Luminescence properties of NaGd(PO3)4:Eu3+ and energy transfer from Gd3+ to Eu3+.

The luminescence properties of polyphosphates NaEu xGd(1− x)(PO3)4 ( x = 0–1.00) and the energy transfer from Gd3+ to Eu3+ were studied. In undoped NaGd(PO3)4 sample, the photon cascade emission of Gd3+ was observed under 8S7/2 → 6GJ excitation (201 nm) in which the emission of a red photon due to 6GJ → 6PJ transition is followed by an ultraviolet photon emission due to 6PJ → 8S7/2 transition. When part of Gd3+ ions in the host NaGd(PO3)4 were substituted by Eu3+ ions, the NaGd(PO3)4:Eu3+ sample showed intensive red emission under 172-nm vacuum-ultraviolet (VUV) excitation which is suitable for mercury-free fluorescent lamps and plasma display panel applications. Based on the VUV–visible spectroscopic characteristics and the luminescence decay properties of NaGd(PO3)4:Eu3+, it was found that the quantum cutting by a two-step energy transfer from Gd3+ to Eu3+ can improve the red emission of Eu3+ ions under VUV excitation but only a part of the excitation energy in the excited 6PJ states within Gd3+ ions can be transferred to Eu3+ ions for its red emission, and the nonradiative energy transfer efficiencies from the excited 6PJ states within Gd3+ to Eu3+ were calculated. [ABSTRACT FROM AUTHOR]