Subgrid cage confinement engineering enabled ultra-efficient near-infrared Cr3+–Ln3+ co-doped phosphors

Abstract

Precise control of energy migration between Cr³⁺ sensitizers and Ln³⁺ activators at the topochemical subgrid level remains a fundamental challenge. Herein, a novel subgrid cage confinement engineering strategy was proposed, achieving ultra-efficient near-infrared (NIR) Cr³⁺–Ln³⁺ (Ln = Yb, Nd, Er) co-doped phosphors. The bilayer cage architecture of GdAl_1.5Ga_1.5(BO₃)₄ precisely confines Ln³⁺ at the central Gd³⁺ sites, while providing octahedral lattice positions for Cr³⁺ substitution within the Al/GaO₆ framework. This unique confinement constrains Cr³⁺–Ln³⁺ separation to the optimal 3.67 Å while increasing the Ln³⁺–Ln³⁺ distance to 5.92 Å, enabling highly efficient Cr³⁺–Ln³⁺ energy transfer (η_ETE: 61% for Yb³⁺, 82% for Nd³⁺, 46% for Er³⁺) and suppressing energy losses between neighbouring Ln³⁺ ions. Consequently, the Cr³⁺–Yb³⁺ co-doped system achieved a high photoluminescence quantum yield of 86% and retained 94% of its intensity even at 423 K, demonstrating exceptional thermal stability. The fabricated NIR phosphor-converted light-emitting diodes delivered a NIR output power of 127 mW with a photoelectric efficiency of 13% under a 300 mA operating current. These capabilities enabled high-contrast biological imaging applications, such as vein visualization and non-destructive testing, as validated by prototype demonstrations.