kvanttisaannos

Kvanttisaannos, also known as quantum yield, is a fundamental concept in photochemistry and photophysics. It quantifies the efficiency of a photochemical process. Specifically, it is defined as the ratio of the number of specific events (such as a molecule undergoing a photochemical reaction or emitting a photon) to the number of photons absorbed by the system.

The quantum yield is typically represented by the Greek letter phi ($\Phi$). For instance, $\Phi_{reaction}$ would denote the quantum yield for a particular reaction, while $\Phi_{emission}$ would represent the quantum yield for fluorescence or phosphorescence. A quantum yield of 1 means that for every photon absorbed, one molecule undergoes the desired process. A quantum yield greater than 1 is possible in certain chain reactions where a single absorbed photon can initiate a series of events. Conversely, a quantum yield less than 1 indicates that not every absorbed photon leads to the desired outcome, due to factors like non-radiative decay or competing processes.

Measuring quantum yield involves determining both the number of photons absorbed and the number of events occurring. This is often achieved using techniques like spectrophotometry to measure absorption and appropriate detectors to count emitted photons or quantify product formation. Quantum yield is a crucial parameter for understanding reaction mechanisms, designing photochemical devices like solar cells and photocatalysts, and studying molecular properties. It helps in comparing the efficiency of different molecules or experimental conditions.