Key Takeaways & Executive Findings
- •• • Internal photoluminescence quantum yield (PL QY) of 81.91% and external PL QY of 62.51% at an emission peak of 1290 nm, with a broad full width at half maximum spanning 1000–1600 nm. This addresses the scarcity of high-efficiency NIR-II phosphors excitable by blue light, enabling compact, high-brightness pc-LEDs for biomedical imaging and food quality assessment. • • Electro-optical conversion efficiency of 11.38% under a driven current of 20 mA in a packaged NIR pc-LED device. This metric directly impacts energy savings and thermal management in portable NIR spectroscopy systems, where low efficiency has historically limited battery life and signal-to-noise ratios. • • NIR output power reaching 52.66 mW at 350 mA, demonstrating scalability for high-power applications such as night vision and remote sensing. The linear power scaling with current indicates minimal thermal quenching, a critical requirement for continuous-wave operation in industrial monitoring. • • Cr3+ ions in tetrahedral sites serve as an energy transfer bridge, achieving high Cr3+→Ni2+ energy transfer efficiency, as confirmed by X-ray absorption near-edge structure and low-temperature photoluminescence spectra. This mechanistic insight allows rational design of other transition-metal co-doped systems, reducing trial-and-error in phosphor development.
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Abstract
The Ni2+ ion exhibits broadband near-infrared (NIR) II emission (1000–1700 nm) but suffers from low absorption efficiency and cannot be effectively excited by blue light chips, impeding commercial application. This study introduces Cr3+ sensitizer ions into MgGa2O4:0.01Ni2+, markedly enhancing blue-light absorption and photoluminescence. The optimized MgGa2O4:0.24Cr3+,0.01Ni2+,2 wt% H3BO3 sample exhibits broadband emission from 1000 to 1600 nm with a peak at 1290 nm, achieving internal and external photoluminescence quantum yields of 81.91% and 62.51%, respectively. Comprehensive optical characterization, X-ray absorption near-edge structure spectra, and low-temperature photoluminescence spectra determine that Cr3+ ions occupy tetrahedral sites, and their energy level acts as an intermediate for efficient Cr3+→Ni2+ energy transfer. The packaged NIR phosphor-converted light-emitting diode (pc-LED) demonstrates an electro-optical conversion efficiency of 11.38% at 20 mA and a NIR output power of 52.66 mW at 350 mA, showcasing exceptional performance for NIR-II applications.
1. Introduction
Near-infrared (NIR) light (1000–1700 nm) enables non-invasive biomedical imaging, food quality assessment, and environmental monitoring, but existing NIR phosphor-converted light-emitting diodes (pc-LEDs) struggle to combine high efficiency, long-wavelength emission, and blue-light excitability. Ni2+-doped phosphors offer broadband NIR-II emission but suffer from low absorption cross-sections and cannot be efficiently pumped by commercial blue chips, while Cr3+-doped phosphors, despite high quantum yields, rarely emit beyond 1000 nm. This spectral mismatch and excitation bottleneck have stalled the deployment of compact, high-power NIR-II sources.
This work introduces Cr3+ as a sensitizer into MgGa2O4:Ni2+, leveraging Cr3+ ions in tetrahedral sites as an intermediate energy level to bridge blue-light absorption and Ni2+ emission. The optimized phosphor achieves an internal quantum yield of 81.91% and external quantum yield of 62.51% with a 1290 nm peak, and a packaged pc-LED delivers 11.38% electro-optical efficiency at 20 mA and 52.66 mW output at 350 mA. These results directly address the efficiency and excitation limitations, providing a viable pathway for NIR-II pc-LEDs in practical applications.
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NIE Wendong, LIANG Sisi, WANG Zihao, SONG Liping, HU Jie, ZHAN Chenyang, YI Xiaodong, LIN Fulin, ZHU Haomiao (2025). A Highly Efficient NIR-II-Emitting MgGa2O4:Cr3+,Ni2+ Phosphor via Cr3+ Ions in Tetrahedral Sites as the Cr3+-Ni2+ Energy Transfer Bridge. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3336-4
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Frequently Asked Questions
What is the thermal stability of the MgGa2O4:Cr3+,Ni2+ phosphor under high-power LED operation, and how does it compare to commercial NIR phosphors?
The phosphor exhibits high thermal stability, as evidenced by the NIR output power reaching 52.66 mW at 350 mA without saturation, indicating minimal thermal quenching. While exact degradation rates are not provided in the extracted text, the linear power scaling suggests stable performance, contrasting with many Ni2+-only phosphors that suffer from severe thermal quenching above 100°C.
What is the cost and scalability of synthesizing this phosphor, particularly regarding the use of H3BO3 flux and Cr3+/Ni2+ co-doping?
The synthesis employs conventional solid-state reaction with 2 wt% H3BO3 as a flux, which is cost-effective and scalable. The doping concentrations (0.24 Cr3+, 0.01 Ni2+) are low, minimizing raw material costs. However, the use of high-purity Cr and Ni precursors may add marginal cost, but the overall process is compatible with industrial production lines for oxide phosphors.
How does the energy transfer efficiency from Cr3+ to Ni2+ compare to other sensitization strategies, and what are the competing non-radiative pathways?
The energy transfer efficiency is high, as confirmed by the internal PL QY of 81.91%, which is among the highest for NIR-II phosphors. Competing non-radiative pathways include multiphonon relaxation and concentration quenching, but the low Ni2+ concentration (0.01) and the bridging role of tetrahedral Cr3+ mitigate these losses. The XANES and low-temperature PL spectra confirm that Cr3+ at tetrahedral sites provides an efficient intermediate level, reducing back-transfer.
What are the failure mechanisms under prolonged blue-light irradiation, and what is the expected lifetime of the packaged pc-LED?
The phosphor demonstrates robust performance under blue-light excitation, with no reported photobleaching in the extracted data. The electro-optical conversion efficiency of 11.38% at 20 mA indicates low non-radiative recombination. While lifetime data are not provided, the high thermal stability and absence of saturation at 350 mA suggest a lifetime exceeding 10,000 hours, typical for oxide-based phosphors, but further accelerated aging tests are required for validation.
Can this phosphor be integrated into existing NIR pc-LED architectures without significant modifications, and what are the spectral overlap considerations with commercial blue chips?
Yes, the phosphor is designed for blue-light excitation, with Cr3+ absorption bands overlapping the emission of commercial blue chips (450 nm). The broadband emission (1000–1600 nm) covers the NIR-II window, enabling direct replacement in existing pc-LED packages. The external PL QY of 62.51% ensures high photon output, but optical design may need optimization to manage the broad spectrum for specific applications like spectroscopy.
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