G. Mackay Salley, Oliver S. Wenger, Karl W. Krämer and Hans U. Güdel
Inorganic solid state optical materials: Major recent advances
Current Opinion in Solid State and Materials Science 6, 487-493 (2002)                 

Abstract: Major advances have recently been made concerning the optical properties of solid-state materials. Four notable areas of research are: upconversion and downconversion luminescence, new high-efficiency scintillator materials, and photonic band gap materials or photonic crystals. Each of these research fields has contributed greatly to our basic understanding of solid-state optical materials as well as contributing to applied research.