Mn<sup>2+</sup>–Mn<sup>2+</sup> Dimers Induced Robust Light Absorption in Heavy Mn<sup>2+</sup> Doped ZnAl<sub>2</sub>O<sub>4</sub> Near‐Infrared Phosphor with an Excellent Photoluminescence Quantum Yield and Thermal Stability
Chenyang Zhan, Haomiao Zhu, Sisi Liang, Wendong Nie, Zihao Wang, Maochun Hong
Abstract
Abstract 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.