Light measurement device and light measurement method

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 analyzer configured to analyze the photoluminescence quantum yield of the long afterglow emission material on the basis of the spectral data;
• and
• a controller 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 controller
• controls 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
• controls 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,
• wherein the detection light and the spectral data contain a component having a longer wavelength than the excitation light,
• wherein the first period is one during which input of the excitation light into the internal space is maintained, and the second period is one during which input of the excitation light into the internal space is stopped,
• wherein the start timing of the second period is determined based on the fluctuation per unit time of a peak value of intensity of light emission,
• wherein the spectroscopic detector acquires a peak value of an intensity of the excitation light in the first period and the peak value of the intensity of light emission in the long afterglow emission material on the basis of the spectral data, and
• the controller determines an exposure time of the detection light during start of the second period on the basis of a product of a ratio of the peak value of the intensity of the excitation light to the peak value of the intensity of light emission and the exposure time of the detection light in the first period.