Unveiling Temperature-Induced Structural Phase Transition and Luminescence in Mn²⁺-Doped Cs₂NaBiCl₆ Double Perovskite

Abstract

Halide double perovskites like Cs 2 NaBiCl 6 are good host materials for luminescent dopants like Mn 2+ . The nature of photoluminescence (PL) depends on the local structure around the dopant ion, and doping may sometimes influence the global structure of the host. Here, we unveil the correlation between the temperature-induced (global) structural phase transition of Mn 2+ -doped Cs 2 NaBiCl 6 with the local structure and PL of the Mn 2+ dopant. X-ray diffraction analysis shows Mn 2+ -doped Cs 2 NaBiCl 6 is in a cubic (Fm3m) phase between 300 and 110 K, below which the phase changes to tetragonal (I4/mmm), which persists at least until 15 K. The small (∼1%) doping amount does not alter the phase transition behavior of Cs 2 NaBiCl 6 . Importantly, the phase transition does not influence the Mn 2+ d-electron PL. The PL peak energy, intensity, spectral width, and lifetime do not show any signature of the phase transition between 300−6 K. The hyperfine splitting in temperature-dependent electron paramagnetic spectra of Mn 2+ ions also remain unchanged across the phase transition. These results suggest that the global structural phase transition of the host does not influence the local structure and emission property of the dopant Mn 2+ ion. This structure−property insight might be explored for other transition-metal-and lanthanide-doped halide double perovskites as well. The stability of dopant emission regardless of the structural phase transition bodes well for their potential applications in phosphor-converted light emitting diodes.