Abstract

This study investigated the effect of magnetic coupling of Fe3+ on Ho3+ luminescence in the double perovskite Cs2NaScCl6. Under 980 nm laser excitation, red emission from Ho3+ ions was observed in Cs2NaScCl6:Ho3+/Fe3+ samples. We propose that this arises from spin-selective up-conversion mediated by magnetic polarons (EMPs). However, green emission from the 5F4/5S2 levels was not observed in this system. The experimental results suggest that localized EMPs form via ferromagnetic short-range ordering between Fe3+ and Ho3+ or among Fe3+ ions. These EMPs can be directly excited to higher energy levels via a biexciton absorption transition, then relaxed to the 5F5 level of Ho3+ through ferromagnetic coupling. Under X-ray excitation, the characteristic emission peaks of Ho3+ in Cs2NaScCl6:Ho3+/Fe3+ become smoother, lose fine structure, and significantly decrease in intensity with increasing Fe3+ concentration. Based on this, we prepared Fe3+-free Cs2NaScCl6:Ho3+ and explored its excellent scintillation performance, with a detection limit as low as 37.73 nGyair s−1, below the medical diagnostic dose, surpassing the performance of commercial scintillators such as LuAG:Ce and BGO. This work reports the phenomenon of using Fe3+ as a sensitizer to achieve up-conversion sensitization in chloride double perovskites and demonstrates the application potential of Fe-free systems in ultra-low-dose X-ray imaging.

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