JP4934986B2 - Emitter material for thermophotovoltaic power generation - Google Patents

Description

  The present invention relates to an emitter material used in thermophotovoltaic power generation technology, and more specifically, radiation from an emitter heated to a high temperature is received by a photoelectric conversion cell (PV cell) matched to the sensitivity of the radiation wavelength peak. The present invention relates to a selective emitter material having a high emissivity at a selective wavelength, which is used in a thermo-photo-voltaic (TPV) power generation technology, which is a solid-state power generation system that converts power with high efficiency.

  Response to the deterioration of the global environment, such as global warming and depletion of fossil fuels, is an urgent issue, and there is a need for a highly efficient and highly reliable power generation system that has a low environmental impact. A promising candidate for a power generation system that satisfies such conditions is TPV power generation technology. In the TPV power generation technology, power can be obtained with high efficiency by applying wavelength filtering to radiation energy from a certain solid substance (emitter) heated to about 1000 ° C. to 2000 ° C. and irradiating the photoelectric conversion cell. In solar power generation, the spectrum distribution of light received by a cell is determined, but in TPV power generation technology, the spectrum can be artificially manipulated mainly by the type of emitter material. In addition, the TPV power generation technology is characterized in that it is superior in quality and quantity with respect to solar power generation because the light irradiation density is extremely high.

  By integrating such a TPV generator into a conventional heat utilization system and generating electric power using the generated high heat, the total power generation efficiency can be increased. In addition, it has features such as the combustion of fossil fuels, sunlight condensing heat, radioactive isotope decay heat, and other heat sources, as well as low noise and excellent maintainability due to the absence of moving parts. Applications to scale-distributed power supplies are underway.

  The TPV power generation technology is a system that obtains electric power with high efficiency by irradiating a photoelectric conversion cell with wavelength filtering of radiation energy from a certain solid substance (emitter) heated to about 1000 ° C. to 2000 ° C. For this reason, the development of materials that emit strong radiant light suitable for the sensitivity region of photoelectric conversion cells has been advanced. Emitter materials for TPV power generation include gray body radiators that emit radiation over a wide wavelength band, and rare earth selective emitters that utilize 4f orbital transitions of rare earth elements. Rare earth elements tend to be in a trivalent state with three electrons in 6s and 6p orbitals. For example, the 4f shell electron system of holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb) It is a multi-electron system having 10, 11, 12, and 13 electrons. When a transition from the high energy level to the low energy level occurs, the energy difference is emitted as light. Since the 4f-shell electron system is not directly involved in solid bonding, the energy level does not vary greatly depending on the base material. Therefore, the f-shell electron system of rare earth ions shows an emission spectrum that is sharp and stable with respect to a temperature change like an isolated atom even in a solid. The peak wavelengths of Yb, Tm, Er, and Ho are 1.1 μm, 1.3 μm, 1.5 μm, and 2.0 μm, respectively.

  The peak wavelength of the sunlight spectrum is about 550 nm, and in photovoltaic power generation, a Si photoelectric conversion cell having a sensitivity region close to that is used. The band gap of Si is 1.1 eV, and its absorption edge is about 1100 nm. That is, only light having a wavelength shorter than 1100 nm contributes to power generation. The wavelength of 1100 nm corresponds to a peak wavelength of the black body radiation spectrum of 2500 ° C. or higher, and the emitter materials and heat sources that can be used at such high temperatures are limited. Therefore, the Si photoelectric conversion cell is applied to the thermophotovoltaic power generation technology. Then, it is difficult to generate electricity with high efficiency. Therefore, the thermophotovoltaic power generation technology uses a low-bandgap photoelectric conversion cell that can generate power even with long-wavelength light. Currently, a GaSb cell having a sensitivity region of 0.8 to 1.7 μm is generally used. Is done.

