Co-doped aluminum metaphosphate-based phosphor for thermally robust and efficient broadband near-infrared-II light-emitting diodes

Abstract

Broadband near-infrared (NIR) light sources based on phosphor-converted light-emitting diodes (pc-LEDs) are of great interest for advanced biochemical analysis, medical diagnostics, and sensing. Nonetheless, the development of NIR phosphors that can be excited by blue light and maintain strong thermally stable emissions above 900 nm remains a key challenge. Herein, we report an aluminum metaphosphate AlP₃O₉ phosphor featuring Cr³⁺ → Yb³⁺ energy transfer (ET) that exhibits the most simultaneous intense and thermally robust NIR emission spanning the NIR-I and NIR-II regions (650–1200 nm) under blue LED excitation. We prove that effective ET from Cr³⁺ to Yb³⁺ can both boost the quantum yield (QY) to ∼82% and preserve nearly 100% of the initial room temperature emission intensity at 150 °C, the highest values reported so far. Photoluminescence decay measurements confirm that Cr³⁺ → Yb³⁺ ET mitigates nonradiative decay of Cr³⁺ and contributes to the superior thermal stability of NIR-II emission from Yb³⁺. Furthermore, a prototype NIR-II pc-LED integrating the optimized APO:0.12Cr³⁺,0.03Yb³⁺ phosphor delivers strong NIR-II output with standard blue LED chips. Leveraging this emission, we have demonstrated accurate detection of alcohol concentrations in water–alcohol mixtures, highlighting the significant potential of these luminescent materials in analytical sensing. Overall, this work presents the most efficient and thermally stable broadband NIR-II phosphor suitable for next-generation pc-LED-based applications along with a promising strategy for designing them.