摘要： There is significant interest in earth-abundant plasmonic materials, but whether or not their performance can match or even surpass their noble metal counterparts remains to be established. An important step in determining the extent of their versatility is to understand basic aspects of their plasmonic features. In this work, we measure near-infrared plasmonic molar extinction coefficients of water-dispersible copper selenide nanoparticles of different diameters. Obtaining molar extinction coefficients of these materials has traditionally been challenging because particles could not be synthesized at size ranges that avoid convoluting factors such as carrier density anomalies, surface depletion, and quantum confinement effects. Here, we report a straightforward synthesis that can control particle diameter within a size range that mitigates these convolutions, and then use these materials to establish their molar extinction coefficients. Importantly, we determine that size-dependent increases in molar extinction coefficients are likely a result of increases only in scattering cross-section, much like their noble metal analogues. Further, we show that the size-dependent trends in molar extinction coefficient follow the trends predicted by Mie theory well. These results suggest a promising outlook for the future implementation of earth-abundant and alternative plasmonic technologies from this material class.