Anomalous fluorescence features of Eu2+ in apatite-pyromorphite type matrices

Divalent europium doped chloro-apatites, the well-known blue phosphor in high efficiency fluorescent lamps, exhibit anomalous fluorescence properties ascribed to photoionization process and the allied process. The photoionization properties of Eu2+-luminescent centre(s) in this system of materials has profound dependence on the chemical constituents of the matrix as exemplified by the diadochic substitution of (SiO4)(4-) for [(PO4)(3-) + Cl-]. The anomalous impurity trapped exciton emission can be better observed in Ba-compound than in the Ca- and Sr analogues, possibly due to the effect of the position of the conduction band.