Negatively charged boron vacancy center in diamond

The negatively charged boron-vacancy pair - the BV${}^{\ensuremath{-}}$ center was a missing defect in diamond. It is expectedly very similar to NV${}^{\ensuremath{-}}$ center, which one of most famous spin defects or qubits semiconductors. has now been identified by electron paramagnetic resonance on specially prepared diamonds. Its spin-triplet state resembles lot that NV${}^{\ensuremath{-}}$, while its optically detected magnetic signal invisible, posing puzzle why luminescence so weak.