Photophysics of quantum emitters in hexagonal boron nitride

Abstract

Since the discovery of graphene in 2004, two-dimensional (2D) materials have attracted a great deal of attention. Due to its distinct optical, mechanical, and electrical properties, hexagonal boron nitride (h-BN) has been considered for both fundamental research and device applications. The recent observation of room temperature single photon emission from h-BN defect centers makes it also ex-citing material platform for applications of quantum photonics. Single-photon sources play an essential role in quantum technologies such as quantum comput-ing, quantum sensing, and quantum telecommunication. These quantum tech-nologies correspond to quantum physics and utilize features namely, interference, superposition, entanglement, and squeezed states. Therefore, require bright, in-distinguishable, and pure single-photons. Quantum emitters in h-BN have been investigated extensively in recent years due to their high brightness, high stabil-ity, and spectral tunability. Although the exact microscopic origin of quantum emitters is unknown, it is attributed to deep-defect emission because of the pres-ence of defect centers in h-BN. In order to study the photophysics of quantum emitters in h-BN, we have utilized thermal annealing processes to create optically active defect centers on commercially available solution-based h-BN flakes. First, we performed optical characterizations at room temperature to see whether we created defect centers successfully or not. Then, to investigate the photostability of emitters, we performed photoluminescence (PL) and spectral diffusion mea-surements at liquid helium temperature. After confirming the photostability of those PL emissions, we performed photon antibunching measurements by using Hanbury Brown and Twiss interferometer in order to investigate the quantum nature of those PL emissions. By using the time-correlated single-photon counting method, we have also mea-sured the lifetimes of those quantum emitters. Finally, we performed magneto-PL measurements and studied spin defects under an applied out-of-plane magnetic field. A substantial decrease in the integrated PL intensity of the emitters by up to one order of magnitude was observed when the applied field is increased from 0T to 7T. The observed photodarkening in the PL emission intensity of the quan-tum emitters has been attributed to the presence of spin-selective, nonradiative intersystem crossing (ISC) transitions.