“…The broad emission band below 575 nm, corresponding to green emission, is attributed to the recombination luminescence of single-ionized oxygen vacancies [23]. Strong emission peaks are detected at 580, 592, 612, 653, and 705 nm, which originate from the transition of Eu 3+ ions from the 5 D 0 excited state to the 7 F J (J = 0, 1, 2, 3, and 4) ground state, respectively [24,25]. It is observed that the emission peak at 612 nm ( 5 D 0 → 7 F 2 ), corresponding to the red emission, is much stronger than that at 592 nm ( 5 D 0 → 7 F 1 ), corresponding to orange emission.…”