  Although a rare earth oxide sintered body was initially used as the selective emitter using rare earth elements, rare earth oxides were generally difficult to sinter and the emission spectrum intensity of the rare earth elements was also weak. Therefore, a material in which a rare earth oxide is laminated on a substrate such as silicon carbide has been developed, but the selective radiator on the surface layer is optically transparent except for the selected wavelength. When the emissivity is high, the emitted light of the substrate appears through the selective radiator on the surface layer, the monochromaticity is lost, and the selective radiation efficiency is lowered.

  As a device for improving this, a fiber-shaped emitter containing a rare earth metal element has been developed as described in Patent Document 1 and the like. By making a fiber with a diameter of about 10 μm, the influence of the substrate on the emitted light is eliminated, the thermal stress is relaxed and the thermal shock resistance can be improved, and the temperature rises faster because the heat capacity is small, from the start of the device to the steady operation Therefore, there is an advantage that the backup power source requires a small capacity. However, the biggest drawback is that the mechanical strength is so low that vibrations are of course brittle enough to break even if touched by hand. In addition, when the combustion flame blows out from the gap between the net-like emitters, not only the emitted light of the emitter but also the emitted light of the combustion flame is superimposed, and there is a problem that monochromaticity of the emitted light is hindered. .

  On the other hand, as described in Patent Document 2 and Non-Patent Document 1, NASA has developed an emitter in which YAG (Yttrium Aluminum Garnet) single crystal is doped with Er (1.5 μm light emission) and Ho (2.0 μm light emission). High luminous efficiency is obtained. However, the doping of the light-emitting rare earth element to the single crystal has a drawback that the concentration cannot be increased so much, and that the single crystal has problems in thermal shock resistance and mechanical strength.

  As a material that has improved these defects, Patent Document 3 has excellent mechanical strength from room temperature to high temperature, excellent heat resistance, oxidation resistance, and thermal shock resistance at the operating temperature of the TPV generator, and high selective radiation. Rare earth-containing oxide ceramic composite emitter materials exhibiting rates are described. However, this specification describes a rare earth-containing oxide ceramic composite material containing at least one kind of rare earth element among Er, Yb, Nd, and Ho. There is no mention, and there is no description of a specific composition therefor.

US Pat. No. 5,080,963 US Pat. No. 5,080,724 JP 2000-272955 A NASA Technical Memorandum 103290 "Reappraisal Solid Selective Emitters"

As described above, GaSb cells are mainly used as photoelectric conversion cells for TPV power generation technology. The quantum efficiency of the photoelectric conversion cell, that is, the ratio of the number of electrons flowing out to the external circuit per unit time with respect to the number of irradiated photons has a wavelength dependency. 1 to ^{29 th IEEE Photovoltaic Specialists Conference 2002 Proceedings} , LM Fraas, et. Al., Showing the wavelength dependence of the quantum efficiency of GaSb cell described in "ELECTRICITY FROM CONCENTRATED SOLAR IR IN SOLAR LIGHTING APPLICATIONS". The GaSb cell can convert 0.8 to 1.7 μm light into electric power with high efficiency. Furthermore, by optimizing the antireflection film on the cell surface, it is possible to perform conversion with almost the same quantum efficiency within the sensitivity region.

FIG. 2 shows a radiation spectrum at 1900 K of an oxide ceramic composite material composed of Al ₂ O ₃ and Er ₃ Al ₅ O ₁₂ described in Patent Document 3 having excellent heat resistance, oxidation resistance, and thermal shock resistance. . The peak wavelength of the selective radiation of this material is 1.3 to 1.7 μm, and these radiations are in the sensitivity region 0.8 to 1.7 μm of the GaSb cell and contribute to photoelectric conversion. However, there is a need for a system that has even better electromotive force of thermophotovoltaic power generation. Therefore, within the sensitivity region 0.8 to 1.7 μm of the GaSb cell, an emitter material having a large radiant energy intensity exceeding the oxide ceramic composite material composed of Al ₂ O ₃ and Er ₃ Al ₅ O ₁₂ described in Patent Document 3. Is required.

