Lanthanide-doped upconversion nanoparticles (UCNPs) have unique photoluminescent properties that are useful in many biomedical applications. Modification of UCNPs with a polymer layer can confer additional functionality such as biocompatibility, stability in vivo, or drug delivery capability. It is also important that the modification process can be controlled precisely and without having adverse effects on the UCNPs luminescence properties. Herein, a polymer shell was grafted directly from the surface of UCNPs (grafting from) via visible light (λ_max = 635 nm, 0.7 mW/cm²) regulated photoenergy/electron transfer–reversible addition fragmentation chain transfer polymerization (PET-RAFT). The polymerization kinetics, grafting density, and thickness of the surface-tethered polymer chains can be tuned precisely by adjusting the monomer and RAFT agent ratio or the light exposure time. This approach also permits temporal control of the polymerization process. That is, the polymerization process can be initiated, halted, or terminated by switching the light source on and off. By limiting the non-radiative decay caused by surface defects, as well as from vibrational deactivation from solvents, the polymer shell enhanced the upconversion luminescence of the silica-coated UCNPs. This investigation paves the way for the development of UCNPs with controlled properties for various application requirements.

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通过可见光调节聚合可控制的聚合物壳在上转换纳米粒子表面上的直接生长

掺杂镧系元素的上转换纳米粒子（UCNP）具有独特的光致发光特性，可用于许多生物医学应用中。用聚合物层修饰UCNP可以赋予其他功能，例如生物相容性，体内稳定性或药物传递能力。同样重要的是，可以精确控制修饰过程，并且不会对UCNPs发光特性产生不利影响。本文中，通过可见光（_λmax = 635 nm，0.7 mW / cm ²）从UCNPs表面直接接枝聚合物壳（从中接枝）。）调节光能/电子转移-可逆加成断裂链转移聚合反应（PET-RAFT）。通过调节单体与RAFT试剂的比例或曝光时间，可以精确地调节表面动力学连接的聚合物链的聚合动力学，接枝密度和厚度。该方法还允许对聚合过程进行时间控制。即，可以通过打开和关闭光源来启动，停止或终止聚合过程。通过限制由表面缺陷以及溶剂引起的振动失活引起的非辐射衰减，聚合物壳增强了二氧化硅包覆的UCNP的上转换发光。这项研究为开发具有可控制特性的UCNPs为各种应用需求铺平了道路。