Physics:Cooperative luminescence and cooperative absorption

Cooperative luminescence is the radiative process in which two excited ions simultaneously make downward transition to emit one photon with the sum of their excitation energies. The inverse process is cooperative absorption, in which a photon can be absorbed by a coupled pair of two ions, making them excited simultaneously.

References

• Nakazawa, Eiichiro; Shionoya, Shigeo (1970-12-21). "Cooperative Luminescence in YbPO4". Physical Review Letters (American Physical Society (APS)) 25 (25): 1710–1712. doi:10.1103/physrevlett.25.1710. ISSN 0031-9007. Bibcode: 1970PhRvL..25.1710N. 
• Dexter, D. L. (1962-06-15). "Cooperative Optical Absorption in Solids". Physical Review (American Physical Society (APS)) 126 (6): 1962–1967. doi:10.1103/physrev.126.1962. ISSN 0031-899X. Bibcode: 1962PhRv..126.1962D.