= Photoluminescence
{wiki}
<Photoluminescence> is <light> emission following absorption of incident <photons>. The excitation first puts matter into excited states; subsequent relaxation can emit at a different <wavelength>. <Fluorescence> and <phosphorescence> are distinct forms whose timing and transition mechanisms differ.
An excitation source, sample, rejection filter and <spectrometer> form a simple experiment. Place collection optics away from the directly transmitted beam and suppress excitation <light> before measuring the emission <optical spectrum>. Recording an empty holder or solvent blank helps identify background. Emission <intensity> alone does not determine absorption or <quantum yield>, because collection geometry and nonradiative relaxation also affect the signal.
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