A method and apparatus is provided for implementing a parametric down-conversion (PDC)-based calibration comprising calibrating a measuring instrument; disposing a pinhole at a position of a light-emitting sample for which the measuring instrument needs to be calibrated; irradiating a nonlinear crystal with a light source; setting the nonlinear crystal by ensuring a phase-matching wavelength of the nonlinear crystal is set at one boundary of a desired bandwidth; acquiring one or more PDC spectrums by the measuring instrument; obtaining peak values and their corresponding wavelengths from each acquired spectrum; and obtaining a response function based on the peak values and corresponding wavelengths.