Achieving broadband NIR emission through multiple centers of isolated Cr3+ and Cr3+–Cr3+ ion pairs resulting from phase segregation in SrLa2Ga2O7

Abstract

Cr³⁺-doped broadband near-infrared (NIR) phosphors are strongly sought after for emerging applications in spectroscopy and optical communication. A novel phosphor material activated by Cr³⁺, designed with a Ruddlesden–Popper double-layer perovskite structure, was developed in this research. We successfully synthesized the SrLa₂Ga₂O₇:Cr³⁺ (SLG:Cr) phosphor via a conventional high-temperature solid-state reaction. This phosphor exhibits an ultra-broad emission spanning 700–1200 nm, originating from three distinct emission centers: Cr³⁺ doped into the host SLG lattice (weak crystal field, ⁴T₂ → ⁴A₂ transition), isolated Cr³⁺, and Cr³⁺–Cr³⁺ ion pairs doped into the impurity phase La₄GaO₉ (strong crystal field, ²E → ⁴A₂ transition). Optimal performance was achieved at 0.4% Cr³⁺ doping concentration. At this level, the phosphor exhibited its highest performance, producing a broad emission band with a full width at half maximum (FWHM) of 231 nm upon excitation with 430 nm blue light. Notably, sintering under an N₂ atmosphere significantly enhanced both luminescence intensity and thermal stability, with the phosphor maintaining 88.31% of its room-temperature emission intensity at 420 K (thermal activation energy ΔE = 0.41 eV). Meanwhile, the internal quantum efficiency (IQE) and external quantum efficiency (EQE) were improved to 81% and 30%, respectively. The output power of the pc-NIR-LED based on the SLG:0.4% Cr³⁺ phosphor and a 430 nm chip reached 90.75 mW@150 mA. The unique multi-center emission mechanism and controllable synthesis conditions demonstrated in this work provide new insights for designing high-performance broadband NIR phosphors destined for next-generation light-emitting devices.