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

• VUV spectroscopic properties of rare-earth ions in MZr4(PO4)6 have been investigated.
• The f–d spin-allowed (5.52 eV) and spin-forbidden (4.76 eV) transitions of Tb3+ were observed.
• The disappearance of O2−–Sm3+ and O2−–Dy3+ charge transfer bands was discussed.
• Energy transfer from the host to rare-earth activators has been demonstrated.

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 4G5/2 → 6HJ (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.

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