  The present invention has been made in view of the above problems, has excellent mechanical strength from room temperature to high temperature, has excellent heat resistance, oxidation resistance, and thermal shock resistance at the operating temperature of the TPV generator, and An object of the present invention is to provide an emitter material for thermophotovoltaic power generation that exhibits a high selective emissivity suitable for a GaSb photoelectric conversion cell.

  As a result of intensive studies to obtain an oxide ceramic composite material that has excellent mechanical properties from room temperature to high temperature and dramatically improves the thermal stability of the structure at high temperature, the present inventors have obtained a specific composition. It was found that a solidified body of metal oxide was suitable as a selective emitter material.

That is, the present invention is an emitter material for thermophotovoltaic power generation that emits radiant light at a selective wavelength by heat, and includes Al ₂ O ₃ and a general formula (M _x Er _1-x ) ₃ Al ₅ O _12. A heat light characterized by comprising a solidified body composed of a composite oxide of M (M is Yb or Tm), Er, and Al, wherein x is 0.05 or more and 0.5 or less The present invention relates to an emitter material for electromotive force power generation.

  The emitter material for thermophotovoltaic power generation of the present invention has excellent mechanical strength from room temperature to high temperature, excellent heat resistance, oxidation resistance, and thermal shock resistance at the operating temperature of the TPV generator, and high selective radiation. Indicates the rate.

In the present invention, the selective radiation efficiency η _SEF is defined in order to evaluate the performance of the selective radiation emitter material. Since the present invention is directed to a GaSb cell that is most often used as a photoelectric conversion cell for TPV power generation technology, radiant energy (selective radiation) in the range of 0.8 to 1.7 μm with respect to the _total radiant energy (E _total ) of the emitter. The ratio of energy E _{0.8-1.7 μm} ) was _defined as the selective radiation efficiency η _SEF (see the following formula).

Selected radiation efficiency η _SEF = (Selected radiation energy E _0.8-1.7μm ) / (Total radiation energy E _total )

However, in the case of the present invention, the photoelectric conversion cell is a GaSb cell (sensitivity region 0.8 to 1.7 μm) that is generally used for a TPV generator. It is not limited to cells. The photovoltaic power in the _{thermophotovoltaic} power generation is obtained by the product of the selected radiant energy E _{0.8-1.7 μm} and the quantum efficiency of the photoelectric conversion cell, and the quantum efficiency of the GaSb cell is 0. 0 as shown in FIG. Since it shows a substantially constant value within the wavelength range of 8 to 1.7 μm, the efficiency of thermophotovoltaic power generation can be evaluated by the selective radiation efficiency η _SEF described above.

The emitter material for thermophotovoltaic power generation according to the present invention is an emitter material for thermophotovoltaic power generation that emits radiation at a selective wavelength by heat, and is not a sintered body but Al ₂ O ₃ and a general formula. (M _x Er _1-x ) ₃ Al ₅ O ₁₂ represented by M (M is at least one of Yb or Tm), a composite oxide of Er and Al, Is 0.05 or more and 0.5 or less. Particularly preferably, the emitter material for thermophotovoltaic power generation of the present invention is a solidification composed of Al ₂ O ₃ and a composite oxide represented by the general formula (Yb _x Er _1-x ) ₃ Al ₅ O _12. (Hereinafter referred to as an Al ₂ O ₃ / (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ solidified body). (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ is composed of oxides of Yb, Er, and Al, and a garnet structure in which part of Er in the Er ₃ Al ₅ O ₁₂ crystal structure is substituted with Yb. It is a complex oxide having In the present invention, the x is 0.05 or more and 0.5 or less.

