Patent Publication Number: US-8119996-B2

Title: Quantum efficiency measurement apparatus and quantum efficiency measurement method

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus and a method for measuring the quantum efficiency of an object to be measured. 
     BACKGROUND ART 
     In recent years, development of fluorescent lamp and display has advanced swiftly. With such development, the quantum efficiency has become of interest as an index for more accurately evaluating the performance of a phosphor used for the lamp and display. In general, the quantum efficiency refers to the ratio of the number of photons of fluorescence to the number of photons absorbed by an object to be measured (typically phosphor). 
     As a typical method for measuring such a quantum efficiency, “Absolute Fluorescent Quantum. Efficiency of NBS Phosphor Standard Samples” by Ohkubo and Shigeta discloses a measurement optical system for the phosphor quantum efficiency. Alternatively to the configuration as disclosed, Japanese Patent Laying-Open Nos. 09-292281 (Patent Document 1), 10-142152 (Patent Document 2) and 10-293063 (Patent Document 3) for example propose configurations and methods for measuring the quantum efficiency. 
     The quantum efficiency measurement apparatuses according to the above-referenced conventional technologies all use an integrating sphere for trapping fluorescence emitted from an object to be measured (phosphor). Generally, the fluorescence emitted from a phosphor is weak. It is therefore preferable to use an integrating sphere having a smaller diameter in order to enhance the measurement accuracy. 
     In such an integrating sphere, a baffle is provided for hindering fluorescence emitted from a phosphor and/or an excitation light reflected from the surface of the phosphor from directly entering a detector.
     Patent Document 1: Japanese Patent Laying-Open No. 09-292281   Patent Document 2: Japanese Patent Laying-Open No. 10-142152   Patent Document 3: Japanese Patent Laying-Open No. 10-293063   Non-Patent Document 1: Ohkubo and Shigeta, “Absolute Fluorescent Quantum Efficiency of NBS Phosphor Standard Samples,” Journal of the Illuminating Engineering Institute of Japan, The Illuminating Engineering Institute of Japan, 1999, Vol. 83, No. 2, pp. 87-93   

