JP4401264B2 - Phosphor, method for manufacturing the same, and light emitting device - Google Patents

Description

  The present invention relates to a phosphor, a manufacturing method thereof, and a light emitting device. Such phosphors and light emitting devices are used for illumination devices such as full color display devices and liquid crystal panel backlights, for example.

  As a display device and an illumination device including a phosphor and a light-emitting element as a light source for exciting the phosphor, 2 to 3 ZnCdSe semiconductors having a particle size that is not more than twice the exciton Bohr radius and different from each other, and It includes a GaN-based semiconductor light-emitting element as a light source for excitation, and excites a phosphor with excitation light emitted from the excitation light source to convert it into secondary light of green and red, or green, red and blue, and mix these colors Thus, a display device or a lighting device that obtains white light emission has been proposed (see, for example, Patent Document 1).

  In Patent Document 1, since the surface of the semiconductor is dominated by dangling bonds (unbonded hands), the semiconductor has a band gap larger than its band gap (referred to below as the energy gap between bands, the same applies hereinafter). A technique for capping semiconductor surface defects by covering with a material having the following is described. As an example, a phosphor in which the surface of a ZnCdSe semiconductor is covered with ZnS is disclosed.

  Such a so-called “surface modification” method is an effective method for suppressing the non-radiative transition and increasing the quantum confinement effect. In addition to the method of Patent Document 1, a carboxyl group or a phosphate group is used. There has been proposed a technique for improving the light emission efficiency (referred to as quantum efficiency at the time of light emission, hereinafter the same) by coating the surface with an organic acid or a surfactant that is included (see, for example, Non-Patent Document 1).

  However, the above surface modification technique requires a surface modification process separately from the generation of microcrystals of the semiconductor that becomes the phosphor because the phosphor and the modifier to be activated are made of different materials.

  For example, in order to produce a CdSe semiconductor microcrystal coated with ZnS, it is necessary to first produce a CdSe semiconductor microcrystal and then put it into a medium containing zinc acetate and sodium sulfide to react. Further, even when modifying with an organic acid or inorganic glass, it is necessary to first produce semiconductor microcrystals to be phosphors and then adsorb them by a coprecipitation method or a reverse micelle method.

  These methods are laborious and expensive to manufacture the phosphor. In particular, when the microcrystals constituting the phosphor are vapor-phase grown by CVD (Chemical Vapor Deposition) method or PLD (Pulse Laser Deposition) method, chemical synthesis using chemicals is used. Surface modification methods significantly reduce productivity.

Furthermore, the improvement in luminous efficiency by the above surface modification method has been confirmed to be effective for phosphors using semiconductor microcrystals such as ZnCdSe and ZnS, but II-VI group compound semiconductors are not reliable and environmentally friendly. In other compound semiconductor materials, the effect of surface modification and the formation method thereof have not been established yet.
JP 11-340516 A Isobe, “Luminescence mechanism and local analysis of organic / inorganic composite ZnS: Mn nanocrystal phosphor”, Surface Science, Japan Surface Science Society, May 1, 2001, Vol. 22, No. 5, p. 315-322

  In view of the above-described circumstances, the present invention provides a phosphor with high emission efficiency (referred to as internal quantum efficiency during light emission, hereinafter the same) and high reliability with a simple manufacturing method, a manufacturing method thereof, and a light emitting device. With the goal.

In the present invention, a base semiconductor composed of a group III nitride semiconductor is composed of an oxide of a group III element constituting a group III compound semiconductor constituting the base semiconductor, and the band gap of the group II nitride semiconductor (the energy gap between the bands is defined). say, the same below) is covered by an outer layer that have a band gap greater than, the host semiconductor luminescent center is added, the energy of the excitation light absorbed in the matrix semiconductor transits the luminescent center, It is a phosphor whose luminescence center emits light by intraorbital transition of orbital electrons.

In the phosphor according to the present invention, the particle size of the upper Symbol host semiconductor is preferably less than twice the exciton Bohr radius. Here, the emission center is preferably at least one element selected from the group consisting of transition elements, and the transition element is preferably a rare earth element.

In the phosphor according to the present invention, the group III nitride semiconductor forming the base semiconductor is preferably a nitride semiconductor containing at least In as a group III element. In addition, the Group III nitride semiconductor forming the base semiconductor preferably has an In composition ratio adjusted so that the wavelength of the absorption edge is 420 nm .

The present invention provides a method for producing the above phosphor, comprising a step of forming a base semiconductor made of a group III nitride semiconductor by a laser ablation method, and supplying oxygen to the base semiconductor, thereby forming a group III nitride semiconductor. And a step of coating a base semiconductor with an outer layer made of a Group III element oxide.

The present invention also relates to a method for producing the above-described phosphor, comprising a step of forming a base semiconductor composed of a group III nitride semiconductor by a chemical synthesis method, and oxidizing the base semiconductor in a medium, thereby And a step of coating a base semiconductor with an outer layer made of an oxide of a group III element constituting a physical semiconductor.

The present invention has a peak wavelength by Uchi励 force of the phosphor constituting a red phosphor that exhibits red in the range of 600Nm～670nm, and maternal semiconductor formed of a group III nitride semiconductor, the group III nitride semiconductor An outer layer made of an oxide of a group III element and covering a base semiconductor, and a green phosphor exhibiting a green color having a peak wavelength in the range of 500 nm to 540 nm by excitation , and the red phosphor and the green phosphor Is a light emitting device that emits white light by exciting and mixing with a blue light emitting element.

In the light emitting device according to the present invention, a base semiconductor made of a group III nitride semiconductor and an outer layer made of an oxide of a group III element constituting the group III nitride semiconductor and covering the base semiconductor have a peak wavelength by excitation. It is preferable that the phosphor further includes a blue phosphor exhibiting a blue color in a range of 420 nm to 480 nm, and the red phosphor, the green phosphor, and the blue phosphor are excited and mixed with the blue light emitting element.

  As described above, according to the present invention, it is possible to provide a phosphor with high emission efficiency and high reliability, a method for manufacturing the same, and a light emitting device by a simple manufacturing method.

