Abstract:
The present invention addresses the problem of providing a heat conversion member capable of efficiently converting light to heat. This heat conversion member includes at least one type of semiconductor, and is characterized in that the band gap of the semiconductor is 0.5-1.2 eV.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a heat conversion member and to a heat conversion laminate. 
       BACKGROUND ART 
       [0002]    Photovoltaic power generation systems are known that convert sunlight to heat and utilize the heat for electric power generation. In the known systems, sunlight is collected with a collector and the collected sunlight is used to heat a heating medium (such as oil, dissolved salts or molten sodium) in a container or flow channel. Provision of covering materials, thin-films and the like on the surfaces of containers or flow channels is also being studied as a way of accelerating heating of the heating medium by the collected sunlight. 
         [0003]    For example, PTL 1 proposes a cermet layer (ceramic+metal=cermet) as a member for conversion of sunlight to heat. Also, PTL 2, for example, proposes a solar energy collecting device having one section that receives the action of sunlight rays and another section that is situated at a gap from that section away from sunlight rays and receives the action of a heat absorption medium, and a section situated between the two sections, wherein the absorbing element is made of a covered sheet material, the sheet material having a sunlight ray-selective coating on one side of the sheet facing the section that receives the action of sunlight rays, and having a radiative coating on the other side of the sheet that faces the section that receives the action of the heat absorption medium. 
       CITATION LIST  
     Patent Literature 
     [PTL 1] European Patent No. 1397622 
     [PTL 2] Japanese Unexamined Patent Publication No. 57-55363 
     SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    At the current time, it is desirable to accelerate heating of heating media by collected sunlight and achieve more efficient light-to-heat conversion. 
         [0005]    It is an object of the present invention to provide a heat conversion member that can efficiently convert light to heat. It is another object of the present invention to provide a heat conversion laminate comprising a heat conversion member that can efficiently convert light to heat. 
       Solution to Problem 
       [0006]    The means for achieving these objects is described by the following (1) to (10). 
         [0007]    (1) A heat conversion member comprising at least one type of semiconductor, 
         [0008]    the band gap of the semiconductor being between 0.5 eV and 1.2 eV. 
         [0009]    (2) A heat conversion member comprising a composite material of at least one type of semiconductor and a transparent dielectric material, 
         [0010]    the band gap of the semiconductor being between 0.5 eV and 1.2 eV. 
         [0011]    (3) The heat conversion member according to (1) or (2) above, wherein the semiconductor comprises FeS 2 . 
         [0012]    (4) The heat conversion member according to (1) or (2) above, wherein the semiconductor comprises Mg 2 Si. 
         [0013]    (5) The heat conversion member according to (1) or (2) above, wherein the semiconductor comprises Zn 3 As 2 . 
         [0014]    (6) The heat conversion member according to (1) or (2) above, wherein the semiconductor comprises Ge. 
         [0015]    (7) The heat conversion member according to any one of (1) to (6) above, which has a film shape. 
         [0016]    (8) The heat conversion member according to (7), wherein the film shape has a thickness of 1 nm to 10 μm. 
         [0017]    (9) A heat conversion laminate having laminated at least one or more layers including the heat conversion member according to (7) or (8), and a metal layer. 
         [0018]    (10) A heat conversion laminate having laminated at least a metal layer, one or more layers including the heat conversion member according to (7) or (8), and a transparent dielectric layer, in that order. 
       Advantageous Effects of Invention 
       [0019]    According to the present invention, there is provided a heat conversion member that can efficiently convert light to heat. According to the present invention, there is further provided a heat conversion laminate comprising a heat conversion member that can efficiently convert light to heat. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is a graph showing an optical spectrum for sunlight and an optical spectrum for heat radiant light. 
           [0021]      FIG. 2  is a cross-sectional schematic drawing showing a heat conversion laminate  1  as one embodiment of a heat conversion laminate according to the present invention. 
           [0022]      FIG. 3  is a graph showing the results for the absorption properties of a Mo—SiO 2  cermet monolayer film (calculated). 
           [0023]      FIG. 4  is a graph showing the results for the absorption properties of a Mo—SiO 2  cermet monolayer film (an actual film). 
           [0024]      FIG. 5  is a graph showing the results for the absorption properties of a FeS 2 —SiO 2  cersemi monolayer film. 
           [0025]      FIG. 6  is a graph showing the results for the absorption properties of a Mg 2 Si—SiO 2  cersemi monolayer film. 
           [0026]      FIG. 7  is a graph showing the results for the absorption properties of a Ge—SiO 2  cersemi monolayer film. 
           [0027]      FIG. 8  is a graph showing the results for the absorption properties of a Zn 3 As 2 —SiO 2  cersemi monolayer film. 
           [0028]      FIG. 9  is a graph showing the results for the absorption properties of a Mo—SiO 2  cermet monolayer film. 
           [0029]      FIG. 10  is a figure showing the laminar structures of FeS 2 —SiO 2  cersemi laminates that operate at a heat collecting temperature of 580° C. 
