Mn2+-Activated Zero-Dimensional Metal (Cd, Zn) Halide Hybrids with Near-Unity PLQY and Zero Thermal Quenching

Highly luminescent self-trapped exciton (STE)-based emission in low-dimensional antimony halide hybrids typically suffers from severe thermal quenching that limits their use in lighting applications. Interestingly, Mn2+-activated low-dimensional metal halide hybrids, with their characteristic d–d transitions, are less susceptible to thermal quenching. Consequently, developing Mn2+-activated metal halide hybrids with high PLQY and zero thermal quenching has received increasing research efforts. Herein, we synthesized Mn2+-doped zero-dimensional metal (Cd2+, Zn2+) bromide hybrids utilizing DABCO (1,4-diazabicyclo[2.2.2]octane) as the organic cation. Structural analysis confirms the presence of substitutional dopants (Mn2+) in the host metal (Cd, Zn) halide hybrids. Optically, the Mn2+-doped Cd system (C6H14N2Cd0.94Mn0.06Br4H2O) shows (i) dual emission bands (green emission due to tetrahedral Mn center and orange emission due to host STEs), (ii) strong evidence of energy transfer from dopants to host (Mn → Cd), and (iii) zero thermal quenching behavior albeit with low PLQY. On the other hand, Mn2+-doped Zn hybrids (C6H14N2Zn0.81Mn0.19Br4) demonstrate robust optical properties with highly luminescent (PLQY ∼ 94%) green emission (tetrahedral Mn center) and zero thermal quenching behavior. Such strongly luminescent zero thermal quenching behavior of Mn2+-activated metal halide hybrids could pave the way for the search for new functional materials for their use in high-temperature lighting applications.