JP2005285800A - Light emitting device - Google Patents

Abstract

A light emitting device having high luminous efficiency is provided.
A light-emitting device including a light-emitting element that emits excitation light on a substrate and a wavelength converter that converts the excitation light into visible light by a phosphor, the light-emitting device using the visible light as output light, the fluorescent device The body is made of a semiconductor having a band gap energy of 1.6 eV or less.
[Selection] Figure 1

Description

  The present invention relates to a light emitting device using a light emitting element, and more particularly to a light emitting device suitably used for a backlight light source for an electronic display or an illumination light source such as a fluorescent lamp.

  A light emitting element made of a semiconductor material (hereinafter referred to as an LED chip) emits light with a small size, power efficiency, and vivid colors. LED chips have excellent features 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 a part of the light of the LED chip is wavelength-converted by the phosphor, and the wavelength-converted light and the LED light that is not wavelength-converted are mixed and emitted, thereby It has already been manufactured as a light emitting device that emits an emission 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 including a YAG phosphor represented 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 to present white has been proposed (for example, Patent Documents) 1).

  An example of such a light emitting device is shown in FIG. FIG. 1 shows an example of a general light-emitting device. A substrate 2 on which an electrode 1 is formed, an LED light-emitting element 3 including a semiconductor material that emits light having a central wavelength of 470 nm on the substrate 2, and light emission on the substrate 2. A wavelength conversion layer 4 provided so as to cover the element 3, and the wavelength conversion layer 4 contains a phosphor 5. If desired, the side surfaces of the light-emitting element 3 and the wavelength conversion layer 4 may be provided with a reflector 6 that reflects light, and the light escaping to the side surface may be focused forward to increase the intensity of the output light.

  In this light emitting device, when light emitted from the light emitting element 3 is irradiated onto the phosphor, the phosphor is excited to emit visible light, and this visible light is used as an output.

  However, when the brightness of the LED light emitting element 3 is changed, the light quantity ratio between blue and yellow changes, so that the color tone of white changes and the color rendering property is inferior.

  Therefore, by providing a wavelength conversion layer in which three types of phosphors are mixed in a polymer resin so as to cover a purple LED chip having an emission wavelength intensity peak at 400 nm or less on the substrate, purple light is converted into red, Attempts have been made to convert light into green and blue wavelengths to emit white light, and it has become possible to cover the light emission wavelength in a wide range, and the color rendering properties have been greatly improved (see Patent Document 2). However, since the fluorescent quantum yield of the phosphor is low, particularly the red fluorescent quantum yield in the 600 to 750 nm region is low, there is a problem that sufficient emission luminance cannot be obtained.

Therefore, in order to obtain high fluorescence emission intensity, semiconductor nanoparticles having an average particle diameter of 10 nm or less have been studied (for example, see Non-Patent Document 1). Semiconductor nanoparticles exhibit a variety of light emission from red (long wavelength) to blue (short wavelength) by changing the size of the nanoparticles. If the energy is higher than the band gap, the excitation wavelength is not limited, and the emission lifetime Is 100,000 times shorter than rare earths, and has a feature of high luminous efficiency and much less deterioration than organic dyes because it repeats absorption and emission cycles quickly. For this reason, it is expected that a light-emitting device with high efficiency and long life can be realized.
JP 11-261114 A JP 2002-314142 A RNBhargava, Phys. Rev. Lett., 72 (1994)

  However, the semiconductor nanoparticles reported so far have a problem that the fluorescence quantum yield is about 20 to 30% and the amount of light is small, so that the semiconductor nanoparticles cannot be used for special lighting or general lighting applications. . In particular, there is a problem that the red fluorescent quantum yield is particularly low in the region of 600 to 750 nm.

  Therefore, in order to increase the amount of converted light, it is necessary to increase the driving voltage of the light emitting element to increase the light amount of the light emitting element. In this case, there is a problem that the power consumption increases and the amount of heat generation increases. .

  Accordingly, an object of the present invention is to provide a light emitting device having high luminous efficiency.

  In the present invention, the phosphor contained in the wavelength converter is composed of semiconductor nanoparticles having a band gap of 1.6 eV or less, thereby efficiently performing interband transition of electrons in the photoluminescence reaction of the phosphor. And the peak wavelength of the output light can be easily controlled within the range of 400 to 900 nm, so that a light emitting device that realizes high light emission efficiency and excellent color rendering can be provided.

