Large-scale irrigation of Cr3+into different octahedra of zinc aluminate toward continual broadband near-infrared emission

Broadband near-infrared (NIR) phosphors, as key materials in NIR phosphor-converted light-emitting diodes (pcLEDs) for emerging applications, have recently attracted considerable attention. Herein, by selecting a comprehensive engineering strategy of co-substituting [Al3+-Al3+] with [Mg2+-Ge4+] units and increasing Cr3+ concentration, a novel Cr3+-doped ZnAl1.16Mg0.4Ge0.4O4 (ZA(MG)0.4:2 at.%Cr3+) phosphor with continual broadband NIR emission was synthesized. The site occupation of Mg2+/Ge4+ in ZnAl2O4 is unraveled by Rietveld structure refinement and density functional theory (DFT) calculations. According to the photoluminescence behaviors, the formed defect clusters of ZnAl defects to serve as new traps to obtain long-persistent luminescence but can also enhance the emission intensity at -689 nm and -694 nm. The quantity and scale of Cr3+-Cr3+ pairs and Cr3+ in distorted sites, which can improve the thermal quenching resistance and emission intensity in the range of 700-800 nm, can be accurately regulated by varying the concentration of Cr3+. Under 387 nm excitation, the designed material exhibits intensive NIR emission from 685 to 750 nm with a wide full-width at half maximum (FWHM) of 95 nm. The electroluminescence spectrum and potential applications of the NIR pc-LED prepared using ZA(MG)0.4:2 at.% Cr3+ phosphor are also reported. The results promise a feasible strategy to develop NIR phosphors as NIR pc-LEDs lighting sources for applications in non-destructive detection and anti-counterfeiting.