Ce

3+

ion has a 4f configuration.The ground state consists of doublet

2

F

5/2

and

2

F

7/2

. The lower excited states are the crystal-field components of the 5d configuration.Ce

3+

emission is due to a 5d-4f transition. Usually the emission consists of a broad band with two peaks in the long-wavelength ultraviolet region.The 5

d

-4

f

transition is an allowed electric dipole transition and therefore the decay time of the fluorescence is very short (

<

10

-7

sec).In a number of cases the 5d level varies strongly with host lattice.The position of Ce

3+

emission bands can be in the region from ultraviolet to visible.The position of Ce

3+

emission bands has something to do with elec-tronegativity of ligands which is directly coordinated with Ce

3+

ion.As the electronegativity of the ligand (F.O.S) decreases

it moves to long wavelength.The position of Ce

3+

emission bands in several host lattices are related to the crystal-field splitting

the cation

the indirect coordinated ligand which is in negatively charged ion group etc.The energy transfer and sensitization of Ce

3+

ion have been described. These results will provide the basis for material design.