Key Takeaways & Executive Findings
- •• • The co-doped Cs3GdCl6 microcrystals exhibit a 2.3-fold increase in integrated NIR-II emission intensity from 298 K to 373 K, directly addressing thermal quenching limitations in conventional phosphors. • • Energy transfer efficiency from Sb3+ to Er3+ reaches 86% at room temperature and increases further with temperature, enabling efficient sensitization of NIR-II emission. • • The material demonstrates high photostability, retaining 95% of initial emission after 120 minutes of continuous UV irradiation, suitable for long-term operation in bioimaging and communication devices. • • A proof-of-concept wireless optical communication link using the microcrystals achieves a signal-to-noise ratio of 30 dB at 400 Hz modulation, indicating practical viability for NIR-II optical communication.
Abstract
Near-infrared-II (NIR-II, 1000-1700 nm) luminescent materials are pivotal for deep-tissue bioimaging and optical communication, yet their performance is often limited by low quantum yields and thermal quenching. Here, we report a thermal-enhanced NIR-II luminescence in Sb3+/Er3+ co-doped Cs3GdCl6 microcrystals synthesized via a modified Bridgman method. Under ultraviolet excitation, the co-doped microcrystals exhibit intense NIR-II emission centered at 1532 nm corresponding to Er3+: 4I13/2 → 4I15/2 transition, with a maximum relative sensitivity of 1.2% K−1 at 303 K. Notably, the integrated NIR-II emission intensity increases by 2.3-fold from 298 K to 373 K, demonstrating anomalous thermal enhancement. This behavior is attributed to the thermally activated energy transfer from Sb3+ sensitizers to Er3+ activators, as confirmed by temperature-dependent photoluminescence spectra and decay kinetics. The energy transfer efficiency reaches 86% at room temperature and further improves with rising temperature. The microcrystals also show excellent photostability, retaining 95% of initial intensity after 120 min continuous UV irradiation. Furthermore, we demonstrate a proof-of-concept wireless optical communication link using the microcrystals as a NIR-II phosphor, achieving a signal-to-noise ratio of 30 dB at 400 Hz modulation frequency. These findings provide a new strategy for designing thermal-enhanced NIR-II luminescent materials and expand their potential in temperature sensing and optical communication.
1. Introduction
Near-infrared-II (NIR-II) luminescence is critical for deep-tissue imaging and high-speed optical communication, but conventional rare-earth doped materials suffer from low quantum yields and severe thermal quenching, limiting their practical deployment. Existing strategies, such as core-shell engineering or organic dye sensitization, often involve complex synthesis or poor photostability, failing to meet the demands of real-world applications.
This work introduces Sb3+/Er3+ co-doped Cs3GdCl6 microcrystals that exhibit anomalous thermal-enhanced NIR-II emission, overcoming the thermal quenching bottleneck. By leveraging thermally activated energy transfer from Sb3+ to Er3+, the material achieves a 2.3-fold emission increase from 298 K to 373 K, while maintaining high photostability. This approach provides a simple, robust route to high-performance NIR-II phosphors, with demonstrated utility in temperature sensing and wireless optical communication.
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LIU Junxiang, MA Zimeng, ZHANG Wei, HUANG Ping, SHAO Zhiqing, HU Yaqiong, YANG Guangyao, ZHENG Wei, CHEN Xueyuan (2026). Thermal-enhanced near-infrared-II luminescence from Sb3+/Er3+ co-doped Cs3GdCl6 microcrystals. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4502-1
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Frequently Asked Questions
What is the mechanism behind the thermal-enhanced NIR-II emission, and how does it differ from conventional thermal quenching behavior?
The thermal enhancement is attributed to thermally activated energy transfer from Sb3+ sensitizers to Er3+ activators. As temperature rises, the energy transfer efficiency increases, leading to enhanced Er3+ emission. This contrasts with typical phosphors where increased temperature accelerates non-radiative decay and quenches luminescence.
What are the key performance metrics of the material for temperature sensing applications?
The material exhibits a maximum relative sensitivity of 1.2% K−1 at 303 K, based on the temperature-dependent intensity ratio of the NIR-II emission. This sensitivity is competitive with existing optical temperature sensors, and the material's thermal enhancement provides a distinct advantage for high-temperature sensing.
How does the material's photostability compare to existing NIR-II phosphors, and what implications does this have for long-term device operation?
The microcrystals retain 95% of initial emission intensity after 120 minutes of continuous UV irradiation, demonstrating superior photostability compared to many organic-based NIR-II emitters. This ensures reliable performance in prolonged bioimaging or communication applications.
What is the demonstrated performance in optical communication, and what are the potential data rates?
In a proof-of-concept wireless communication link, the material achieved a signal-to-noise ratio of 30 dB at 400 Hz modulation frequency. While this is a low data rate, it validates the feasibility of using the phosphor for NIR-II optical communication, and higher modulation frequencies could be explored with optimized setups.
What are the scalability and synthesis challenges for industrial production of these microcrystals?
The synthesis uses a modified Bridgman method, which is scalable but requires high-temperature furnaces and controlled cooling. The raw materials (CsCl, GdCl3, SbCl3, ErCl3) are relatively inexpensive, but achieving uniform doping and crystal size distribution may require optimization. Further scale-up studies are needed to assess cost-effectiveness.
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