     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the case where an integrating sphere with a smaller diameter is used, however, the influence of light absorption by the baffle is relatively larger, resulting in a possibility that the measurement accuracy is negatively impacted. 
     The present invention has been made to solve the problem above, and an object of the invention is to provide a quantum efficiency measurement apparatus and a quantum efficiency measurement method with which the quantum efficiency can be measured with a higher accuracy. 
     Means for Solving the Problems 
     A quantum efficiency measurement apparatus according to an aspect of the present invention includes a hemispheric portion with an inner surface having a light diffuse reflection layer, and a plane mirror disposed to pass through a substantial center of curvature of the hemispheric portion and close an opening of the hemispheric portion. The plane mirror includes a first window provided at a position of the substantial center of curvature of the hemispheric portion for attaching an object to be measured to the first window, and a second window provided at a position apart by a predetermined distance from the first window. The quantum efficiency measurement apparatus further includes: a spectrometer for measuring a spectrum in the hemispheric portion through the second window; a light source for applying an excitation light, through a third window provided in the hemispheric portion, at a predetermined angle with respect to a normal to the plane mirror toward the first window; and a processor for calculating a quantum efficiency of the object to be measured, based on a first spectrum measured by the spectrometer in a case where the object to be measured is disposed at the first window, and a second spectrum measured by the spectrometer in a case where a standard object having a known reflectance characteristic is disposed at the first window instead of the object to be measured. 
     Preferably, the first window is configured such that the object to be measured can be attached in a state where an exposed surface of the object to be measured substantially coincides with a surface of the plane mirror, the surface of the plane mirror being located on an inner side of the hemispheric portion. 
     Preferably, the second window includes a light transmission diffusion member disposed between an inside of the hemispheric portion and the spectrometer. 
     A quantum efficiency measurement apparatus according to another aspect of the present invention includes a hemispheric portion with an inner surface having a light diffuse reflection layer, and a plane mirror disposed to pass through a substantial center of curvature of the hemispheric portion and close an opening of the hemispheric portion. The plane mirror includes a first window provided near the substantial center of curvature of the hemispheric portion and a second window provided at a position apart by a predetermined distance from the first window. The quantum efficiency measurement apparatus further includes a light source for applying an excitation light through the first window toward an object to be measured disposed in a state where at least a part of the object to be measured is exposed in the hemispheric portion, and a spectrometer for measuring a spectrum in the hemispheric portion through the second window. The second window restrains light from the object to be measured from directly entering the spectrometer. The quantum efficiency measurement apparatus further includes a processor for calculating a quantum efficiency of the object to be measured, based on a first spectrum measured by the spectrometer in a case where the object to be measured is disposed in the hemispheric portion, and a second spectrum measured by the spectrometer in a case where a standard object having one of a known reflectance characteristic and a known transmittance characteristic is disposed in the hemispheric portion instead of the object to be measured. 
     Preferably, the second window is an opening having a larger diameter on an outer side of the hemispheric portion than a diameter of the opening on an inner side of the hemispheric portion. 
     Preferably, the hemispheric portion includes a third window provided at a position where the hemispheric portion intersects with a normal that is normal to the plane mirror and passes through the substantial center of curvature of the hemispheric portion, for attaching the object to be measured and the standard object to the third window, and the light source is disposed to apply the excitation light at a predetermined angle with respect to the normal to the plane mirror toward the third window. 
     Preferably, the object to be measured is a liquid enclosed in a transparent container and is disposed on an optical axis of the light source. 
     More preferably, the object to be measured is entirely contained in the hemispheric portion. 
     Preferably, the hemispheric portion includes a third window provided at a position where the hemispheric portion intersects with a normal that is normal to the plane mirror and passes through the substantial center of curvature of the hemispheric portion, for attaching the object to be measured and the standard object to the third window. The first window is provided at a position of the substantial center of curvature of the hemispheric portion on the plane mirror, and the object to be measured is a liquid enclosed in a tubular container, a surface of the tubular container that is attached to the third window is formed of a transparent material, and a remaining part of the tubular container is formed of a light-reflective member. 
     A quantum efficiency measurement method according to still another aspect of the present invention includes the steps of: preparing an apparatus including a hemispheric portion with an inner surface having a light diffuse reflection layer, and a plane mirror disposed to pass through a substantial center of curvature of the hemispheric portion and close an opening of the hemispheric portion; attaching an object to be measured to a first window provided at a position of the plane mirror, the position including the substantial center of curvature of the hemispheric portion; applying an excitation light, through a third window provided in the hemispheric portion, at a predetermined angle with respect to a normal to the plane mirror toward the object to be measured; measuring, as a first spectrum, a spectrum in the hemispheric portion in a case where the object to be measured is attached, through a second window provided at a position of the plane mirror, the position being apart by a predetermined distance from the first window; attaching a standard object having a known reflectance characteristic to the first window; applying the excitation light through the third window, at the predetermined angle with respect to the normal to the plane mirror toward the standard object; measuring, as a second spectrum, a spectrum in the hemispheric portion through the second window in a case where the standard object is attached; and calculating a quantum efficiency of the object to be measured, based on the first spectrum and the second spectrum. 
     Effects of the Invention 
     In accordance with the present invention, the quantum efficiency can be measured with a higher accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration diagram of a quantum efficiency measurement apparatus relevant to a first embodiment of the present invention. 
         FIG. 2  is an external view of a quantum efficiency measurement apparatus according to the first embodiment of the present invention. 
         FIG. 3  is a cross section showing main components of the quantum efficiency measurement apparatus according to the first embodiment of the present invention. 
         FIG. 4  is a diagram illustrating a principle of measurement by the quantum efficiency measurement apparatus according to the first embodiment of the present invention. 
         FIG. 5  is a diagram showing a control configuration of a processor of the quantum efficiency measurement apparatus according to the first embodiment of the present invention. 
         FIG. 6  is a flowchart showing a process procedure for measurement of the quantum efficiency using the quantum efficiency measurement apparatus according to the first embodiment of the present invention. 
         FIG. 7  is a plan view showing a positional relation between a spectrometer and a light source of a quantum efficiency measurement apparatus according to a first modification of the first embodiment of the present invention. 
         FIG. 8  is a cross section showing main components of a quantum efficiency measurement apparatus according to a second modification of the first embodiment of the present invention. 
         FIG. 9  is a cross section showing main components of a quantum efficiency measurement apparatus according to a second embodiment of the present invention. 
         FIG. 10  is a schematic configuration diagram of a quantum efficiency measurement apparatus relevant to a third embodiment of the present invention. 
         FIG. 11  is a cross section showing main components of a quantum efficiency measurement apparatus according to the third embodiment of the present invention. 
         FIG. 12  is a diagram showing a control configuration of a processor of the quantum efficiency measurement apparatus according to the third embodiment of the present invention. 
         FIG. 13  is a cross section showing main components of a quantum efficiency measurement apparatus according to a first modification of the third embodiment of the present invention. 
         FIG. 14  is a cross section showing main components of a quantum efficiency measurement apparatus according to a second modification of the third embodiment of the present invention. 
         FIG. 15  is a cross section showing main components of a quantum efficiency measurement apparatus according to a fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE REFERENCE SIGNS 
