Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
J Phys Chem Lett. 2023 Feb 23;14(7):1899-1909. doi: 10.1021/acs.jpclett.2c03443. Epub 2023 Feb 13.
Nanocrystal (NC)-sensitized triplet-fusion upconversion is a rising strategy to convert long-wavelength, incoherent light into higher-energy output photons. Here, we chart the photophysics of tailor-functionalized CdSe NCs to understand energy transfer to surface-anchored transmitter ligands, which can proceed via correlated exciton transfer or sequential carrier hops. Varying NC size, we observe a pronounced acceleration of energy transfer (from = 0.0096 ns ligand to 0.064 ns ligand) when the barrier to hole-first sequential transfer is lowered from 100 ± 25 meV to 50 ± 25 meV. This acceleration is 5.1× the expected effect of increased carrier wave function leakage, so we conclude that sequential transfer becomes kinetically dominant under the latter conditions. Last, transient photoluminescence shows that NC band-edge and trap states are comparably quenched by functionalization (up to ∼98% for sequential transfer) and exhibit matched dynamics for > 300 ns, consistent with a dynamic quasi-equilibrium where photoexcitations can ultimately be extracted even when a carrier is initially trapped.
纳米晶（NC）敏化三重态融合上转换是一种新兴策略，可将长波长、非相干光转换为高能输出光子。在这里，我们绘制了定制功能化 CdSe NC 的光物理图谱，以了解能量转移到表面锚定的发射器配体，这可以通过相关激子转移或顺序载流子跳跃来进行。通过改变 NC 的尺寸，我们观察到当空穴优先顺序转移的势垒从 100 ± 25 meV 降低到 50 ± 25 meV 时，能量转移明显加速（从 = 0.0096 ns 配体到 0.064 ns 配体）。这种加速是增加载流子波函数泄漏预期效应的 5.1 倍，因此我们得出结论，在后者条件下，顺序转移成为动力学主导。最后，瞬态光致发光表明，NC 带边和陷阱态都可以通过功能化（对于顺序转移高达约 98%）进行相当程度的猝灭，并且对于 > 300 ns 表现出匹配的动力学，这与动态准平衡一致，即使最初捕获了一个载流子，也可以最终提取光激发。
