Photocontrol of Single-Photon Generation in Boron Nitride Nanoparticles: Implications for Quantum Photon Sources, Sub-Diffraction Nanoscopy, and Bioimaging

Hexagonal boron nitride (h-BN) is a promising material for nanophotonics. Intrinsic and artificially induced defects in h-BN films, flakes, and nanoparticles are potential candidates as quantum emitters at room temperature. However, the energy structure and the methods for controlling these defects are still unclear. In this paper, we have obtained single-photon sources in ultrafine h-BN nanoparticles fabricated by a cost-effective ammonothermal dehydration. We demonstrate quantum-dot-like emission using photon autocorrelation and fluorescence intensity trace measurements in the red range. The results obtained using low-power near-ultraviolet coexcitation reveal the distinctive photophysical properties of fluorescent defects in the synthesized h-BN nanoparticles. We show that quantum emitters in nanoparticles can be switched from dark to bright mode by coexcitation photocontrol. The observed effects in nanoparticles were explained by various mechanisms of metastable state disabling. We also report a 2-fold improvement in the contrast of fluorescence images from h-BN nanoparticles under low-intensity laser scanning coexcitation. The research results can be used to develop efficient solid-state photon sources, as well as in nanoscopy employing biocompatible fluorescent nanoparticles.