Synthesis of Cs₃MnBr₅ Green Phosphors Using an Eco-Friendly Evaporative Crystallization Process

Abstract

Green (G) and red (R) light-emitting materials, such as quantum dots, perovskite nanocrystals, and inorganic phosphor powders, owing to their excellent optical characteristics, have attracted researchers’ attention as color-conversion materials for lighting and display applications. However, these materials contain environmentally harmful elements, such as Pb or Cd, and/or they are synthesized using environmentally harmful synthetic approaches and conditions, involving the use of organic solvents, high pressure, high temperature, harsh atmosphere, and long reaction time. In this study, as an eco-friendly synthetic approach to synthesize lead-free Cs 3 MnBr 5 G powder phosphor, we suggest an evaporative crystallization process of aqueous reactant solution. This synthetic process does not use toxic elements or solvents and the crystallization process utilizes only low reaction temperature and short reaction time under air atmosphere conditions. We successfully synthesized Cs 3 MnBr 5 green powder phosphor, with excellent optical properties, by evaporative heating of a 200 nm syringe-filtered solution at 150 °C for 2 h. The synthesized Cs 3 MnBr 5 phosphors have a photoluminescence quantum yield of 66.3%, a peak wavelength of 520 nm, a narrow bandwidth of 38 nm, and a photoluminescence decay time of 0.34 ms under blue excitation. This phosphor is expected to be a useful alternative G-emitting material that can compete with commercial green quantum dots, perovskite nanocrystals, or inorganic phosphors.

New Antisolvent Precipitation Synthesis of Green-Emitting Lead-Free Zinc-Alloyed Perovskite-Inspired Manganese Halides Cs3Mn1–xZnxBr5

“…As shown in Figure 4b, under 458 nm excitation, the material produces a green emission band centered at 520 nm, due to the 4 T 1 (G) → 6 A 1 transition of Mn 2+ in the tetrahedral environment, with a 40 nm full width at half-maximum (FWHM), which is in agreement with the literature. 22,24,25 The same spectral profile was obtained by excitation at 306 and 375 nm (see Figure S2). A quick decrease in emitted intensity was observed after 7 h of air exposure, as highlighted in Figure 4b.…”

“…This is in good agreement with Mn 2+ behavior in a tetrahedral bromide environment. 22,24,33 However, there is no general tendency in the literature concerning the excitation band area ratio. If the as-produced Cs 3 MnBr 5 is favorably excited in UV (375 nm), this behavior is different from previously published work for the same phase.…”

“…In this case, Mn and Cs bromides are generally dissolved in an acidic (HBr) medium 23 to avoid the formation of hydroxides, whose presence in the final product was correlated with a drop in its quantum yield. 24 Aqueous solvent is then evaporated to reach saturation. This can be done through heating (heat or microwave source) 24,25 or freezing (lyophilization) 26,27 the solution.…”

“…Finally, easier precipitation routes have also been developed. In this case, Mn and Cs bromides are generally dissolved in an acidic (HBr) medium to avoid the formation of hydroxides, whose presence in the final product was correlated with a drop in its quantum yield . Aqueous solvent is then evaporated to reach saturation.…”

“…Aqueous solvent is then evaporated to reach saturation. This can be done through heating (heat or microwave source) , or freezing (lyophilization) , the solution. Generally, micrometer-sized crystals are obtained, even though single crystals could be obtained if the evaporation rate is sufficiently low.…”