Thermo-enhanced nanothermometry has attracted considerable attention owing to its high thermal sensitivity; however, most studies are focused on upconversion nanoparticles (NPs) in the form of powder. In the field of bioapplication, it is imperative to investigate the performance of NPs dispersed in aqueous solutions to expedite their in vivo utilization. Particularly, the influence of –OH on the thermal properties of these NPs remains unclear. Herein, we investigated the thermal properties of α-NaYbF₄:2%Er,2%Ce@NaYF₄ NPs with different shell thicknesses emitting in the second near-infrared (NIR-II) region. Both powder and aqueous solution-dispersed NPs exhibit thermal enhancements due to a reduction in the –OH content and a blue shift of –OH vibration at elevated temperatures, respectively. The observed blue shift of –OH vibration is attributed to the conversion of 4-coordinated hydrogen-bound water into 2-coordinated hydrogen-bound water. By separately introducing LiCl and D₂O to an aqueous solution, we demonstrated how the blue shift and –OH content affect the thermal enhancement factor in aqueous solutions. These findings underscore the crucial role of –OH groups in nanothermometry for bioapplications while also providing insights for designing highly thermally sensitive nanothermometers.

中文翻译：

---

–OH对NIR-II镧系元素掺杂纳米粒子在水中热增强性能的影响

热增强纳米测温技术由于其高热灵敏度而引起了广泛的关注；然而，大多数研究都集中在粉末形式的上转换纳米粒子 (NP)。在生物应用领域，有必要研究分散在水溶液中的纳米颗粒的性能，以加快其在体内的利用。特别是，–OH 对这些纳米粒子热性能的影响仍不清楚。在此，我们研究了不同壳厚度的α-NaYbF ₄ :2%Er,2%Ce@NaYF ₄ NPs在第二近红外（NIR-II）区域发射的热性质。粉末和水溶液分散的纳米颗粒均表现出热增强作用，这分别是由于高温下 -OH 含量的减少和 -OH 振动的蓝移。观察到的-OH振动的蓝移归因于4配位氢结合水转化为2配位氢结合水。通过分别将LiCl和D ₂ O引入到水溶液中，我们演示了蓝移和-OH含量如何影响水溶液中的热增强因子。这些发现强调了–OH基团在生物应用纳米测温中的关键作用，同时也为设计高热敏纳米温度计提供了见解。