that is chemically coupled to the matrix resin in terms of stability after curing.

Next, a mixture of the blue phosphor 5a, the green phosphor 5b, the yellow phosphor 5c, the red phosphor 5d, and an uncured matrix resin is formed into a sheet shape. Examples of the molding method include a molding method capable of forming a sheet such as a doctor blade method, a die coater method, an extrusion method, a spin coating method, a dip method, and in particular, if a doctor blade method or a die coater method is used, productivity Can be improved. Next, the blue phosphor 5a, the green phosphor 5b, the yellow phosphor 5c, and the red phosphor 5d in the sheet are hierarchically dispersed according to the average particle diameter of the particles. In order to disperse the phosphors hierarchically, a sedimentation method or a centrifugal separation method can be used. Furthermore, the phosphor can be dispersed in layers by changing the sedimentation rate between the phosphors by optimizing the specific gravity of the phosphor, the viscosity of the matrix resin, the curing temperature and the curing time of the matrix resin. For example, dimethyl silicone resin is used as the matrix resin, [(Ca, Mg) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu] (average particle diameter: 7 μm) is used as the blue phosphor 5a, and [BaMgAl ₁₀ O _{17 is used} as the green phosphor 5b. : Eu, Mn] (average particle diameter 4 μm), ZnAgInS ₂ (average particle diameter 2.8 nm) as the yellow phosphor 5c, and ZnAgInS ₂ (average particle diameter 3.8 nm) as the red phosphor 5d, By setting the viscosity of the matrix resin to 200 to 1000 cps, the curing temperature of the matrix resin to 130 to 170 ° C., and the curing time of the matrix resin to 5 to 24 hours (hours), the sedimentation rate between the phosphors can be changed to form a layer Can be dispersed.

  The amount of the phosphors 5a to 5d to be added to the resin may be determined in consideration of the light emission intensity of the light emitting element, the size of the light emitting element, and the film thickness of the wavelength conversion layer 4. It is preferable to add 10 to 50% by mass of the total amount of the phosphor with respect to the total amount of the layer 4.

  The thickness of the wavelength conversion layer 4 is preferably 0.1 to 5 mm, particularly preferably 0.5 to 1 mm. Within this range, the excitation light emitted from the light emitting element 3 can be converted into output light with high efficiency, and the converted output light can be transmitted to the outside with high efficiency.

  The reflecting member 6 is provided on the side surfaces of the light emitting element 3 and the wavelength conversion layer 4, and can reflect the light escaping to the side surface forward to increase the intensity of the output light. Examples of the material of the reflecting member 6 include aluminum (Al), nickel (Ni), silver (Ag), chromium (Cr), titanium (Ti), copper (Cu), gold (Au), iron (Fe), and these. These laminated structures and alloys, ceramics such as alumina ceramics, or resins such as epoxy resins can be used.

  In the light emitting device, the peak wavelength of the output light from the wavelength conversion layer 4 is preferably 400 to 750 nm. By emitting output light having such a peak wavelength, it is possible to realize a light emitting device that is further excellent in color rendering.

  FIG. 2 is a diagram showing another embodiment of the light emitting device according to the present invention, and is a schematic cross-sectional view of a light emitting device having a wavelength conversion layer 4 having a two-layer structure. In FIG. 2, the same members as those of the light emitting device shown in FIG. 1 are denoted by the same reference numerals as those in FIG.

  In the light emitting device shown in FIG. 2, the wavelength conversion layer 40 has a two-layer structure of a first conversion layer 41 and a second conversion layer 42, the conversion layer 42 is converted to the surface of the light emitting element 3, and the conversion layer 41 is converted. It is formed on the surface of the layer 42. The conversion layer 41 contains a blue phosphor 5a and a green phosphor 5b, and the conversion layer 42 contains a yellow phosphor 5c and a red phosphor 5d. By forming such a wavelength conversion layer 40, it is possible to efficiently convert excitation light while suppressing a decrease in light emission efficiency due to self absorption between the phosphors 5a to 5d, as in the light emitting device of FIG. In order to form the wavelength conversion layer 40 having such a two-layer structure, a resin containing a blue phosphor 5a and a green phosphor 5b and a resin containing a yellow phosphor 5c and a red phosphor 5d are prepared. The conversion layers 41 and 42 may be formed. If the conversion layers 41 and 42 are formed in this way, the phosphor can be arranged at a desired position without using the sedimentation method or the centrifugal separation method as in the case of forming the wavelength conversion layer 4 in FIG. it can.