A solidified body composed of Al ₂ O ₃ of the present invention in which x is 0.05 or more and 0.5 or less and a composite oxide represented by the general formula (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ ( Hereinafter, Al ₂ O ₃ / (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ solidified body) is a solidified body composed of Al ₂ O ₃ and Yb ₃ Al ₅ O ₁₂ (hereinafter referred to as Al ₂ O ₃ and / Yb ₃ Al ₅ O ₁₂ solidified body), and a solidified body composed of Al ₂ O ₃ and Er ₃ Al ₅ O ₁₂ (hereinafter referred to as Al ₂ O ₃ and / Er ₃ Al ₅ O _12). The radiant energy intensity is larger in the sensitivity region of 0.8 to 1.7 μm of the GaSb cell than any of the above.

In the case of the Al ₂ O ₃ / (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ solidified body, Er ions and Yb ions have levels close to each other in their respective energy levels. In other words, the mechanism that the excitation light of Yb ions excites Er ions by interaction between Er ions and ions, and the peak intensity of 1.5 μm does not decrease due to the decrease in Er ion concentration by adding Yb. The mechanism is not clear. The present invention is not limited by the mechanism.

Another emitter material for thermophotovoltaic power generation of the present invention is a solidified body composed of Al ₂ O ₃ and a composite oxide represented by the general formula (Tm _x Er _{1- x} ) ₃ Al ₅ O ₁₂ ( Hereinafter, it is expressed as Al ₂ O ₃ / (Tm _x Er _{1- x} ) ₃ Al ₅ O ₁₂ solidified body). (Tm _x Er _{1- x} ) ₃ Al ₅ O ₁₂ is composed of an oxide of Tm, Er, and Al, and a part of Er in the Er ₃ Al ₅ O ₁₂ crystal structure is substituted with Tm. It is a complex oxide having In the present invention, the y is 0.05 or more and 0.5 or less.

The Al ₂ O ₃ / (Tm _x Er _{1− x} ) ₃ Al ₅ O ₁₂ solidified body of the present invention in which x is 0.05 or more and 0.5 or less is composed of Al ₂ O ₃ and Tm ₃ Al ₅ O _12. The sensitivity region of the GaSb cell is greater than any of the solidified body (hereinafter referred to as the Al ₂ O ₃ / Tm ₃ Al ₅ O ₁₂ solidified body) and the Al ₂ O ₃ / Er ₃ Al ₅ O ₁₂ solidified body. A large radiant energy intensity is exhibited within 0.8 to 1.7 μm.

Al ₂ O ₃ / (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ solidified body (where 0.05 ≦ x ≦ 0.5), and Al ₂ O ₃ / (Tm _x Er _{1- x} ) ₃ Al Each of the ₅ O ₁₂ solidified bodies (0.05 ≦ x ≦ 0.5) has a eutectic composition, each component is composed of a crystalline phase, and Al ₂ O ₃ and the complex oxide are three-dimensionally complicated. Has a unique organizational structure intertwined with each other.

According to the present invention, a thermophotovoltaic power that exhibits a higher selective radiation efficiency by controlling the content of these rare earth elements as a solidified body of a composite oxide containing Al ₂ O ₃ , Er, Yb, or Tm. It can be an emitter material for power generation.

  The solidified body, which is the emitter material for thermophotovoltaic power generation of the present invention, is obtained by solidifying an oxide melt of a constituent element. Since it is a solidified body having a crystal structure containing two or more kinds of metal oxides, it has a lower melting point than that of a simple substance containing rare earth metal elements such as Yb, Tm, and Er. Because of its low viscosity, it can be manufactured under relatively mild temperature and growth conditions.It has excellent high-temperature strength characteristics because two or more crystals grow intricately intertwined. Compared with crystals, it has the feature that the orientation dependency of various characteristics is small. As a result, it is easy to manufacture, has the necessary strength and thermal stability, and can contain a large amount of rare earth metal elements such as Yb, Tm, and Er, so that an emitter with high selective radiation efficiency can be obtained. .

