fluorescent

Fluorescent describes materials that emit light after absorbing electromagnetic radiation, usually ultraviolet or blue light. In fluorescence, electrons are promoted from the ground state to an excited singlet state and return quickly to the ground state, emitting photons with longer wavelengths. The emitted light is observed only while the excitation source is present, and the process is typically completed within nanoseconds. By contrast, phosphorescent materials can continue to glow after excitation due to different electronic states and slower decay.

Fluorescent materials include organic dyes such as fluorescein and rhodamine, fluorescent proteins like GFP, and inorganic systems such as quantum dots and certain phosphors. The brightness of fluorescence is described by the quantum yield, and the emission spectrum depends on the material and its environment, producing characteristic colors. Factors such as solvent polarity, pH, and concentration can influence fluorescence.

Applications are widespread. In biology and medicine, fluorescence underpins microscopy, flow cytometry, and diagnostic assays. In chemistry and materials science, fluorescence spectroscopy is used to study interactions and quantify substances. Security printing, forensics, and environmental sensing rely on fluorescent labels and dyes. Lighting technologies use fluorescent materials in lamps and as phosphors in LEDs.

Safety considerations include potential toxicity of some fluorescent materials, notably certain cadmium-containing quantum dots, and the need for proper handling and disposal. Evolution in molecular biology has popularized genetically encoded fluorescent proteins for live-cell imaging, driving advances in imaging techniques and data analysis.