       1 ,  1 A hemispheric portion,  1   a  light diffuse reflection layer,  2 ,  9  sample window,  3 ,  13  observation window,  4 ,  10 ,  12  light source window,  5 ,  5 A,  5 B,  5 C plane mirror,  5   a  reflection surface,  6  spectrometer,  6   a  attachment portion,  6   b  fiber end,  6   c  reflection portion,  6   d  optical fiber,  6   e  detector,  7  light source,  7   a  lamp,  7   b  collective optical system,  14  light transmission diffusion member,  15 ,  15 A seal member,  16 ,  16 A,  16 B transparent cell,  100  integrating hemisphere,  102  base portion,  104  rotational shaft,  200 ,  200 A processor,  202  switch unit,  204 ,  206  buffer,  208 ,  210  selection unit,  212 ,  222  multiplication unit,  214 ,  224  integration unit,  216 ,  226  division unit,  218  initial setting holding unit,  220  addition and subtraction unit,  300 ,  350  quantum efficiency measurement apparatus,  302 ,  352  integrating sphere,  304 ,  358  baffle,  306 ,  360  light receiving unit,  308 ,  362  optical fiber,  310 ,  364  spectrometer apparatus,  312  sample window,  314 ,  366  light source window,  316 ,  368  observation window,  320 ,  370  excitation light,  354  support,  356  transparent container, Ax 1 , Ax 2 , Ax 3  optical axis, L 1  excitation light, OBJ, OBJ 1 , OBJ 2  sample, REF, REF 1 , REF 2  standard object, SYS 1 , SYS 1 A, SYS 2 , SYS 3 , SYS 3 A, SYS 3 B quantum efficiency measurement apparatus 
     BEST MODES FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be described in detail with reference to the drawings. Like or corresponding components in the drawings are denoted by like reference characters, and a description thereof will not be repeated. 
     First Embodiment 
     &lt;Related Art&gt; 
     For the sake of facilitating understanding of a quantum efficiency measurement apparatus according to the present embodiment, a quantum efficiency measurement apparatus relevant to the present embodiment will be described first with reference to  FIG. 1 . 
     Quantum efficiency measurement apparatus  300  relevant to the present embodiment shown in  FIG. 1  measures the quantum efficiency of an object to be measured such as phosphor (also referred to as “sample OBJ” hereinafter). Specifically, quantum efficiency measurement apparatus  300  includes an integrating sphere  302 , a baffle  304 , a light receiving unit  306 , an optical fiber  308 , and a spectrometry apparatus  310 . In quantum efficiency measurement apparatus  300 , sample OBJ is attached to a sample window  312  provided in integrating sphere  302 , and an excitation light  320 , which is emitted through a light source window  314  from a light source (not shown) provided outside integrating sphere  302 , is applied to sample OBJ. As excitation light  320 , monochromatic ultraviolet radiation in 200 to 400 nm is used in the case of a low-pressure mercury fluorescent lamp, and monochromatic ultraviolet or visible radiation in 300 to 600 nm or the like is used in the field of LED (Light Emitting Diode). Sample OBJ receives excitation light  320  to emit fluorescence. The fluorescence radiated from sample OBJ is multiple-reflected from the inner surface of integrating sphere  302  and accordingly integrated (made uniform). A part of the applied excitation light  320  is reflected from sample OBJ, and this reflected excitation light  320  is also multiple-reflected in integrating sphere  302 . 
     Light receiving unit  306  extracts, through an observation window  316  provided in integrating sphere  302 , a part of the light in integrating sphere  302  to direct the extracted light to spectrometry apparatus  310  via optical fiber  308 . The portion facing observation window  316  of light receiving unit  306  is generally provided with a light transmission diffusion member. In general, the view angle characteristic at observation window  316  is thus made closer to ideal diffusion characteristic, and the illuminance (light spectrum) of the light from the whole inner wall surface of integrating sphere  302  is directed to optical fiber  308 . 
     Spectrometry apparatus  310  measures the spectrum of the light extracted by light receiving unit  306 . Namely, spectrometry apparatus  310  measures the illuminance (light spectrum) on the inner wall surface of integrating sphere  302 . 
     Measurement similar to the above-described one is also performed on a standard object REF having a known reflectance characteristic that is attached instead of sample OBJ. Based on the spectrum measured for sample OBJ as attached and the spectrum measured for standard object REF as attached, the quantum efficiency of sample OBJ is calculated. 
     As described above, integrating sphere  302  can be used to accurately measure the quantum efficiency even if sample OBJ does not have the ideal diffuse reflection characteristic such as sample OBJ whose surface has specularity. Further, since integrating sphere  302  itself functions as a light shielding container, an effect of restraining the influence of the external light is also obtained. 
     Regarding quantum efficiency measurement apparatus  300 , however, a measurement error occurs if the fluorescence generated from sample OBJ and a part of excitation light  320  reflected from sample OBJ directly enter observation window  316 . Therefore, baffle  304  is provided between sample window  312  and observation window  316 . 
     The fluorescence from a phosphor is generally weak. Therefore, in order to enhance the measurement accuracy, it is preferable to use integrating sphere  302  having a smaller diameter. In the case where integrating sphere  302  with a smaller diameter is used, however, the influence of light absorption by baffle  304  is relatively larger, resulting in a possibility that the measurement accuracy is negatively impacted. In other words, a problem is that baffle  304  could be a factor of the measurement error, since baffle  304  hinders interreflection on the inner wall surface of integrating sphere  302 , and light absorption by baffle  304  decreases the integration efficiency. 
     &lt;Apparatus Configuration&gt; 
     Referring next to  FIGS. 2 and 3 , a quantum efficiency measurement apparatus SYS 1  according to the present embodiment will be described. 
     Quantum efficiency measurement apparatus SYS 1  shown in  FIG. 2  includes an integrating hemisphere  100  and a processor  200 . As shown in  FIG. 3 , integrating hemisphere  100  is formed of a hemispheric portion  1  and a disk-shaped plane mirror  5  disposed to close the opening of hemispheric portion  1 . Hemispheric portion  1  is rotatably coupled to a base portion  102  via a rotational shaft  104 . Quantum efficiency measurement apparatus SYS 1  further includes a spectrometer  6  for measuring the illuminance (light spectrum) on the inner wall surface of hemispheric portion  1 , and a light source  7  generating an excitation light L 1 . 
     In quantum efficiency measurement apparatus SYS 1  according to the present embodiment, a sample OBJ 1  that is an object whose quantum efficiency is to be measured and a standard object REF 1  having a known reflectance characteristic are each attached to a sample window  2  provided in plane mirror  5 , as described hereinlater. The quantum efficiency of sample OBJ 1  is then measured based on respective spectrums measured by spectrometer  6  in respective cases where sample OBJ 1  is attached and standard object REF 1  is attached. 
     Quantum efficiency measurement apparatus SYS 1  according to the present embodiment is typically suitable for measurement of the quantum efficiency of a solid sample such as a phosphor for a florescent lamp and a phosphor for an LED. Standard object REF 1  is typically an object having its surface to which barium sulfate is applied. Each of sample OBJ 1  and standard object REF 1  is shaped to nearly conform to the diameter of sample window  2 . This is for the reason that it is preferable to allow integrating hemisphere  100  to function as a light shielding container for the purpose of avoiding influence of the external light on the measurement accuracy. As long as the diameter of sample OBJ 1  and standard object REF 1  each is nearly identical to the diameter of sample window  2 , respective shapes of other portions of the sample and the standard object are not particularly limited to specific ones. 
     As shown in  FIG. 3 , the inner surface (inner wall) of hemispheric portion  1  is provided with a light diffuse reflection layer  1   a . Light diffuse reflection layer  1   a  is typically formed by applying or spraying a light diffusion material such as barium sulfate or PTFE (polytetrafluoroethylene). 
     Hemispheric portion  1  is provided with a light source window  4  for guiding excitation light L 1  radiated from light source  7  provided outside hemispheric portion  1  to the inside of hemispheric portion  1 . Excitation light L 1  is applied toward sample OBJ 1  or standard object REF 1  along an optical axis Ax 1  with an angle θ with respect to a normal N 1  to plane mirror  5 . This is for the purpose of preventing a specular reflection component from being generated on sample OBJ 1  or standard object REF 1  from excitation light L 1  from light source  7 . Namely, this is for the purpose of guiding a part of excitation light L 1  applied from light source  7  and then reflected from sample OBJ 1  or standard object REF 1 , in a direction different from the direction of optical axis Ax 1  that is the incident light path. Preferably, angle θ is approximately 5°. 
     Plane mirror  5  is disposed to pass through a substantial center of curvature O of hemispheric portion  1  and close the opening of hemispheric portion  1 . Here, center of curvature O of hemispheric portion  1  typically refers to the geometric center of the inner surface side of hemispheric portion  1 . A reflection surface (mirror surface)  5   a  is formed at least on the side, located on the inner surface side of hemispheric portion  1 , of plane mirror  5 . 
     Plane mirror  5  is provided with sample window  2  and observation window  3  that are each able to communicate with the inner surface side and the outer surface side of hemispheric portion  1 . Sample window  2  is an opening for attaching sample OBJ 1  or standard object REF 1  to the sample window, and provided at a position of substantial center of curvature O of hemispheric portion  1 . In other words, sample window  2  is formed in a region including substantial center of curvature O of hemispheric portion  1 . Observation window  3  is an opening for observing the illuminance on the inner surface of hemispheric portion  1 , and provided at a position separated from sample window  2  toward the outer circumference side by a predetermined distance. Light is directed to spectrometer  6  through observation window  3 . 
