NIR-I Excitable and NIR-II Emissive Cr, Yb, Co-Doped Cs₂NaScCl₆ Double Perovskite Halides for Biodetection

Lanthanide doping has been instrumental in tuning the emissions of double perovskite halides (DPHs) into the near-infrared (NIR) region. However, the limited penetration depth of UV excitation and typically low photoluminescence quantum yield (PLQY) of these materials restrict their utility in biomedical applications. In this paper, Cr3+-doped lead-free DPHs (Cs2NaScCl6:Cr3+) have been explored, featuring a broadband NIR emission spanning 800–1300 nm and an impressive PLQY of 76.9%. Oriented toward biological applications, we employ Yb3+ as a codopant to be introduced into Cs2NaScCl6:Cr3+. The novel Cs2NaScCl6:Cr3+,Yb3+ crystal powder displays a red-shifted emission (peaking at 995 nm) with a remarkably narrower full width at half-maximum (fwhm) of 51 nm. Importantly, the efficient energy transfer between Cr3+ and Yb3+ enables Cs2NaScCl6:Cr3+,Yb3+ to maintain a PLQY of 46.1% upon 780 nm excitation. Leveraging its NIR-I excitable and NIR-II emissive properties, Cs2NaScCl6:Cr3+,Yb3+ presents great potential in biodetection and bioimaging applications. Its superior energy transfer efficiency, high PLQY, and favorable spectral characteristics position this material as a promising candidate for advanced biomedical techniques requiring deep tissue penetration and high imaging contrast.