Abstract The upconversion of near-infrared (NIR) fluorescence, with a high tissue penetration depth, possesses a distinct advantage in biological temperature detection but is limited by the lack of rare earth-doped nanophosphors with intense and selective NIR UC emission. Here, we show that high-efficiency NIR temperature sensing can be achieved by appropriately doping Tm3+ activators into a polarized layered host, utilizing the high environmental sensitivity of the 3H4→3H6 electric dipole transition (808 nm) of Tm3+. To confirm this concept, Yb3+/Tm3+ codoped Bi7F11O5 upconverting nanosheets were synthesized and characterized. Furthermore, the thermometric performance of the samples was analyzed based on the temperature-dependent fluorescence intensity ratio from the thermally coupled levels (3F3/3H4) of Tm3+. The results showed that, under 980 nm diode laser excitation, the prepared samples can produce a high NIR-to-visible UC emission ratio (I800nm/I475nm) of over 2000 for Tm3+. The maximum sensitivity Sa/Sr was 1.4% K−1/0.577 K−1 at 303 K based on the 3F3 and 3H4 levels, and the material exhibited a wide functional temperature range of 303–573 K. The results of our work not only improve the understanding of the optical properties of RE3+ ions in layered materials but also show a potential application for physiological temperature sensing in biological tissues and cells.

中文翻译：

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基于 Yb3+-Tm3+ 共掺杂 Bi7F11O5 纳米片热耦合能级的 NIR-NIR 上转换光学温度传感

摘要 近红外 (NIR) 荧光上转换具有高组织穿透深度，在生物温度检测方面具有明显优势，但由于缺乏具有强烈和选择性 NIR UC 发射的稀土掺杂纳米磷光体而受到限制。在这里，我们表明，利用 Tm3+ 的 3H4→3H6 电偶极跃迁（808 nm）的高环境​​敏感性，可以通过将 Tm3+ 活化剂适当掺杂到极化层状主体中来实现高效 NIR 温度传感。为了证实这一概念，合成并表征了 Yb3+/Tm3+ 共掺杂 Bi7F11O5 上转换纳米片。此外，基于来自 Tm3+ 的热耦合水平 (3F3/3H4) 的温度依赖性荧光强度比分析了样品的测温性能。结果表明，在980 nm二极管激光激发下，制备的样品对Tm3+可以产生超过2000的高NIR-可见光UC发射比（I800nm/I475nm）。基于 3F3 和 3H4 能级，在 303 K 时 Sa/Sr 的最大灵敏度为 1.4% K-1/0.577 K-1，并且该材料表现出 303-573 K 的宽功能温度范围。我们的工作结果不仅提高了对层状材料中 RE3+ 离子光学特性的理解，但也显示了在生物组织和细胞中生理温度传感的潜在应用。