  It is preferable that the wavelength conversion layer 40 has a thickness of 0.1 to 5 mm, the conversion layer 41 has a thickness of 0.05 to 3 mm, and the conversion layer 42 has a thickness of 0.05 to 3 mm. Thereby, since the conversion efficiency in each layer is high and the light from each layer is sufficiently transmitted, more excellent light emission characteristics can be exhibited. Since the wavelength can be efficiently converted by the phosphor, and the converted light can be suppressed from being absorbed by other phosphors, a highly efficient light-emitting device can be obtained.

  FIG. 3 is a diagram showing another embodiment of the light emitting device according to the present invention, and is a schematic cross-sectional view of a light emitting device having a wavelength conversion layer 50 having a four-layer structure. In FIG. 3, the same members as those of the light emitting device shown in FIG. 1 are denoted by the same reference numerals as those in FIG.

  As shown in FIG. 3, the wavelength conversion layer 50 includes a plurality of conversion layers 51, a conversion layer 52, a conversion layer 53, and a conversion layer 54 having different emission wavelengths, and the conversion layer 54 is formed on the surface of the light emitting element 3. Are formed on the surface of the conversion layer 54, the conversion layer 52 is formed on the surface of the conversion layer 53, and the conversion layer 51 is formed on the surface of the conversion layer 52. The conversion layers 51, 52, 53, and 54 are arranged so that the peak wavelength of the converted light by the conversion layer becomes shorter from the light emitting element 3 side toward the outside.

  For example, in the light emitting device shown in FIG. 3, the conversion layer 51 contains the blue phosphor 5a, the conversion layer 52 contains the green phosphor 5b, the conversion layer 53 contains the yellow phosphor 5c, and the conversion layer 54 contains the red phosphor 5d. is doing. As a result, the peak wavelength of the converted light by the conversion layer 51 is shorter than the peak wavelength of the converted light by the conversion layer 52, and the peak wavelength of the converted light by the conversion layer 52 is shorter than the peak wavelength of the converted light by the conversion layer 53. Further, the conversion layers 51, 52, 53 and 54 are arranged so that the peak wavelength of the converted light by the conversion layer 53 is shorter than the peak wavelength of the converted light by the conversion layer 54.

  Thus, the wavelength conversion layer 50 formed by laminating the conversion layers 51 to 54 may be prepared by preparing four types of resins each including four types of phosphors and sequentially forming the layers. Moreover, you may produce the wavelength conversion layer 50 by making the sheet | seat containing each fluorescent substance into a laminated structure.

  The excitation light emitted from the light emitting element 3 is converted by the blue phosphor 5a, the green phosphor 5b, the yellow phosphor 5c, and the red phosphor 5d into the converted light A, B, C, D, but the converted light D Is longer than the converted lights A, B, and C, the converted light D does not have sufficient energy to excite the phosphors 5a, 5b, and 5c to generate visible light. As a result, self-quenching between the phosphors in the wavelength conversion layer 50 can be reduced, and high conversion efficiency can be realized without increasing the phosphor concentration in the conversion layers 51, 52, and 53.

  Similarly, since the converted light C has a longer wavelength than the converted lights A and B, the converted light C does not excite the phosphors 5a and 5b, and the self of the converted light C is absorbed in the conversion layers 51 and 52. Quenching can be reduced. Further, since the converted light B has a longer wavelength than the converted light A, the converted light B does not excite the blue phosphor 5 a, and self-quenching due to absorption of the converted light B in the conversion layer 51 can be reduced.