  The solidified body which is the emitter material for thermophotovoltaic power generation of the present invention is obtained by solidifying a melt of two or more kinds of metal oxides to obtain a crystal structure of two or more kinds of oxides, and the oxidation constituting the solidified body. Each of the objects is a single crystal or a polycrystalline crystal phase, and the plurality of crystal phases can have a three-dimensional entanglement or a sea-island structure structure by controlling solidification conditions. For this purpose, the present invention is not limited to such a structure, but may be a solidified body obtained by solidifying a melt of two or more kinds of oxides to obtain a crystal structure of two or more kinds of oxides. Moreover, the solidification conditions can be controlled to obtain a structure free from pores, voids or colonies in the crystal structure.

As described above, the emitter material for thermophotovoltaic power generation according to the present invention is a solidified body containing two or more kinds of oxides obtained by solidifying an oxide melt, and the oxide contained in the solidified body. That is, the composite oxide constituting the oxide composite material is characterized by containing Er, Yb and / or Tm. For example, in the case of the composition Al ₂ O ₃ / (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ , a eutectic reaction from a melt of a mixture of Al ₂ O ₃ , Yb ₂ O ₃ and Er ₂ O ₃ is used. This is a solidified eutectic ceramic obtained by three-dimensionally intricately intertwining an Al ₂ O ₃ single crystal and (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ single crystal in which part of Er is substituted with Yb. Because of its unique structure, 1) room temperature strength can be maintained up to about 1800 ° C. just below the melting point. 2) It has high temperature characteristics not found in conventional materials, such as excellent thermal stability without causing weight change, structural change and strength reduction even after heat treatment at 1700 ° C. in air for 500 hours. In addition, although thermal conductivity is an important factor that determines radiation characteristics, the thermoelectric emitter material of the present invention has higher thermal conductivity than the YAG-based selective emitters that NASA has developed so far. And is excellent as a selective emitter material.

In the case of the solidified body of Al ₂ O ₃ and (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ , the emitter material for thermophotovoltaic power generation of the present invention can be produced by the following method. First, powders of Al ₂ O ₃ , Yb ₂ O ₃ , and Er ₂ O ₃ are mixed at a ratio that generates a ceramic composite material having a desired component ratio to prepare a mixed powder. There is no particular limitation on the mixing method, and a known mixing method can be employed. Next, the mixed powder is heated and melted at a temperature at which both raw materials are melted, for example, 1900 to 1950 ° C., using a known melting furnace, for example, an arc melting furnace.

  Subsequently, the melted product is charged into the crucible as it is, or the melted product is once solidified and then pulverized, and the ground product is charged into the crucible and then melted and solidified to solidify the oxide of the present invention. Manufacture ceramic composite materials. As another method, it is possible to employ a method in which the melt is held at a predetermined temperature and then cast into a crucible and cooled to obtain a solidified body.

During the solidification, the constituent crystal phases are entangled three-dimensionally by controlling the atmospheric pressure at the time of dissolution and solidification, and controlling the crystal growth by solidification. Alternatively, a solidified body having a sea-island structure and a crystal structure free from bubbles, voids, or colonies can be obtained. Such a solidified body becomes an emitter material for a thermophotovoltaic material that is more excellent in thermal stability such as high-temperature strength and creep characteristics. In order to produce such a solidified body, the atmospheric pressure during dissolution and solidification is preferably 4 × 10 ⁴ Pa or less, and more preferably 0.13 Pa or less. Further, the moving speed of the crucible for unidirectional solidification, in other words, the growth speed of the oxide ceramic composite material is preferably 1 to 100 mm / hour.

The emitter material for thermophotovoltaic power generation is a solidified body (0.05 ≦ y ≦ 0.05) composed of Al ₂ O ₃ and a composite oxide represented by the general formula (Tm _x Er _{1 -x} ) ₃ Al ₅ O ₁₂ In the case of 0.5), a method similar to the method for producing a solidified body of Al ₂ O ₃ and (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ using an oxide of each constituent element as a raw material Can be manufactured.

