Excitation wavelength dependent triple-mode photoluminescence of copper-based halides for advanced anti-counterfeiting

New fluorescent materials with a low cost, hypotoxicity, and concealment are desired for the application of anti-counterfeiting. Herein, we report a CsCu2I3@Cs3Cu2I5 composite with a triple-mode photoluminescence (PL) feature by simply adjusting the excitation wavelengths, which are ascribed to the multiple excited states of different phases in the CsCu2I3@Cs3Cu2I5 composite. The broadband emission and high quantum yield (∼51%) of the composite originate from the structure-oriented self-trapped excitons effect of Cs3Cu2I5 and CsCu2I3 phases. Moreover, the incorporation of polyethylene oxide (PEO) into this composite improves the stability of CsCu2I3@Cs3Cu2I5@PEO against harsh environments. The CsCu2I3@Cs3Cu2I5@PEO composite has a slight decay of ∼5% of its initial PL intensity and only a 3.5% shift of the corresponding color coordinate after 30 days of storage. More importantly, its initial PL intensity shows only 10.3% decay under ultraviolet exposure for 200 h. Our work provides a promising approach to design materials for advanced anti-counterfeiting applications.