Optical coherence in the upconversion luminescence of Er[formula omitted

Abstract

Trivalent lanthanide ions exhibit the ability to convert near-infrared absorption into visible radiation through photon upconversion. Despite decades of extensive investigations, the role of optical coherence in this process has been overlooked. Here, we investigate the spatial coherence of upconversion photoluminescence from Erbium (Er3+) ions. Experimental results and simulations reveal that the emitted light displays correlations over longer distances than expected from an incoherent source. Moreover, the Er3+ emission profile exhibits two prominent spectral features at room temperature. Leveraging the bimodal nature of Er3+ luminescence, we observe coherence-induced modifications in the far-field spectrum, typically associated with broadband sources. These findings highlight the overlooked coherence properties of trivalent lanthanide ions and their potential impact on photon upconversion applications.