SITE MAP

Achieving simultaneous near-infrared (NIR) and shortwave infrared (SWIR) emissions from single-phase phosphors is challenging because of the distinct electronic configurations and local coordination environments required for these emissions. Multivalence transition metal doping enables diverse optical transitions from coexisting oxidation states. In this study, we demonstrated that the coexistence of Cr³⁺ and Cr⁴⁺ ions in a CaAl12O19 host leads to broad NIR and SWIR emissions, respectively. The Cr³⁺ ions were stabilized in octahedral sites and exhibited broadband NIR emission via the spin-allowed ⁴T2(4F) → ⁴A2(4F) transition, while the Cr⁴⁺ ions occupied tetrahedral or distorted coordination sites and contributed broadband SWIR emission through the ³T2→³A2 transition. Crystal field parameters derived from a Tanabe–Sugano diagram analysis (Dq/B values of 2.1 and 1.6 for Cr³⁺and Cr⁴⁺, respectively) confirmed the octahedral and tetrahedral environments and the origin of the dual emissions. We propose an emission mechanism where the Cr³⁺/Cr⁴⁺ interplay enables efficient dual-band NIR–SWIR luminescence.