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

Transition metal ions, such as Cr 3+ , Fe 3+ , and Ni 2+ , are widely recognized activators for efficient broadband near-infrared (NIR) phosphors. However, the potential of Mn 2+ 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 Mn 2+ -doped Zn 1-x Al 2 O 4 : xMn 2+ (ZAO: xMn 2+ ) 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 Mn 2+ ions within the MnO 6 octahedra. Importantly, the formation of Mn 2+ –Mn 2+ dimers breaks the spin-forbidden rule and significantly enhances the transition probability, as supported by the excited state dynamic analysis. Consequently, the optimal ZAO: 0.70Mn 2+ 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: 0.70Mn 2+ 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 Mn 2+ -activated NIR phosphors.