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Controlling the thermal switching in upconverting nanoparticles through surface chemistry
Nanoscale ( IF 5.8 ) Pub Date : 2021-08-31 , DOI: 10.1039/d1nr03223b Eduardo D Martínez 1 , Alí F García-Flores 2 , Albano N Carneiro Neto 3 , Carlos D S Brites 3 , Luís D Carlos 3 , Ricardo R Urbano 2 , Carlos Rettori 2, 4
Nanoscale ( IF 5.8 ) Pub Date : 2021-08-31 , DOI: 10.1039/d1nr03223b Eduardo D Martínez 1 , Alí F García-Flores 2 , Albano N Carneiro Neto 3 , Carlos D S Brites 3 , Luís D Carlos 3 , Ricardo R Urbano 2 , Carlos Rettori 2, 4
Affiliation
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Photon upconversion taking place in small rare-earth-doped nanoparticles has been recently observed to be thermally modulated in an anomalous manner, showing thermal enhancement of the emission intensity. This effect was proved to be linked to the role of adsorbed water molecules as surface quenchers. The surface capping of the particles has a direct influence on the thermal dynamics of water adsorption and desorption, and therefore on the optical properties. Here, we show that the upconversion intensity of small-size (<25 nm) nanoparticles co-doped with Yb3+ and Er3+ ions, and functionalized with different capping molecules, presents clear irreversibility patterns upon thermal cycling that strongly depend on the chemical nature of the nanoparticle surface. By performing temperature-controlled luminescence measurements we observed the formation of a thermal hysteresis loop, resembling an optical switching phenomenon, whose shape and trajectory depend on the hydrophilicity of the surface. Additionally, an intensity overshoot takes place immediately after turning off the heating source, affecting each radiative transition differently. We performed numerical modelling to understand this effect considering non-radiative energy transfer from the surface defect states to the Er3+ ions. These findings are relevant for the comprehension of nanoparticle-based luminescence and the interplay between the surface and volume effects, and more generally, for applications involving UCNPs such as nanothermometry and bioimaging, and the development of optical encoding systems.
中文翻译：
通过表面化学控制上转换纳米粒子的热转换
最近观察到在稀土掺杂的小纳米粒子中发生的光子上转换以异常方式进行热调制，显示出发射强度的热增强。这种效应被证明与吸附的水分子作为表面猝灭剂的作用有关。颗粒的表面封端对水吸附和解吸的热动力学有直接影响，因此对光学特性有直接影响。在这里，我们展示了与 Yb 3+和 Er 3+共掺杂的小尺寸（<25 nm）纳米颗粒的上转换强度离子，并用不同的封端分子进行功能化，在强烈依赖于纳米颗粒表面化学性质的热循环中呈现出明显的不可逆模式。通过进行温控发光测量，我们观察到热滞回线的形成，类似于光开关现象，其形状和轨迹取决于表面的亲水性。此外，关闭热源后立即发生强度过冲，对每个辐射过渡产生不同的影响。考虑到从表面缺陷状态到 Er 3+ 的非辐射能量转移，我们进行了数值建模以了解这种影响离子。这些发现与理解基于纳米粒子的发光以及表面和体积效应之间的相互作用有关，更一般地说，对于涉及 UCNP 的应用，如纳米测温和生物成像，以及光学编码系统的开发。
更新日期：2021-09-22
中文翻译：
通过表面化学控制上转换纳米粒子的热转换
最近观察到在稀土掺杂的小纳米粒子中发生的光子上转换以异常方式进行热调制，显示出发射强度的热增强。这种效应被证明与吸附的水分子作为表面猝灭剂的作用有关。颗粒的表面封端对水吸附和解吸的热动力学有直接影响，因此对光学特性有直接影响。在这里，我们展示了与 Yb 3+和 Er 3+共掺杂的小尺寸（<25 nm）纳米颗粒的上转换强度离子，并用不同的封端分子进行功能化，在强烈依赖于纳米颗粒表面化学性质的热循环中呈现出明显的不可逆模式。通过进行温控发光测量，我们观察到热滞回线的形成，类似于光开关现象，其形状和轨迹取决于表面的亲水性。此外，关闭热源后立即发生强度过冲，对每个辐射过渡产生不同的影响。考虑到从表面缺陷状态到 Er 3+ 的非辐射能量转移，我们进行了数值建模以了解这种影响离子。这些发现与理解基于纳米粒子的发光以及表面和体积效应之间的相互作用有关，更一般地说，对于涉及 UCNP 的应用，如纳米测温和生物成像，以及光学编码系统的开发。
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