           [0030]      FIG. 11  is a figure showing the laminar structures of FeS 2 —SiO 2  cersemi laminates that operate at a heat collecting temperature of 400° C. 
           [0031]      FIG. 12  is a graph showing the results for the absorption properties of a FeS 2 —SiO 2  cersemi laminate and a Mo—SiO 2  cermet laminate, that operate at a heat collecting temperature of 580° C. 
           [0032]      FIG. 13  is a graph showing the results for the absorption properties of a FeS 2 —SiO 2  cersemi laminate and a Mo—SiO 2  cermet laminate, that operate at a heat collecting temperature of 400° C. 
           [0033]      FIG. 14  is a graph showing the results for the film efficiency of a FeS 2 —SiO 2  cersemi laminate and a Mo—SiO 2  cermet laminate, that operate at a heat collecting temperature of 580° C. 
           [0034]      FIG. 15  is a graph showing the results for the film efficiency of a FeS 2 —SiO 2  cersemi laminate and a Mo—SiO 2  cermet laminate, that operate at a heat collecting temperature of 400° C. 
           [0035]      FIG. 16  is a figure showing the laminar structures of Mo—SiO 2  cermet laminates that operate at a heat collecting temperature of 580° C. 
           [0036]      FIG. 17  is a figure showing the laminar structures of Mo—SiO 2  cermet laminates that operate at a heat collecting temperature of 400° C. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     (1) Heat Conversion Member 
       [0037]    The heat conversion member of the present invention is a heat conversion member comprising at least one type of semiconductor, wherein the band gap of the semiconductor is between 0.5 eV and 1.2 eV. The heat conversion member of the present invention is also a heat conversion member comprising a composite material of one or more types of semiconductor and a transparent dielectric material, wherein the band gap of the semiconductor is between 0.5 eV and 1.2 eV.  FIG. 1  is a graph showing an optical spectrum for sunlight and an optical spectrum for heat radiant light, and since the heat conversion member of the present invention has a steep change between absorption and non-absorption of sunlight with a wavelength in the range of 2480 nm to 1000 nm (light energy: 0.5 to 1.2 eV), it can efficiently absorb sunlight while minimizing heat release by heat radiation from the heating medium at 200° C. to 600° C., and can thus efficiently convert light to heat. If the slope of the absorbance for light is gentle and there is no steep change between absorption and non-absorption in a wavelength range of 2480 nm to 1000 nm, the solar absorbance will be low and the thermal radiation rate will increase, resulting in greater loss of thermal energy. 
         [0038]    The one or more semiconductors in the heat conversion member of the present invention may be of a single type of semiconductor, or a mixture of two or more different types of semiconductor. 
         [0039]    The semiconductor in the heat conversion member of the present invention is not particularly restricted, and examples include FeS 2 , Mg 2 Si, Zn 2 As 2  and Ge. 
         [0040]    The band gap of the one or more types of semiconductor in the heat conversion member of the present invention is between 0.5 eV and 1.2 eV and preferably between 0.7 eV and 1.0 eV. 
         [0041]    The transparent dielectric material in the composite material in the heat conversion member of the present invention (hereunder simple referred to as “composite material”) is not particularly restricted, and examples include SiO 2 , Al 2 O 2  and AlN, with SiO 2  being preferred. 
         [0042]    The one or more types of semiconductor in the heat conversion member of the present invention preferably include FeS 2 , Mg 2 Si, Zn 2 As 2  or Ge. The values of the band gaps of FeS 2 , Mg 2 Si, Zn 2 As 2  and Ge vary depending on the measuring method and measuring conditions, however generally speaking the value of the FeS 2  band gap is 0.95 eV, the value of the Mg 2 Si band gap is 0.77 eV, the value of the Zn 2 As 2  band gap is 0.86 eV and the value of the Ge band gap is 0.89 eV. The one or more types of semiconductor in the heat conversion member of the present invention may also be a mixture of at least two different compounds selected from the group consisting of FeS 2 , Mg 2 Si, Zn 2 As 2  and Ge. The band gap can be measured by a photoabsorption method or photoelectron spectroscopy. 
         [0043]    The heat conversion member of the present invention may be in any desired form, such as in the form of a film shape, tube shape, sheet shape or the like, however a film shape is preferred. The thickness of a film of the heat conversion member of the present invention may be any desired thickness so long as the effect of the present invention is exhibited; however, preferably a film of the heat conversion member of the present invention has a thickness of 1 nm to 10 μm, and more preferably it has a thickness of 5 nm to 100 nm. 
         [0044]    The content of the one or more semiconductors in the heat conversion member of the present invention may be as desired, and for example, it may be 10 vol % or greater, 20 vol % or greater, 30 vol % or greater, 40 vol % or greater, 50 vol % or greater, 60 vol % or greater, 70 vol % or greater, 80 vol % or greater, 90 vol % or greater or 95 vol % or greater. 
         [0045]    The heat conversion member of the present invention may also essentially consist entirely of the one or more semiconductors, in which case the content of the one or more semiconductors will be 100 vol %. 
         [0046]    The heat conversion member of the present invention may also contain any desired material other than the one or more semiconductors. The heat conversion member of the present invention may yet also contain any desired material other than a composite material of the one or more semiconductors and a transparent dielectric material. 
         [0047]    The heat conversion member of the present invention can be obtained by any desired publicly known production method. For example, the heat conversion member of the present invention can be produced by physical vapor phase deposition (PVD), sputtering or the like. 
