Photoluminescence and photochemistry of the $V_B^-$ defect in hexagonal boron nitride

TL;DR

This study combines advanced computational and experimental techniques to elucidate the photophysical and photochemical properties of the $V_B^-$ defect in hexagonal boron nitride, revealing insights into its electronic structure and spectral behavior.

Contribution

It introduces new computational approaches and experimental findings that clarify the defect's electronic states, spectral features, and photochemical processes in hexagonal boron nitride.

Findings

Observed photoemission linked to specific defect states.

Identified spectral narrowing and zero-phonon-line shifts due to Jahn-Teller effect.

Ruled out alternative spectral assignments based on photochemical properties.

Abstract

Extensive photochemical and spectroscopic properties of the $V_B^-$ defect in hexagonal boron nitride are calculated, concluding that the observed photoemission associated with recently observed optically-detected magnetic resonance is most likely of (1)3E" to (1)3A2' origin. Rapid intersystem crossing from the defect's triplet to singlet manifolds explains the observed short excited-state lifetime and very low quantum yield. New experimental results reveal smaller intrinsic spectral bandwidths than previously recognized, interpreted in terms spectral narrowing and zero-phonon-line shifting induced by the Jahn-Teller effect. Different types of computational methods are applied to map out the complex triplet and singlet defect manifolds, including the doubly ionised formulation of the equation-of-motion coupled-cluster theory that is designed to deal with the open-shell nature of defect states, and mixed quantum-mechanics/molecular-mechanics schemes enabling 5763-atom simulations. Two other energetically feasible spectral assignments from amongst the singlet and triplet manifolds are considered, but ruled out based on inappropriate photochemical properties.