  In order to use the solidified body according to the present invention as a selective emitter, in the case of a shape necessary as an emitter material, for example, in the case of a thin film, a bulk material manufactured by a unidirectional solidification method may be cut into thin pieces. Also, if a fiber-like material is required, a capillary hole is created by making a predetermined hole in the bottom of the melting crucible and making it into a fiber while drawing the melt from the hole, or immersing a tube having a predetermined gap in the melt. A method of forming a fiber according to the phenomenon may be adopted. Either method is a solidification process from a melt, and by controlling the solidification process, it has a high temperature characteristic with a unique structure in which two kinds of oxide crystals are intricately intertwined. It is possible to obtain an excellent emitter material.

  Further, when the surface structure is obtained by removing the metal oxide phase not containing Yb, Tm, and Er from the emitter surface to a certain depth among the two or more kinds of oxides constituting the solidified body according to the present invention, the TPV power generation technology It is preferable because the emissivity at a selective wavelength can be improved while having the mechanical strength and heat resistance necessary for the selective emitter used in the above.

  Examples of the present invention are shown below.

(Examples 1 to 10)
It is obtained by mixing α-Al ₂ O ₃ powder, Er ₂ O ₃ powder, Yb ₂ O ₃ powder and / or Tm ₂ O ₃ powder as raw materials in a wet ball mill using an ethanol solvent in the ratio shown in Table 1. The ethanol was removed from the resulting slurry using a rotary evaporator.

  The obtained mixed powder was charged into a molybdenum crucible installed in the chamber, maintained at an atmospheric pressure of 0.013 Pa, and the crucible was heated to 1900-2000 ° C. using a high frequency coil to dissolve the mixed powder, 30 After holding for a minute, an ingot was produced by casting into a molybdenum mold having an inner diameter of 40 mm and a height of 200 mm. The obtained ingot was charged into a molybdenum crucible having an outer diameter of 50 mm, a height of 200 mm, and a thickness of 2 mm. After melting at 1920 ° C. in the same atmosphere, the crucible was lowered at a rate of 5 mm / hour and solidified unidirectionally, and φ40 mm A solidified body of × 70 mm was obtained.

As an example, the scanning structure of the cross-sectional structure perpendicular to the solidification direction of the solidified body of Al ₂ O ₃ and (Yb _0.2 Er _0.8 ) ₃ Al ₅ O ₁₂ obtained in this manner in Example 3 was used. An electron micrograph is shown in FIG. In FIG. 3, the black part is an α-Al ₂ O ₃ phase, and the white part is a composite oxide generated from Al ₂ O ₃ , Yb ₂ O ₃ , Er ₂ O ₃ (Yb _0.2 Er _0.8 ) ₃ Al ₅ O ₁₂ phase. This solidified body has a uniform structure free from colonies and pores.

Next, from the obtained solidified body, a thin piece having a thickness of 10 × 10 × 0.3 was cut out at right angles to the solidification direction, and both surfaces were mirror-polished. Next, the flakes are put in a graphite vessel and heat-treated at a temperature of 1600 ° C. for 1 hour in a vacuum of 0.013 Pa to reduce and remove only the Al ₂ O ₃ phase on the surface portion by about 100 μm. It was set as the radiation characteristic evaluation test piece. In order to evaluate the selective radiation performance of the test piece shown in Table 1 at a high temperature, a radiation intensity spectrum was measured with a radiation intensity measuring apparatus comprising a Fourier spectrometer and a standard blackbody furnace. Radiation of Al ₂ O ₃ / (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ solidified body and Al ₂ O ₃ / (Tm _x Er _{1- x} ) ₃ Al ₅ O ₁₂ solidified body measured at 1900K The spectra are shown in FIGS. 4 and 5, respectively. The selective radiation efficiency was determined from this radiation intensity spectrum. The results are shown in Table 1. In Table 1, x denotes the general formula _{(Yb x Er 1-x)} 3 Al 5 O 12 or the formula _{(Tm x Er 1- x) 3} Al 5 O 12 in x,.

