Luminescence constitutes a unique source of insight into hot carrier processes in metals, including those in plasmonic nanostructures used for sensing and energy applications. However, being weak in nature, metal luminescence remains poorly understood, its microscopic origin strongly debated, and its potential for unraveling nanoscale carrier dynamics largely unexploited. Here, we reveal quantum-mechanical effects in the luminescence emanating from thin monocrystalline gold flakes. Specifically, we present experimental evidence, supported by first-principles simulations, to demonstrate its photoluminescence origin (i.e., radiative emission from electron/hole recombination) when exciting in the interband regime. Our model allows us to identify changes to the measured gold luminescence due to quantum-mechanical effects as the gold film thickness is reduced. Excitingly, such effects are observable in the luminescence signal from flakes up to 40 nm in thickness, associated with the out-of-plane discreteness of the electronic band structure near the Fermi level. We qualitatively reproduce the observations with first-principles modeling, thus establishing a unified description of luminescence in gold monocrystalline flakes and enabling its widespread application as a probe of carrier dynamics and light-matter interactions in this material. Our study paves the way for future explorations of hot carriers and charge-transfer dynamics in a multitude of material systems.

发光是了解金属热载流子过程的独特来源，包括用于传感和能源应用的等离子体纳米结构中的热载流子过程。然而，由于金属发光本质上很弱，人们对它的了解仍然知之甚少，其微观起源存在激烈争议，而且其解开纳米级载流子动力学的潜力在很大程度上尚未得到开发。在这里，我们揭示了薄单晶金片发出的光的量子力学效应。具体来说，我们提出了由第一原理模拟支持的实验证据，以证明其在带间区域激发时的光致发光起源（即电子/空穴复合的辐射发射）。我们的模型使我们能够识别随着金膜厚度的减小，由于量子力学效应而导致的测量的金发光的变化。令人兴奋的是，在厚度达 40 nm 的薄片的发光信号中可以观察到这种效应，这与费米能级附近电子能带结构的面外离散性相关。我们通过第一原理建模定性地重现了观察结果，从而建立了金单晶薄片中发光的统一描述，并使其能够作为该材料中载流子动力学和光与物质相互作用的探针得到广泛应用。我们的研究为未来探索多种材料系统中的热载流子和电荷转移动力学铺平了道路。