  In the case of a conventional light emitting device, since four types of phosphors having different emission wavelengths are randomly contained in the same wavelength conversion layer, light emitted from the phosphor is once absorbed by another phosphor. The luminous efficiency of the entire device was not sufficiently high. On the other hand, in the light emitting device shown in FIG. 3, the wavelength conversion layer 50 is a plurality of layers, and the light emission wavelengths of the conversion layers 51 to 54 are sequentially decreased from the side closer to the light emitting element toward the far side. In other words, by setting the wavelength closer to the light emitting element 3 to a longer wavelength and the wavelength farther from the shorter wavelength, the phenomenon that the phosphor absorbs the converted light having a shorter wavelength can be suppressed. Even if the concentration of the phosphors 5a to 5d is not increased to increase the content, high conversion efficiency can be obtained. As a result, high light output can be expected with low power consumption.

  The wavelength conversion layer 50 has a thickness of 0.1 to 5 mm, the conversion layer 51 has a thickness of 0.05 to 1 mm, the conversion layer 52 has a thickness of 0.05 to 1 mm, and the conversion layer 53 has a thickness of 0.05 to 1 mm. The thickness of the layer 54 is preferably 0.05 to 1 mm. Thereby, since the conversion efficiency in each layer is high and the light from each layer is sufficiently transmitted, more excellent light emission characteristics can be exhibited. Since the wavelength can be efficiently converted by the phosphor, and the converted light can be suppressed from being absorbed by other phosphors, a highly efficient light-emitting device can be obtained.

[Example]
The light-emitting device of FIG. 1 and a light-emitting device having three conversion layers were manufactured. First, a light emitting element in which a nitride semiconductor was formed on a sapphire substrate (light emitting element substrate) by metal organic vapor phase epitaxy was prepared.

