Persistent Luminescence: Cerium-Doped Phosphors

Luminescent materials are found in a broad range of everyday applications. The existence of luminous organisms such as bacteria in the sea and in decaying organic matters, glowworms, and fireflies have mystified and thrilled man since time immemorial. The phenomenon of certain kinds of substances emitting light on absorbing various kinds of energies without heat generation is called luminescence. While in the seventies and eighties, the field of luminescent materials seemed to be fairly well covered, research in the nineties has been revitalized both in industry and academia. Improvements over the last three decades have led to the phosphor materials that operate close to their physical limits. In the present chapter, an interesting subclass of luminescent materials, long 50persistent materials, is discussed. Various aspects of persistent materials, which include their historical perspective, the important parameters for good persistent phosphors, a review of different mechanisms, and their applications, especially bioimaging, are discussed. In the later sections, cerium (Ce³⁺)-doped luminescent materials and the influences of symmetry and coordination on luminescence output of Ce³⁺-doped materials are discussed. Ce³⁺- doped persistent materials and an interesting case of codoped materials exhibiting white, long persistent behavior have been discussed. The future scope of long persistent materials with Ce³⁺ as the dopant has also been included to motivate the potential reader.