As is well known, the [sup.5][D.sub.0] [right arrow] [sup.7][F.sub.1] line originates from magnetic dipole transition whilst the [sup.5][D.sub.0] [right arrow] [sup.7][F.sub.2] line results from the electric dipole transition
. In terms of the Judd-Ofelt theory, the magnetic dipole transition is permitted, but the electric dipole transition
is allowed only on condition that the Eu ion occupies a site without an inversion center.
There are several typical emission bands around 560-720 nm assigned to the [sup.5][D.sub.0] [right arrow] [sup.7][F.sub.J] (J = 0-4) transitions of [Eu.sup.3+] [59-63], of which the red emission band at 617 nm is the most intense one due to the electric dipole transition
[sup.5][D.sub.0] [right arrow] [sup.7][F.sub.2].
The intense peak at 611 nm and a small peak at 628 nm correspond to the hypersensitive transition between the [sup.5][D.sub.0] and [sup.7][F.sub.2] levels of [Eu.sup.3+] ion in calcium bromofluoride host aroused due to forced electric dipole transition