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

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.