Temperature-Dependent Emission Spectroscopy of Quantum Emitters in Hexagonal Boron Nitride

The potential of color centers in hexagonal boron nitride (hBN) for quantum technology applications has driven research to create emitters across a broad spectral range by using diverse techniques. Electron beam irradiation is one such approach that creates yellow emitters at room temperature; however, their behavior at low temperatures remains unexplored. Here, we present a comprehensive photophysical characterization of these yellow emitters in hBN under cryogenic conditions. We identify a bright and photostable defect with a zero-phonon line (ZPL) at 547.5 nm and a phonon sideband (PSB) approximately 90 meV from the ZPL. Excitation through this PSB enhances the emission intensity by nearly 5-fold at 4.5 K. Temperature-dependent photoluminescence (PL) from 4.5 to 220 K shows a decreasing Debye–Waller (DW) factor with elevated temperature, reflecting enhanced phonon-assisted emission. Further analysis reveals the presence of an additional low-energy phonon mode, leading to a T³ dependence of the ZPL line width and a T² dependence of the ZPL peak shift. These observations deepen our understanding of the nature of the emitters, opening new avenues for the precise tuning of quantum light sources.