     Light source  7  includes a lamp  7   a , a collective optical system  7   b  and a wavelength control optical system  7   c . A xenon discharge lamp (Xe lamp) or the like is typically used as lamp  7   a . Collective optical system  7   b  directs the light generated from lamp  7   a  in such a manner as to concentrate the light on sample OBJ 1  or standard object REF 1 . In other words, collective optical system  7   b  narrows the optical path of excitation light L 1  so that excitation light L 1  entirely falls within the sample OBJ 1  or standard object REF 1 . Wavelength control optical system  7   c  controls the wavelength component of excitation light L 1 . Wavelength control optical system  7   c  is typically disposed between lamp  7   a  and collective optical system  7   b , and an optical interference filter (wavelength band-pass filter) or spectrometer is used as wavelength control optical system  7   c.    
     Spectrometer  6  includes an attachment portion  6   a , a fiber end  6   b , a reflection portion  6   c , an optical fiber  6   d , and a detector  6   e . Attachment portion  6   a  is disposed on plane mirror  5  in such a manner as to cover observation window  3 . Optical fiber  6   d  and fiber end  6   b  connected to optical fiber  6   d  are inserted into attachment portion  6   a . Reflection portion  6   c  is provided on a virtual line extended downward as seen on the drawing along a normal to observation window  3 . Reflection portion  6   c  changes the direction of propagation of the light entering through observation window  3 , by approximately 90°, and then directs the light to fiber end  6   b.    
     Detector  6   e  detects the spectrum of the light introduced by optical fiber  6   d . Detector  6   e  is typically configured to include a diffraction grating and a line sensor associated with the direction of diffraction of the diffraction grating, and outputs the intensity of the input light for each wavelength. In the case where sample OBJ 1  is a phosphor, the measurable range of detector  6   e  is designed to cover both of the wavelength range of excitation light L 1  applied from light source  7  and the wavelength range of the fluorescence generated from sample OBJ 1  receiving excitation light L 1 . 
     &lt;Integration Function&gt; 
     Next, the integration function of quantum efficiency measurement apparatus SYS 1  according to the present embodiment will be described. As shown in  FIG. 3 , excitation light L 1  applied from light source  7  is incident on sample OBJ 1  attached to sample window  2 . Then, excitation light L 1  is absorbed in sample OBJ 1  at a ratio according to the material and shape, and a part of the energy causes fluorescence to be generated. Further, excitation light L 1  that has not been absorbed by sample OBJ 1  is reflected from sample OBJ 1 . The light including the fluorescence radiated from sample OBJ 1  and excitation light L 1  reflected from sample OBJ 1  chiefly propagates toward the inner surface of hemispheric portion  1 . 
     Plane mirror  5  reflects the light from sample OBJ 1  that is incident on the mirror after being reflected from hemispheric portion  1 , and generates a virtual image of the inner surface of hemispheric portion  1 . Since plane mirror  5  is disposed to pass through the center of curvature of hemispheric portion  1  as described above, the space formed between plane mirror  5  and hemispheric portion  1  is a hemisphere having a constant curvature. Therefore, from the inner surface of hemispheric portion  1  and the virtual image generated by plane mirror  5 , an illuminance distribution can be obtained that is identical to the one obtained in the case where a substantially spherical integrating sphere is used. In other words, this can be considered as if excitation light L 1  is applied to two samples OBJ 1  arranged symmetrically with each other in a spherical integrating sphere. 
     The fluorescence generated from sample OBJ 1  and excitation light L 1  reflected from sample OBJ 1  are repeatedly reflected in the space surrounded by hemispheric portion  1  and plane mirror  5 , and accordingly the illuminance on the inner surface of hemispheric portion  1  is made uniform. The uniform illuminance (spectrum) can be measured to measure the quantum efficiency of sample OBJ 1 . 
     As heretofore described, regarding quantum efficiency measurement apparatus SYS 1  according to the present embodiment, the state where the space formed between plane mirror  5  and hemispheric portion  1  and the virtual image of this space generated by plane mirror  5  are integrated may be substantially regarded as a sphere. Thus, “substantial center of curvature of the hemispheric portion” is a concept including the absolute center of curvature of hemispheric portion  1  and, in addition thereto, a position near the absolute center of curvature with which an illuminance distribution substantially identical to the one obtained using a spherical integrating sphere as described above can be obtained. 
     A similar integration effect can also be achieved when standard object REF 1  is attached to sample window  2  instead of sample OBJ 1 . Fluorescence is not generated from standard object REF 1 . Therefore, when excitation light L 1  applied from light source  7  is incident on standard object REF 1  attached to sample window  2 , the light is reflected according to the reflectance characteristic of standard object REF 1 . 
     &lt;Attachment of Sample and Standard Object&gt; 
     Sample OBJ 1  and standard object REF 1  are each attached to sample window  2  provided in plane mirror  5  as described above. At this time, it is preferable to attach sample OBJ 1  and standard object REF 1  in such a manner that the exposed surface of sample OBJ 1  or standard object REF 1  substantially coincides with the surface (reflection surface  5   a ), located on hemispheric portion  1  side, of plane mirror  5 . If the plane of the opening of observation window  3  does not substantially coincide with the exposed surface of sample OBJ 1  or standard object REF 1 , for example, if the exposed surface of sample OBJ 1  is lower than the plane of the opening of observation window  3 , the fluorescence generated from sample OBJ 1  receiving excitation light L 1  and excitation light L 1  reflected from sample OBJ 1  are absorbed by the side surface of observation window  3 , resulting in occurrence of a measurement error. On the contrary, if the exposed surface of sample OBJ 1  protrudes from the plane of the opening of observation window  3 , the protruded portion hinders interreflection of the fluorescence generated from sample OBJ 1  receiving excitation light L 1  and excitation light L 1  reflected from sample OBJ 1 , in the integrating space formed by light diffuse reflection layer  1   a  on the inner surface of hemispheric portion  1  and reflection surface  5   a  of plane mirror  5 . 
     In the configuration shown in  FIG. 3 , sample window  2  and observation window  3  are coplanar with plane mirror  5 . Therefore, as long as the exposed surfaces of sample OBJ 1  and standard object REF 1  are flat, the fluorescence and the reflected light from sample OBJ 1  and standard object REF 1  do not directly enter the observation field of observation window  3 . It is thus unnecessary to dispose baffle  304  as shown in  FIG. 1 . In this way, a light absorption error due to the baffle can be prevented, and the illuminance on the inner wall surface of hemispheric portion  1  can be further increased by means of the above-described “virtual image.” With these two functions, the quantum efficiency can be measured with a higher accuracy. 
     &lt;Principle of Measurement&gt; 
     Next with reference to  FIG. 4  (A) and  FIG. 4  (B), a principle of measurement by quantum efficiency measurement apparatus SYS 1  according to the present embodiment will be described. 
     When excitation light L 1  is applied to sample OBJ 1  that is typically a phosphor, a part of the excitation light (photons) is absorbed to be used for generating fluorescence, while the remaining part of excitation light L 1  is reflected from the surface of the sample. It is supposed here that excitation light L 1  has a wavelength range of λ 1L -λ 1H  and the fluorescence component generated from sample OBJ 1  has a wavelength range of λ 2L -λ 2H . Generally, excitation light L 1  is ultraviolet light and fluorescence is visible light. Therefore, the wavelength range λ 1L -λ 1H  and the wavelength range λ 2L -λ 2H  do not overlap each other. Thus, from the spectrum measured by spectrometer  6 , respective components corresponding to these wavelength ranges can be selectively extracted to separate them from each other. 
     As shown in  FIG. 4  (A), it is supposed that excitation light L 1  has a spectrum E 0  (λ). Here, it is supposed that a fluorescence component is generated from sample OBJ 1  as a result of application of excitation light L 1  to sample OBJ 1  has a spectrum P (λ) and a reflected light component reflected from sample OBJ 1  has a spectrum R (λ). In other words, spectrum P (λ) of the fluorescence component is equivalent to the component of the wavelength range (λ 2L -λ 2H ) corresponding to the fluorescence in spectrum E (1)  (λ) which is measured by spectrometer  6  when sample OBJ 1  is attached, and spectrum R (λ) of the reflected light component is equivalent to the component of the wavelength range (λ 1L -λ 1H ) corresponding to excitation light L 1  in spectrum E (1)  (λ) which is measured by spectrometer  6 . 
     Further, as shown in  FIG. 4  (B), it is supposed that standard object REF 1  has a reflectance characteristic ρ S  (λ). Then, the spectrum measured when excitation light L 1  having spectrum E 0  (λ) is applied to standard object REF 1  is represented as E (2)  (λ)=ρ S  (λ)·E 0  (λ). From this expression, spectrum E 0  (λ) of excitation light L 1  can be represented by expression (1).
 
