Photoluminescence of Tb and Mn activated Ca8MgGd(PO4)7 under vacuum ultraviolet excitation

Novel Tb³⁺ and Mn²⁺ activated Ca₈MgGd(PO₄)₇ phosphors were synthesized by solid-state reaction and their photoluminescence properties in vacuum ultraviolet region were investigated for the first time. It can be observed from the excitation spectra that the host-related absorption band is located around 170 nm, and it overlaps the O²⁻ → Tb³⁺ charge transfer band of Ca₈MgGd(PO₄)₇:Tb³⁺ around 161 nm and the 3d⁵ → 3d⁴4s transition band of Ca₈MgGd(PO₄)₇:Mn²⁺ near 200 nm. The 4f-4f 5d spin-allowed and spin-forbidden transitions of Tb³⁺ are verified to be located at 170-250 and 257-271 nm, respectively. Upon 147 nm excitation, the dominant emission peak intensity of the Ca₈MgGd_0.1(PO₄)₇:0.9Tb³⁺ phosphor is about 2.7 times stronger than that of the commercial Zn₂SiO₄:Mn²⁺ green phosphor, and the brightness of the former with a short decay time of 2.5 ms is about 98% of the latter’s. The Ca₈MgGd(PO₄):Mn²⁺ phosphor excited at 147 nm exhibits a deep red emission around 650 nm, which could be attributed to the ⁴T₁ → ⁶A₁ transition of Mn²⁺, with the CIE index (0.679, 0.321). In a word, the results above indicate that both Tb³⁺ and Mn²⁺ activated Ca₈MgGd(PO₄)₇ phosphors could be promising for PDP or Hg-free lamp applications.