       (2) Heat Conversion Laminate 
       [0048]    As one feature, the heat conversion laminate of the present invention has laminated one or more layers comprising a film-like heat conversion member of the present invention, and a metal layer, and it may have a metal layer and one or more layers comprising a film-like heat conversion member of the present invention laminated in that order, or the lamination may be in the reverse order. 
         [0049]    As another feature, the heat conversion laminate of the present invention also have at least a metal layer, one or more layers comprising a film-like heat conversion member of the present invention and a transparent dielectric layer, laminated in that order. 
         [0050]    The one or more layers comprising a film-like heat conversion member of the present invention in the heat conversion laminate of the present invention may be constructed as a photoabsorbing layer, and because it has a steep change between absorption and non-absorption in a sunlight wavelength range of 2480 nm to 1000 nm, it can efficiently absorb sunlight while minimizing heat release by heat radiation from the heating medium at 200° C. to 600° C., thereby efficiently convert light to heat. The thickness of the one or more layers comprising a film-like heat conversion member in the heat conversion laminate of the present invention may be any desired thickness so long as the effect of the present invention is exhibited, and it is preferably a thickness of 5 nm to 100 nm. The layer comprising the film-like heat conversion member in the heat conversion laminate of the present invention may be a single layer or multiple layers. The one or more layers comprising a film-like heat conversion member in the heat conversion laminate of the present invention may also include any materials other than the film-like heat conversion member. 
         [0051]    The metal layer in the heat conversion laminate of the present invention may be constructed as an infrared anti-reflection layer. The metal layer in the heat conversion laminate of the present invention is not particularly restricted, and for example, it may be a molybdenum (Mo) layer, tungsten (W) layer, silver (Ag) layer, gold (Au) layer, copper (Cu) layer or the like, and is preferably a molybdenum (Mo) layer. The thickness of the metal layer in the heat conversion laminate of the present invention may be any desired thickness so long as the effect of the present invention is exhibited, and it is preferably a thickness of 100 nm or greater. 
         [0052]    The transparent dielectric layer in the heat conversion laminate of the present invention may also be constructed as an anti-reflection layer. The transparent dielectric layer in the heat conversion laminate of the present invention is not particularly restricted, and examples include a SiO 2  layer, Al 2 O 3 , AlN layer or the like, with a SiO 2  layer being preferred. The thickness of the transparent dielectric layer in the heat conversion laminate of the present invention may be any desired thickness so long as the effect of the present invention is exhibited, and it is preferably a thickness of 10 nm to 500 nm. 
         [0053]    The heat conversion laminate of the present invention can be obtained by any desired publicly known production method. For example, the heat conversion laminate of the present invention can be produced by physical vapor phase deposition (PVD), sputtering or the like. 
         [0054]    The heat conversion laminate of the present invention will now be explained in greater detail with reference to  FIG. 2 . Incidentally, the heat conversion laminate of the present invention is not limited to the embodiment of the present invention shown in  FIG. 2 , such as is within the scope of the object and gist of the present invention. 
         [0055]      FIG. 2  is a drawing showing a heat conversion laminate  1  as one embodiment of a heat conversion laminate according to an embodiment of the present invention. The heat conversion laminate  1  according to an embodiment of the present invention is formed from a transparent dielectric layer  11 , a layer comprising a heat conversion member (photoabsorbing layer)  12 , and a metal layer  13 . Also, the layer comprising a heat conversion member (photoabsorbing layer)  12  comprises a semiconductor  121  and a transparent dielectric material  122 . As shown in  FIG. 2 , the particles of the semiconductor  121  are dispersed within the transparent dielectric material  122 . 
       EXAMPLES 
       [0056]    Examples will now be provided for a more concrete explanation of the present invention. The present invention is not limited to these examples, however, provided that the object and gist of the present invention are maintained. 
       &lt;Verification of Reproducibility of Film Properties According to Bruggeman&#39;s Effective Medium Approximation&gt; 
       [0057]    The reproducibility of the film properties according to Bruggeman&#39;s effective medium approximation was verified by Example 1 and Comparative Example 1. 
       Example 1 
       [0058]    The absorption properties of a Mo—SiO 2  cermet monolayer film were determined using Bruggeman&#39;s theory of computation. The term “cermet” means “ceramic+metal”. 
         [0059]    The optical constants (n, k) of the Mo—SiO 2  cermet monolayer film were calculated by Bruggeman&#39;s effective medium approximation formula (formula (1) below). The optical constants for Mo and SiO 2  in the Mo—SiO 2  cermet were obtained by forming a monolayer film of each component by sputtering, and performing calculation from the measurement data obtained using a spectroscopic ellipsometer, and the reflectance property and the transmittance property as measured with a spectrophotometer. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       f 
                        
