Proximal nitrogen reduces the fluorescence quantum yield of nitrogen-vacancy centres in diamond

Abstract

The nitrogen-vacancy colour centre in diamond is emerging as one of the most important solid-state quantum systems. It has applications to fields including high-precision sensing, quantum computing, single photon communication, metrology, nanoscale magnetic imaging and biosensing. For all of these applications, a high quantum yield of emitted photons is desirable. However, diamond samples engineered to have high densities of nitrogen-vacancy centres show levels of brightness varying significantly within single batches, or even within the same sample. Here we show that nearby nitrogen impurities quench emission of nitrogen-vacancy centres via non-radiative transitions, resulting in a reduced fluorescence quantum yield. We monitored the emission properties of nitrogen-vacancy centre ensembles from synthetic diamond samples with different concentrations of nitrogen impurities. All samples were irradiated with high energy electrons to create high densities of nitrogen-vacancy centres relative to the concentration of nitrogen impurities. While at low nitrogen densities of 1.81 ppm we measured a lifetime of 13.9 ns, we observed a strong reduction in lifetime with increasing nitrogen density. We measure a lifetime as low as 4.4 ns at a nitrogen density of 380 ppm. The change in lifetime matches a reduction in relative fluorescence quantum yield from 77.4 % to 32 % with an increase in nitrogen density from 88 ppm to 380 ppm, respectively. These results will inform the conditions required to optimise the properties of diamond crystals devices based on the fluorescence of nitrogen-vacancy centres. Furthermore, this work provides insights into the origin of inhomogeneities observed in high-density nitrogen-vacancy ensembles within diamonds and nanodiamonds.

Modeling of Radiative Emission from Shallow Color Centers in Single Crystalline Diamond

“…The quantum efficiency quantifies the relative contributions of the radiative and non‐radiative rates and is defined as the ratio between the radiative rate and the total decay rate. While only radiative transitions are shown in the simplified energy scheme in Figure 1b, excited NVs can also decay via non‐radiative channels which include an intersystem crossing mechanism, [ 37 ] electron tunneling between NV centers and nitrogen impurities, [ 38 ] and recombination with other electron traps in the diamond crystal and at the interface. [ 39 ] For the NV center, the spin‐dependent intersystem crossing decay is the basis of optical initialization and readout of the NV spin and occurs on a timescale much longer (on the order of hundreds of ns) than the radiative lifetime.…”

Singly doped colloidal quantum dots as optically addressed nanopositionable qubits

“…The PL QY can vary significantly between NV nanodiamonds with values ranging between 5% and 20% reported [111] whilst QY ∼ 100% can be achieved for CQDs ensembles, which implies that the individual CQDs all have the same QY [11,112]. NV nanodiamonds have excellent photostability [113] and whilst core-only CQDs typically suffer from PL intermittency (known as 'blinking') well-engineered core/shell CQDs can exhibit photostability and be blinking-free [112]._The radiative lifetime, τ r , for NV nanodiamonds can be estimated from the PL lifetime τ PL ,via τ r = τ PL , /QY, which for τ PL ∼ 10 ns [114] and QY ∼ 10% [111] yields τ r ∼ 100 ns. In comparison, τ r for CQDs depends on their size, composition and structure but are typically 10-100 ns [10] and so broadly similar to NV nanodiamonds.…”

Ultrasmall Nanodiamonds: Perspectives and Questions

“…(2) Charge transfer between color centers and other dopants is often required to create the desired so-called “charge state” of the color center (in case of the NV center a nearby substitutional, N often donates an additional electron to create the desired NV – , whereas in the absence of an electron donor, the NV center cannot be used for sensing). (3) Interactions between color centers and other dopants can lead to spin decoherence or fluorescence quenching (excess of N in the vicinity of NV centers causes magnetic noise that reduces the coherence time of the NV – electron spin and the sensitivity of quantum sensing and can also lead to fluorescence quenching). As a result, state-of-the-art ND quantum sensing experiments such as magnetometry and thermometry based on optically detected magnetic resonance (ODMR) of NV centers generally employ particles with a diameter well above 50 nm .…”