Cs₄Cd_1–<i>x</i>Mn_<i>x</i>Bi₂Cl₁₂—A Vacancy-Ordered Halide Perovskite Phosphor with High-Efficiency Orange-Red Emission

The structural, optical, and magnetic properties of the vacancy-ordered quadruple perovskites Cs4CdBi2Cl12 and Cs4MnBi2Cl12 and their solid solution have been investigated. Both compounds crystallize with the R3̅m space group symmetry that arises from the ordering of Bi3+, Mn2+/Cd2+, and cation vacancies into layers that run perpendicular to the ⟨111⟩ direction of the cubic perovskite structure. Cs4MnBi2Cl12 is paramagnetic down to 2 K with a Weiss constant of −2.88(3) K and an effective moment of 5.840(1) μB. This compound exhibits weak orange-red luminescence, which involves Bi3+ ions absorbing near-UV photons, followed by energy transfer to Mn2+ ions and finally radiative decay that is attributed to a spin-forbidden 4T1(G) → 6A1(S) d–d transition. The emission peak is centered near 605 nm with a fullwidth at half-maximum of ∼90 nm and a photoluminescence quantum yield (PLQY) of ∼4%. The isostructural Cs4CdBi2Cl12 is neither magnetic nor does it show detectable PL at room temperature. Replacing Mn2+ with Cd2+ to form Cs4Cd1–xMnxBi2Cl12 leads to a zero-dimensional electronic structure that inhibits energy migration to defect sites where nonradiative decay can occur, increasing the room temperature PLQY to 57% in the x = 0.27 sample. Cs4Cd1–xMnxBi2Cl12 phosphors are easily synthesized from solution, do not contain rare-earth ions, and possess emission spectra that compare favorably to narrow band, red phosphors containing Eu2+.