Particularly developed transition from the 5D1 level of Eu3+ and its significant contribution to the improved photocatalysis of (Bi3Li)O4Cl2via prolonging the decay time of the excited state†
There is a close correlation between the photoluminescence and photocatalysis of a semiconductor because the two processes involve the same electronic transition. Eu3+ is one of the most popular rare-earth ions; it presents efficient luminescence and improved photocatalysis. Usually, the luminescence from the higher states (5D1,2) of Eu3+ can be hardly observed due to cross-relaxation processes. This work demonstrates a particularly developed transition from the 5D1 level of Eu3+ and its significant contribution to the improved photocatalysis of (Bi3Li)O4Cl2 via prolonging the decay time of the excited state. Single-phase (Bi3−3xEu3xLi)O4Cl2 (x = 0, 0.01, 0.03, 0.05) was synthesized by the sol–gel method in combination with a solid-state reaction. This is a bismuth layer structure with [(Bi/Li)O2]2+ layers formed by alternative Bi3+ and Li+ stripes. The intrinsic luminescence of (Bi3Li)O4Cl2 (λem = 500 nm) with a decay time of 0.26 μs was detected even at 300 K. Unusually, the phosphor shows a prominent transition from 5D1 in (Bi3−3xEu3xLi)O4Cl2. Moreover, in addition to 5D0 → 7F3, 5D0 → 7FJ (J = 0, 1, 2, 4) is characterized by intense transitions with comparable intensities. The intrinsic emission of (Bi3Li)O4Cl2 has a decay time which involves the band transition of an electron from the valence band to the conduction band. In Eu3+-doped (Bi3Li)O4Cl2, there are midgap states formed by the 5D1 level with a longer lifetime of about 60 μs. The D1 levels of Eu3+ significantly contribute to the separation of light-induced charges by prolonging the decay time of the excited states. This work demonstrates a simple strategy to develop optical materials with simultaneous luminescence and has improved the photocatalysis in bismuth oxychlorides featuring strong polarization and rigid phonons.