Luminescence of Eu~(2+) and Energy Transfer from Ce~(3+)to Eu~(2+) in Lanthanum Phosphate

A new luminescence material——LaPO4 doped with Eu2+ and Ce3+ was prepared by high temperature solid state reaction. And the optical properties of Eu2+activated and Ce3+,Eu2+ coactivated lanthanum phosphates were investigated by using photoluminescence(PL) measurements.Emission spectrum of LaPO4∶Eu2+ recorded at room temperature with 324nm excitation shows a broad emission band centered at 423nm. And it is possible to determine the distribution of this broad emission band in the spectrum associated with transition from the 4f5d level of Eu2+ ion.The excitation spectrum of Eu2+activated lanthanum phosphate recorded at room temperature monitoring 423nm emission exhibits absorption in UV region (220～400nm) assigned to the 4f→5d transition of Eu2+ ion.Lanthanum phosphate doped with Ce3+ was also prepared by high temperature solid state reaction. The room temperature photoluminescence spectra of LaPO4∶Ce3+ show the broad emission and excitation band of Ce3+ ion ,around 342nm and 284nm,respectively.From these spectra above, it's possible to deduce that energy transfer between the Eu2+ and Ce3+ ion will probably happen because of the well overlapping between Ce3+ emission and Eu2+ excitation. And it's well proved in the excitation spectrum of LaPO4 coactivated by Eu2+ and Ce3+ at room temperature, monitoring Eu2+ emission. This spectrum shows a strong absorption band of Ce3+, ranging over 220～340nm, in addition to original f→d transition of Eu2+(220～400nm). That is to say there happens a sensitization of Eu2+ by the presence of Ce3+ ion. The Eu2+ emission intensity of LaPO4∶Ce3+001, Eu2+001 is 56 times higher than that of the corresponding phosphor activated by Eu2+ only.A series of LaPO4∶Ce3+001, Eu2+x were prepared to study the mechanism of the energy transfer between the Eu2+ and Ce3+ ion. The emission spectra of the LaPO4∶Ce3+001, Eu2+x at room temperature were measured. The relationship between the Ce3+ donor emission intensity and the Eu2+ acceptor concentration was fit to the d→d (dipoledipole) energy transfer model for multipolemultipole interaction. So it is concluded that the energy transfer between the Ce3+ and Eu2+ ions in lanthanum phosphate is to be a process of dipoledipole resonance interaction.