  Referring to FIG. 1, one phosphor according to the present invention includes an outer layer 13 made of an oxide in which a base semiconductor 11 made of a group III nitride semiconductor has a band gap larger than the band gap of the group III nitride semiconductor. It is covered with. Since this phosphor is formed of a base semiconductor microcrystal made of a group III nitride semiconductor, it has a lower environmental impact and is chemically stable compared to conventional II-VI compound semiconductor microcrystals such as CdSe and ZnS. It is. In addition, since the outer layer made of oxide capping the surface defects of the microcrystal, this phosphor suppresses non-radiative transition, and even when the particle size of the base semiconductor is made small enough to have a quantum size effect, the phosphor emits light. Reduction in efficiency can be suppressed. As a result, a phosphor with high luminous efficiency and excellent reliability can be obtained.

  It is preferable that a luminescent center 12 as shown in FIG. 1 is added to the phosphor base semiconductor according to the present invention. Light emission due to intra-shell transition of the element added as the light emission center 12 is high in luminous efficiency because there is no self-absorption in the phosphor composed of the base semiconductor and the outer layer. In addition, since the transition energy varies depending on the type of the additive element serving as the emission center, it can be controlled to a predetermined emission wavelength by appropriately selecting impurities. As a result, light emission with high efficiency can be obtained at a desired wavelength.

  The light emission mechanism of one phosphor according to the present invention will be described as follows with reference to FIG. 1 and FIG. The energy of the excitation light that excites the base semiconductor 11 made of a group III nitride semiconductor, which is the main body of the phosphor, is smaller than the band gap of the outer layer 13, so that it passes through the outer layer 13 and is absorbed by the base semiconductor 11. When the energy absorbed by the base semiconductor 11 transitions to the added emission center 12, the emission center 12 emits light due to orbital electron transition in the shell. Since the outer layer 13 has a band gap larger than the energy of light emission from the base semiconductor 11, the light emission is emitted outside the phosphor without being self-absorbed. In this way, a phosphor with high luminous efficiency can be obtained.

In the phosphor according to the present invention, it is preferable that a particle diameter of the base semiconductor is not more than twice the exciton Bohr radius. If the particle size of the host semiconductor is less than or equal to twice the exciton Bohr radius, the quantum size effect becomes remarkable, and the electron orbit coupling between the host semiconductor and the emission center increases, so that the light emission efficiency increases. Here, the exciton Bohr radius indicates the spread of the existence probability of the exciton, and 4πεh ² / me ² (where ε is a dielectric constant, h is a Planck constant, m is an effective mass, and e is an elementary charge amount. Represented). When the base semiconductor is a group III nitride semiconductor, for example, the exciton Bohr radius of the GaN semiconductor is about 3 nm, and the exciton Bohr radius of the InN semiconductor is about 7 nm. Furthermore, the grain size of the base semiconductor is more preferably not less than 1/2 times and not more than 3/2 times the Bohr radius. As the grain size of the base semiconductor becomes smaller, the quantum effect becomes more prominent. In particular, if it is 3/2 times or less the Bohr radius, the internal quantum efficiency is further increased significantly, which is preferable. On the other hand, if the quantum effect becomes too large, the emission wavelength changes greatly depending on the particle size of the base semiconductor, making it difficult to control. Therefore, the quantum effect is preferably at least ½ times the Bohr radius. For example, the grain size of the base semiconductor made of GaN semiconductor is preferably 1.5 nm to 4.5 nm, and the grain size of the base semiconductor made of InN semiconductor is preferably 3.5 nm to 10.5 nm.

  In the phosphor according to the present invention, the emission center 12 is preferably at least one element selected from the group consisting of transition elements. Since transition element ions have high efficiency as a luminescent center and the transition energy of the inner shell corresponds to visible light of red to blue, white light emission with extremely high color rendering properties can be obtained by combining them.

  In the phosphor according to the present invention, it is more preferable that the transition element is a rare earth element, that is, the emission center 12 is at least one element selected from the group consisting of rare earth elements. Rare earth element ions have a particularly high efficiency as an emission center, and the inner shell transition energy corresponds to visible light of red to blue. By combining these, white light emission with extremely high color rendering properties can be obtained.

  In the phosphor according to the present invention, the group III nitride semiconductor is preferably a nitride semiconductor containing at least In as a group III element. Group III nitride semiconductors are chemically stable, reliable and have a low environmental impact. In addition, since the group III nitride semiconductor contains at least In as a group III element, the band gap can be easily controlled by the composition ratio of In. In particular, a nitride semiconductor containing at least In and Ga as group III elements can control the band gap over a wide range of approximately 1 eV to 3 eV.

  In the phosphor according to the present invention, the outer layer is preferably an oxide of a group III element constituting a group III nitride semiconductor. If the outer layer is an oxide of a group III element, it can be coated by a simple method such as surface oxidation of the phosphor base semiconductor as it is. Also, it has higher adhesion and higher reliability than surface modification methods such as adsorption.

  In another phosphor according to the present invention, referring to FIG. 3, an outer layer 13 made of an oxide in which a base semiconductor 11 made of a group III nitride semiconductor has a band gap larger than the band gap of the group III nitride semiconductor. A two-layer structure in which the base semiconductor 11 has a quantum size effect and emits fluorescence, and a shell 22 having a band gap larger than the band gap of the core 21. Consists of.

  Since the shell has a larger band gap than the core, the light emission efficiency is increased by the quantum confinement effect, and it can be emitted outside the phosphor without being self-absorbed. In addition, since the ground level corresponding to the transition energy can be controlled by the grain size of the host semiconductor, a predetermined emission wavelength can be obtained. Thereby, light emission of a predetermined wavelength can be obtained with high efficiency.

  With reference to FIGS. 3 and 4, the emission mechanism of another phosphor according to the present invention is such that the energy of the excitation light that excites the base semiconductor 11 made of a group III nitride semiconductor that is the main body of the phosphor is the outer layer 13. Therefore, the light passes through the outer layer 13 and is absorbed by the shell 22 of the parent semiconductor 11, and then transitions to the core 21 surrounded by the shell 22. Here, since the particle size of the core 21 is small enough to have a quantum size effect, the core 21 can take only a plurality of discrete energy levels. The light energy transitioned to the core 21 transitions between the ground level of the conduction band and the ground level of the valence band among the energy levels (transition between ground quantum levels), and the wavelength corresponding to the energy. Light is emitted. Since the shell 22 and the outer layer 13 have a band gap larger than the energy of light emission from the core 21, the light emission is emitted outside the phosphor without being self-absorbed. In this way, a phosphor with high luminous efficiency can be obtained.

