Origin of the Cr 3+ concentration-dependent broadband near-infrared emission in Sc 2 Si 2 O 7 .

The challenge of developing phosphors with tailored near-infrared (NIR) emission ranges to meet the diverse demands of various applications is a paramount concern in the contemporary realm of NIR phosphor research. A strong dependence of NIR emission on Cr ³⁺ concentration has been demonstrated in Sc _{2- x} Si ₂ O ₇ : x Cr ³⁺ , which exhibits an NIR emission band at 840 nm for low Cr ³⁺ doping concentrations ( x = 0.001-0.01) and an anomalous NIR emission band at 1300 nm for high Cr ³⁺ doping concentrations ( x = 0.01-0.10). Careful investigation of the crystal structure, excitation and emission spectra, and luminescence decay curves indicates that the two NIR emissions can be attributed to the isolated Cr ³⁺ ions and the Cr ³⁺ -Cr ³⁺ pairs, respectively. The strong interaction of exchange-coupled Cr ³⁺ -Cr ³⁺ pairs is supported by temperature-dependent emission spectra, luminescence decay curves and electron paramagnetic resonance (EPR) measurements. This work provides a new insight into the study of Cr ³⁺ -Cr ³⁺ pairs for broadband NIR emission.