This light emitting element was mounted on a substrate made of alumina on which a Cu electrode was formed by a flip chip mounting method. Further, a silicone resin in which a phosphor was dispersed was applied with a dispenser so as to cover the light emitting element, thereby forming a wavelength conversion layer. The wavelength conversion layer comprises a red phosphor (“ZnAgInS ₂ ” with an average particle size of 3.8 nm), a yellow phosphor (“ZnAgInS ₂ ” with an average particle size of 2.8 nm), and a green phosphor (BaMgAl _{10 with an} average particle size of 4 μm). O ₁₇ : Eu, Mn), blue phosphor (one layer structure containing (Sr, Ca, Ba, Mg) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu) having an average particle diameter of 7 μm and three layers A structure was prepared. The three wavelength conversion layers consist of a first conversion layer (layer thickness 0.1 mm), a second conversion layer (layer thickness 0.1 mm), and a third conversion layer (layer thickness 0.1 mm). The conversion layer was laminated on the surface of the light emitting element, the second conversion layer was laminated on the surface of the first conversion layer, and the third conversion layer was laminated on the surface of the second conversion layer. Also, a red phosphor (“ZnAgInS ₂ ” with an average particle diameter of 3.8 nm) and a yellow phosphor (“ZnAgInS ₂ ” with an average particle diameter of 2.8 nm) are used for the first conversion layer, and a green phosphor is used for the second conversion layer. (BaMgAl ₁₀ O ₁₇ : Eu, Mn) having an average particle diameter of 4 μm is used as a blue phosphor ((Sr, Ca, Ba, Mg) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu having an average particle diameter of 7 μm in the third conversion layer. ).
Note that commercially available phosphors were used as the blue phosphor and the green phosphor. The average particle diameter was measured using a laser diffraction scattering method.
The yellow phosphor and the red phosphor were synthesized by hot soap method using semiconductor ultrafine particles of 10 nm or less. Semiconductor ultrafine particles having different conversion efficiencies (quantum efficiency) were synthesized by changing the reaction time, reaction temperature, and post-treatment method. The conversion efficiency of the phosphor used was determined by preparing a reference substance (rhodamine B) having a known conversion efficiency and relative comparison with the reference substance as described below. The average particle diameter of the used semiconductor ultrafine particles was confirmed by a transmission electron microscope (TEM).
In addition, the detailed method for confirming the average particle diameter of each fluorescent substance is shown below.
The transmission electron microscope used was JEOL JEM2010F, and an acceleration voltage of 200 kV was observed according to the following procedure. The semiconductor ultrafine particles obtained above were placed in a sample bottle, and IPA or toluene in an amount such that the particle concentration was in the range of 0.002 to 0.02 mol / liter was added and dispersed. This was scooped with a TEM observation microgrid, dried, and then set on a transmission electron microscope. The average particle diameter was measured by confirming the particles from the lattice image. First, the part where the particles adhered to the mesh was searched at a low magnification. At this time, the portion where a large amount of phosphor is attached is not suitable for measurement of the average particle diameter because the particles overlap in the direction of the electron beam. Further, the phosphor adhering to the Cu mesh portion of the microgrid is not suitable for observation of the average particle diameter because the lattice image cannot be observed. Therefore, the semiconductor ultrafine particles for measuring the average particle diameter were selected by selecting a portion having as little overlap as possible in the resin portion of the microgrid. Next, this portion is enlarged to about 1,000,000 times to confirm the lattice image.
At this time, when many organic components used at the time of synthesis remain around the phosphor, the lattice image is blurred, and thus the average particle diameter cannot be measured correctly. In such a case, observation was performed by changing the location, or in some cases, a sample was prepared by repeatedly removing organic components during synthesis, and observation was performed.
Removal of organic components at the time of synthesis is performed by adding chloroform, toluene or hexane to the precipitated phosphor and dispersing it with ultrasonic waves, and then adding alcohol (for example, ethanol) thereto and centrifuging it. be able to. The organic components at the time of synthesis are dissolved in the supernatant ethanol, and the phosphor is precipitated. This operation was repeated as necessary. Thus, after searching for semiconductor ultrafine particles with less organic component adhesion used during synthesis, a lattice image was photographed at a magnification of 4,000,000. At this time, if the electron beam was kept on for a long time, the semiconductor ultrafine particles moved, and thus the image was taken promptly.
The average particle diameter of the phosphor was determined by processing according to the following method based on the diameter of 200 photographed lattice images.
A length average diameter was calculated by statistically processing the diameter of the measured lattice image by creating a histogram. The length average diameter was calculated by counting the number belonging to the diameter section and dividing the sum of the product of the center value and the number of the diameter section by the total number of measured grid images (average Particle shape and calculation formula, “Ceramic manufacturing process” p.11-12, edited by ceramic industry association editorial committee lecture subcommittee). The length average diameter thus calculated was regarded as the average particle diameter of the phosphor.
(Conversion efficiency measurement method)
(1) Dissolve phosphor and reference substance in toluene. At this time, the concentration of each solution was adjusted so that the absorbance was 0.2 at the emission wavelength (wavelength 395 nm) of the light-emitting element.
(2) Each adjusted solution was diluted 10 times with toluene, and luminescence characteristics were measured with a fluorimeter manufactured by Shimadzu Corporation. The excitation wavelength was 395 nm.
(3) Each fluorescence spectrum area was determined. Using each area, the conversion efficiency of the phosphor was determined according to the following formula.

以上の結果を下記表１〜２に示す。

The above results are shown in Tables 1 and 2 below.

(Production of wavelength conversion layer)
In preparation of the wavelength conversion layer, first, a phosphor-containing resin paste was prepared by adding and mixing with a silicone resin having a dimethyl silicone skeleton so that the total amount of the phosphor was 30% by mass. The mass ratio of the blue phosphor, the green phosphor, the yellow phosphor and the red phosphor was 48: 48: 3: 3.