  In another phosphor according to the present invention, it is preferable that the particle diameter of the core is not more than twice the exciton Bohr radius. If the particle size of the core is not more than twice the exciton Bohr radius, the quantum size effect becomes significant, and the electron orbit coupling between the core and the shell increases, so that the luminous efficiency increases. When the core is a group III nitride semiconductor, for example, the exciton Bohr radius of the GaN semiconductor is about 3 nm, and the exciton Bohr radius of the InN semiconductor is about 7 nm. Further, the particle diameter of the core is more preferably 1/2 times or more and 3/2 times or less of the Bohr radius. The smaller the core particle size, the more prominent the quantum effect. In particular, if it is 3/2 or less the Bohr radius, it is preferable because the internal quantum efficiency further increases remarkably. On the other hand, if the quantum effect becomes too large, the emission wavelength changes greatly depending on the particle size of the core, making it difficult to control. Therefore, the quantum effect is preferably ½ times the Bohr radius. For example, the particle diameter of the core made of GaN semiconductor is preferably 1.5 nm to 4.5 nm, and the particle diameter of the core made of InN semiconductor is preferably 3.5 nm to 10.5 nm.

  With reference to FIG. 1, a method for manufacturing a phosphor according to the present invention includes a step of forming a base semiconductor 11 made of a group III nitride semiconductor by laser ablation, and a step of forming the base semiconductor 11 in a laser ablation apparatus. And supplying a base semiconductor with an outer layer 13 made of an oxide of a group III element constituting a group III nitride semiconductor by supplying oxygen.

  The laser ablation method has high non-equilibrium and the composition deviation from the raw material target is extremely small. Therefore, the laser ablation method is a preferable growth method for generating group III nitride semiconductor microcrystals, particularly InGaN semiconductor microcrystals, which are difficult to grow. is there. Further, since the plume (scattered particles) is in a high active state, only the surface of the base semiconductor can be oxidized and coated by blowing a gas having strong oxidizing power before reaching the substrate or the like. This method can form the oxide layer of the base semiconductor in-situ and has high productivity.

  FIG. 5 shows one laser ablation apparatus 200 used in the present invention. Referring to FIG. 5, in this laser ablation apparatus, a substrate holder 202 is disposed on an upper part of a growth chamber 201 that can be evacuated to an ultrahigh vacuum, and a substrate 203 is fixed to the substrate holder 202. The back surface of the substrate holder 202 is heated by the heater 204 disposed on the substrate holder 202, and the substrate 203 is heated by the heat conduction. A target table 205 is disposed immediately below the substrate holder 202 at an appropriate distance, and a raw material target 206 is disposed on the target table 205. In addition, a gas introduction pipe 210 is provided in the growth chamber 201 so that a gas can be introduced, and the substrate can be irradiated with an atomic beam activated by the radical cell 209.

  Here, the surface of the source target 206 is ablated by irradiating the source target 206 with the pulse laser beam 208 through the view port 207 provided on the side surface of the growth chamber 201 using the group III nitride as the source target 206. The group III nitride which is the raw material of the raw material target 206 evaporated on the substrate 203 is deposited on the substrate 203, so that a group III nitride semiconductor microcrystal which becomes the host semiconductor of the phosphor grows.

At this time, O ₂ gas is supplied from a gas introduction pipe 210 installed in the vicinity of the substrate 203, and the surface of the plate made of group III nitride semiconductor microcrystals just before reaching the substrate is oxidized to thereby oxidize the base semiconductor. Is covered with an outer layer made of an oxide of a group III element constituting a group III nitride semiconductor.

  In this manufacturing method, the coating with the outer layer necessary for capping the surface defects of the base semiconductor is performed by oxidizing the group III element on the base semiconductor surface in the final stage of the phosphor generation, and this is a complicated surface modification. Luminous efficiency can be improved without adding a technique.

  In the laser ablation apparatus, a phosphor formed by coating a base semiconductor with an outer layer made of an oxide layer is directly introduced into an exhaust pipe (not shown) separately provided without providing the substrate 203 and the heater 204. If collected, a phosphor of microcrystalline powder can be obtained.

Referring to FIGS. 1 and 5, in the present manufacturing method, the additive concentration of the element that becomes the light emission center 12 can be controlled by the addition amount to the raw material target 206. Further, the particle size of the phosphor can be controlled by the pulse laser output at the time of laser ablation, the growth chamber vacuum degree, and the distance between the raw material target 206 and the substrate 203. Furthermore, the thickness of the outer layer 13 can be controlled by the flow rate of O ₂ gas supplied from the gas introduction pipe 210 and the supply position. That is, if the O ₂ gas supply position is close to the substrate 203 or the exhaust pipe (not shown), the outer layer 13 becomes thin, and if it is close to the raw material target 206, the outer layer 13 becomes thick. The O ₂ gas need not always be supplied, and may be supplied in a pulse manner in synchronization with the laser pulse for ablating the raw material target. Further, in order to strengthen the oxidizing power, instead of supplying the O ₂ gas from the gas introduction pipe 210, oxygen radicals converted into plasma using a separately provided radical cell (not shown) may be supplied.

  In another method for producing a phosphor according to the present invention, a base semiconductor composed of a group III nitride semiconductor is formed by a chemical synthesis method, and the base semiconductor is oxidized in a medium to form a group III nitride semiconductor III. Covering the base semiconductor with an outer layer made of an oxide of a group element.

  Here, the chemical synthesis method refers to a synthesis method in which a plurality of starting materials containing the constituent elements of a product substance are dispersed in a medium and reacted to obtain a target product substance. The sol-gel method (colloid method), reverse Examples include micelle method, molecular precursor method, hydrothermal synthesis method, flux method and the like. The chemical synthesis method can obtain a base semiconductor at a low cost by a very simple method. Since a chemical reaction is caused through the medium, only the surface can be oxidized and coated by a technique such as adding an oxidizing agent to the medium after completion of the synthesis. This method can form an outer oxide layer in-situ and has high productivity.

