Photoluminescence properties of RE3+-activated Na3GdP2O8 (RE3+Â =Â Tb3+, Dy3+, Eu3+, Sm3+) under VUV excitation

RE3+-activated monoclinic Na3GdP2O8 (RE3+ = Tb3+, Dy3+, Eu3+, Sm3+) phosphors have been synthesized by a solid-state reaction method. Their photoluminescence properties in the vacuum ultraviolet (VUV) region were investigated. By analyzing their excitation spectra, the host-related absorption band was determined to be around 166 nm. The f-d transition bands and the charge transfer bands for Na3GdP2O8:RE3+ (RE3+ = Tb3+, Dy3+, Eu3+, Sm3+) were assigned and corroborated. For the sample Na3GdP2O8:5%Tb3+, the strong bands at around 202 and 221 nm are assigned to the 4f-5d spin-allowed transitions and the weak band at 266 nm is related to the spin-forbidden transition of Tb3+. For Na3GdP2O8:5%Dy3+, the broad band at 176 nm could be related to the f-d transitions of Dy3+ and the O2− → Dy3+ charge transfer band (CTB) besides the host-related absorption. In the excitation spectrum of Eu3+ doped sample, the O2− → Eu3+ CTB is observed to be at 245 nm. For the Sm3+ doped sample, the O2− → Sm3+ CTB is not distinguished obviously and is overlapped with the host-related absorption band.