Triplet–triplet annihilation photon upconversion (TTA-UC) is attracting a great deal of attention as a viable approach to exploit unutilized wavelengths of light in solar-driven devices. Recently, ligand-protected metal nanoclusters have emerged as a compelling platform for serving as triplet sensitizers for TTA-UC. In this study, we developed an atomically precise, triplet-mediator ligand (TL)-protected metal nanocluster, Au₂Cu₆(S-Adm)₆[P(DPA)₃]₂ (Au₂Cu₆DPA; S-Adm = 1-adamanthanethiolate, DPA = 9,10-diphenylanthracene). In Au₂Cu₆DPA, the excitation of the Au₂Cu₆ core rapidly generates a metal-to-ligand charge transfer state, followed by the formation of the long-lived triplet state (approximately 150 μs) at a DPA site in the TL. By combining Au₂Cu₆DPA with a DPA annihilator, we achieved a red-to-blue upconversion quantum yield (Φ_UCg) of 20.7 ± 0.4% (50% max.) with a low threshold excitation intensity of 36 mW cm^–2 at 640 nm. This quantum yield almost reaches the maximum limit achievable using a DPA annihilator and establishes a record-setting value, outperforming previously reported nanocrystal and nanocluster sensitizers. Furthermore, strong upconversion emission based on a pseudo-first-order TTA process was observed under 1 sun illumination, indicating that the Au₂Cu₆DPA sensitizer holds promise for applications in solar-energy-based systems.

中文翻译：

---

用于光子上转换的三重态介体配体保护的金属纳米团簇敏化剂

三重态-三重态湮没光子上转换（TTA-UC）作为一种在太阳能驱动设备中利用未利用的光波长的可行方法引起了广泛的关注。最近，配体保护的金属纳米团簇已成为一个引人注目的平台，可用作 TTA-UC 的三重态敏化剂。在这项研究中，我们开发了一种原子级精确的三重介体配体（TL）保护的金属纳米簇，Au ₂ Cu ₆ (S-Adm) ₆ [P(DPA) ₃ ] ₂ ( Au ₂ Cu ₆ DPA ; S-Adm = 1-金刚烷硫醇盐，DPA = 9,10-二苯基蒽）。在Au ₂ Cu ₆ DPA中，Au ₂ Cu ₆核的激发快速产生金属到配体的电荷转移态，然后在 DPA 位点形成长寿命的三重态（大约 150 μs）。 TL。通过将Au ₂ Cu ₆ DPA与 DPA 湮灭器相结合，我们实现了 20.7 ± 0.4%（最大值 50%）的红蓝上转换量子产率 (Φ _UCg )，低阈值激发强度为 36 mW cm ^–2 640 nm。这种量子产率几乎达到了使用 DPA 湮灭器可实现的最大极限，并创下了纪录设定值，优于之前报道的纳米晶体和纳米团簇敏化剂。此外，在1个太阳光照下观察到基于伪一级TTA过程的强上转换发射，表明Au ₂ Cu ₆ DPA敏化剂有望在太阳能系统中应用。