  That is, the light-emitting device of the present invention is a light-emitting device that includes a light-emitting element that emits excitation light on a substrate and a wavelength converter that converts the excitation light into visible light by a phosphor, and uses the visible light as output light. The phosphor is made of a semiconductor having a band gap energy of 1.6 eV or less.

  In particular, it is preferable that the wavelength converter includes a phosphor corresponding to a plurality of visible light wavelengths. Thereby, since it becomes possible to cover the light emission wavelength in a wide range, the color rendering properties of the light emitting device can be further improved.

  The wavelength converter is composed of a laminate of a plurality of wavelength conversion layers, and the plurality of the wavelength conversion layers converted so that the peak wavelength of the converted light becomes shorter from the light emitting element side toward the outside. It is preferable to arrange the wavelength conversion layer. As described above, the wavelength converter includes a plurality of wavelength conversion layers having different emission wavelengths, and the wavelength conversion layer is formed in a layer shape on the substrate so as to cover the light emitting element, and is included in each wavelength conversion layer. The wavelength conversion layer device can reduce the self-quenching of the phosphors in the wavelength conversion layer by arranging the phosphor so that the average particle diameter of the phosphor gradually decreases from the side closer to the light emitting element. Sufficient luminous efficiency can be obtained without increasing the dispersion concentration of the phosphor contained in.

  It is preferable that the number of wavelength conversion layers is at least three, and the converted light converted by the wavelength conversion layer has wavelengths corresponding to red, green, and blue, respectively. When the semiconductor particles are distributed in a plurality of intermittent average crystal grain size ranges, the light emission wavelength can be covered in a wide range, so that the color rendering properties of the light emitting device can be further improved.

  The wavelength conversion layer preferably has a thickness of 0.05 to 50 μm. Thereby, wavelength conversion can be efficiently performed by the phosphor in the wavelength converter, and the converted light can be suppressed from being absorbed by other phosphors, and thus a highly efficient light-emitting device can be realized.

  It is preferable that the average particle diameter of the phosphor contained in each wavelength conversion layer is arranged so as to gradually become smaller from the side closer to the light emitting element. Thereby, even if the dispersion concentration of the phosphor is low, that is, even if the content of the phosphor is small, sufficient luminous efficiency can be obtained.

  It is preferable that the phosphors included in the plurality of wavelength conversion layers are made of substantially the same material and have different average particle diameters. Thereby, light having a broad spectrum in the visible light region can be emitted from the wavelength conversion layer, and excellent white light can be realized.

  The phosphor preferably includes semiconductor particles having an average particle diameter of 1 to 2 nm and a half-value width of the particle diameter distribution of 0.5 nm or less. Thereby, the color rendering properties of the light emitting device can be further improved.

  The phosphor preferably contains semiconductor particles having an average particle size of 2 to 3 nm and a half-value width of the particle size distribution of 1 nm or less. Thereby, the color rendering properties of the light emitting device can be further improved.

  The phosphor preferably contains semiconductor particles having an average particle diameter of 3 to 5 nm and a half-value width of the particle diameter distribution of 2 nm or less. Thereby, the color rendering properties of the light emitting device can be further improved.

  The peak wavelength of the output light is preferably 400 to 900 nm. Thereby, a color rendering property can be remarkably improved.

  The central wavelength of the excitation light is preferably 450 nm or less. In this wavelength region, since the light emission efficiency of the light emitting element is improved, the light emission efficiency of the white LED lamp can be increased.

  The present invention will be described with reference to the drawings. 1 and 2 are schematic cross-sectional views showing one embodiment of the light-emitting device of the present invention.

  According to FIG. 1, the light emitting device includes a substrate 2 on which an electrode 1 is formed, a light emitting element 3 made of a semiconductor material that emits light having a central wavelength of 450 nm or less on the substrate 2, and a light emitting element 3 on the substrate 2. And a wavelength converter 4 that includes a phosphor 5 that emits visible light when excited by light emitted from the light emitting element 3, and visible light is output from the light emitting device.

  According to the present invention, it is important that the phosphor 5 is composed of semiconductor particles having a band gap of 1.6 eV or less. When the band gap is larger than 1.6 eV, the excited electrons are not efficiently transferred to the ground state and deactivated, so that the quantum efficiency is lowered and the light emission efficiency is lowered. On the other hand, when semiconductor particles having a band gap energy of 1.6 eV or less are used as the phosphor, the excited electrons transition efficiently, so that a device with excellent luminous efficiency and color rendering can be realized.

