Cs₂NaBiCl₆:Mn²⁺A New Orange-Red Halide Double Perovskite Phosphor

In this work, we report on the promising photoluminescent behavior of the cubic double perovskite Cs₂NaBiCl₆ doped with Mn²⁺ ions. Localized excitations centered on Bi³⁺ ions in the host lattice strongly absorb near-UV light. In the undoped host compound, only very weak photoluminescence is observed, but in manganese-doped samples, energy transfer from Bi³⁺ to Mn²⁺ leads to intense orange-red photoluminescence. A broad emission peak centered at 590 nm is assigned to the ⁴T₁ → ⁶A₁ transition of octahedrally coordinated Mn²⁺. The excitation spectrum contains peaks at 294 and 354 nm that arise from 6s² → 6s¹6p¹ excitations of Bi³⁺ ions. If the chloride ions are partially replaced by bromide ions, the strongest excitation peak red-shifts to 375 nm. The lack of expensive reagents and toxic elements and the ability to tune the excitation and emission spectra through chemical substitution make Cs₂NaBiCl_6–xBr_x:Mn²⁺ a promising phosphor system.