Artifacts in fluorescence emission spectroscopy related to Wood's anomaly

Fluorescence emission spectra of porphyrins acquired with a monochromator using a 1500 line/mm holographic grating were affected by polarization-induced effects (Wood's anomaly) which affected the transmission of different wavelengths of light. This effect resulted in a blue-shift in the emission optimum, and distortions in the fluorescence spectrum at longer wavelengths. These anomalies could be eliminated by insertion of polarizers, orientation = 0 degrees, in emission and excitation paths. A monochromator with a 1200 line/mm holographic grating was essentially free from these distortions.