  One light-emitting device according to the present invention has a base semiconductor made of a group III nitride semiconductor and an outer layer made of an oxide covering the base semiconductor with reference to FIG. A red phosphor 103 having a red color in a range of 670 nm, a base semiconductor made of a group III nitride semiconductor, and an outer layer made of an oxide covering the base semiconductor, and having a peak wavelength of 500 nm to 540 nm by excitation. The green phosphor 104 having a green color is included, and the red phosphor 103 and the green phosphor 104 are excited together with the blue light emitting element 102 and mixed to obtain white light emission.

  More specifically, in one light emitting device according to the present invention, referring to FIG. 7, a blue light emitting element 102 is disposed on a support substrate 101, and a red phosphor 103 and a green phosphor 104 are further disposed thereon. A phosphor dispersion layer 105 in which is uniformly dispersed is disposed. The blue light emitting elements 102 are arranged in an array at equal intervals. Here, the size and arrangement interval of the blue light emitting elements 102 are arbitrary. Further, the blue light emitting element 102 may be partitioned by a partition wall 106. In the case where the partition wall 106 is provided, the partition wall 106 is reflected so that light incident on the partition wall 106 is reflected with high efficiency toward the phosphor dispersion layer 105 including the phosphor (referred to as the red phosphor 103 and the green phosphor 104 hereafter). At least the surface of 106 is preferably formed of a material having high light reflectance.

  The red phosphor and the green phosphor used in the present light emitting device emit white light as a whole by emitting light together with the blue light emitting element, and are composed of phosphor materials that are stable and have high luminous efficiency. A light-emitting device with excellent power and reliability can be obtained. Further, when the fluorescence peak wavelength is in the predetermined range, the color purity of white light is improved because the color purity of the single primary color is high.

  Another light-emitting device according to the present invention is the light-emitting device according to the first aspect, wherein the light-emitting device includes a base semiconductor made of a group III nitride semiconductor and an outer layer made of an oxide covering the base semiconductor, and has a peak wavelength by excitation. Further includes a blue phosphor exhibiting a blue color in the range of 420 nm to 480 nm, and the red phosphor, the green phosphor and the blue phosphor are excited and mixed with the blue light emitting element to obtain white light emission. Such a light-emitting device includes a blue phosphor independent of the excitation light source, so that it is not necessary to control light absorption and / or light scattering, and the degree of phosphor filling in the light-emitting device can be increased. Further, since the fluorescence peak wavelength is in the predetermined range, the color purity of the single primary color by the blue phosphor is high, so that the color rendering properties are not impaired even when the excitation light source is optimized to a wavelength with high internal quantum efficiency. By these things, the light-emitting device excellent in luminous efficiency and productivity can be obtained.

  Hereinafter, based on an Example, the fluorescent substance concerning this invention, the manufacturing method of a fluorescent substance, and a light-emitting device are demonstrated concretely. In the examples, the internal quantum efficiency or the external quantum efficiency was used as the light emission efficiency, that is, the quantum efficiency at the time of light emission. Here, the external quantum efficiency is the ratio of the number of photons emitted by the phosphor to the number of photons irradiated to the phosphor, and the internal quantum efficiency is the number of photons emitted by the phosphor relative to the number of photons absorbed by the phosphor. A ratio.

Example 1
In this example, the above phosphor is one in which a luminescent center is added to a base semiconductor, that is, a base semiconductor composed of a group III nitride semiconductor to which a luminescent center is added is a group III nitride. It is an Example about the fluorescent substance coat | covered with the outer layer which consists of an oxide which has a larger band gap than the band gap of a semiconductor.

The phosphor according to this example was manufactured by a laser ablation method. With reference to FIG. 5, the cleaned sapphire substrate was placed in the laser ablation apparatus 200 as the substrate 203 and heated at 600 ° C. for 30 minutes to clean the substrate 203. Next, after the temperature of the substrate 203 is lowered to 25 ° C., pulse irradiation of a KrF excimer laser (wavelength: 248 nm, with In _0.1 Ga _0.9 N added with Eu at a concentration of 1 × 10 ²⁰ cm ⁻³ as a raw material target) Ablation was performed with a pulse number of 10 Hz and an output of 1 J / cm ² . At this time, plasma N ₂ gas was supplied from the radical cell 209 to compensate for nitrogen deficient during ablation. Further, at this time, an O ₂ gas is further supplied to the gas introduction pipe 210 in the vicinity of the substrate 203 so that the plume surface immediately before reaching the substrate is oxidized, so that the base semiconductor is formed by an outer layer made of an oxide of In and Ga. A phosphor coated with was formed.

With reference to FIG. 1, the phosphor obtained in this manner is a fine particle of an In _0.1 Ga _0.9 N semiconductor having a particle diameter of 100 nm to which Eu as the emission center 12 is added at a concentration of 1 × 10 ²⁰ cm ^−3. The base semiconductor 11 which is a crystal was covered with an outer layer 13 made of an oxide of In and Ga and having a thickness of about 1 nm.

In this phosphor, the In _0.1 Ga _0.9 N semiconductor, which is the base semiconductor, has an In composition ratio adjusted so that the wavelength of the absorption edge is 420 nm, and thus excites a blue light-emitting element made of Group III nitride. It can be used as a light source, and can particularly efficiently absorb light emitted in the vicinity of 400 nm with high external quantum efficiency.

  As described above, the light emission mechanism of the phosphor is described as follows with reference to FIGS. 1 and 2. The energy of the excitation light that excites the base semiconductor 11 made of a group III nitride semiconductor, which is the main body of the phosphor, is smaller than the band gap of the outer layer 13, so that it passes through the outer layer 13 and is absorbed by the base semiconductor 11. When the energy absorbed by the base semiconductor 11 transitions to the added emission center 12, the emission center 12 emits light due to orbital electron transition in the shell. Here, since the outer layer 13 has a band gap larger than the energy of light emission from the base semiconductor 11, the light emission is emitted outside the phosphor without being self-absorbed. In this way, the luminous efficiency of the phosphor is improved.

