In situ preparation of highly luminescent Sb3+/Mn2+ co-doped Cs2KInCl6 lead-free double perovskites in a PVDF matrix and application to white light emitting diodes and anti-counterfeiting†

Recently, lead-free double perovskites have been regarded as a promising alternative to lead halide perovskites due to their wide emission band, and environmental protection and stability properties, and are expected to become a series of rising star materials in the lighting field. However, currently, the growth of most lead-free double perovskites occurs in the strong acid environment, which not only brings high cost and environment risk, but also makes it hard to realize large-scale applications with powder products. Herein, we apply a strategy of in situ synthesis of lead-free double perovskites in a polymer matrix by using a small amount of precursors and relatively friendly DMSO solvent to obtain efficiently luminescent Sb³⁺/Mn²⁺ co-doped Cs₂KInCl₆/PVDF composite films in a large-area. The co-doping of Mn²⁺/Sb³⁺ into this inorganic double perovskite matrix makes microcrystals with good crystallinity and size distribution in this polymer. The as prepared co-doping composite film with Mn/Sb feeding ratio 16 : 1 shows the brightest white light emission under 320 nm excitation, with a photoluminescence quantum yield (PLQY) as high as 86.98%. The energy transfer (E-T) from the charge-transfer band to the triplet self-trapped exciton (STE) around Sb³⁺ and then to the ferromagnetic (FM) coupled Mn²⁺ pair 3d state was confirmed by the temperature-dependent PL spectra and density functional theory calculations. Finally, a single-compound white light emitting diode with chromatic coordinates of (0.31, 0.33) and fluorescent anti-counterfeiting labels could be fabricated based on this composite film with the best white emission. This work provides a new strategy for the application of lead-free double perovskites in the fields of lighting and anti-counterfeiting.