Upconversion nanosensitizers have been widely considered to have important applications in the treatment of major diseases such as tumors and the utilization of solar energy. Majority of the efforts so far have been focused on improving the efficiency of energy transfer (ET) between upconversion nanoparticles (UCNPs) and the anchored sensitizers with premise that high ET efficiency will lead to high acceptor efficacy. This premise is, however, proved by our current work to be invalid for commonly used load. Interaction between adjacent sensitizing molecules was found to be critical which undermines the amount of excited monomer sensitizers and thus fades the efficacy. Here NaYF₄:Yb³⁺,Er³⁺ UCNPs and rose bengal (RB) photosensitizer molecules were used as the model energy donors and acceptors, respectively. Contrary to monotonous increase of the ET efficiency from UCNPs to RB species with increasing RB loading, acceptor efficacy characterized by the reactive oxygen species, as well as the RB fluorescence, exhibits bizarre dependence on the RB loading. The underlying mechanism was well studied by the steady-state and time-resolved spectroscopy of a series of samples. RB aggregates are believed to be responsible for the severe deviation between the ET efficiency and acceptor efficacy. The conclusion was validated by in vitro test where the photodynamic therapy with the most monomer RB in UCNPs-RB nanosensitizers kills 35.8% more cells than that with the highest RB loading. This understanding sheds light on construction of new ET based nanosystems for broad applications, such as medicine, solar energy utilization and optical storage.

上转换纳米增敏剂已被广泛认为在治疗肿瘤等重大疾病和利用太阳能方面具有重要应用。到目前为止，大部分努力都集中在提高上转换纳米粒子 (UCNP) 和锚定敏化剂之间的能量转移 (ET) 效率，前提是高 ET 效率将导致高受体效率。然而，我们目前的工作证明这个前提对于常用负载是无效的。发现相邻敏化分子之间的相互作用至关重要，这会破坏激发的单体敏化剂的数量，从而降低功效。这里 NaYF ₄ :Yb ³⁺ ,Er ³⁺UCNPs 和玫瑰红 (RB) 光敏剂分子分别用作模型能量供体和受体。与从 UCNPs 到 RB 物种的 ET 效率随着 RB 负载的增加而单调增加相反，以活性氧和 RB 荧光为特征的受体功效表现出对 RB 负载的奇怪依赖性。通过一系列样品的稳态和时间分辨光谱学很好地研究了潜在机制。RB 聚集体被认为是造成 ET 效率和受体效率之间严重偏差的原因。结论通过体外验证测试中，UCNPs-RB 纳米增敏剂中单体 RB 最多的光动力疗法杀死的细胞比 RB 负载最高的细胞多 35.8%。这种理解为构建新的基于 ET 的纳米系统提供了启示，用于广泛的应用，例如医学、太阳能利用和光存储。