 E   0 (λ)= E   (2) (λ)/ρ S (λ)  (1)
 
     Further, as shown in  FIG. 4  (A), the remaining component (photons) obtained by subtracting spectrum R (λ) of the reflected light component reflected from sample OBJ 1 , from spectrum E 0  (λ) of excitation light L 1 , can be regarded as being absorbed by sample OBJ 1 . 
     Therefore, in order to convert the spectrum (radiation power) into the number of photons, the spectrum is divided by hc/λ (where h: Planck&#39;s constant, c: light velocity). Then, the number of photons Ab absorbed by sample OBJ 1  can be represented by expression (2) where k=1/hc. 
     
       
         
           
             
               
                 
                   Ab 
                   = 
                   
                     k 
                     · 
                     
                       
                         ∫ 
                         
                           λ 
                           
                             1 
                             ⁢ 
                             L 
                           
                         
                         
                           λ1 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           H 
                         
                       
                       ⁢ 
                       
                         
                           λ 
                           · 
                           
                             { 
                             
                               
                                 
                                   
                                     E 
                                     
                                       ( 
                                       2 
                                       ) 
                                     
                                   
                                   ⁡ 
                                   
                                     ( 
                                     λ 
                                     ) 
                                   
                                 
                                 
                                   
                                     ρ 
                                     S 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     λ 
                                     ) 
                                   
                                 
                               
                               - 
                               
                                 
                                   E 
                                   
                                     ( 
                                     1 
                                     ) 
                                   
                                 
                                 ⁡ 
                                 
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                                   λ 
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                             } 
                           
                         
                         ⁢ 
                         δλ 
                       
                     
                   
                 
               
               
                 
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                   ) 
                 
               
             
           
         
       
     
     The number of photons Pph of the fluorescence can be represented by expression (3).
 
 Pph=k·∫   λ     2L     λ     2H     λ·E   (1) (λ)δλ  (3)
 
     Accordingly, the internal quantum efficiency QEin of sample OBJ 1  can be represented by expression (4).
 