                       
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   s 
                                 
                                 - 
                                 
                                   ik 
                                   s 
                                 
                               
                               ) 
                             
                             2 
                           
                           - 
                           
                             
                               ( 
                               
                                 n 
                                 - 
                                 ik 
                               
                               ) 
                             
                             2 
                           
                         
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   s 
                                 
                                 - 
                                 
                                   ik 
                                   s 
                                 
                               
                               ) 
                             
                             2 
                           
                           + 
                           
                             2 
                              
                             
                               
                                 ( 
                                 
                                   n 
                                   - 
                                   ik 
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                       
                     
                     + 
                     
                       
                         ( 
                         
                           1 
                           - 
                           f 
                         
                         ) 
                       
                        
                       
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   c 
                                 
                                 - 
                                 
                                   ik 
                                   c 
                                 
                               
                               ) 
                             
                             2 
                           
                           - 
                           
                             
                               ( 
                               
                                 n 
                                 - 
                                 ik 
                               
                               ) 
                             
                             2 
                           
                         
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   c 
                                 
                                 - 
                                 
                                   ik 
                                   c 
                                 
                               
                               ) 
                             
                             2 
                           
                           + 
                           
                             2 
                              
                             
                               
                                 ( 
                                 
                                   n 
                                   - 
                                   ik 
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                       
                     
                   
                   = 
                   0 
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
       
         
           
             i: imaginary unit 
             f: Mo mixing ratio (vol %) 
             n s , k s : Optical constants of Mo 3 Si 
             n c , k c : Optical constants of SiO 2    
           
         
       