  When this phosphor was excited by a blue light emitting element of a GaN semiconductor having a peak wavelength of 405 nm, red fluorescence having a wavelength of 620 nm was obtained. The internal quantum efficiency of this phosphor (the ratio of the number of photons emitted by the phosphor to the number of photons absorbed by the phosphor (%), hereinafter the same) was measured by the measuring apparatus 300 shown in FIG. . Further, the lifetime of the phosphor (the time until the energy conversion efficiency when excited at the peak wavelength of the excitation spectrum reaches 50% of the initial value, the same applies hereinafter) is measured using the measuring apparatus 300 in FIG. It was 10,000 hours when calculated by evaluating the dependency. The results are summarized in Table 1. Here, the energy conversion efficiency refers to the ratio of the total luminous flux (unit: lm (lumen)) to the input power (unit: W (watt)), and the excitation light source 301 is set to the peak wavelength using the measuring device 300 of FIG. It can be measured by using a blue light emitting element of 405 nm GaN semiconductor.

  Here, a method for measuring the internal quantum efficiency and the external quantum efficiency using the apparatus 300 shown in FIG. 8 will be described. The apparatus 300 of FIG. 8 uses a xenon lamp as the excitation light source 301, splits the excitation light distributed in continuous wavelengths into a single wavelength by the monochromator 302, and enters the incident hole 305 of the integrating sphere 304 through the mirror 303. . The excitation light incident on the incident hole 305 enters the opposite measurement hole 306 and enters the sample 307 installed there. The light emission from the sample and the reflection component of the excitation light are collected in the integrating sphere 305 and exit from the exit hole 308. The emitted light is spectrally measured by the spectroscope 309 and measured. The driving of the monochromator 302 and the spectroscope 309 is controlled by the control computer 310.

  The internal quantum efficiency is measured and calculated as follows. That is, if the intensity of the excitation light is measured using a standard sample whose reflectance at the excitation wavelength is already known (here, a reflector coated with barium sulfate is used), and then the intensity of the excitation light is measured for the measurement sample The absorption rate of the phosphor can be determined from the ratio between the two. Multiplying the absorption rate of this phosphor by the absorption factor to the number of photons emitted from the excitation light source 301 leads to the number of photons absorbed by the phosphor. The internal quantum efficiency is calculated by dividing the number of photons emitted from the phosphor by the number of photons absorbed by the phosphor.

  Further, the measurement and calculation of the external quantum efficiency can also be performed using the measuring apparatus of FIG. In this case, the external quantum efficiency is calculated by dividing the number of photons emitted from the phosphor by the number of photons emitted from the excitation light source 301.

(Comparative Example 1)
In Example 1, Eu, which is the light emission center 12, was added at a concentration of 1 × 10 ²⁰ cm ^{−3 in} the same manner as in Example 1 except that O ₂ gas was not passed through the gas introduction tube 210 in the vicinity of the substrate 203. Thus, a phosphor composed of the base semiconductor 11 which is a microcrystal of an In _0.1 Ga _0.9 N semiconductor having a particle size of 100 nm was obtained. The internal quantum efficiency of this phosphor was 20%, and the phosphor lifetime was 5000 hours. The results are summarized in Table 1.

(Comparative Example 2)
For comparison, the internal quantum efficiency and the phosphor lifetime of a phosphor (fluorescence peak wavelength: 580 nm) made of a Mn-doped ZnS semiconductor having a particle size of 3 nm and surface-modified with methacrylic acid were measured. The internal quantum efficiency of this phosphor was 30%, and the phosphor lifetime was 2000 hours. The results are summarized in Table 1.

(Comparative Example 3)
For comparison, the internal quantum efficiency of a phosphor (fluorescence peak wavelength: 625 nm) made of an Eu-doped Y ₂ O ₂ S semiconductor having a particle size of 10 nm was 60%, and the phosphor lifetime was 3000 hours. The results are summarized in Table 1.

  In Table 1, it is clear from comparison between Example 1 and Comparative Example 1 that the base semiconductor made of a group III nitride semiconductor is an oxide having a band gap larger than the band gap of the group III nitride semiconductor. It can be seen that the internal quantum efficiency and lifetime of the phosphor covered with the outer layer are significantly superior to the internal quantum efficiency and lifetime of the phosphor not covered with the outer layer. Further, as is clear when Example 1 is compared with Comparative Example 2 or Comparative Example 3, the internal quantum efficiency and lifetime of the phosphor according to the present example are compared with the internal quantum efficiency and lifetime of the conventional phosphor. It can be seen that it is also excellent.

(Example 2)
In this example, another phosphor described above, that is, a fluorescent material in which a base semiconductor made of a group III nitride semiconductor is covered with an outer layer made of an oxide having a band gap larger than that of the group III nitride semiconductor. This is an example of a phosphor having a two-layer structure in which the base semiconductor has a quantum-size-effect core that emits fluorescence and a shell having a band gap larger than the band gap of the core. .

The phosphor according to this example was manufactured by a chemical synthesis method using InCl ₃ (indium chloride), GaCl ₃ (gallium chloride) and Li ₃ N (lithium nitride) as raw materials. That is, 0.03 mol of powdered InCl ₃ , 0.07 mol of powdered GaCl ₃ and 0.1 mol of powdered Li ₃ N were each dispersed in 100 cm ³ of xylene and mixed, and then mixed in an autoclave at 300 atm. (30.39 MPa) and kept at 300 ° C. for 12 hours. The core was obtained by cooling to 25 ° C. and evaporating xylene. Next, 0.01 mol of powdered InCl ₃ , 0.09 mol of powdered GaCl ₃ and 0.1 mol of powdered Li ₃ N were each dispersed in 100 cm ³ of xylene and mixed, and the mixture was mixed. The above cores were mixed and reacted in an autoclave at 300 atm (30.39 MPa) and 350 ° C. for 24 hours. After cooling to 25 ° C. and evaporating xylene to obtain a shell, pure water is added as a medium to dissolve and remove LiCl as a by-product, and the main product of the shell is dissolved by dissolved oxygen in pure water. The surface of a _0.1 Ga _0.9 N semiconductor was oxidized and covered with InGaO ₃ with an outer layer made of In and Ga oxides and having a thickness of about 1 nm to obtain a fine powder phosphor.

