Local structure engineering via Ca2+-Si4+ Aliovalent Co-substitution enables synergistic enhancement of NIR luminescence in β-Ga2O3:Cr3+

Heterovalent Ca 2+ -Si 4+ co-substitution tunes local coordination of Cr 3+ . • Double NIR luminescence without altering Cr 3+ average crystal field. • Optimized phosphor achieves greatly improved absorption and quantum efficiency. • High-brightness pc-NIR-LED is fabricated for imaging and plant lighting. Cr 3+ -doped near-infrared (NIR) phosphors are highly desirable for NIR illumination, biological detection and auxiliary imaging. Herein, we propose a heterovalent Ca 2+ -Si 4+ co-substitution strategy to replace Ga 3+ sites in β -Ga 2 O 3 :Cr 3+ . This approach precisely tailors the local coordination and defect structures surrounding Cr 3+ , leading to remarkable enhancement in NIR luminescence. Characterizations demonstrate that Ca 2+ -Si 4+ co-substitution barely changes the average crystal field of Cr 3+ , but introduces local lattice distortion and reduces coordination symmetry. Such local structure engineering relaxes the d-d transition selection rules of Cr 3+ , thereby enhancing the absorption of the 4 A 2g → 4 T 1g and 4 T 2g transitions and strengthen the broadband NIR emission from the 4 T 2g → 4 A 2g transition. For the optimal Ga 1.81 Ca 0.08 Si 0.08 O 3 :0.03Cr 3+ phosphor, the NIR emission intensity is approximately two times higher relative to pristine β -Ga 2 O 3 :Cr 3+ . Its internal quantum efficiency increases from 81.8% to 88.6%, and absorption efficiency rises from 10.9% to 30.6%. A comparative study on various M A 2+ –M B 4+ ion pairs (M A  = Mg, Ca, Sr, Ba; M B = Si, Ge, Sn) verifies that Ca 2+ -Si 4+ yields the strongest luminescence enhancement for β -Ga 2 O 3 :Cr 3+ . Moreover, this universal strategy also improves blue light absorption and NIR emission of MgGa 2 O 4 :Cr 3+ and LiGa 5 O 8 :Cr 3+ . The assembled phosphor-converted NIR light-emitting diode achieves a NIR output power of 107.9 mW at 400 mA and a photoelectric conversion efficiency of 14.8% at 40 mA. The as-prepared phosphors possess promising practical values for NIR imaging and plant lighting. Download: Download high-res image (288KB) Download: Download full-size image