     
         [0064]    A multilayer film approximation based on the optical constants (n, k) for Mo—SiO 2  cermet obtained by calculation based on formula (1) was used to calculate the absorbance of the Mo—SiO 2  cermet monolayer film (corresponding to a film thickness of 30 nm). The results for the absorption properties of a Mo—SiO 2  cermet monolayer film (calculated) are shown in  FIG. 3 . 
       Comparative Example 1 
       [0065]    The absorption properties of a Mo—SiO 2  cermet monolayer film were determined using an actual film (prepared film). 
         [0066]    A film was formed by simultaneous sputtering of Mo and SiO 2  on a quartz substrate that had been heated to a temperature of 500° C. to 600° C., to obtain a sample of a Mo—SiO 2  cermet monolayer film. The optical constants (refractive index n, extinction coefficient k) of the Mo—SiO 2  cermet were calculated for the obtained sample from the measurement data with a spectroscopic ellipsometer and the reflectance property and transmittance property measured with a spectrophotometer. 
         [0067]    The calculated multilayer film approximation based on the optical constants (n, k) for Mo—SiO 2  cermet was used to calculate the absorbance of the Mo—SiO 2  cermet monolayer film (corresponding to a film thickness of 30 nm). The results for the absorption properties of the Mo—SiO 2  cermet monolayer film (an actual film) are shown in  FIG. 4 . 
       &lt;Verification Results&gt; 
       [0068]    As is clear by referring to  FIG. 3  and  FIG. 4 , it was verified that the results for the absorption properties based on Bruggeman&#39;s theory of computation ( FIG. 3 ) reasonably equated with the results for the absorption properties of the actual film (prepared film) ( FIG. 4 ). 
       &lt;Evaluation of Absorption Properties of Heat Conversion Member&gt; 
       [0069]    The absorption properties of a heat conversion member were evaluated using Example 2 and Comparative Example 2. 
       Example 2 
       [0070]    Evaluation of the absorption properties of a heat conversion member of the present invention was conducted using a FeS 2 —SiO 2  cersemi monolayer film, a Mg 2 Si—SiO 2  cersemi monolayer film, a Ge—SiO 2  cersemi monolayer film and a Zn 2 As 2 —SiO 2  cersemi monolayer film. The term “cersemi” means “ceramic+semiconductor”. 
         [0071]    The optical constants (n, k) of the FeS 2 —SiO 2  cersemi, Mg 2 Si—SiO 2  cersemi, Ge—SiO 2  cersemi and Zn 2 As 2 —SiO 2  cersemi were calculated by Bruggeman&#39;s effective medium approximation formula (formula (2) below). For the optical constants (n s , k s ) for FeS 2 , Ge and Zn 2 As 2 , refer to “Handbook of Optical Constants of Solids”, Edward D. Palik, Academic Press, Boston, 1985”, and for the optical constants (n s , k s ) of Mg 2 Si, refer to “T. Kato et al., J. Appl. Phys. 110, 063723(2011)”. Experimental data were used for the optical constants (n c , k c ) of SiO 2 . 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       f 
                        
                       
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   s 
                                 
                                 - 
                                 
                                   ik 
                                   s 
                                 
                               
                               ) 
                             
                             2 
                           
                           - 
                           
                             
                               ( 
                               
                                 n 
                                 - 
                                 ik 
                               
                               ) 
                             
                             2 
                           
                         
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   s 
                                 
                                 - 
                                 
                                   ik 
                                   s 
                                 
                               
                               ) 
                             
                             2 
                           
                           + 
                           
                             2 
                              
                             
                               
                                 ( 
                                 
                                   n 
                                   - 
                                   ik 
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                       
                     
                     + 
                     
                       
                         ( 
                         
                           1 
                           - 
                           f 
                         
                         ) 
                       
                        
                       
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   c 
                                 
                                 - 
                                 
                                   ik 
                                   c 
                                 
                               
                               ) 
                             
                             2 
                           
                           - 
                           
                             
                               ( 
                               
                                 n 
                                 - 
                                 ik 
                               
                               ) 
                             
                             2 
                           
                         
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   c 
                                 
                                 - 
                                 
                                   ik 
                                   c 
                                 
                               
                               ) 
                             
                             2 
                           
                           + 
                           
                             2 
                              
                             
                               
                                 ( 
                                 
                                   n 
                                   - 
                                   ik 
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                       
                     
                   
                   = 
                   0 
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
       
       
         
           
             i: imaginary unit 
             f: Semiconductor mixing ratio (vol %) 
             n s , k s : Optical constants of semiconductor 
             n c , k c : Optical constants of SiO 2    
           
         
       
     
         [0076]    Using the multilayer film approximations based on the optical constants (n, k) for FeS 2 —SiO 2  cersemi, Mg 2 Si—SiO 2  cersemi, Ge—SiO 2  cersemi and Zn 3 As 2 —SiO 2  cersemi, obtained by each calculation using formula (2), each absorbance was calculated for the FeS 2 —SiO 2  cersemi monolayer film, Mg 2 Si—SiO 2  cersemi monolayer film, Ge—SiO 2  cersemi monolayer film and Zn 3 As 2 —SiO 2  cersemi monolayer film (corresponding to a film thickness of 30 nm).  FIG. 5  to  FIG. 8  show the results for the absorption properties of a FeS 2 —SiO 2  cersemi monolayer film, Mg 2 Si—SiO 2  cersemi monolayer film, Ge—SiO 2  cersemi monolayer film and Zn 3 As 2 —SiO 2  cersemi monolayer film. 
       Comparative Example 2 
       [0077]    The absorption properties of a Mo—SiO 2  cermet monolayer film were evaluated. 
         [0078]    The optical constant (n, k) of the Mo—SiO 2  cermet monolayer film was calculated by Bruggeman&#39;s effective medium approximation formula (formula (1) below). The optical constants for Mo and SiO 2  in the Mo—SiO 2  cermet were obtained by forming a monolayer film of each component by sputtering, and performing calculation from the measurement data obtained using a spectroscopic ellipsometer, and the reflectance property and the transmittance property as measured with a spectrophotometer. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       f 
                        