Referring to FIG. 3, the phosphor thus obtained has a core 21 having a particle diameter of 10 nm made of an In _0.3 Ga _0.7 N semiconductor and a shell 22 having a particle diameter of 1.2 μm made of an In _0.1 Ga _0.9 N semiconductor. The base semiconductor 11 made of was covered with an outer layer 13 made of an oxide of In and Ga and having a thickness of about 1 nm.

In this phosphor, the In composition ratio of the In _0.1 Ga _0.9 N semiconductor that is the shell 22 of the base semiconductor 11 is adjusted so that the wavelength of the absorption edge is 420 nm, as in the case of the first embodiment. Therefore, a blue light-emitting element made of a group III nitride can be used as an excitation light source, and light emission in the vicinity of 400 nm with high external quantum efficiency can be efficiently absorbed.

  As described above, the light emission mechanism of the phosphor is described as follows with reference to FIGS. 3 and 4. That is, the energy of the excitation light that excites the base semiconductor 11 made of a group III nitride semiconductor, which is the main body of the phosphor, is smaller than the band gap of the outer layer 13, and thus passes through the outer layer 13 and is absorbed by the shell 22 of the base semiconductor 11. Then, transition is made to the core 21 surrounded by the shell 22. Here, since the particle size of the core 21 is small enough to have a quantum size effect, the core 21 can take only a plurality of discrete energy levels. The light energy transitioned to the core 21 transitions between the ground level of the conduction band and the ground level of the valence band among the energy levels (transition between ground quantum levels), and the wavelength corresponding to the energy. Light is emitted. Since the shell 22 and the outer layer 13 have a band gap larger than the energy of light emission from the core 21, the light emission is emitted outside the phosphor without being self-absorbed. In this way, the luminous efficiency of the phosphor is improved.

  When this phosphor was excited by a blue light emitting element of a GaN semiconductor having a peak wavelength of 405 nm, green fluorescence having a peak wavelength of 530 nm was obtained. The phosphor had an internal quantum efficiency of 80% and a phosphor lifetime of 10,000 hours.

In the present embodiment, the particle size of the core 21 can be controlled by the pressure in the autoclave and the reaction time. Further, the thickness of the outer layer 13 can be controlled by the amount of dissolved oxygen in pure water as a medium and the water immersion time of the main product In _0.3 Ga _0.7 N. As an oxidizing agent for oxidizing the surface of the shell, a highly oxidizing agent such as hydrogen peroxide solution may be used in addition to dissolved oxygen in the medium.

  As the solvent for synthesizing the core and the shell, a nonpolar organic solvent is preferable, and in addition to xylene, benzene or the like can be used.

  In addition, it is also possible to manufacture a phosphor added with an emission center using the manufacturing method of this embodiment. Similarly, it is also possible to manufacture a phosphor having a core and a shell as a base semiconductor using the manufacturing method of Example 1.

FIG. 6 shows changes in the internal quantum efficiency of the phosphor when the particle diameter of the core 21 is changed in the phosphor according to this example. FIG. 6 clearly shows that the internal quantum efficiency increases remarkably when the core particle size is 10 nm or less. This particle size corresponds to approximately twice the exciton Bohr radius. Here, the exciton Bohr radius indicates the spread of the existence probability of the exciton, and 4πεh ² / me ² (where ε is a dielectric constant, h is a Planck constant, m is an effective mass, and e is an elementary charge amount. Represented). Here, in this example, the exciton Bohr radius of the In _0.3 Ga _0.7 N semiconductor constituting the core 21 is 5 nm. Thus, a phosphor having a core particle size less than or equal to twice the exciton Bohr radius is preferable because the internal quantum efficiency is increased by the quantum size effect and the light emission efficiency is increased.

  If the particle diameter of the core in this embodiment is 7.5 nm or less, that is, 3/2 times or less the Bohr radius, it is preferable because the internal quantum efficiency is further remarkably increased. On the other hand, if the quantum effect becomes too large, the emission wavelength varies greatly depending on the particle size of the core, making control difficult. For this reason, it is preferable that it is 2.5 nm or more, that is, 1/2 times or more of the Bohr radius.

(Example 3)
The present embodiment shows an example of the above-described one light emitting device, that is, a surface light emitting device that emits white light using the blue light emitting element, the red phosphor of the first embodiment, and the green phosphor of the second embodiment.

  In the light emitting device according to the present embodiment, referring to FIG. 7, a blue light emitting element 102 made of a group III nitride semiconductor is disposed on a support substrate 101, and a red light having an InGaN semiconductor as a base semiconductor thereon. A phosphor dispersion layer 105 made of a plate-like epoxy resin in which a phosphor 103 and a green phosphor 104 having an InGaN semiconductor as a base semiconductor are uniformly dispersed is disposed. The peak wavelength of the blue light emitting element 102 which is an excitation light source is 450 nm. The blue light emitting elements 102 are 300 μm square and are arranged in an array at equal intervals of 50 μm. Note that the size and arrangement interval of the blue light emitting elements 102 can be arbitrarily set. The blue light emitting element 102 may be partitioned by a partition wall 106. In the case where the partition wall 106 is provided, the surface of the partition wall 106 is preferably made of a material having high light reflectance so that light incident on the partition wall 106 is reflected with high efficiency toward the phosphor dispersion layer 105 including the phosphor. .

As in Example 1, the red phosphor 103 dispersed in the phosphor dispersion layer 105 has an In _0.1 Ga _0.9 N particle size of 100 nm to which Eu, which is the emission center, is added at a concentration of 1 × 10 ²⁰ cm ^−3. A base semiconductor, which is a semiconductor, is covered with an outer layer 13 made of an oxide of In and Ga and having a thickness of about 1 nm, and its fluorescence peak wavelength is 620 nm.

As in Example 2, the green phosphor 104 dispersed in the phosphor dispersion layer 105 has a core 21 made of In _0.3 Ga _0.7 N semiconductor having a particle size of 10 nm and a particle size made of In _0.1 Ga _0.9 N semiconductor of 1.2 μm. The base semiconductor 11 made of the shell 22 is covered with an outer layer 13 made of In and Ga oxide and having a thickness of about 1 nm, and the fluorescence peak wavelength is 530 nm.

