Electronic Structures and Spectroscopic Signatures of Noble-Gas-Doped Nanodiamonds

Abstract

Fluorescent nanodiamonds, that is, those containing optically active defects, have attracted interest for their ability to be used as qubits; for in vivo imaging; and as sensors for spin, stress, and temperature. One of the most commonly studied nanodiamond color centers is the nitrogen vacancy. However, there is strong interest in discovering other impurity centers that provide localized midband gap transitions. Noble gas atoms have garnered attention since they have been discovered within nanodiamonds produced through high-pressure–high-temperature laser-heated diamond anvil cell synthesis methods, where they are commonly used as hydrostatic pressure media. Noble gas atoms that exist in macrosized natural or synthetic diamonds have been shown to be able to form color centers. This research uses ab initio density functional theory and cluster models to systematically study the localized electronic structure for group VIII impurities of nanodiamond, including helium, neon, argon, krypton, and xenon. An in-depth examination of the interaction between the noble gas atom and diamond lattice has been carried out. The changes to the vibrational and UV/vis absorption spectra have been analyzed. It was determined that the energetically preferred geometry is dependent on the atom size. Most noble gas defects are stabilized within the nanodiamond lattice and exist in tetrahedral interstitial positions, except for the largest noble gas studied in this work, Xe, which was determined to prefer a substitutional configuration. Both Kr and Xe are expected to be able to manifest visible/near-IR optical responses when included in the diamond lattice.

Impurity atom configurations in diamond and their visibility via scanning transmission electron microscopy imaging

“…In a double vacancy the atom occupies the split-vacancy site [216,217,223] in a D 3d symmetry, although also the off-center configuration was reported early on [190]. Interestingly, both the substitutional site [216] and the split-vacancy site [223] have been reported as the most stable one for Xe, most likely due to different supercell structures used in the studies. In a vacancy cluster with three vacancies, Xe takes an interstitial position between the vacancy sites.…”

“…Computational work [216] discusses different configurations. No midgap states were predicted for any of the studied sites within nanodiamond structures.…”

“…So far, no photoluminescence has been measured in Ar-doped diamond. Nevertheless, Ar substitution and double vacancy configurations are predicted [216] to create midgap states in the band gap of nanodiamond, that can produce transitions in the visible range of the spectrum. This is achieved when the atom is able to chemically react with the diamond, similar to Kr and Xe.…”

“…In bulk diamond the interstitial configuration with T d symmetry is favored [217]. This site is also the most stable one in nanodiamond [216]. Substitutional He will cause large repulsion in the surrounding lattice and the neighboring carbon atoms relax outward from the dopant.…”

Excited State Properties of Point Defects in Semiconductors and Insulators Investigated with Time-Dependent Density Functional Theory

“…TDDFT has been used to study excited states of point defects in diamond using cluster models and atomic-centered basis sets. − However, depending on the size and the system, cluster models may exhibit quantum confinement, and their electronic structure may also be impacted by the chosen surface termination. In addition, the optimized geometries in the ground and excited states may differ from the corresponding geometries in the solid state.…”