Vacuum ultraviolet spectroscopic properties of rare earth (RE=Ce,Tb,Eu,Tm,Sm)-doped hexagonal KCaGd(PO4)2 phosphate

Abstract

Hexagonal KCaGd(PO4)2:RE3+ (RE=Ce,Tb,Eu,Tm,Sm) were synthesized by coprecipitation method and their vacuum ultraviolet–ultraviolet (VUV-UV) spectroscopic properties were investigated. The bands at about 165nm in the VUV excitation spectra are attributed to the host lattice absorptions. For Ce3+-doped samples, the bands at 207, 256, 275, and 320nm are assigned to the 4f-5d transitions of Ce3+ in KCaGd(PO4)2. For Tb3+-doped sample, the bands at 203 and 222nm are related to the 4f-5d spin-allowed transitions. For Eu3+-doped sample, the O2−–Eu3+ charge-transfer band (CTB) at 229nm is observed, and the fine emission spectrum of Eu3+ indicates that Eu3+ ions prefer to occupy Gd3+ or Ca2+ sites in the host lattice. For Tm3+- and Sm3+-doped samples, the O2−–Tm3+ and O2−–Sm3+ CTBs are observed to be at 176 and 186nm, respectively. From the standpoints of the absorption band, color purity, and luminescent intensity, Tb3+-doped KCaGd(PO4)2 is a potential candidate for 172nm excited green plasma display phosphors.