  The degree of filling and ratio of the red phosphor 103 and the green phosphor 104 into the phosphor dispersion layer 105 is such that the red emission and the green emission from the phosphor are mixed with the blue emission scattering component of the excitation light to produce white emission. Have been adjusted so that.

  The closer the distance between the blue light emitting element 102 and the phosphor dispersion layer 105 including the red phosphor 103 and the green phosphor 104, the higher the light emission efficiency. Therefore, they may be in contact with each other, but the blue light emitting element 102 generates heat. A gap may be provided so as not to deteriorate the phosphor dispersion layer 105 made of epoxy resin. For example, a light-transmitting heat conductive material made of AlN or SiC can be provided therebetween.

When the light emitting device 100 according to the present example was driven by supplying a current to the blue light emitting element 102 as the excitation light source, white light was emitted from the surface of the phosphor dispersion layer 105. At this time, the energy conversion efficiency of the light emitting device was 80 lm / W, and the average color rendering index was Ra90. Here, the energy conversion efficiency refers to the ratio of the total luminous flux (unit: lm (lumen)) to the input power (unit: W (watt)), and can be measured by using the measuring apparatus of FIG. The average color rendering index is a scale that represents the fidelity of color reproduction by a reference light source. CIE daylight (color temperature 5000K) is used as the reference light, and the test colors are red, yellow, yellow green, green, and blue. Using eight colors of green, blue-purple, purple, and magenta (lightness 6, saturation 7), the color rendering index of this light-emitting device
Ri = 100-4.6 × ΔE _i
(Where i is a code representing one of the above eight test colors and takes a value of 1 to 8)
And the total arithmetic average of each color rendering index
Ra = Σ (i = 1 to 8) R _i × 1/8
Can be obtained by calculating.

  In the light emitting device according to this example, the red phosphor 103 has a fluorescence peak wavelength in the range of 600 nm to 670 nm, and the green phosphor 104 has a fluorescence peak wavelength in the range of 500 nm to 540 nm. High color purity. Furthermore, since the excitation light is pure blue having a light emission peak wavelength in the range of 440 nm to 480 nm of the blue light emitting element, it is considered that excellent color rendering properties are obtained in white light emission due to these mixed colors.

  In this example, a blue light emitting element composed of a group III nitride having an emission peak wavelength at 450 nm was used as the phosphor excitation light source. In this case, as described in Example 1, the excitation light source was used. Has a light emission peak wavelength in the range of 380 nm to 420 nm, since the external quantum efficiency of the light emitting element becomes higher.

  Here, as the blue light emitting element 102, a II-VI group compound semiconductor such as MgCdZnO or ZnMgSSe can be used in addition to the group III nitride semiconductor. Further, the light emitting element may be not only a light emitting element using spontaneous emission light but also a SLD (Super Luminescent Diode) or a semiconductor laser element using stimulated emission light. In particular, a semiconductor laser device has a narrow spectral line width, and realizes a light emitting device with extremely high energy conversion efficiency by adjusting the emission peak wavelength to a wavelength that maximizes the external quantum efficiency of the light emitting device and the excitation efficiency of the phosphor. Can do.

  Moreover, as an organic resin used for the phosphor dispersion layer 105 in which the phosphor is dispersed, an epoxy resin having a low hygroscopic property and an excellent durability and dimensional stability, an acrylic resin having an excellent visible light transmission property, and an ultraviolet ray. Silicon resin or polycarbonate resin that is resistant to deterioration is suitable. These may be used in combination. For example, by forming a two-layer structure using a silicon resin on the excitation light source side and an epoxy resin on the opposite light emission surface, the short wavelength component of the excitation light and Durability is improved against any outside air. Further, glass may be used for the phosphor dispersion layer, which is further superior in terms of visible light transmission, durability and the like as compared with the organic resin.

  The support substrate 101 may be made of any material, for example, glass, plastic, ceramics, etc., as long as it can support the arrayed blue light emitting elements 102 and the phosphor dispersion layer 105. A substrate for epitaxial growth of a group III nitride semiconductor such as sapphire can also be used. Furthermore, if a substrate on which blue light emitting elements are formed in an array is used as it is as a supporting substrate, the arrangement of the blue light emitting elements and the labor of wiring can be saved greatly.

  In order to obtain uniform light emission with no color unevenness in the surface, a light guide plate may be provided between the blue light emitting element and the phosphor dispersion layer. In that case, the blue light emitting element may be attached to the side surface of the light emitting device. Good. Further, a light diffusing material such as silica fine particles may be dispersed in the phosphor dispersion layer. The light diffusing material itself has a function of scattering without absorbing light, and red light and green light from the red phosphor and green phosphor dispersed in the phosphor dispersion layer and blue light from the blue light emitting element. Has the function of mixing the colors uniformly. As a result, the color unevenness of white light can be prevented and the visibility of white light can be improved.

  Further, a reflection plate that reflects excitation light and secondary light may be provided on the surface of the support substrate opposite to the fluorescent dispersion layer side. By providing the reflecting plate, it is possible to contribute to light emission by suppressing loss of light emitted from the light emitting device, and the efficiency of the light emitting device is significantly improved.

  Furthermore, an optical filter that shields light having a wavelength smaller than 380 nm may be provided between the blue light emitting element and the phosphor dispersion layer. By providing such an optical filter, it is possible to shield an ultraviolet light component slightly contained in the bottom of the excitation light source spectrum. This ultraviolet component does not contribute to the excitation of the phosphor, and when the material of the phosphor dispersion layer is an organic resin, this becomes a factor of deterioration. That is, by providing an optical filter, the reliability of the light emitting device can be significantly improved.

Example 4
In this example, in addition to the above-described another light emitting device, that is, a blue light emitting element, the red phosphor of Example 1, and the green phosphor of Example 2, a surface-emitting type that exhibits white light using a blue phosphor. The example of a light-emitting device is shown.

