Luminescence of NaGdFPO 4: Ln3+ after VUV excitation: A comparison with GdPO 4: Ln3+ ( Ln=Ce, Tb)

Abstract

The phosphors NaGdFPO 4: Ln 3+ and GdPO 4: Ln 3+ (for Ln 3+=Ce 3+ and Tb 3+) were prepared by solid-state reaction technique, the VUV–vis spectroscopic properties of the phosphors were investigated, and we vividly compare the luminescence of Ce 3+ and Tb 3+ in the hosts. For phosphors GdPO 4: Ln 3+, the band near 155 nm in VUV excitation spectrum is assumed to be the host-related absorption, and for NaGdFPO 4: Ln 3+ the absorption is moved to longer wavelength, near 170 nm, showing the P–O bond covalency increased after fluoridation. The f– d transitions of Ce 3+ and Tb 3+ in the host lattices are assigned and corroborated, and it was found that the 5 d states are with lower energy in NaGdFPO 4: Ln 3+ than those in GdPO 4: Ln 3+. For fluoridation of GdPO 4: Ln 3+ to NaGdFPO 4: Ln 3+, the energy change of Ln 3+ ( Ln=Ce, Tb) 5 d states is consistent with that of host-related absorption.