Effects of Precursor Purity and Post-Synthesis Treatments on Mechanochemical Mn²⁺ and Rb¹⁺ Co-Doped CsPbCl₃ Perovskite Powder

Inorganic halide perovskites (HPs) exhibit optimum optoelectronic material characteristics such as wider band gaps, enhanced atmospheric stability, and improved photoluminescence quantum yield, as well as demonstrated balanced and higher carrier mobility in comparison to hybrid organic-inorganic HPs. The synthesis of perovskite material often involves the utilization of toxic and large quantities of hazardous complex solution-based techniques which are not eco-friendly. Alternately, crystal growth methods require highly purified precursors that have negative ecological impacts on the environment, leading to increased pollutants within the atmosphere, and accompanied by high-energy consumption deemed an unsustainable practice. Mechano-chemical synthesis is considered a green chemistry method that significantly can reduce the use of complex and time-consuming reactions, energetic-enabled conditions, expensive precursor sources, hazardous reagents, catalysts, additives, surfactants, and overall waste. In this study we report fluorometric characterization results of mechano-chemical synthesis of manganese (Mn²⁺) and rubidium (Rb¹⁺) co-doped CsPbCl₃ halide perovskite powder thermal calcination treatment and post-synthesis ligand-mediated techniques. The grinding process is considered a non-homogeneous synthesis approach which may result in residual unconsumed precursor present in the sample leading to surface defects during post-synthetic treatments. Dry and wet high-energy ball-milling experiments used different (low = 2N-99%, med = 3N-99.9%, and high = 5N-99.999%) purity precursors: CsCl (5N), PbCl₂(5N & 2N), RbCl (5N) and the (non-anhydrous) hydrated dopant source: MnCl₂4H₂O (3N). Synthesized theoretically ~ 4.5 wt % Mn²⁺ and ~ 11 wt% Rb¹⁺ co-doped CsPbCl₃ HPs were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and steady-state & time-resolved spectroscopic studies. The HPs powder suspension and supernatant (colloidal) exhibited a broad band Mn²⁺ emission band at room temperature with average peak wavelengths of ~ 600 nm and ~ 598 nm, respectively. Room-temperature (RT) lifetime transients of the HPs raw powders were 0.50 – 1.17 ms, powder suspension ranged from 1.65 – 1.71 ms and colloidal solution demonstrated the longest transients ranging from 1.72 – 1.75 ms, comparable to previously reported RT lifetimes for Mn²⁺ doped CsPbCl₃ nanoparticles and bulk crystals at 1.10 ms and 0.70 ms, respectively.