Vacuum ultraviolet spectroscopic properties of rare-earth (RE3+ = Sm3+, Tb3+, Dy3+)-activated zirconium-based phosphates MZr4(PO4)6 (M2+ = Ca2+, Sr2+)

Vacuum ultraviolet (VUV) spectroscopic properties of Sm3+, Tb3+ and Dy3+-activated MZr4(PO4)(6) (M2+ = Ca2+, Sr2+) phosphates, which have been prepared by solid-state reaction method, are presented. The strong absorption bands in the VUV range of undoped and rare-earth activated MZr4(PO4)(6) were observed. The band range from 7.76-9.56 eV is due to the host lattice absorption, and the band at 6.21-7.76 eV is attributed to the charge transfer transition of O2--Zr4+. Doped with Sm3+ resulted in bright red emission originating from (4)G(5/2) -> H-6(J) (J = 5/2, 7/2 and 9/2) transitions. For Tb3+-activated samples, the broad band around 5.52 and 4.76 eV are identified as the spin-allowed and spin-forbidden f-d transitions of Tb3+. Typical f-f transitions of Dy3+ were observed in Dy3+-activated samples. Because the 2p electrons of O2- are tightly bound to Zr4+ rather than RE3+, making the O2--Sm3+ and O2--Dy3+ charge transfer bands too weak to be observed. It is demonstrated that there is energy transfer from the host to the luminescent activators. (C) 2014 Elsevier B.V. All rights reserved.