A spectrometry device configured to irradiate a long afterglow emission material with excitation light and measure a photoluminescence quantum yield, the device comprising: a light source configured to output the excitation light; an integrator configured to have an internal space in which the long afterglow emission material is disposed, and output light from the internal space as detection light; a spectroscopic detector configured to spectroscopically disperse the detection light and acquire spectral data; an analysis unit (5, 21) configured to analyze the photoluminescence quantum yield of the long afterglow emission material on the basis of the spectral data; and a control unit (5, 22) configured to control switching between presence and absence of input of the excitation light to the internal space and an exposure time of the detection light in the spectroscopic detector, wherein the control unit (5, 22) is configured to: control the light source so that the input of the excitation light to the internal space is maintained in a first period in which the acquisition of the spectral data through the spectroscopic detector is started, and that the input of the excitation light to the internal space is stopped in a second period subsequent to the first period, and control the spectroscopic detector so that an exposure time of the detection light in the second period becomes longer than an exposure time of the detection light in the first period. a light source configured to output the excitation light; an integrator configured to have an internal space in which the long afterglow emission material is disposed, and output light from the internal space as detection light; a spectroscopic detector configured to spectroscopically disperse the detection light and acquire spectral data; an analysis unit (5, 21) configured to analyze the photoluminescence quantum yield of the long afterglow emission material on the basis of the spectral data; and a control unit (5, 22) configured to control switching between presence and absence of input of the excitation light to the internal space and an exposure time of the detection light in the spectroscopic detector, wherein the control unit (5, 22) is configured to: control the light source so that the input of the excitation light to the internal space is maintained in a first period in which the acquisition of the spectral data through the spectroscopic detector is started, and that the input of the excitation light to the internal space is stopped in a second period subsequent to the first period, and control the spectroscopic detector so that an exposure time of the detection light in the second period becomes longer than an exposure time of the detection light in the first period. control the light source so that the input of the excitation light to the internal space is maintained in a first period in which the acquisition of the spectral data through the spectroscopic detector is started, and that the input of the excitation light to the internal space is stopped in a second period subsequent to the first period, and control the spectroscopic detector so that an exposure time of the detection light in the second period becomes longer than an exposure time of the detection light in the first period.