  The band gap energy of the semiconductor particles is 0.8 to 1.6 eV, particularly 0.9 to 1.55 eV, more preferably 1.0 to 1.5 eV, because the fluorescence wavelength in a single nanosize is in the visible light region. It is preferable.

The type of such a phosphor is not particularly limited as long as it is a semiconductor particle having a band gap of 1.6 eV or less. Specifically, InN, InP, CdTe, ZnS: Ag, ZnS: Ag, Al, ZnS: Ag, Cu, Ga, Cl, ZnS: Al + In ₂ O ₃ , ZnS: Zn + In ₂ O ₃ , (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, ZnS: Cl, Al, (Zn, Cd) S: Cu, Al, Y 3 Al ₅ O ₁₂ : Tb, Y 3 (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 , (Zn, 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 it can.

  Among these, nitride-based nanoparticles, InN and InP are preferable in terms of wavelength conversion efficiency and durability.

  As the phosphor 5, conventionally used semiconductor particles having a particle size of about 1 μm or more can be used, but it is preferable to use semiconductor nanoparticles having a particle size of nanometer size. In particular, the average particle size is preferably 10 nm or less. Semiconductor nanoparticles with a particle diameter of 10 nm or less show various emission from red (long wavelength) to blue (short wavelength) by changing the size of the nanoparticles, and if the energy is higher than the band gap, it is limited to the excitation wavelength The emission lifetime is 100,000 times shorter than that of rare earths, and the absorption and emission cycles are repeated quickly, resulting in extremely high brightness and much less deterioration than organic dyes (photons that appear as fluorescence before deterioration) Is about 100,000 times the number of dyes), and therefore, excellent light emission efficiency can be realized and a long-life light emitting device can be realized.

  As the substrate 1, a substrate having excellent thermal conductivity and a large total reflectivity is used. In addition to ceramic materials such as alumina and aluminum nitride, a polymer resin in which metal oxide fine particles are dispersed is preferably used.

  The center wavelength of the excitation light emitted from the light emitting element 3 is preferably 450 nm or less, particularly 380 to 420 nm, from the viewpoint of obtaining a high light output. Moreover, it is preferable that the light emitting element 3 includes a light emitting layer made of a semiconductor material in terms of high external quantum efficiency. Examples of such semiconductor materials include various semiconductors such as ZnSe and nitride semiconductors (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 laminated structure having a light emitting layer made of a semiconductor material on a light emitting element substrate is formed by crystal growth methods such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy from these semiconductor materials.

When the light emitting element substrate has a light emitting layer made of a nitride semiconductor, materials such as sapphire, spinel, SiC, Si, ZnO, ZrB ₂ , GaN, and quartz are preferably used. In order to form a nitride semiconductor with good crystallinity with high productivity, it is preferable to use a sapphire substrate.

  It is preferable that the wavelength converter 4 includes a phosphor corresponding to a plurality of visible light wavelengths. Light emitted from a plurality of phosphors is synthesized, and light in a wide wavelength range can be emitted. The peak wavelength of the visible light thus obtained is preferably 400 to 900 nm, particularly 450 to 850 nm, and more preferably 500 to 800 nm. Since the emission wavelength can be covered in a wide range of 400 to 900 nm, the color rendering can be greatly improved.

  In particular, in the case of semiconductor particles, it is preferably distributed in a plurality of intermittent average crystal grain size ranges. Semiconductor nanoparticle phosphors with a particle size of 10 nm or less exhibit various luminescence from red (long wavelength) to blue (short wavelength) by changing the size of the nanoparticles. Therefore, the wavelength of light emitted from the semiconductor nanoparticle phosphor can be covered in a wide range. As a result, the color rendering properties of the light emitting device can be greatly improved.

  When one of the average particle diameter ranges of the semiconductor particles is 1 to 3 nm and the half width of the particle diameter distribution is 0.5 nm or less, the color rendering properties of the light emitting device can be further improved.

  When one of the average particle size ranges of the semiconductor particles is 3 to 5 nm and the half width of the particle size distribution is 1.0 nm or less, the color rendering properties of the light emitting device can be further improved.

  When one of the average particle diameter ranges of the semiconductor particles is 5 to 8 nm and the half-value width of the particle diameter distribution is 2.0 nm or less, the color rendering properties of the light emitting device can be further improved.

