Impurity-vacancy complexes in diamond are an attractive family of spin defects since NV -, SiV -, GeV -, and SnVhave emerged as promising platforms for quantum applications. Although boron is most easily incorporated into diamond, a boron-vacancy complex in the negative charge state (BV -) has eluded experimental observation. This center was theoretically predicted as another promising spin qubit. In this work, we experimentally observed an electron paramagnetic resonance (EPR) spectrum identified as BVin synthetic diamonds via a Fermi-level tuning. Fingerprints of BVsuch as the spin multiplicity of S = 1, C 3v symmetry, and the zero-field splitting (D = 2913 MHz), in addition to 10 B and 11 B hyperfine (HF) interactions, have been confirmed. Moreover, optically pumped spin polarization has been observed with 3.0-3.6 eV excitation. However, unlike the NVcenter, the photoluminescence as well as optically detected magnetic resonance from BVhave not been confirmed even at low temperatures. We speculate that the Jahn-Teller instability in the triplet excited states of the NVand BVcenters results in different optical properties.

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