                       
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   s 
                                 
                                 - 
                                 
                                   ik 
                                   s 
                                 
                               
                               ) 
                             
                             2 
                           
                           - 
                           
                             
                               ( 
                               
                                 n 
                                 - 
                                 ik 
                               
                               ) 
                             
                             2 
                           
                         
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   s 
                                 
                                 - 
                                 
                                   ik 
                                   s 
                                 
                               
                               ) 
                             
                             2 
                           
                           + 
                           
                             2 
                              
                             
                               
                                 ( 
                                 
                                   n 
                                   - 
                                   ik 
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                       
                     
                     + 
                     
                       
                         ( 
                         
                           1 
                           - 
                           f 
                         
                         ) 
                       
                        
                       
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   c 
                                 
                                 - 
                                 
                                   ik 
                                   c 
                                 
                               
                               ) 
                             
                             2 
                           
                           - 
                           
                             
                               ( 
                               
                                 n 
                                 - 
                                 ik 
                               
                               ) 
                             
                             2 
                           
                         
                         
                           
                             
                               ( 
                               
                                 
                                   n 
                                   c 
                                 
                                 - 
                                 
                                   ik 
                                   c 
                                 
                               
                               ) 
                             
                             2 
                           
                           + 
                           
                             2 
                              
                             
                               
                                 ( 
                                 
                                   n 
                                   - 
                                   ik 
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                       
                     
                   
                   = 
                   0 
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
       
         
           
             i: imaginary unit 
             f: Mo mixing ratio (vol %) 
             n s , k s : Optical constants of Mo Si 
             n c , k c : Optical constants of SiO 2    
           
         
       