(Comparative Examples 1-5)
As raw materials, α-Al ₂ O ₃ powder and Er ₂ O ₃ powder were mixed in a wet ball mill using an ethanol solvent at a ratio shown in Table 1, and ethanol was removed from the resulting slurry using a rotary evaporator. The obtained powder was dissolved in the same manner as in the example, and then solidified in one direction to obtain a solidified body having a diameter of 40 mm × 70 mm. From the obtained solidified body, a selective radiation characteristic evaluation test piece was prepared by the same method as in the example, and a radiation intensity spectrum was measured. _Al 2 _O when measured at _{1900K 3 / (Yb x Er 1} -x) 3 Al 5 O 12 each emission of the solidified body and _{Al 2 O 3 / (Tm y} Er 1-y) 3 Al 5 O 12 clots The spectra are shown in FIGS. 4 and 5, respectively. The selective radiation efficiency was determined from this radiation spectrum. The results are shown in Table 1.

From the radiation spectra of the examples and comparative examples shown in FIGS. 4 and 5, even if the Er concentration in the solidified body is decreased, the radiation intensity of 1.5 μm derived from Er does not immediately decrease, In the Al ₂ O ₃ / (Yb _x Er _1-x ) ₃ Al ₅ O ₁₂ solidified body, it can be seen that even if the Er content is decreased, the strength is rather increased if the amount is small. Selective radiant light from ions in a solid such as rare earth elements repeats light emission and absorption with adjacent ions, and the resulting light is emitted from the surface. Accordingly, in general, the relationship between the radiation intensity and the ion concentration is not proportional to a certain concentration or less, and at a concentration higher than that, a so-called concentration quenching phenomenon occurs and the radiation intensity decreases. In the present invention as well, it can be said that the radiation intensity increased because the Er ion concentration decreased.

Further, from Table 1, the emitter material for thermophotovoltaic power generation of the present invention is a solidified body having a specific composition containing Er and Yb and / or Tm, so that Al ₂ O ₃ / Er ₃ Al ₅ O ₁₂ solidified. Body, Al ₂ O ₃ / Yb ₃ Al ₅ O ₁₂ coagulum, Al ₂ O ₃ / Tm ₃ Al ₅ O ₁₂ coagulum, and higher selective radiation efficiency than these mixed coagulations outside the composition range of the present invention. It can be seen that this is an excellent emitter material for thermophotovoltaic power generation.

It is a characteristic view which shows the wavelength dependence of the quantum efficiency of a GaSb cell. A radiation spectrum of _{Al 2 O 3 / Er 3 Al} 5 O 12 solidified body. 4 is an electron micrograph in place of a drawing showing a cross-sectional structure perpendicular to the solidification direction of the Al ₂ O ₃ / (Yb _0.2 Er _0.8 ) ₃ Al5O ₁₂ solidified body obtained in Example 3. A radiation spectrum diagram when changing the value of the _{Al 2 O 3 / (Yb x} Er 1-x) 3 Al 5 O 12 solidified body of x. A radiation spectrum diagram when changing the value of the _{Al 2 O 3 / (Tm x} Er 1- x) 3 Al 5 O 12 solidified body of x.

Claims (2)

An emitter material for thermophotovoltaic power generation that emits radiant light at a selective wavelength by heat, which is expressed by Al ₂ O ₃ and M (M _x Er _1-x ) ₃ Al ₅ O ₁₂ represented by M (M Yb or Tm), a solidified body composed of a composite oxide of Er and Al, wherein x is 0.05 or more and 0.5 or less, and the emitter material for thermophotovoltaic power generation . 2. The emitter material for thermophotovoltaic power generation according to claim 1, wherein x is 0.05 or more and 0.4 or less.

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