The obtained phosphor-containing resin paste was applied and formed on a smooth substrate with a dispenser, and this was heated on a hot plate at 150 ° C. for 5 minutes to prepare a temporarily cured film. Then, this was put into a 150 degreeC dryer for 5 hours, and the fluorescent substance containing film (wavelength conversion layer) shown in Table 1 was produced. At this time, the dispersion state and average particle diameter of the phosphor inside the phosphor-containing film were confirmed by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). First, the dispersed state was determined by dividing the phosphor-containing film, and the fracture surface was observed by SEM at 500 to 100,000 times.
At this time, for particles having an average particle diameter of 0.1 μm or more, 200 or more particles were extracted and the average particle diameter was measured. At this time, the diameter of the particle was treated as the diameter of the entire particle by multiplying the diameter of the portion exposed on the fracture surface by a factor of 1.5 (intercept method, “ceramic characterization technology” p.7). ~ 8, Ceramics Association).
On the other hand, since the semiconductor ultrafine particles of 10 nm or less cannot be found in the resin because the magnification is low, this phosphor-containing film was processed into thin sections with a microtome with a thickness of 30 to 200 nm as a guide. It is desirable that the thickness of the slice is properly used depending on the average particle diameter of the semiconductor ultrafine particles. When the average particle diameter is 5 to 10 times as a guide, the semiconductor ultrafine particles can be clearly observed. At this time, when the phosphor-containing film was soft, a thin slice could not be obtained, and the slice processing was performed with a target of 50 nm in thickness by cooling with liquid nitrogen. The section of the semiconductor ultrafine particles in this section was observed with a transmission electron microscope, and the lattice image was photographed at a magnification of 4,000,000. As the transmission electron microscope, JEOL JEM2010F was used, and observation was performed under the condition of an acceleration voltage of 200 kV. After confirming the presence or absence of aggregation of the semiconductor ultrafine particles again at 500,000 times, the lattice image of the semiconductor ultrafine particles was observed at a magnification of 4,000,000 times. At this time, because the semiconductor ultrafine particles are completely fixed by the resin, the particles did not move even when the electron beam was applied for a longer time than when the synthesized semiconductor ultrafine particles were observed.
Further, 200 semiconductor ultrafine particles having a confirmed lattice image were selected, and the diameter of the lattice image of each semiconductor ultrafine particle was measured. The diameter of the measured lattice image was statistically processed by creating a histogram in the same manner as described above to calculate the length average diameter, and this was regarded as the average particle diameter of the semiconductor ultrafine particles.
At this time, all the lattice images were measured in the same direction with respect to the photographic paper so that the length of the lattice image was not measured with a bias toward a long portion or a short portion. The average particle size of the ultrafine semiconductor particles of the phosphor-containing film thus obtained did not change from the average particle size of the ultrafine semiconductor particles at the time of synthesis.
(Evaluation of wavelength conversion layer)
This film was attached to the upper surface of the inner layer to obtain a light emitting device. The wavelength conversion layer having a three-layer structure was formed by interposing three wavelength conversion layers with the same material resin as that of the same silicone resin as the inner layer as an adhesive.

  The luminous efficiency of the light-emitting device consisting of each wavelength conversion layer is determined by applying a current of 20 mA to the light-emitting device, turning it on, measuring the total luminous flux, and dividing the total luminous flux by the injected current. It was. Further, the color rendering property (Ra) was measured by a light emission characteristic evaluation apparatus manufactured by Otsuka Electronics Co., Ltd. Table 1 shows the results of the single-layer wavelength conversion layer, and Table 2 shows the results of the three-layer wavelength conversion layer.

  According to Tables 1 and 2, in Comparative Example 1 and Comparative Example 5, the difference in conversion efficiency between the phosphors is within 15%, but the conversion efficiency itself is less than 60%. Efficiency became low. Further, in Comparative Examples 2 to 4 and Comparative Examples 6 to 8, the difference in conversion efficiency is 15% or more, and the conversion efficiency of some phosphors is less than 60%. Therefore, color rendering properties (Ra), light emission The conversion efficiency of the device was low.

  On the other hand, in Examples 1 to 4 including the wavelength converter according to the present invention, it was confirmed that a color rendering property of 90 or more and a luminous efficiency of 30 lm / W or more were exhibited. In particular, Example 1 and Example 3 showed high luminous efficiency of 50 lm / W or more.

  In addition, it confirmed that the peak wavelength of the output light of the light-emitting device using the said wavelength conversion layer entered into the range of 400-700 nm.

