Mn2+–Mn2+ Dimers Induced Robust Light Absorption in Heavy Mn2+ Doped ZnAl2O4 Near‐Infrared Phosphor with an Excellent Photoluminescence Quantum Yield and Thermal Stability

Abstract

Transition metal ions, such as Cr3+, Fe3+, and Ni2+, are widely recognized activators for efficient broadband near‐infrared (NIR) phosphors. However, the potential of Mn2+ ions as NIR‐emitting activators is relatively overlooked due to their typically narrowband emission in the visible spectral region and relatively weak absorption. Herein, a heavy Mn2+‐doped Zn1‐xAl2O4: xMn2+ (ZAO: xMn2+) phosphor is presented that exhibits a single NIR emission band peaked at 830 nm with a bandwidth of 135 nm under excitation at 450 nm. Through comprehensive structural and spectral analysis, this NIR band is attributed to the emission originating from Mn2+ ions within the MnO6 octahedra. Importantly, the formation of Mn2+–Mn2+ dimers breaks the spin‐forbidden rule and significantly enhances the transition probability, as supported by the excited state dynamic analysis. Consequently, the optimal ZAO: 0.70Mn2+ sample shows high internal/external photoluminescence quantum yields of 85.8%/36.9%, along with good thermal stability demonstrated by the emission intensity at 423 K retains 60% of that at 298 K. Finally, a prototype NIR pc‐LED device is fabricated by combining ZAO: 0.70Mn2+ phosphor with a 450 nm blue diode chip, generating an NIR output power of 28.84 mW at 100 mA. This study provides novel insights into high‐performance Mn2+‐activated NIR phosphors.