Exclusive confinement of Bi 3+ -activators in the triangular prism enabling efficient and thermally stable green emission in the tridymite-type phosphor CaBaGa 4 O 8 :Bi 3 .

Recently, Bi 3+ -activated phosphors have been extensively studied for potential applications in phosphor-converted white light-emitting diodes (pc-WLEDs). However, Bi 3+ activators usually exhibit low quantum efficiency and poor thermal stability due to the outermost 6s6p-orbitals of Bi 3+ being strongly coupled with the host lattice, inhibiting potential applications. Herein, we rationally design a novel phosphor CaBaGa 4 O 8 :Bi 3+ , which adopts a tridymite-type structure and crystallizes in the space group of Imm 2. CaBaGa 4 O 8 :Bi 3+ presents a bright green light emission peaking at 530 nm with a FWHM narrower than 90 nm. Comprehensive structural and spectroscopic analyses unravelled that Bi 3+ emitters were site-selectively incorporated into the triangular prism (Ca 2+ -site) in CaBaGa 4 O 8 :Bi 3+ since there exist two distinct crystallographic sites that can accommodate the Bi 3+ ions. An excellent luminescence thermal stability of 73% of the ambient temperature photoluminescence intensity can be maintained at 423 K for CaBaGa 4 O 8 :0.007Bi 3+ . Impressively, the quantum efficiency (QE) of CaBaGa 4 O 8 :0.007Bi 3+ was remarkably improved to 47.2% for CaBaGa 4 O 8 :0.007Bi 3+ ,0.03Zn 2+ via incorporating the Zn 2+ compensators without sacrificing the luminescence thermal stability. The high thermal stability and QE of CaBaGa 4 O 8 :0.007Bi 3+ ,0.03Zn 2+ are superior to most of the Bi 3+ -activated green-emitting oxide phosphors. The perspective applications in pc-WLEDs for CaBaGa 4 O 8 :0.007Bi 3+ ,0.03Zn 2+ were also studied by fabricating LED devices.