P 2095 (OTTO) POPOP, scintillation grade, 99%+ Cas 1806-34-4 - used as a wavelength shifter (also called a "secondary scintillator"), which means that it converts shorter wavelength light to longer wavelength light. Its output spectrum peaks at 410 nm, which is violet. P 2095 (OTTO) POPOP, scintillation grade, 99%+ Cas 1806-34-4 - used in both solid and liquid organic scintillators.