# Kasha's rule

> English word · Proper noun

## Definitions
1. A principle in the photochemistry of electronically excited molecules, stating that photon emission (fluorescence or phosphorescence) occurs in appreciable yield only from the lowest excited state of a given multiplicity.

## Etymology
Named after American spectroscopist Michael Kasha, who proposed it in 1950.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/kasha-s-rule