     
         [0083]    A multilayer film approximation based on the optical constants (n, k) for Mo—SiO 2  cermet obtained by calculation based on formula (1) was used to calculate the absorbance of the Mo—SiO 2  cermet monolayer film (corresponding to a film thickness of 30 nm). The results for the absorption properties of the Mo—SiO 2  cermet monolayer film are shown in  FIG. 9 . 
       &lt;Evaluation Results&gt; 
       [0084]    Referring to  FIG. 5  to  FIG. 8  and  FIG. 9 , the results for the absorption properties of the Mo—SiO 2  cermet monolayer film ( FIG. 9 ) show a gentle slope for the absorbance of light in a wavelength range of 2480 to 1000 nm, whereas the results for the absorption properties of the FeS 2 —SiO 2  cersemi monolayer film, Mg 2 Si—SiO 2  cersemi monolayer film, Ge—SiO 2  cersemi monolayer film and Zn 3 As 2 —SiO 2  cersemi monolayer film ( FIG. 5  to  FIG. 8 ) show an abrupt slope for the absorbance of light in a wavelength range of 2480 to 1000 nm, by which it is seen that the FeS 2 —SiO 2  cersemi monolayer film, Mg 2 Si—SiO 2  cersemi monolayer film, Ge—SiO 2  cersemi monolayer film and Zn 3 As 2 —SiO 2  cersemi monolayer film efficiently absorb sunlight while minimizing heat release by heat radiation from the heating medium at 200° C. to 600° C. 
       &lt;Evaluation of Absorption Property of Heat Conversion Laminate and Evaluation of Film Efficiency&gt; 
       [0085]    Evaluation of the absorption properties of a heat conversion laminate and evaluation of the film efficiency were conducted using Example 3 and Comparative Example 3. 
       Example 3 
       [0086]    Evaluation of the absorption properties of a heat conversion laminate of the present invention and evaluation of the film efficiency were conducted using a FeS 2 —SiO 2  cersemi laminate. The structure of the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 580° C. was a 4-layer structure comprising a SiO 2  layer (film thickness: 70 nm), a cersemi layer with a FeS 2  mixing ratio of 30% (film thickness: 70 nm), a cersemi layer with a FeS 2  mixing ratio of 100% (film thickness: 15 nm) and a Mo (molybdenum) layer (film thickness: 100 nm) from the light incident side, as shown in  FIG. 10 . The structure of the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 400° C. was a 4-layer structure comprising a SiO 2  layer (film thickness: 80 nm), a cersemi layer with a FeS 2  mixing ratio of 30% (film thickness: 75 nm), a cersemi layer with a FeS 2  mixing ratio of 100% (film thickness: 25 nm) and a Mo (molybdenum) layer (film thickness: 100 nm) from the light incident side, as shown in  FIG. 11 . The film structures (FeS 2  mixing ratio and film thickness) for the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 580° C. and the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 400° C., were set so as to exhibit the maximum film efficiency, as described below. 
         [0087]    The optical constants (n, k) of the FeS 2 —SiO 2  cersemi layers of the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 580° C. and the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 400° C. were determined by exactly the same calculation method as used for the optical constants (n, k) of Example 2. For the optical constants (n, k) of Mo, refer to “Handbook of Optical Constants of Solids”, Edward D. Palik, Academic Press, Boston, 1985”. Experimental data were used for the optical constants (n c , k c ) of SiO 2 . 
         [0088]    The absorbance of the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 580° C. was calculated using multilayer film approximation, based on the optical constants (n c , k c ) of the SiO 2  layer (film thickness: 70 nm), the optical constants (n, k) of the cersemi layer with a FeS 2  mixing ratio of 30% (film thickness: 70 nm), the optical constants (n, k) of the cersemi layer with a FeS 2  mixing ratio of 100% (film thickness: 15 nm) and the optical constants (n, k) of the Mo (molybdenum) layer (film thickness: 100 nm). The results for the absorption properties of the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 580° C. are shown in  FIG. 12 . 
         [0089]    Similarly, the absorbance of the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 400° C. was calculated using multilayer film approximation, based on the optical constants (n c , k c ) of the SiO 2  layer (film thickness: 80 nm), the optical constants (n, k) of the cersemi layer with a FeS 2  mixing ratio of 30% (film thickness: 75 nm), the optical constants (n, k) of the cersemi layer with a FeS 2  mixing ratio of 100% (film thickness: 25 nm) and the optical constants (n, k) of the Mo (molybdenum) layer (film thickness: 100 nm). The results for the absorption properties of the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 400° C. are shown in  FIG. 13 . 
         [0090]    Next, the values of the film efficiency η for the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 580° C. and the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 400° C., were determined by formula (3) below. The film efficiency η is an index representing the function of sunlight to heat conversion. 
         [0000]    
       
         
           
             
               
                 
                   η 
                   = 
                   
                     α 
                     - 
                     
                       
                         
                           σ 
                            
                           
                               
                           
                            
                           
                             T 
                             4 
                           
                         
                         CI 
                       
                        
                       ɛ 
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   
                     ( 
                     3 
                     ) 
                   
                 
               
             
           
         
       
       
         
           
             α: Solar absorbance 
             ∈: Thermal radiation rate 
             σ: Stefan-Boltzmann constant 
             T: Absolute temperature 
             C: Amount of solar collection 
             I: Total solar energy, calculated from AM1.5 (solar intensity data based on ASTM) 
           
         
       
