Kvanttituotto

Kvanttituotto, often translated as quantum yield, is a concept in photochemistry and photophysics that expresses the efficiency of a photo-induced process. It is defined as the ratio of the number of molecules formed (or events such as isomerization, radical formation, or quenching) to the number of photons absorbed by the system. The quantum yield is a dimensionless quantity and can vary with wavelength, intensity, and the specific reaction conditions.

In a simple single-photon process, the quantum yield is at most 1, meaning that one absorbed photon leads to at most one product formation event. In more complex systems, such as chain reactions or catalytic cycles initiated by a photon, the effective quantum yield can exceed 1 because multiple products may result from a single absorbed photon. Conversely, when not all incident photons are absorbed, the apparent quantum yield is used, defined as the number of events per incident photon rather than per absorbed photon.

Quantum yield is often measured as a function of wavelength, producing an action spectrum that reflects the efficiency of the process across the light spectrum. Determination typically involves quantifying the rate of product formation and the rate of photon absorption, the latter often via actinometry or integrating-sphere measurements. The resulting ratio Φ = (number of molecules formed) / (number of photons absorbed) provides a concise metric for comparing photochemical efficiencies of different systems or reactions.