QEin= Pph/Ab   (4)
 
     &lt;Control Configuration&gt; 
     Next with reference to  FIG. 5 , a control configuration of processor  200  of quantum efficiency measurement apparatus SYS 1  according to the present embodiment will be described. 
     As shown in  FIG. 5 , the control configuration of processor  200  includes a switch unit  202 , buffers  204 ,  206 , selection units (SEL)  208 ,  210 , division units  216 ,  226 , an initial setting holding unit  218 , an addition and subtraction unit  220 , multiplication units  212 ,  222 , and integration units  214 ,  224 . 
     Switch unit  202  switches the storage where an output (detected spectrum) of spectrometer  6  is to be stored, to one of buffers  204  and  206 , following a signal that is input according to the state of attachment to sample window  2 . Specifically, when sample OBJ 1  is attached to sample window  2 , switch unit  202  stores spectrum E (1)  (λ) detected by spectrometer  6  in buffer  204  and, when standard object REF 1  is attached to sample window  2 , switch unit  202  stores spectrum E (2)  (λ) detected by spectrometer  6  in buffer  206 . 
     Buffers  204  and  206  are memories for storing the spectrums detected by spectrometer  6 , and have regions according to the wavelength resolution of spectrometer  6 . Specifically, in the case where spectrometer  6  outputs a spectrum composed of n wavelengths in total, namely wavelengths λ 1 , λ 2 , . . . , λn, the buffer has respective areas for storing respective intensities for n wavelengths. 
     Selection units  208  and  210  selectively read wavelength components of the spectrums stored in buffers  204  and  206 , respectively. From the wavelength components of read spectrum E (1)  (λ), selection unit  208  outputs a component included in the wavelength range λ 1L -λ 1H  of excitation light L 1  to multiplication unit  222 , and outputs a component included in the wavelength range λ 2L -λ 2H  of the fluorescence component generated from sample OBJ 1  to multiplication unit  212 . Selection unit  208  further outputs the value of wavelength λ of the read wavelength component to multiplication units  212  and  222 . 
     Multiplication unit  212  and integration unit  214  perform a computation corresponding to expression (3) as described above to calculate the number of photons Pph of the fluorescence. Specifically, multiplication unit  212  multiplies the wavelength component of spectrum E (1)  (λ) read by selection unit  208  by the wavelength λ itself. Multiplication unit  212  then outputs the value of the product to integration unit  214 . Integration unit  214  calculates the sum of values that are output from multiplication unit  212 . As described above, wavelength components included in spectrum E (1)  (λ) that correspond to the wavelength range λ 2L -λ 2H  of the fluorescence component are output to multiplication unit  212 . Therefore, a computation corresponding to above-described expression (3) is substantially performed for each wavelength. 
     Division unit  216 , addition and subtraction unit  220 , multiplication unit  222 , and integration unit  224  perform a computation corresponding to above-described expression (2) to calculate the number of photons Ab absorbed by sample OBJ 1 . Specifically, division unit  216  divides the wavelength component of spectrum E (2)  (λ) read by selection unit  210  by a component of corresponding wavelength in reflectance characteristic ρ S  (λ) of standard object REF 1  stored in initial setting holding unit  218 . Division unit  216  outputs the quotient (E (2)  (λ)/ρ S  (λ)) to addition and subtraction unit  220 . Addition and subtraction unit  220  subtracts the quotient calculated by division unit  216  from the wavelength component of spectrum E (2)  (λ) read by selection unit  208 . Addition and subtraction unit  220  then outputs the calculated value to multiplication unit  222 . Multiplication unit  222  multiplies the value calculated by addition and subtraction unit  220  by the corresponding wavelength λ. Multiplication unit  222  then outputs the value of the product to integration unit  224 . Integration unit  224  calculates the sum of values that are output from multiplication unit  222 . As described above, wavelength components included in spectrum E (1)  (λ) that correspond to the wavelength range λ 1L -λ 1H  of excitation light L 1  are output to multiplication unit  222 , and thus a computation corresponding to above-described expression (2) is substantially performed for each wavelength. 
     Division unit  226  divides the number of photons Pph of the fluorescence that is calculated by integration unit  214  by the number of photons Ab absorbed by sample OBJ 1  that is calculated by integration unit  224 . Division unit  226  then outputs the quotient (Pph/Ab) as internal quantum efficiency QEin of sample OBJ 1 . 
     &lt;Process Procedure&gt; 
     Referring next to  FIG. 6 ,  FIG. 6  is a flowchart showing a process procedure for measurement of the quantum efficiency using quantum efficiency measurement apparatus SYS 1  according to the present embodiment. 
     A user prepares quantum efficiency measurement apparatus SYS 1  (step S 100 ). The user then attaches sample OBJ 1  to sample window  2  (step S 102 ), and causes light source  7  to start applying excitation light L 1  and causes spectrometer  6  to start taking a measurement (step S 104 ). At this time, the user may input, to processor  200 , the fact that sample OBJ 1  is attached to sample window  2 . Accordingly, processor  200  stores spectrum E (1)  (λ) measured by spectrometer  6  (step S 106 ). 
     Then, the user attaches standard object REF 1  to sample window  2  (step S 108 ), and causes light source  7  to start applying excitation light L 1  and causes spectrometer  6  to start taking a measurement (step S 110 ). At this time, the user may input, to processor  200 , the fact that standard object REF 1  is attached to sample window  2 . Accordingly, processor  200  stores spectrum E (2)  (λ) measured by spectrometer  6  (step S 112 ). 
     After spectrum E (1)  (λ) and spectrum E (2)  (λ) have been obtained, processor  200  calculates internal quantum efficiency QEin of sample OBJ 1  based on these spectrums (step S 114 ). More specifically, based on the wavelength components corresponding to the wavelength range λ 1L -λ 1H  of spectrum E (1)  (λ), the wavelength components of spectrum E (2)  (λ) and reflectance characteristic ρ S  (λ) of standard object REF 1 , processor  200  calculates the number of photons Ab absorbed by sample OBJ 1 . Further, based on the wavelength components corresponding to the wavelength range λ 2L -λ 2H  of spectrum E (1)  (λ), processor  200  calculates the number of photons Pph of the fluorescence. Processor  200  further calculates internal quantum efficiency QEin of sample OBJ 1  based on the number of photons Ab and the number of photons Pph. 
     Processor  200  further outputs the calculated internal quantum efficiency QEin of sample OBJ 1  (step S 116 ). Here, examples of the output of internal quantum efficiency QEin may include indication of internal quantum efficiency QEin on a monitor or the like, print output of internal quantum efficiency QEin and storage of internal quantum efficiency QEin on a recording medium, for example. 
     While the flowchart shown in  FIG. 6  illustrates an example of a measurement procedure where spectrum E (1)  (λ) for sample OBJ 1  is obtained first and subsequently spectrum E (2)  (λ) for standard object REF 1  is obtained, the procedure does not limited to the illustrated procedure as long as spectrum E (1)  (λ) and spectrum E (2)  (λ) can be obtained. For example, after spectrum E (2)  (λ) for standard object REF 1  is obtained, spectrum E (1)  (λ) for sample OBJ 1  may be obtained. In this case, spectrum E (2)  (λ) obtained for standard object REF 1  is used to successively obtain spectrum E (1)  (λ) for each of a plurality of samples OBJ 1  so that internal quantum efficiency QEin of a plurality of samples OBJ 1  can be efficiently calculated. In other words, after standard object REF 1  is attached to sample window  2  to obtain spectrum E (2)  (λ), a plurality of samples OBJ 1  may be attached one after another to sample window  2 . 
     Effects of the Present Embodiment 
     The present embodiment does not require a baffle to be provided in the integrating hemisphere for the purpose of preventing direct incidence of light from a sample and therefore, can reduce occurrence of a measurement error due to light absorption by the baffle. Further, the present embodiment uses a virtual image generated by the plane mirror so that a twofold light intensity can be obtained in principle as compared with the case where an integrating sphere of the same radius is used. The quantum efficiency can thus be measured with a higher accuracy. 
     Further, since the present embodiment can achieve a twofold light intensity in principle, it is unnecessary to excessively decrease the radius of the hemispheric portion for the purpose of enhancing the measurement accuracy. Accordingly, the opening area of the observation window can be made relatively small with respect to the inner surface area of the integrating hemisphere, so that occurrence of a measurement error due to the observation window can be reduced. 
     First Modification of the First Embodiment 
     While the above-described first embodiment does not particularly limit the positional relation between spectrometer  6  and light source  7 , it is preferable to arrange spectrometer  6  and light source  7  with the positional relation as shown in  FIG. 7 . 
     As shown in the plan view of  FIG. 7  where integrating hemisphere  100  is seen from hemispheric portion  1  side, a first modification of the first embodiment arranges attachment portion  6   a  of spectrometer  6  to extend in the direction of a normal LN 1  orthogonal to optical axis Ax 1  of excitation light L 1  applied from light source  7 . The arrangement of spectrometer  6  and light source  7  with this positional relation can prevent excitation light L 1  applied to a sample OBJ 1  from directly entering spectrometer  6 . 
     Second Modification of the First Embodiment 
     In quantum efficiency measurement apparatus SYS 1  according to the first embodiment as described above, preferably a light transmission diffusion member is disposed on the light propagation path of observation window  3 . In the following, a quantum efficiency measurement apparatus SYS 1 A according to a second modification of the present embodiment will be described with reference to  FIG. 8 . 
     Quantum efficiency measurement apparatus SYS 1 A shown in  FIG. 8  additionally includes a light transmission diffusion member  14  provided to observation window  3  as compared with quantum efficiency measurement apparatus SYS 1  according to the first embodiment shown in  FIG. 3 . Specifically, light transmission diffusion member  14  is disposed between the inside of hemispheric portion  1  and spectrometer  6 . Other components are similar to those shown in  FIG. 3 , and the detailed description thereof will not be repeated. 
     Light transmission diffusion member  14  diffuses the light in integrating hemisphere  100  and then guides the light to spectrometer  6 . Therefore, even if the observation field of observation window  3  is relatively small, the influence of unevenness of the reflectance or the like on light diffuse reflection layer  1   a  provided on the inner surface of hemispheric portion  1  can be reduced. In other words, if light transmission diffusion member  14  is not provided, only the illuminance on a part of the inner surface of hemispheric portion  1 , the part corresponding to the observation field of observation window  3 , is observed. Thus, if there is unevenness of the reflectance or the like on the part corresponding to the observation field, the result of the measurement is likely to be influenced by the unevenness. In contrast, in the case where light transmission diffusion member  14  is provided, the light present around observation window  3  is diffused and then directed to spectrometer  6 , so that the above-described problem can be avoided. 
     Second Embodiment 
     In connection with the above-described first embodiment, quantum efficiency measurement apparatus SYS 1  where a sample is attached to the sample window provided in the plane mirror is illustrated. In connection with a second embodiment, a configuration will be illustrated where a sample is attached to a sample window provided in the hemispheric portion. 
     The appearance of a quantum efficiency measurement apparatus SYS 2  according to the second embodiment of the present invention is similar to that in  FIG. 2  as described above, and the detailed description thereof will not be repeated. Referring to  FIG. 9 , an integrating hemisphere of quantum efficiency measurement apparatus SYS 2  further includes a hemispheric portion  1 A, a disk-shaped plane mirror  5 A disposed to close an opening of hemispheric portion  1 A, a spectrometer  6  for measuring the illuminance (light spectrum) on the inner wall surface of hemispheric portion  1 A, and a light source  7  generating excitation light L 1 . 