  Further, according to FIG. 2, the wavelength converter 4 is composed of three layers 14a, 14b, 14c having different emission wavelengths, and the emission peak wavelengths of the plurality of wavelength conversion layers 14a, 14b, 14c are as follows: The structure is smaller in order from the side closer to the light emitting element 3. That is, the wavelength conversion layer so that the emission peak wavelength of the wavelength conversion layer 14b is shorter than the emission peak wavelength of the wavelength conversion layer 14a and the emission peak wavelength of the wavelength conversion layer 14c is shorter than the emission peak wavelength of the wavelength conversion layer 14b. 14a, 14b, 14c are arranged. In FIG. 2, the same parts as those in FIG.

  By adopting such a configuration, self-quenching between the phosphors in the wavelength conversion layer can be reduced, so higher conversion efficiency can be realized without increasing the dispersion concentration of the phosphors in the wavelength conversion layer. .

  The wavelength converter 4 is composed of a plurality of wavelength conversion layers having different emission wavelengths, and the wavelength conversion layer is arranged so that the peak wavelength of the converted light by the plurality of wavelength conversion layers becomes shorter from the light emitting element 3 side toward the outside. Deploy. For example, in the case of FIG. 2, the wavelength converter 4 includes three wavelength conversion layers 14a, 14b, and 4c, and the peak wavelength of the converted light by the wavelength conversion layer 14b is larger than the peak wavelength of the converted light by the wavelength conversion layer 14a. The wavelength conversion layers 14a, 14b, and 14c are arranged so that the peak wavelength of the converted light by the wavelength conversion layer 14c is shorter than the peak wavelength of the converted light by the wavelength conversion layer 14b.

  Excitation light emitted from the light-emitting element 3 is converted by the phosphors 15a, 15b, and 15c to become converted light A, B, and C. However, the converted light A has a longer wavelength than the converted light B and C. The converted light A does not have sufficient energy to excite the phosphors 15b and 15c to generate visible light. As a result, self-quenching between the phosphors in the wavelength converter 4 can be reduced, and high conversion efficiency can be realized without increasing the phosphor concentration in the wavelength conversion layers 14a, 14b, and 14c. .

  Similarly, since the converted light B has a longer wavelength than the converted light C, the converted light B does not excite the phosphor 15c, and self-quenching due to absorption of the converted light B within the wavelength conversion layer 14c is reduced. Can do.

  In the case of the light-emitting device of FIG. 1, since three types of phosphors having different emission wavelengths are contained in the same wavelength conversion layer, another phosphor may absorb light emitted from the phosphor once. As shown in FIG. 2, a plurality of wavelength conversion layers are provided, a plurality of wavelength conversion layers 4 are provided, and the emission wavelength of the wavelength conversion layer is decreased in order from the side closer to the light emitting element. When the near wavelength is long and the far wavelength is short, the phenomenon that the phosphor absorbs the short wavelength conversion light can be suppressed, and the content of the phosphor 5 in the wavelength conversion layer is increased by increasing the concentration. Even without increasing, high conversion efficiency can be obtained. As a result, high light output can be expected with low power consumption.

  The wavelength converter 4 is composed of a plurality of wavelength conversion layers having different emission wavelengths, and the wavelength conversion layer is formed in a layer shape on the substrate so as to cover the light emitting element, and the fluorescence included in each wavelength conversion layer Since the average particle size of the body is arranged so as to gradually become smaller from the side closer to the light emitting element, self-quenching between the phosphors in the wavelength conversion layer can be reduced, so that the wavelength conversion layer device Sufficient luminous efficiency can be obtained without increasing the dispersion concentration of the phosphor contained.

  By setting the number of wavelength conversion layers to at least three layers and corresponding to the wavelengths of red, green, and blue, respectively, it is possible to cover the emission wavelength in a wide range, and to further improve the color rendering of the light emitting device. it can. Moreover, since the phosphor can be made of the same material or substantially the same material, light having a wide spectrum in the visible light region can be emitted, and excellent white light can be realized.

  Furthermore, when the thickness of the wavelength converter is 0.05 to 5 μm, the wavelength can be efficiently converted by the phosphor in the wavelength converter, and the converted light is prevented from being absorbed by another phosphor. Therefore, a highly efficient light-emitting device can be realized.

  The light emitting device of FIG. 1 was created.