It is an example of the light-emitting device of this invention, and is a schematic sectional drawing which shows the structure of the light-emitting device which has one wavelength conversion layer. It is an example of the light-emitting device of this invention, and is a schematic sectional drawing which shows the structure of the light-emitting device which has two wavelength conversion layers. It is an example of the light-emitting device of this invention, and is a schematic sectional drawing which shows the structure of the light-emitting device which has four wavelength conversion layers. It is a schematic sectional drawing which shows the structure of the conventional light-emitting device. It is a schematic sectional drawing which shows the structure of the conventional light-emitting device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Substrate 3 ... Light emitting element 4 ... Wavelength conversion layer 5 ... Phosphor 5a ... Blue phosphor 5b ... Green phosphor 5c ... Yellow phosphor 5d ... Red Phosphor 6 ... reflective member 40 ... wavelength conversion layer 50 ... wavelength conversion layer

Claims (16)

A light emitting element that emits excitation light in a wavelength range of 370 nm to 420 nm on a substrate, and a wavelength conversion layer that converts the excitation light formed so as to cover the light emitting element into visible light, and outputs the visible light as output light A light emitting device,
In the wavelength conversion layer, a blue phosphor emitting fluorescence of 430 nm to 490 nm, a green phosphor emitting fluorescence of 500 nm to 560 nm, a yellow phosphor emitting fluorescence of 540 nm to 600 nm, and a fluorescence of 590 nm to 700 nm are emitted. And a red phosphor that emits,
Each phosphor has a conversion efficiency of 60% or more, and a difference in conversion efficiency between the phosphors is 15% or less. The yellow phosphor and the red phosphor are mostly contained in a portion close to the light emitting element,
2. The light emitting device according to claim 1, wherein a large amount of the blue phosphor and the green phosphor are contained in a portion farther from the light emitting element than the yellow phosphor and the red phosphor.   The light emitting device according to claim 2, wherein the wavelength conversion layer comprises one layer. The wavelength conversion layer has a laminated structure of two or more layers,
3. The light emitting device according to claim 1, wherein a yellow phosphor and a red phosphor are contained in a layer closer to the light emitting element than a layer containing the blue phosphor and the green phosphor.   The light emitting device according to claim 1, wherein the phosphor is dispersed in a polymer resin mainly composed of silicon-oxygen bonds.   The light emitting device according to claim 1, wherein a peak wavelength of the output light is 400 to 750 nm.   The light emitting device according to any one of claims 1 to 6, wherein the wavelength conversion layer has a thickness of 0.1 to 5 mm.   The light emitting device according to claim 1, wherein a reflection member that emits light emitted from the light emitting element forward is provided on side surfaces of the light emitting element and the wavelength conversion layer.   The light emitting device according to any one of claims 1 to 8, wherein the blue phosphor has an average particle diameter of 0.1 to 50 µm. The blue phosphor is [(M, Mg) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu] (M is at least one selected from Ca, Sr and Ba) or [BaMgAl ₁₀ O ₁₇ : Eu]. The light-emitting device according to claim 1.   The light emitting device according to any one of claims 1 to 10, wherein the green phosphor has an average particle diameter of 0.1 to 50 µm. The green phosphor, [BaMgAl ₁₀ O _17: Eu, Mn), (ZnS: Cu, Al] or: according to any one of claims 1 to 11, characterized in that the [MGa ₂ S ₄ Eu] Light-emitting device.   The light-emitting device according to claim 1, wherein the red phosphor is a semiconductor ultrafine particle having an average particle diameter of 10 nm or less.   The red phosphor is a semiconductor composition comprising at least two kinds of elements belonging to Group I, Group II, Group III, Group IV, Group V, and Group VI of the Periodic Table The light-emitting device according to claim 1.   The light-emitting device according to claim 1, wherein the yellow phosphor is a semiconductor ultrafine particle having an average particle diameter of 10 nm or less. The yellow phosphor is a semiconductor composition comprising at least two kinds of elements belonging to Group I, Group II, Group III, Group IV, Group V, and Group VI of the Periodic Table The light-emitting device according to claim 1.

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