Vibronically Coupled Visible and Near‐Infrared Dual‐Band Emission From Te 4+ /Mo 4+ Emitters in Cs 2 HfCl 6

ABSTRACT Luminescent metal halides have garnered considerable attention in a variety of optoelectronic applications owing to their intriguing optical properties and ease of solution processing; however, achieving efficient visible and near‐infrared (NIR) dual‐band emission in these materials remains a persistent challenge. Herein, we report a new class of highly efficient visible/NIR dual‐emitting phosphors based on Te 4+ /Mo 4+ co‐doped Cs 2 HfCl 6 microcrystals (MCs). Benefiting from efficient energy transfer from Te 4+ to Mo 4+ , these MCs display dual‐broadband emission in the visible and NIR regions, originating from the inter‐configurational 3 P 1,0 → 1 S 0 transition of Te 4+ and the intra‐configurational 1 T 1g / 1 E g → 3 T 1g transition of Mo 4+ , respectively, in parallel with exceptional physicochemical stability and remarkable internal (91.8%) and external (81.0%) photoluminescence quantum yields. Specifically, we provide direct evidence for the localized Te 4+ and Mo 4+ emissions, including well‐resolved equidistant vibrational fine structures in the 7 K low‐temperature emission spectra and a strong temperature dependence of the Te 4+ PL lifetime, governed by the interplay between spin‐forbidden and spin‐orbital allowed transitions. These findings provide not only deep insights into the excited‐state dynamics of Te 4+ and Mo 4+ , but also a general co‐doping strategy utilizing s‐ and d‐electron ions for exploring efficient, single‐component visible/NIR dual‐emitters based on lead‐free metal halides.