Comparing the structure and photoluminescence properties of Bi-doped lead-free double perovskites prepared by solution-based synthesis and green mechanochemistry.

In search for less environmentally harmful materials, lead-free double halide perovskites (DPs) have emerged as promising candidates with tuneable photoluminescence properties. In this study, we present a comparative analysis of DPs with composition CsAgNaBiInCl CANBIC, y = 0.01-0.04, y is Bi content in mol% obtained via solution-based (SB) and green solvent-free mechanochemical (MC) methods. Comprehensive characterization of the resulting materials was performed via X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning and transmission electron microscopy (SEM/TEM), optical diffuse reflectance and photoluminescence (PL) spectroscopies. Both synthesis routes yielded cubic (Fm-3 m) perovskite structures, with all CANBIC samples exhibiting broad emission spectra ranging from 400 to 900 nm (1.3-3.1 eV), originating from the recombination of self-trapped excitons (STEs). Bi doping significantly enhanced photoluminescence quantum yield (PLQY) up to 84%. The solution-based (SB) method produced samples with higher PLQY, attributed to improved control over particle morphology and dopant distribution as compared to the mechanochemistry (MC) route. Thermal analysis confirmed the structural integrity of CANBIC samples up to 300 °C, with no significant decomposition below  560 °C, indicating their suitability for optoelectronic applications requiring moderate thermal stability. This work provides valuable insights into the relationship between synthesis methodology and material performance, advancing the development of environmentally friendly lead-free perovskites for next-generation optoelectronic devices such as white-LEDs.