A Defect Study and Classification of Brown Diamonds with Deformation-Related Color

For this study, the properties of a large sample of various types of brown diamonds with a deformation-related (referred to as “DR” in this work) color were studied to properly characterize and classify such diamonds, and to compare them to pink to purple to red diamonds. The acquisition of low temperature NIR spectra for a large range of brown diamonds and photoexcitation studies combined with various treatment experiments have opened new windows into certain defect characteristics of brown diamonds, such as the amber centers and naturally occurring H1b and H1c centers. It was determined that the amber centers (referred to as “AC” in this work) exhibit rather variable behaviors to annealing and photoexcitation; the annealing temperature of these defects were determined to range from 1150 to >1850 °C and it was found that the 4063 cm−1 AC was the precursor defect of many other ACs. It is suggested that the amber centers in diamonds that contain at least some C centers are essentially identical to the ones seen in diamonds without C centers, but that they likely have a negative charge. The study of the naturally occurring H1b and H1c link them to the amber centers, specifically to the one at 4063 cm−1. Annealing experiments have shown that the H1b and H1c defects and the 4063 cm−1 AC were in line with each other. The obvious links between these defects points towards our suggestion that the H1b and H1c defects are standalone defects that consist of multiple vacancies and nitrogen and that they are—in the case of brown diamonds—a side product of the AC formation. A new classification of DR brown diamonds was elaborated that separates the diamonds in six different classes, depending on type and AC. This classification had been completed recently with the classification of brown diamonds with a non-deformation-related color (referred to as “NDR”), giving a total of 11 classes of brown diamonds.

Superresolution Microscopy of Single Rare-Earth Emitters in YAG and H3 Centers in Diamond

We demonstrate superresolution imaging of single rare-earth emitting centers, namely, trivalent cerium, in yttrium aluminum garnet crystals by means of stimulated emission depletion (STED) microscopy. The achieved all-optical resolution is ≈50  nm. Similar results were obtained on H3 color centers in diamond. In both cases, STED resolution is improving slower than the conventional inverse square-root dependence on the depletion beam intensity. In the proposed model of this effect, the anomalous behavior is caused by excited state absorption and the interaction of the emitter with nonfluorescing crystal defects in its local surrounding.

IR-stimulated visible fluorescence in pink and brown diamond

Irradiation of natural pink and brown diamond by middle-ultraviolet light (photon energy ϵ ≥ 4.1 eV ) is seen to induce anomalous fluorescence phenomena at N3 defect centres (structure N3-V). When diamonds primed in this fashion are subsequently exposed to infrared light (even with a delay of many hours), a transient burst of blue N3 fluorescence is observed. The dependence of this IR-triggered fluorescence on pump wavelength and intensity suggest that this fluorescence phenomena is intrinsically related to pink diamond photochromism. An energy transfer process between N3 defects and other defect species can account for both the UV-induced fluorescence intensity changes, and the apparent optical upconversion of IR light. From this standpoint, we consider the implications of this N3 fluorescence behaviour for the current understanding of pink diamond photochromism kinetics.

Luminescence lifetimes of neutral nitrogen-vacancy centres in synthetic diamond containing nitrogen

The decay time of luminescence from neutral nitrogen-vacancy (NV(0)) centres in synthetic diamond is reported. The intrinsic luminescence lifetime of NV (0) is measured as τ(r) = 19 ± 2 ns. Neutral substitutional nitrogen atoms (N(S)(0)) are shown to quench luminescence from NV(0) by dipole-dipole resonant energy transfer at a rate such that the transfer time would equal τ(r) if one (N(S)(0)) atom was ~3 nm from the NV(0). In chemical-vapour-deposited diamonds grown with a small nitrogen content, that are brown as a result of vacancy-cluster defects, the decay time of NV(0) equals τ(r) in the as-grown material. However, after annealing at ≥1700 °C to remove the brown colour, luminescence from the NV(0) centres is severely quenched. This effect is suggested to be a result of the destruction of NV(0) centres and the creation of new NV(0) centres localized in vacancy-rich regions of the crystals.

Luminescence-lifetime mapping in diamond

This paper introduces a new technique to the study of diamonds: mapping the luminescence lifetime of optical centres. The understanding of luminescence lifetimes in diamond is briefly reviewed. Since lifetime mapping involves extended measuring times with focused laser excitation, the stability of the H3 optical centre is investigated. We show that saturation of the H3 luminescence requires excitation power densities in excess of 10 MW cm(-2). The non-radiative energy transfer time from an H3 centre to an A aggregate is found to be equal to that from N3 centres to A aggregates, at ∼3 × 10(-16)r(8) s, where there are r bond lengths between the H3 and A centres. Non-radiative energy transfer is shown to occur from the NV(-) band to the single substitutional nitrogen atoms: the single N atoms may quench luminescence as well as the A aggregates of nitrogen. In contrast, a comparison of the decays from the very similar H3 and H4 centres demonstrates that the B aggregate produces very weak quenching of the visible luminescence from diamond.