In this example, the blue phosphor dispersed in the phosphor dispersion layer together with the red phosphor and the green phosphor is a core 21 made of an InN semiconductor and having a particle size of 4.5 nm and an In _0.1 Ga _0.9 N semiconductor. A base semiconductor 11 made of a 1.2 μm shell 22 is covered with an outer layer 13 made of an oxide of In and Ga and having a thickness of about 1 nm, and its fluorescence peak wavelength is 425 nm. As the excitation light source, a blue light-emitting element having an emission peak wavelength of 455 nm composed of a group III nitride semiconductor was used. Other configurations are the same as those of the third embodiment.

  In the present embodiment, since a phosphor that emits blue light independently of the excitation light source is used, it is not necessary to control the absorption and scattering of the excitation light source, and the filling degree of the phosphor inside can be improved. Further, since the fluorescence wavelength of the blue phosphor and the emission wavelength of the blue light emitting element can be controlled independently of each other, the color rendering is improved. Further, from the viewpoint of improving the color rendering properties of white light emission, the fluorescence peak wavelength of the blue phosphor is preferably in the range of 420 nm to 480 nm, and more preferably in the range of 440 nm to 460 nm.

  The energy conversion efficiency of the light emitting device according to this example was 90 lm / W, and the energy conversion efficiency was further improved as compared with Example 3. This is considered to be due to the fact that the emission peak wavelength of the blue light emitting element is set to 405 nm at which the external quantum efficiency is the highest.

  Note that the phosphor according to the present invention is not only the surface light emitting device shown in the above embodiment, but also a linear light emitting device using a light leakage fiber, and a point light emission represented by the shape of the light emitting element. The present invention can also be applied to a light emitting device of a type, and the same effect can be obtained even in that case.

  As described above, the present invention can be widely used in phosphors, methods for manufacturing the same, and light emitting devices for the purpose of improving luminous efficiency and reliability. Such phosphors and light-emitting devices are used, for example, in lighting devices such as full-color display devices and liquid crystal panel backlights.

It is a cross-sectional schematic diagram which shows one fluorescent substance concerning this invention. It is a schematic diagram which shows the light emission mechanism of one fluorescent substance concerning this invention. It is a cross-sectional schematic diagram which shows another fluorescent substance concerning this invention. It is a schematic diagram which shows the light emission mechanism of another fluorescent substance concerning this invention. It is a schematic diagram which shows one laser ablation apparatus used in this invention. In another fluorescent substance concerning this invention, it is a figure which shows the change of the internal quantum efficiency of a fluorescent substance when the particle size of a core is changed. It is a cross-sectional schematic diagram which shows one light-emitting device concerning this invention. It is a schematic diagram which shows the measuring apparatus of the internal quantum efficiency of the fluorescent substance concerning this invention, and a light-emitting device, external quantum efficiency, and power conversion efficiency.

Explanation of symbols

  10, 20 phosphor, 11 host semiconductor, 12 emission center, 13 outer layer, 21 core, 22 shell, 100 light emitting device, 101 support substrate, 102 blue light emitting element, 103 red phosphor, 104 green phosphor, 105 phosphor dispersion Layer, 106 partition, 200 laser ablation apparatus, 201 growth chamber, 202 substrate holder, 203 substrate, 204 heater, 205 target table, 206 raw material target, 207 viewport, 208 pulse laser beam, 209 radical cell, 210 gas introduction tube, 300 measurement apparatus, 301 excitation light source, 302 monochromator, 303 mirror, 304 integrating sphere, 305 entrance hole, 306 measurement hole, 307 measurement sample, 308 exit hole, 309 spectrometer, 310 computer for control.

Claims (10)

Matrix semiconductor composed of a group III nitride semiconductor, have a band gap larger than the band gap of the previous SL III nitride semiconductor made of an oxide of a group III element constituting said III-nitride semiconductor forming the matrix semiconductor is covered by the outer layer you,
An emission center is added to the base semiconductor,
A phosphor in which the energy of excitation light absorbed by the host semiconductor transitions to the emission center, and the emission center emits light by intraorbital electron transition.   The phosphor according to claim 1, wherein a particle size of the base semiconductor is not more than twice an exciton Bohr radius.   The phosphor according to claim 1, wherein the emission center is at least one element selected from the group consisting of transition elements.   The phosphor according to claim 3, wherein the transition element is a rare earth element.   The phosphor according to claim 1, wherein the group III nitride semiconductor constituting the base semiconductor is a nitride semiconductor containing at least In as a group III element. 6. The phosphor according to claim 5 , wherein an In composition ratio of the group III nitride semiconductor forming the base semiconductor is adjusted so that a wavelength of an absorption edge thereof is 420 nm. It is a manufacturing method of the fluorescent substance of Claim 1, Comprising:
A step of forming a base semiconductor composed of a group III nitride semiconductor by a laser ablation method, and supplying an oxygen to the base semiconductor to form an outer layer composed of an oxide of a group III element constituting the group III nitride semiconductor. A method of manufacturing a phosphor, comprising a step of coating a base semiconductor. It is a manufacturing method of the fluorescent substance of Claim 1, Comprising:
A step of forming a base semiconductor made of a group III nitride semiconductor by a chemical synthesis method, and an outer layer made of an oxide of a group III element constituting the group III nitride semiconductor by oxidizing the base semiconductor in a medium And a step of coating the base semiconductor. A red phosphor that exhibits red peak wavelength is in the range of 600nm~670nm by Uchi励 force of the phosphor of claim 1,
A peak semiconductor having a peak wavelength of 500 nm to 540 nm by excitation , comprising a parent semiconductor comprising a group III nitride semiconductor and an outer layer comprising an oxide of a group III element constituting the group III nitride semiconductor and covering the parent semiconductor anda green phosphor exhibited green in,
A light emitting device that emits white light by exciting and mixing the red phosphor and the green phosphor together with a blue light emitting element. A peak semiconductor having a peak wavelength of 420 nm to 480 nm by excitation , comprising: a base semiconductor comprising a group III nitride semiconductor; and an outer layer comprising an oxide of a group III element constituting the group III nitride semiconductor and covering the base semiconductor. Further including a blue phosphor presenting in blue,
The light emitting device according to claim 9 , wherein the red phosphor, the green phosphor, and the blue phosphor are excited and mixed with the blue light emitting element to obtain white light emission.

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