  First, a light emitting element made of a nitride semiconductor was formed on a sapphire substrate by metal organic vapor phase epitaxy. The structure of the light-emitting element is an n-type GaN layer that is an undoped nitride semiconductor on a sapphire substrate, a GaN layer that is an n-type contact layer formed with an Si-doped n-type electrode, and an n-type that is an undoped nitride semiconductor. A GaN layer, a GaN layer that forms a light emitting layer, a GaN layer that constitutes a well layer, an InGaN layer that constitutes a well layer, and a GaN layer that constitutes a barrier layer as a set. A quantum well structure was adopted.

  This light emitting element was mounted on an alumina substrate 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.

  As the phosphor, InP nanoparticles having a bulk gap of 1.55 eV were used. InP was mixed with three types having different particle sizes.

  The obtained light-emitting device of the present invention was suppressed in self-quenching and exhibited a high light emission efficiency of 60 lm / W, which was about twice as high as that of the comparative example.

  It was produced in the same manner as in Example 1 except that a silicone resin in which phosphors having three kinds of particle sizes were dispersed was applied with a dispenser to form a three-layer laminated structure (FIG. 2).

  The obtained light emitting device of the present invention was suppressed in self-quenching and showed a high light emission efficiency of 80 lm / W, which was about twice as high as that of the comparative example.

  It was produced in the same manner as in Example 2 except that the wavelength converter had a four-layer structure (FIG. 3).

  The obtained light-emitting device of the present invention was suppressed in self-quenching and showed a high light emission efficiency of 90 lm / W, which was about twice as high as that of the comparative example.

(Comparative example)
The configuration was the same as in Example 1 except that CdSe having a band gap of 1.8 eV was used as the phosphor. The obtained light-emitting device was 45 lm / W.

It is sectional drawing which shows an example of the structure of the light-emitting device of this invention. It is sectional drawing which shows an example of the structure of the other light-emitting device of this invention. It is sectional drawing which shows an example of the structure of the further another light-emitting device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrode 2 ... Board | substrate 3 ... Light emitting element 4 ... Wavelength converter 5 ... Phosphor 6 ... Reflector 14a, 24a ... 1st layer 14b, 24b ... 2nd layer 14c, 24c ... 3rd layer 15a, 25a ... 1st fluorescent substance 15b, 25b ... 2nd fluorescent substance 15c, 25c ... 3rd fluorescent substance 24d ... 4th layer 25d ... Fourth phosphor

Claims (12)

A light-emitting device that includes a light-emitting element that emits excitation light on a substrate and a wavelength converter that converts the excitation light into visible light by a phosphor, and uses the visible light as output light. A light emitting device comprising a semiconductor having a gap energy of 1.6 eV or less. The light emitting device according to claim 1, wherein the wavelength converter includes a phosphor corresponding to a plurality of visible light wavelengths. The wavelength converter is composed of a laminate of a plurality of wavelength conversion layers, and the plurality of the wavelength conversion layers converted so that the peak wavelength of the converted light becomes shorter from the light emitting element side toward the outside. The light emitting device according to claim 1, wherein a wavelength conversion layer is disposed. 4. The light emitting device according to claim 3, wherein the number of wavelength conversion layers is at least three, and the converted light converted by the wavelength conversion layer has wavelengths corresponding to red, green, and blue, respectively. . The light emitting device according to claim 3 or 4, wherein the wavelength conversion layer has a thickness of 0.05 to 50 µm. The light-emitting device according to claim 3, wherein the phosphors included in each wavelength conversion layer are arranged so that an average particle diameter of the phosphor gradually decreases from a side closer to the light-emitting element. The light-emitting device according to claim 3, wherein the phosphors included in the plurality of wavelength conversion layers are made of substantially the same material and have different average particle diameters. The light emitting device according to any one of claims 1 to 7, wherein the phosphor includes semiconductor particles having an average particle diameter of 1 to 2 nm and a half width of a particle diameter distribution of 0.5 nm or less. The light emitting device according to any one of claims 1 to 8, wherein the phosphor includes semiconductor particles having an average particle diameter of 2 to 3 nm and a half width of a particle diameter distribution of 1 nm or less. The light emitting device according to claim 1, wherein the phosphor includes semiconductor particles having an average particle diameter of 3 to 5 nm and a half-value width of a particle diameter distribution of 2 nm or less. The light emitting device according to claim 1, wherein a peak wavelength of the output light is 400 to 900 nm. The light emitting device according to claim 1, wherein a central wavelength of the excitation light is 450 nm or less.

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