Judd–Ofelt theory is a theory in physical chemistry describing the intensity of electron transitions within the 4f shell of rare-earth ions in solids and solutions.
The theory was introduced independently in 1962 by Brian R. Judd of the University of California, Berkeley, and PhD candidate George S. Ofelt at Johns Hopkins University. Their work was published in Physical Review and the Journal of Chemical Physics, respectively.
Judd and Ofelt did not meet until 2003 at a workshop in Lądek-Zdrój, Poland.
Judd and Ofelts work was cited approximately 2000 times between 1962 and 2004. Brian M. Walsh of NASA Langley places Judd and Ofelts theory at the "forefront" of a 1960s revolution in spectroscopic research on rare-earth ions.