Nunes Coelho Sergio Fernando, Bispo-Jr Airton Germano, de Oliveira Nagyla Alves, Mazali Italo Odone, Sigoli Fernando Aparecido
Department of Inorganic Chemistry, Institute of Chemistry, University of Campinas, Unicamp, Josué de Castro Street, Cidade Universitária, Campinas, 13083-970, Brazil.
Nanoscale. 2024 Apr 18;16(15):7493-7503. doi: 10.1039/d4nr00574k.
Lanthanide (Ln)-doped sodium gadolinium tetrafluoride (NaGdF) nanoparticles have been excelled as attractive upconversion systems for anti-counterfeiting or energy conversion for instance, with a special interest in the visible upconversion of Eu and Tb. The core@shell architecture has enabled the bright upconversion of Eu and Tb in this matrix by interfacial energy transfer sensibilized by the Tm/Yb pair. Another approach to enable Eu and Tb upconversion could be the interparticle energy transfer (IPET) between Ln-doped sensitizer and acceptor nanoparticles. Yet, the low molar absorptivity of the Ln through 4f ↔ 4f electronic transitions and the large distance between the nanoparticles are shortcomings that should decrease the energy transfer efficiency. On the other hand, it is feasible to predict that the association of organic ligands displaying large molar absorptivity on the acceptor nanoparticle surface could help to overcome the absorption limitation. Inspired by this exciting possibility, herein, we present the Eu/Tb upconversion intermediated by IPET between the donor Tm, Yb-doped NaGdF nanoparticle and the acceptor Ln-doped NaGdF (Ln = Eu and/or Tb) nanoparticles functionalized with a series organic ligands on the surface (tta = thenoyltrifluoroacetonate, acac = acetylacetonate, or 3,5-bbza = 3,5-dibromebenzoate). Either in solid state or in suspension, upon excitation at 980 nm, visible Eu/Tb upconversion could be observed. This emission comes from the absorption of the Tm, Yb pair in the donor nanoparticle, followed by IPET from the Tm excited levels to the ligand singlet/triplet states on the acceptor nanoparticle surface, ligand-to-Eu/Tb energy transfer, and upconversion emission. Spectroscopic evidences from the analysis of the donor level lifetimes indicate the contribution of non-radiative energy transfer for the IPET mechanism; the radiative mechanism also contributes for the IPET. Moreover, the design herein introduced enables the development of luminescence temperature probes with relative thermal sensitivity as high as 1.67% K at 373 K. Therefore, this new upconversion pathway opens an avenue of possibilities in an uncharted territory to tune the visible upconversion of Ln ions.
镧系（Ln）掺杂的四氟化钠钆（NaGdF）纳米颗粒作为防伪或能量转换等领域极具吸引力的上转换体系表现出色，尤其对铕（Eu）和铽（Tb）的可见光上转换特别感兴趣。核壳结构通过铥（Tm）/镱（Yb）对敏化的界面能量转移实现了Eu和Tb在该基质中的明亮上转换。实现Eu和Tb上转换的另一种方法可能是掺杂Ln的敏化剂纳米颗粒与受体纳米颗粒之间的颗粒间能量转移（IPET）。然而，Ln通过4f↔4f电子跃迁的低摩尔吸光率以及纳米颗粒之间的大距离是会降低能量转移效率的缺点。另一方面，可以预测在受体纳米颗粒表面显示出大摩尔吸光率的有机配体的结合有助于克服吸收限制。受这种令人兴奋的可能性启发，在此，我们展示了由供体Tm、Yb掺杂的NaGdF纳米颗粒与表面用一系列有机配体（噻吩甲酰三氟丙酮（tta）、乙酰丙酮（acac）或3,5 - 二溴苯甲酸酯（3,5 - bbza））功能化的受体Ln掺杂的NaGdF（Ln = Eu和/或Tb）纳米颗粒之间的IPET介导的Eu/Tb上转换。无论是在固态还是悬浮液中，在980 nm激发时，都可以观察到可见的Eu/Tb上转换。这种发射来自供体纳米颗粒中Tm、Yb对的吸收，随后是从Tm激发态到受体纳米颗粒表面配体单重态/三重态的IPET、配体到Eu/Tb的能量转移以及上转换发射。对供体能级寿命分析的光谱证据表明非辐射能量转移对IPET机制有贡献；辐射机制也对IPET有贡献。此外，本文引入的设计能够开发出在373 K时相对热灵敏度高达1.67% K的发光温度探针。因此，这种新的上转换途径在一个未知领域开辟了一系列可能性，以调节Ln离子的可见光上转换。
