Fig. 4: The optical pumping loop of CB–ONVB.
From: Quantum emission from coupled spin pairs in hexagonal boron nitride
a Bright excitation (red arrow) from the ground state (GS) to the excited state (ES) is localized on \({{{{\rm{O}}}}}_{{{{\rm{N}}}}}{{{{{\rm{V}}}}}_{{{{\rm{B}}}}}}^{-}\). Through internal conversion, the ES can relax to the doublet metastable state of \({{{{\rm{C}}}}}_{{{{\rm{B}}}}}^{0}\)--\({{{{\rm{O}}}}}_{{{{\rm{N}}}}}{{{{{\rm{V}}}}}_{{{{\rm{B}}}}}}^{0}\), denoted as Ds. The Ds level is separated by an energy J > 0 from the quartet metastable state Qs of the same \({{{{\rm{C}}}}}_{{{{\rm{B}}}}}^{0}\)–\({{{{\rm{O}}}}}_{{{{\rm{N}}}}}{{{{{\rm{V}}}}}_{{{{\rm{B}}}}}}^{0}\) configuration. The ± 1/2 and ± 3/2 spin sublevels within Qs are split by zero-field splitting. The black dot indicates spin mixing between Ds and Qs, while the black circle indicates the population magnitude in the ground state. b Spin sublevels in Ds and Qs under magnetic fields, shown for three values of J: − 3000, 0, and + 3000 MHz. Source data are provided as a Source Data file. c Population ratio between the \(| {{{{\rm{D}}}}}_{{{{\rm{s}}}}},+1/2\rangle\) and \(| {{{{\rm{D}}}}}_{{{{\rm{s}}}}},-1/2\rangle\) spin sublevels in the metastable state as a function of applied magnetic field.