     
         [0097]    The results for the film efficiency η of the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 580° C. are shown in  FIG. 14 . The results for the film efficiency η of the FeS 2 —SiO 2  cersemi laminate that operates at a heat collecting temperature of 400° C. are shown in  FIG. 15 . 
       Comparative Example 3 
       [0098]    The absorption property of a Mo—SiO 2  cermet laminate and the film efficiency were evaluated. The structure of a Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 580° C. was a 4-layer structure comprising a SiO 2  layer (film thickness: 80 nm), a cermet layer film with a Mo mixing ratio of 40% (film thickness: 40 nm), a cermet layer with a Mo mixing ratio of 50% (film thickness: 25 nm) and a Mo (molybdenum) layer (film thickness: 100 nm), from the light incident side, as shown in  FIG. 16 . The structure of a Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 400° C. was a 4-layer structure comprising a SiO 2  layer (film thickness: 90 nm), a cermet layer film with a Mo mixing ratio of 30% (film thickness: 50 nm), a cermet layer with a Mo mixing ratio of 50% (film thickness: 50 nm) and a Mo (molybdenum) layer (film thickness: 100 nm), from the light incident side, as shown in  FIG. 17 . The film structures (FeS 2  mixing ratio and film thickness) for the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 580° C. and the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 400° C., were set so as to exhibit the maximum film efficiency, as described below. 
         [0099]    The optical constants (n, k) of the Mo—SiO 2  cermet layers of the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 580° C. and the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 400° C. were determined by the same calculation method as used for the optical constants (n, k) of Comparative Example 2. For the optical constants (n, k) of Mo, refer to “Handbook of Optical Constants of Solids”, Edward D. Palik, Academic Press, Boston, 1985″. Experimental data were used for the optical constants (n c , k c ) of SiO 2 . 
         [0100]    The absorbance of the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 580° C. was calculated using multilayer film approximation, based on the optical constants (n c , k c ) of a SiO 2  layer (film thickness: 80 nm), the optical constants (n, k) of a cermet layer with a Mo mixing ratio of 40% (film thickness: 40 nm), the optical constants (n, k) of a cermet layer with a Mo mixing ratio of 50% (film thickness: 25 nm) and the optical constants (n, k) of a Mo (molybdenum) layer (film thickness: 100 nm). The results for the absorption properties of the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 580° C. are shown in  FIG. 12 . 
         [0101]    Similarly, the absorbance of the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 400° C. was calculated using multilayer film approximation, based on the optical constants (n c , k c ) of a SiO 2  layer (film thickness: 90 nm), the optical constants (n, k) of a cermet layer with a Mo mixing ratio of 30% (film thickness: 50 nm), the optical constants (n, k) of a cermet layer with a Mo mixing ratio of 50% (film thickness: 50 nm) and the optical constants (n, k) of a Mo (molybdenum) layer (film thickness: 100 nm). The results for the absorption properties of the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 400° C. are shown in  FIG. 13 . 
         [0102]    Next, the values of the film efficiency η for the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 580° C. and the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 400° C., were determined by formula (3) below. 
         [0000]    
       
         
           
             
               
                 
                   η 
                   = 
                   
                     α 
                     - 
                     
                       
                         
                           σ 
                            
                           
                               
                           
                            
                           
                             T 
                             4 
                           
                         
                         CI 
                       
                        
                       ɛ 
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   
                     ( 
                     3 
                     ) 
                   
                 
               
             
           
         
       
       
         
           
             α: Solar absorbance 
             ∈: Thermal radiation rate 
             σ: Stefan-Boltzmann constant 
             T: Absolute temperature 
             C: Amount of solar collection 
             I: Total solar energy, calculated from AM1.5 (solar intensity data based on ASTM) 
           
         
       
     
         [0109]    The results for the film efficiency η of the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 580° C. are shown in  FIG. 14 . The results for the film efficiency η of the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 400° C. are shown in  FIG. 15 . 
       &lt;Evaluation Results&gt; 
       [0110]    Referring to  FIG. 12  and  FIG. 13 , the results for the absorption properties of Mo—SiO 2  cermet laminates, that operate at a heat collecting temperature of 580° C. and that operate at a heat collecting temperature of 400° C., indicate that the slope of the absorbance for light in a wavelength range of 2480 to 1000 nm is gentle, while the results for the absorption properties of the FeS 2 —SiO 2  cersemi laminate indicate that the slope of the absorbance for light in a wavelength range of 2480 to 1000 nm is abrupt, thus demonstrating that a FeS 2 —SiO 2  cersemi laminate efficiently absorbs sunlight while minimizing heat release due to heat radiation from the heating medium at 200° C. to 600° C. Referring to  FIG. 14 , the film efficiency η of the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 580° C. was 82.6%, while the film efficiency η of the FeS 2 —SiO 2  cersemi laminate was 84.5%, and therefore the film efficiency η of the FeS 2 —SiO 2  cersemi laminate was superior to the film efficiency η of the Mo—SiO 2  cermet laminate. Referring to  FIG. 15 , the film efficiency η of the Mo—SiO 2  cermet laminate that operates at a heat collecting temperature of 400° C. was 90.5%, while the film efficiency η of the FeS 2 —SiO 2  cersemi laminate was 90.3%, and therefore the film efficiency η of the FeS 2 —SiO 2  cersemi laminate and the film efficiency η of the Mo—SiO 2  cermet laminate were on the same level. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  Heat conversion laminate 
           11  Transparent dielectric layer 
           12  Layer comprising heat conversion member (photoabsorbing layer) 
           13  Metal layer 
           121  Semiconductor 
           122  Transparent dielectric material