Upconversion nanoparticles (UCNPs) with hollow structures exhibit many fascinating optical properties due to their special morphology. However, there are few reports on the exploration of hollow UCNPs and their optical applications, mainly because of the difficulty in constructing hollow structures by conventional methods. Here, we report a one-step template-free method to synthesize NaBiF₄:Yb,Er (NBFYE) hollow UCNPs via Ostwald ripening under solvothermal conditions. Moreover, we also elucidate the possible formation mechanism of hollow nanoparticles (HNPs) by studying the growth process of nanoparticles in detail. By changing the contents of polyacrylic acid and H₂O in the reaction system, the central cavity size of NBFYE nanoparticles can be adjusted. Benefiting from the structural characteristics of large internal surface area and high surface permeability, NBFYE HNPs exhibit excellent luminescence properties under 980 nm near-infrared irradiation. Importantly, NBFYE hollow UCNPs can act as self-referenced ratiometric luminescent thermometers under 980 nm laser irradiation, which are effective over a wide temperature range from 223 K to 548 K and have a maximum sensitivity value of 0.0065 K⁻¹ at 514 K. Our work clearly demonstrates a novel method for synthesizing HNPs and develops their applications, which provides a new idea for constructing hollow structure UCNPs and will also encourage researchers to further explore the optical applications of hollow UCNPs.

具有中空结构的上转换纳米粒子（UCNPs）由于其特殊的形态而表现出许多令人着迷的光学特性。然而，关于空心UCNPs及其光学应用的探索报道很少，主要是因为传统方法难以构建空心结构。在这里，我们报告了一种在溶剂热条件下通过Ostwald 熟化合成 NaBiF ₄ :Yb,Er (NBFYE) 空心 UCNPs的一步法无模板方法。此外，我们还通过详细研究纳米粒子的生长过程，阐明了中空纳米粒子（HNPs）的可能形成机制。通过改变聚丙烯酸和H _2的含量O 在反应体系中，NBFYE 纳米粒子的中心腔尺寸可以调节。得益于大内表面积和高表面渗透性的结构特点，NBFYE HNPs在980 nm近红外照射下表现出优异的发光性能。重要的是，NBFYE 中空 UCNP 可以在 980 nm 激光照射下充当自参考比率发光温度计，在 223 K 至 548 K 的宽温度范围内有效，在 514 K 时的最大灵敏度值为 0.0065 K ^-1 。这项工作清楚地展示了一种合成 HNPs 的新方法并开发了它们的应用，这为构建中空结构 UCNPs 提供了新的思路，也将鼓励研究人员进一步探索中空 UCNPs 的光学应用。