     Hemispheric portion  1 A is similar to hemispheric portion  1  shown in  FIG. 3  except that the former includes a sample window  9  for attaching thereto a sample OBJ 1  and a standard object REF 1 . Sample window  9  is provided at the position where a normal N 2  to plane mirror  5 A that passes through a substantial center of curvature O of hemispheric portion  1 A intersects with hemispheric portion  1 A. Namely, sample window  9  is provided at the position of the apex of the hemisphere surrounded by hemispheric portion  1 A and plane mirror  5 A. Regarding sample OBJ 1  and standard object REF 1  as well, the present embodiment is similar to the above-described first embodiment, and the detailed description thereof will not be repeated. 
     In plane mirror  5 A, a light source window  10  and an observation window  13  that are each able to communicate with the inner surface side and the outer surface side of hemispheric portion  1 A are provided. 
     Light source window  10  is provided in the vicinity of substantial center of curvature O of hemispheric portion  1 A. More specifically, light source window  10  is provided at the position where excitation light L 1  is applied toward sample window  9  at angle θ with respect to normal N 2  to plane mirror  5 . Namely, light source  7  applies excitation light L 1 , along an optical axis Ax 2  having angle θ with respect to normal N 2  to plane mirror  5 A, toward sample OBJ 1  or standard object REF 1  attached to sample window  9 . 
     Observation window  13  is an opening for observing the illuminance on the inner surface of hemispheric portion  1 A, and provided at a position separated from light source window  10  toward the outer circumference side by a predetermined distance. Through observation window  13 , light is directed to spectrometer  6 . Observation window  13  restrains fluorescence generated from sample OBJ 1  receiving excitation light L 1  as well as excitation light L 1  reflected from sample OBJ 1  from directly entering spectrometer  6 . More specifically, observation window  13  is a kind of aperture, namely an opening configured in such a manner that the diameter of the opening on the outer side of hemispheric portion  1 A is larger relative to the diameter of the opening on the inner side of hemispheric portion  1 A. Such an observation window  13  restraining the observation field can be provided to measure the quantum efficiency with a higher accuracy without providing baffle  304  as shown in  FIG. 1 . 
     Other features of plane mirror  5 A are similar to those of plane mirror  5  shown in  FIG. 3 , and the detailed description thereof will not be repeated. Further, regarding spectrometer  6  and light source  7  as well, the detailed description as given above will not be repeated. Spectrometer  6  and light source  7  are preferably arranged with the positional relation as shown in  FIG. 7  as described above. 
     Further, the control configuration of processor  200  of quantum efficiency measurement apparatus SYS 2  according to the present embodiment, and the flowchart showing a process procedure for measurement of the quantum efficiency using quantum efficiency measurement apparatus SYS 2  according to the present embodiment are similar to those of  FIGS. 5 and 6  respectively, and the detailed description thereof will not be repeated. 
     Effects of the Present Embodiment 
     The present embodiment employs the observation window where the observation field is restrained and therefore requires no baffle provided in the integrating hemisphere for preventing direct incidence of light from the sample. Thus, occurrence of a measurement error due to light absorption by the baffle can be reduced. Further, the present embodiment can achieve, by means of a virtual image generated by the plane mirror, a twofold light intensity in principle relative to the case where an integrating sphere with the same radius is used. In this way, even if the observation field of the observation window is restrained, a sufficient brightness can be achieved. 
     Accordingly, the quantum efficiency can be measured with a higher accuracy. 
     Third Embodiment 
     In connection with the first and second embodiments as described above, the configuration suitable for measurement of the quantum efficiency of a solid sample is mainly illustrated. In connection with a third embodiment, a configuration will be illustrated that is suitable for measurement of a liquid sample. 
     &lt;Related Art&gt; 
     For the sake of facilitating understanding of a quantum efficiency measurement apparatus according to the present embodiment, a quantum efficiency measurement apparatus relevant to the present embodiment will be described first with reference to  FIG. 10 . 
     Quantum efficiency measurement apparatus  350  shown in  FIG. 10  that is relevant to the present embodiment chiefly measures the quantum efficiency of a liquid sample OBJ. Specifically, quantum efficiency measurement apparatus  350  includes an integrating sphere  352 , a support  354 , a baffle  358 , a light receiving unit  360 , an optical fiber  362 , and a spectrometer apparatus  364 . In this quantum efficiency measurement apparatus  350 , a transparent container  356  enclosing a sample is hung by support  354  in integrating sphere  352 , and an excitation light  370  is applied to this sample OBJ through a light source window  366  from a light source (not shown) provided outside integrating sphere  352 . Sample OBJ receives excitation light  370  to emit fluorescence. The fluorescence radiated from sample OBJ is multiple-reflected from the inner surface of integrating sphere  352  to be integrated (made uniform). Light receiving unit  360  extracts, through an observation window  368  provided in integrating sphere  352 , a part of the light of integrating sphere  352  to direct the extracted light via optical fiber  362  to spectrometer apparatus  364 . 
     If the fluorescence generated from sample OBJ and excitation light  370  reflected from sample OBJ directly enter observation window  368 , a measurement error occurs. Therefore, baffle  358  is provided between transparent container  356  and observation window  368 . 
     Since support  354  and baffle  358  absorb light such as fluorescence as described above, support  354  and baffle  358  are internal structural components that are factors of a measurement error in quantum efficiency measurement apparatus  350 . 
     &lt;Apparatus Configuration&gt; 
     Next, a quantum efficiency measurement apparatus SYS 3  according to the present embodiment will be described. 
     The appearance of quantum efficiency measurement apparatus SYS 3  according to the third embodiment of the present invention is similar to that in  FIG. 2  as described above, and the detailed description thereof will not be repeated. Referring to  FIG. 11 , an integrating hemisphere of quantum efficiency measurement apparatus SYS 3  further includes a hemispheric portion  1 A, a disk-shaped plane mirror  5 B disposed to close the opening of hemispheric portion  1 A, a spectrometer  6  for measuring the illuminance (light spectrum) on the inner wall surface of hemispheric portion  1 A, and a light source  7  generating excitation light L 1 . 
     Hemispheric portion  1 A is basically identical to hemispheric portion  1 A shown in  FIG. 9  except that a liquid sample OBJ 2  enclosed in a transparent cell  16  is attached instead of sample OBJ 1 . Further, a standard object REF 2  corresponding to sample OBJ 2  can also be attached to hemispheric portion  1 A. Typically, standard object REF 2  is an object that is a reference material (typically only a medium corresponding to the sample from which a phosphor is removed) of the same quantity as sample OBJ 2  and enclosed in the same transparent cell  16 . Standard object REF 2  can be regarded as substantially emitting no fluorescence. 
     Plane mirror  5 B is provided with a light source window  12  and an observation window  13  that are each able to communicate with the inner surface side and the outer surface side of hemispheric portion  1 A. 
     Light source window  12  is provided at the position of a substantial center of curvature O of hemispheric portion  1 A. In other words, light source window  12  is formed in a region including substantial center of curvature O of hemispheric portion  1 A. Light source  7  applies excitation light L 1  through light source window  12  and along an optical axis Ax 3  coinciding with the normal to plane mirror  5 B, toward sample OBJ 2  or standard object REF 2  attached to sample window  9 . 
     Observation window  13  is an opening for observing the illuminance on the inner surface of hemispheric portion  1 A, and provided at a position separated from light source window  12  toward the outer circumference side by a predetermined distance. Light  6  is directed to spectrometer  6  through observation window  13 . Observation window  13  restrains fluorescence generated from sample OBJ 2  receiving excitation light L 1  and excitation light L 1  reflected from sample OBJ 2  from directly entering spectrometer  6 . More specifically, observation window  13  is a kind of aperture, namely an opening configured in such a manner that the diameter of the opening on the outer side of hemispheric portion  1 A is larger relative to the diameter of the opening on the inner side of hemispheric portion  1 A. Such an observation window  13  restraining the observation field can be provided to measure the quantum efficiency with a higher accuracy without disposing baffle  358  as shown in  FIG. 10 . 
     Other features of plane mirror  5 B are similar to those of plane mirror  5  shown in  FIG. 3 , and the detailed description thereof will not be repeated. Further, the detailed description of spectrometer  6  and light source  7  as described above will not be repeated. 
     Transparent cell  16  is a tubular container whose wall is formed of a transparent material. Transparent cell  16  is attached to sample window  9  to be disposed on optical axis Ax 3  of light source  7 . Thus, to sample OBJ 2  enclosed in transparent cell  16 , excitation light L 1  is applied along optical axis Ax 3 . When transparent cell  16  is attached to sample window  9 , the transparent cell is entirely contained in hemispheric portion  1 A. At this time, a seal member  15  is attached to the outermost part of transparent cell  16 . Seal member  15  prevents excitation light L 1  having passed in transparent cell  16  and sample OBJ 2  in the cell from leaking from hemispheric portion  1 A. Therefore, at least the side of seal member  15  that faces transparent cell  16  is provided with a light diffuse reflection layer of substantially the same diffuse reflection capability as light diffuse reflection layer  1   a  of hemispheric portion  1 A. 
     &lt;Principle of Measurement&gt; 
     Next, a principle of measurement by quantum efficiency measurement apparatus SYS 3  according to the present embodiment will be described. 
     As shown in  FIG. 11 , when excitation light L 1  is applied to sample OBJ 2  that is typically a phosphor, a part of the excitation light (photons) is absorbed to be used for generating fluorescence, while the remaining part of excitation light L 1  is scatter-reflected from seal member  15  for example after passing through sample OBJ 2 . It is supposed here that excitation light L 1  has a wavelength range of λ 1L -λ 1H  and the fluorescence component generated from sample OBJ 2  has a wavelength range of λ 2L -λ 2H . 
     It is supposed that excitation light L 1  has a spectrum E 0  (λ). It is further supposed that the fluorescence component generated from sample OBJ 2  by application of excitation light L 1  to sample OBJ 2  has a spectrum P (λ), and the transmitted light component that is transmitted through sample OBJ 2  and thereafter scatter-reflected has a spectrum T (λ). In other words, spectrum P (λ) of the fluorescence component is equivalent to the component of the wavelength range (λ 2L -λ 2H ) corresponding to the fluorescence in spectrum E (1)  (λ) measured by spectrometer  6  when sample OBJ 2  is attached, and spectrum T (λ) of the transmitted light component is equivalent to the component of the wavelength range (λ 1L -λ 1H ) corresponding to excitation light L 1  in spectrum E (1)  (λ). 
     Further, spectrum E (2)  (λ) measured by spectrometer  6  when standard object REF 2  is attached corresponds to the radiation power that can be used for generating fluorescence in standard object REF 1  out of applied light. 
     Therefore, in order to convert the spectrum (radiation power) into the number of photons, the spectrum is divided by hc/X (where h: Planck&#39;s constant, c: light velocity). Then, the number of photons Ab absorbed by sample OBJ 2  can be represented by expression (5) where k=1/hc.
 
 Ab=k·∫   λ     1L     λ     1H     λ·{E   (2) (λ)− E   (1) (λ)}δλ  (5)
 
     The number of photons Pph of the fluorescence can be represented by expression (6).
 
 Pph=k·∫   λ     2L       2H     λ·E   (1) (λ)δλ  (6)
 
     Accordingly, the internal quantum efficiency QEin of sample OBJ 2  can be represented by expression (7).
 
QEin= Pph/Ab   (7)
 
     &lt;Control Configuration&gt; 
     Referring next to  FIG. 12 , a control configuration of a processor  200 A of quantum efficiency measurement apparatus SYS 3  according to the present embodiment will be described. 
     As compared with the control configuration of processor  200  according to the first embodiment shown in  FIG. 5 , processor  200 A shown in  FIG. 12  does not include division unit  216  and initial setting holding unit  218 , but outputs to addition and subtraction unit  220  a wavelength component of spectrum E (2)  (λ) read by selection unit  210 . Namely, according to expression (5) above, the number of photons Ab absorbed by sample OBJ 2  is calculated. 
     Other components are similar to those of processor  200  shown in  FIG. 5 , and the detailed description thereof will not be repeated. 
     &lt;Process Procedure&gt; 
     A flowchart showing a process procedure for measurement of the quantum efficiency using quantum efficiency measurement apparatus SYS 3  according to the present embodiment is similar to that of  FIG. 6  except for the expression for calculating the number of photons Ab, and the detailed description thereof will not be repeated. 
     Effects of the Present Embodiment 
     The present embodiment employs the observation window where the observation field is restrained, and therefore does not require a baffle to be provided in the integrating hemisphere for preventing direct incidence of light from the sample. Thus, occurrence of a measurement error due to light absorption by the baffle can be reduced. Further, the present embodiment can achieve a twofold light intensity in principle, by means of a virtual image generated by the plane mirror, relative to the case where an integrating sphere of the same radius is used. In this way, even if the observation field of the observation window is restrained, a sufficient brightness can be obtained. 
     Accordingly, the quantum efficiency can be measured with a higher accuracy. 
     First Modification of the Third Embodiment 
     In connection with the above-described third embodiment, the configuration is illustrated where excitation light L 1  is applied from light source window  12  provided in hemispheric portion  1  toward the sample attached in hemispheric portion  1 . Alternatively, the light source and the sample may be arranged close to each other. In the following, with reference to  FIG. 13 , a quantum efficiency measurement apparatus SYS 3 A according to a first modification of the present embodiment will be described. 
     Quantum efficiency measurement apparatus SYS 3 A shown in  FIG. 13  differs from quantum efficiency measurement apparatus SYS 3  according to the third embodiment shown in  FIG. 11  in that a transparent cell  16 A enclosing a liquid sample OBJ 2  and a light source  7  are attached to a light source window  12 , and only a seal member  15  is attached to a sample window  9 . 
     Transparent cell  16 A is a tubular container entirely formed of a transparent material. Transparent cell  16 A is attached to face the emission opening of light source  7  to be disposed on an optical axis Ax 3  of light source  7 . Light source  7  applies excitation light L 1  through light source window  12  along optical axis Ax 3  coinciding with the normal to plane mirror  5 B, toward sample OBJ 2  (or standard object REF 2 ) attached to light source window  12 . Accordingly, excitation light L 1  is applied along optical axis Ax 3  to sample OBJ 2  enclosed in transparent cell  16 A. When transparent cell  16 A is attached to light source window  12 , the transparent cell is entirely contained in hemispheric portion  1 A. 
     Other features are similar to those of  FIG. 11  except for the above-described positional relation between transparent cell  16 A and light source  7 , and the detailed description thereof will not be repeated. 
     Further, the control configuration of the processor of quantum efficiency measurement apparatus SYS 3 A according to the first modification as well as the flowchart showing the process procedure for measuring the quantum efficiency using quantum efficiency measurement apparatus SYS 3 A according to the first modification are respectively similar to those of  FIGS. 12 and 6 , and the detailed description thereof will not be repeated. 
     The first modification can further shorten the distance between the light source and the sample, so that a more intense excitation light can be applied to the sample. Thus, the intensity of the fluorescence generated from the sample can be further increased, so that the quantum efficiency can be measured with a higher accuracy. 
     Second Modification of the Third Embodiment 
     In connection with the third embodiment as described above, the configuration is illustrated where the transparent cell enclosing the sample is entirely contained in the hemispheric portion. As long as the excitation light can be applied to the transparent cell (sample), however, the transparent cell enclosing the sample may not entirely be contained in the hemispheric portion. In the following, with reference to  FIG. 14 , a quantum efficiency measurement apparatus SYS 3 B according to a second modification of the present embodiment will be described. 
     Quantum efficiency measurement apparatus SYS 3 B shown in  FIG. 14  substantially corresponds to quantum efficiency measurement apparatus SYS 3  of the third embodiment shown in  FIG. 11  in which the shape of the transparent cell attached to sample window  9  is changed. Preferably, sample window  9  is disposed on the lower side relative to the direction of gravity in quantum efficiency measurement apparatus SYS 3 B as shown in  FIG. 14 . 
     More specifically, to sample window  9  of quantum efficiency measurement apparatus SYS 3 B, a transparent cell  16 B enclosing a liquid sample OBJ 2  and a seal member  15 A are attached. Transparent cell  16 B is basically a tubular container entirely formed of a transparent material. Transparent cell  16 B is attached to sample window  9  to be disposed on optical axis Ax 3  of light source  7 . Namely, to sample OBJ 2  enclosed in transparent cell  16 B, excitation light L 1  is applied along optical axis Ax 3 . At this time, a tubular seal member  15 A is attached to a surface of transparent cell  16 B, except for the surface of transparent cell  16 B on which excitation light L 1  is incident. This seal member  15 A prevents excitation light L 1  after passing through transparent cell  16 B and sample OBJ 2  therein from leaking from hemispheric portion  1 A. Therefore, the inner circumference surface of seal member  15 A is provided with a light diffuse reflection layer of substantially the same degree of light diffuse reflection capability as light diffuse reflection layer  1   a  of hemispheric portion  1 A. 
     Other components are similar to those of  FIG. 11  except for transparent cell  16 B and seal member  15 A, and the detailed description thereof will not be repeated. 
     Further, the control configuration of the processor of quantum efficiency measurement apparatus SYS 3 B according to the present second modification as well as the flowchart showing the process procedure for measuring the quantum efficiency using quantum efficiency measurement apparatus SYS 3 B according to the present second modification are respectively similar to those of  FIGS. 12 and 6 , and the detailed description thereof will not be repeated. 
     The second modification does not require that the sample and the standard object be contained in the integrating hemisphere, so that the sample and the standard object can be attached in a shorter time. Therefore, measurement can be performed more efficiently. 
     Fourth Embodiment 
     In order to implement, as required, any of respective configurations of the quantum efficiency measurement apparatuses described in connection with the second embodiment, the third embodiment and the modifications of the third embodiment, an integrating hemisphere as shown in  FIG. 15  may be employed. 
     Referring to  FIG. 15 , the integrating hemisphere of a quantum efficiency measurement apparatus according to the fourth embodiment of the present invention includes a hemispheric portion  1 A and a disk-shaped plane mirror  5 C disposed to close the opening of hemispheric portion  1 A. In plane mirror  5 C, light source windows  10  and  12  and an observation window  13  that are each able to communicate with the inner surface side and the outer surface side of hemispheric portion  1 A are provided. Light source window  10  is provided for implementing quantum efficiency measurement apparatus SYS 2  of the second embodiment shown in  FIG. 9 . Light source window  12  is provided for implementing quantum efficiency measurement apparatuses SYS 3 , SYS 3 A and SYS 3 B of the third embodiment and the modifications of the third embodiment shown in  FIGS. 11 ,  13  and  14  respectively. 
     To any of light source windows  10  and  12  and observation window  13 , components such as sample OBJ 2  and light source are attached as required, and a corresponding seal member is attached to the window that is not used, so that any of the above-described quantum efficiency measurement apparatuses can be implemented as desired by the user. 
     The present embodiment can use a common integrating hemisphere to measure the quantum efficiency with an apparatus configuration as desired by the user. 
     Other Embodiments 
     Using any of the above-described quantum efficiency measurement apparatuses, the reflectance characteristic of a sample can be measured as well. 
     It should be construed that embodiments disclosed herein are by way of illustration in all respects, not by way of limitation. It is intended that the scope of the present invention is defined by claims, not by the above description, and includes all modifications and variations equivalent in meaning and scope to the claims.